By Michela Centinari, Bryan Hed, Kathy Kelley, and Jody Timer
The 2017 growing season was a rewarding one for many Pennsylvania (PA) grape growers; crop quality and yields generally met or exceeded expectations. However, this season was not without its challenges. Before we start planning for next year, let’s review this past season and discuss the important issues and concerns PA growers faced in 2017. In November a link to a 10-minute Internet survey was sent via email to 110 members of a PA wine grape grower extension mailing list. The survey was designed to solicit their feedback with regards to the 2017 growing and harvest season. Fifty participants completed the survey* and their responses form the basis of this blog article. So that we have a complete accounting for growers throughout the Commonwealth, we encourage PA wine grape growers who may not have received the email to contact us (Michela Centinari; Bryan Hed) and provide their contact information so that they can be included in future surveys.
First, some information about participant demographics
Of those who provided the region where they grew grapes (44 participants), the majority (16) were located in the Southeast region, followed by South Central (9), Northwest (8), Northeast (5), North Central (3), and Southwest (3) regions. Species of grapes survey participants grew are listed in Table 1.
What did we ask the survey participants?
Participants were asked to indicate the average yield of the grapes they grew in 2017 by selecting the appropriate category: “poor,” “below average,” “average,” “above average,” or “record crop.” Although growers often adjust crop load to meet a desired level, environmental or other unexpected factors may cause final yield to differ from expected, “average” values.
Participants were also asked to rank the overall quality of the fruit from “poor” to “excellent,” and the insect and disease pressure from “below average” to “above average.” Respondents were then directed to open-ended questions where they indicated what cultivars performed “below,” “average,” or “above average” and why.
Weather conditions during the growing season
A look at the weather conditions throughout the growing season can help to explain participants’ answers. In Figures 1 and 2, we reported monthly, seasonal (April 1 through October 31) growing degree days (GDD; index of heat accumulation), and precipitation collected by weather stations (http://newa.cornell.edu/) at two locations: Lake Erie Regional Grape Research and Extension center (LERGREC) in North East (Erie County, northwestern PA) and in Reading (Berks County, southeast PA). We compared the 2017 data to the previous 18-year (1999-2016) average.
We recognize that weather conditions might vary greatly from site to site, but some general trends were observed. For example, April GDDs were above-average in many regions of the Commonwealth. On the other hand, May was slightly cooler than the average in both the Southeast and Northwest (Figure 1). Additionally, below freezing temperatures were recorded during the early morning hours of May 8 and May 9 at the agricultural experiment station located near the Penn State main campus in State College. Some of the grape cultivars grown at this research farm, especially those that typically break bud early like Marquette and Concord, sustained crop loss due to frost damage. Fortunately, spring frost affected relatively few growers in PA and only two survey participants, one from the Southwest and another from the Northeast, reported reduced crop yield due to early May frost damage.
Growing degree day accumulations were slightly above the long-term average in June and July. However, August was noticeably cooler than the average in the Southeast and many other regions of the state, but not in Erie which remained warmer than average nearly all season (Figure 1). As the season came to a close, temperatures in September and especially October were warmer than average at both locations (Figure 1).
In most regions of the state, precipitation was abundant, particularly in June, July, and August (Figure 2 and Table 2). The one exception to this trend was in the far Northwest corner of the state where rainfall along the Lake Erie shore was well below average in July and August. September was relatively dry statewide, which was a big relief for many growers after facing a wet summer. As the season came to an end, October saw a return to higher amounts of rainfall in some areas of the state.
Survey participants’ responses
Yield: Twenty-two respondents (44% of the participants) indicated that overall crop yield was “average,” which was close to the target values (Figure 3). Sixteen percent of the participants indicated that overall yield was “above average,” or “record crop,” while for 40% was “below average” or “poor.”
“Poor” or “below average” yield was attributed to several factors, including poor or reduced fruit set, herbicide drift damage from a nearby field (for more information please refer to the newsletter article: Growth regulator herbicides negatively affect grapevine development) and/or disease issues (e.g., downy mildew, bunch rot). Two participants reported crop yield losses due to late spring freeze damage. One respondent indicated that “above average” yield was likely related to bigger berry size.
Fruit quality: Participants were asked to rate fruit quality, with the majority of the respondents (82%) rating fruit quality as “average,” “above average” or “excellent.” Only 18% of the respondents indicated that overall quality was “below average” or “poor,” although in some cases the rating varied depending on the cultivars grown as specified in a follow-up question.
With the exception of the Northwest region, several participants across the state pointed out that despite the wet summer conditions the warm and dry fall weather favorably influenced fruit ripening, especially for late ripening cultivars.
For example, some of them commented:
- “Early cultivars were of lower quality than later cultivars due to the cold, wet weather in the August and early September time frame. The warm and dry later half of September and most of October benefited the later.”
- “Pinot Gris, Sauvignon Blanc, Viognier, Chardonnay all had excellent sugar levels and good pH and acidity. Flavors were well concentrated. Reds were average to good. Some like Merlot had low sugar levels while later varieties had better sugars like Cabernet franc and Cabernet sauvignon. The late reds seemed to ripen more quickly than normal.”
- “Later varieties were above average due to smaller crop size and better weather conditions.”
Disease pressure: Half of the growers who participated in the survey experienced “above average” disease pressure during the 2017 growing season, while 41% reported “average” disease pressure and only 9% reported that the disease pressure was “below average.” This contrasts markedly with results obtained in 2016 when 47% of survey participants experienced “below average” disease pressure (Looking back at the 2016 season).
The major disease problem identified by the growers was downy mildew followed by bunch rot. A few respondents indicated that downy mildew pressure was particularly high in August. This is not surprising; downy mildew pressure is very dependent on rainfall and the threat of this disease would be particularly high in areas where recorded rainfall had been above average for most of the season (for example, Berks County).
It is important to note that areas of the state that experienced “above average” disease pressure may have a relatively high overwintering population of the pathogen(s), particularly if a fair amount of disease was actually observed in the vineyard. This can easily translate into higher disease pressure in 2018, especially if conditions remain wet.
In contrast to the majority of grape growing areas in PA, growers in the Lake Erie region experienced a second consecutive dry season, and disease development in many of the region’s vineyards was limited to powdery mildew in 2017. Therefore vineyards in the Lake Erie region will generally carry relatively low overwintering pathogen levels into 2018, with the exception of powdery mildew (a disease that is only dependent on rainfall for the first primary infections in early spring).
Despite the above-average wet conditions, respondents pointed out that fruit was clean from major diseases: “low fruit disease despite wet season,” and “given the weather conditions during the growing season overall our grapes were kept almost disease free.”
Several of them attributed their ability to keep disease pressure under control to a “persistent spray program,” “solid spray program and very good protective materials available,” and that “rainy season required that growers stay on top of their disease management program. Botrytis, downy and powdery mildew could have been rampant.”
A respondent pointed out that in addition to a solid spray program new canopy management implemented likely helped to reduce Botrytis infection in susceptible varieties: “I also started to leaf pull pre-bloom which I believe has loosened our clusters up and has allowed for better spray penetration and overall less rot.”
Insect pressure: Twenty-two participants (45% of the respondents) experienced “average” insect pressure during the 2017 growing season, while 31% answered “above average” and 24 % “below average.”
The majority of the growers who experienced “average” or “above average” insect pressure indicated problems with late-season insect pests, such as Spotted Wing Drosophila (SWD), wasps and hornets (for more information on those insect pests and how to manage them please refer to: Is Spotted Wing Drosophila a problem in my wine grapes?; Late season insect management)
Some of them commented:
“SWD seems to be more present at the end of the season,” “Drosophila was the primary insect,” “SWD was above normal.”
Japanese Beetles were also named, although answers were divided: some respondents indicated “Japanese beetle pressure was lower than in previous years” while others answered that “Japanese beetles were the most prevalent insect” and they were “very aggressive in the vineyard.” A respondent observed a new insect in the vineyard, the grape leafhopper. Grapevines can tolerate fairly high populations of leaf hoppers and Japanese beetles without harm to the crop. Populations of fewer than 20 leafhopper nymphs/leaf usually does not require spraying (Japanese Beetle: A common pest in the vineyard).
In the Lake Erie region the grape berry moth was once again the most destructive insect present. The unusually dry summer kept a potentially large population to average numbers. Brown Marmorated stink bug damage is beginning to be noticeable in some Lake Erie vineyards (Will the Brown Marmorated stink bug be a problem in wine and juice?)
Unfortunately, the insect who made its big entry this season into southeastern PA vineyards was the Spotted Lanternfly (Lycorma delicatula). Spotted Lanternfly (SLF) is an invasive insect first discovered in Berks County in 2014 and is now threatening parts of southeastern PA and Southern New York (Invasive insect confirmed in New York). Half of the respondents from the Southeast region (8 participants) observed the Spotted Lanternfly in their vineyards, and this was the first year for many of them.
Some of them commented:
- “At the end of the season I started seeing Spotted Lanternfly.”
- “Lantern fly moved into my vineyard this year. Some of us believe honeydew from lantern fly is attracting yellow jackets and other bees, which were really bad.”
- “The Spotted Lanternfly in our vineyard continues to put pressure on the crop; we estimated that we killed 1/2 million adults in September.”
- “The significant increase in the adult Spotted Lantern Fly population this season in our area causes significant concern for our vineyard longevity. While many of the sprays were able to knock the populations back quickly only so many applications could be made. Within a few days of spraying and killing the adults, new adults migrated into the vineyards.”
The quarantined area for SLF at the beginning of the season included three counties of southeastern PA, but by the end of the season, SLF populations had decidedly increased causing the quarantine area to be markedly expanded. The PA Department of Agriculture does not have the quarantine map completely updated at this time, however, they do have a search quarantine map where you can put in your location to check to see if you are included in the quarantine. (https://www.agriculture.pa.gov/spottedlanternfly; http://www.agriculture.pa.gov/plants_land_water/plantindustry/entomology/spotted_lanternfly/pages/default.aspx)
Information on SLF and measures that can be taken to stop its spread can be found at: https://extension.psu.edu/spotted-lanternfly, additional resources are listed on the Penn State Extension website. As stated in the article: “Penn State is at the forefront of education and research aimed at stopping the spread of this exotic species.” Penn State is seeking to hire an entomologist extension associate to coordinate outreach and response efforts for the SLF.
We are also planning to discuss Spotted Lanternfly management options at the Penn State Grape Disease & Insect Management Workshop, soon to be announced through the Penn State extension website and our listserv.
We would like to thank all the growers who participated in the survey. Their time spent responding to these questions provides us with valuable information that research and extension personnel can utilize to customize efforts to help the industry grow and improve. The more responses we receive, the more accurately our efforts can target the needs of our stakeholders statewide. Despite some challenges, it was a rewarding growing season for many PA wine grape growers. We are looking forward to tasting this season’s wines!
* All procedures were approved by the Office of Research Protections at The Pennsylvania State University (University Park, PA). Upon completion of the survey, each participant was entered into a raffle to win one of three $25 gift certificates that could be redeemed toward any Penn State Extension wine or grape program fee.
By: Jody Timer, Entomology & Lake Erie Regional Grape Research and Extension Center
Over the last ten years there have been an inpouring of newcomers to the insect community of Pennsylvania’s grape vineyards. These pest, combined with the numerous indigenous pest, have created an ever evolving challenge for the area’s grape growers. In this blog, I will briefly review the grape pest which I feel are becoming ever increasingly problematic for grape growers to control.
The Spotted wing drosophila has become a progressively severe problem in blueberries raspberries, and grapes. Recent research has shown that they are attracted to all cultivars of grapes that we tested. Spotted wing Drosophila, Drosophila suzukii, Matsumura (Diptera: Drosophilae) (SWD) is an invasive vinegar fly of East Asian origin, that was recently introduced into the United States. It was first found in California in 2008 and is now found in all major fruit-growing regions of the country including Pennsylvania. It was first discovered in Pennsylvania’s Lake Erie grape growing region in the late fall of 2011. The potential infestation rate of spotted wing Drosophila differs from other vinegar flies because the female possess a serrated ovipositor that cuts into healthy fruit to lay eggs. Consequently, spotted wing Drosophila (SWD) larvae can be found in fruit that is just ripening: https://youtu.be/dPr61VC2gyo
During egg-laying, it is believed that sour rot and fungal disease can also be introduced, further affecting the fruit quality. During peak temperatures, a female can lay more than 100 eggs a day. Such a high reproduction rate indicates the SWDs’ high potential for fruit infestation and their potential for spreading rapidly through a field or a vineyard. Because of this prolificity it has become increasing important to protect wine grapes starting at veraison. A good YouTube video on how to identify SWD damage is: https://youtu.be/DLNDnMMfWfs
In our research we have seen SWD showing up earlier in the spring each season and their numbers increasing yearly. SWD do attack injured grapes before non-injured, they tend to wait till veraison before attacking grapes, and they will reproduce in fallen berries. For this reason it is important to keep your vineyards as clean as possible and to maintain coverage of these wine grapes through harvest. Trapping and forecasting can lead to improvements in grower’s capability to optimally time pest management decisions which should reduce both the direct cost of pesticide treatments and the indirect cost to wineries. Information can also be found at:
The brown marmorated stink bug (BMSB) is currently a very serious pest in tree fruits and vegetables, and can be a nuisance when they overwinter in houses. Although BMSB prefer other fruits and vegetables to grapes, they do feed on grapes. Their damage can cause ugly scars on table grapes and grapes grown for sale at fruit stands. This type of damage is not important to wine grape and juice grape growers, however, the holes open pathways for fungal and bacteria late season infections. This season, in the Lake Erie region, we have begun to see a small number of BMSB damaged grapes. BMSB may also be easily harvest with the grapes. The insects tend to move to the interior of the cluster when disturbed and are hard to see. When they are killed they give off a foul odor – which is how they got their name. Our research has shown that this odor and resulting taste do survive the pasteurization of juice grapes, but disappears after being stored for longer periods of time. There is conflicting research on whether this taint transfers to wine, more research is ongoing. There are traps commercially available to trap these insect, but their efficacy is very low. BMSB have been found in both grape foliage and grape clusters; they seek the moisture, sugar, and warmth on the inside the clusters (especially overnight) and they often migrate to the cluster’s interior close to harvest. This makes the possibility of BMSB inside the cluster very likely when these grapes are mechanically harvested and transported to the processor.
With the yearly increase of numbers of BMSB in the Pennsylvania vineyards, it is very important for growers to scout for the adults and the presence of the eggs on the underside of grape leaves. There are one to two generations in Pennsylvania. A compilation of research can be accessed at www.STOPBMSB.org
The newest invasive poised to become a major problem to grape growers, the spotted lanternfly (SLF), Lycorma delicatula, (Hemiptera: Fulgoridae) is native to China, India, Japan, and Vietnam and has been detected for the first time in the United States in northeastern Berks County, Pennsylvania. This approximately one inch long insect with piercing-sucking mouthparts has the potential to impact the green industry, grape growers, tree fruit growers, and the forests and wood products industries in Pennsylvania as well as the United States. The host plants of the SLF in its native habitat include grapes, pines, stone fruits, and up to 50 other hosts. Early detection of the SLF is critical for effective control and protection of Pennsylvania’s agriculture and its related businesses. SLF group feeds on grapevines in numbers great enough to cause destruction of the entire grapevine. Grapes are listed as a primary host in its native regions. To date this insect has been confined to areas of Berks and Bucks counties in Pennsylvania. The PDA has issued a general order of quarantine for these areas over the past few years, however this insect is slowly increasing its range.
The following is a link to the PDA’s information on the SLF: www.pda.state.pa.us/spottedlanternfly. You may find a link to a pdf copy of the SLF Order of Quarantine, a PowerPoint on Lycorma Inspection Tips, and the SLF Pest Alert at this website.
What to do if you:
- See eggs: Scrape them off the tree or smooth surface and place the eggs in a tightly sealed container with 70% alcohol or hand sanitizer to kill them.
- Collect a specimen: Send the adult/nymph specimen or egg mass to the PDA Entomology Lab for verification. The mailing address for the lab is: PDA, Entomology Room-111, 2301 N. Cameron St., Harrisburg, PA 17110. First, place the sample collected in 70% rubbing alcohol or hand sanitizer in a leak proof container. Complete the PDA Entomology Program Sample Submission Form. This sample form can be found in the PDA SLF website www.pda.state.pa.us/spottedlanternfly.
- Report a site: Call the Bad Bug hotline at 1-866-253-7189 with details of the sighting and your contact information.
The most destructive insect pest in the Lake Erie region remains the native Grape Berry Moth (GBM), Paralobesia viteana. This insect is becoming increasingly harder to control as result of shorter residual time of insecticides, resistance to insecticides, and abandoned vineyards. GBM larval burrow into the grape berry soon after hatching, making precise timing of spray applications a critical component of control. This insect has four generations per year. Each generation increases in number exponentially if control measures are not applied to the early generations. Spray timings can be calculated by following the NEWA model recommendations (see earlier posts). Growing seasons with large populations of GBM, will require a second spray in July and/or August to control the populations, and to prevent them from moving farther into the vineyards. Scouting for GBM damage often during the season is a critical component of control, as the pheromone traps capture only the males and are not a good indicator of infestation after the first generation. More information can be found on extension pages and on the LERGP Podcasts on Youtube.
By: Andy Muza, Penn State Extension – Erie County
There are several species of leafhoppers in the genus Erythroneura that feed on grape foliage. Research conducted in New York showed that the eastern grape leafhopper Erythroneura comes (Say) is the most common on American varieties (e.g., Concord, Niagara) while E. bistrata/vitifex complex were more common on Vitis vinifera and interspecific hybrids. Other species found in commercial grapes included E. tricinta, E. vulnerata and E. vitis. (1). Regardless of which of these species is prevalent, their life cycles are similar and the injury caused by these leafhoppers and their management is the same.
Life Cycle and Description
The various Erythroneura leafhoppers overwinter as adults in leaf litter in the vineyard or in plant debris around the vineyard. As temperatures increase in the spring, adults begin feeding on a variety of weeds, bushes and trees. Adults then migrate into vineyards to feed when leaves emerge (2). Eastern grape leafhopper adults are small (only about 1/8”), white-pale yellow, with darker lemon colored markings on the wings, and 3 black spots towards the posterior portion of the wings (Figures 1 & 2). Other Erythroneura species have varying coloration and markings (3).
Initial feeding occurs on sucker growth and basal leaves on shoots in the trellis. Females lay eggs on the undersides of leaves just below the leaf surface. Nymphs of the first generation hatch in mid-late June. Immatures are wingless, pale yellow in coloration with tiny wing pads (Figure 3). Nymphs develop through 5 instars with wings fully developed after the fifth molt (2). Nymphal development to adulthood takes about 30 days or less depending on environmental conditions. In northwestern Pennsylvania nymphs of the second generation can be found in vineyards in mid-late August. There are 1.5 – 2 generations/season in the Lake Erie Region, depending on seasonal temperatures, and in the southwestern portion of the state likely 2.5 – 3 generations.
Grape leafhopper (GLH) adults and nymphs have piercing – sucking type mouthparts and feed on the underside of leaves extracting the contents of leaf cells resulting in white – yellow spotting of the foliage (stippling). Moderate – Heavy feeding causes yellowing and browning of tissue while severe injury can result in premature defoliation (Figure 4).
The greatest risk for economic losses due to grape leafhopper (GLH) feeding occurs during hot, dry years in vineyards with heavy crop loads and high leafhopper populations (4). In most years, the majority of vineyards in Pennsylvania should not require an insecticide treatment specifically for management of grape leafhopper. Therefore, routine, prophylactic insecticide treatments for leafhoppers are unnecessary and not recommended. Insecticide applications should be based on scouting information and threshold levels.
Scouting – Tim Martinson at Cornell designed a scouting procedure for leafhoppers which corresponds to the timings when sampling for grape berry moth injury are conducted (5).
10 Days Postbloom – Usually population levels and feeding is minimal at this time of the season. If however, early in the season, high numbers of adult leafhoppers migrate into the vineyard this can result in enough leaf feeding to reduce bud fruitfulness in the following year (4). Scouting should be conducted to look for leaf feeding on interior leaves in the canopy. If leaf stippling is noticeable throughout the vineyard then an insecticide application is recommended.
Third week in July – Check 4 different areas in the vineyard (2 exterior and 2 interior). At each area look at lower leaves on shoots and check for leaf feeding. If no – minimal injury is observed, proceed to the next sampling site (Figure 5). If moderate-heavy leaf stippling is observed then begin counting nymphs on the undersides of leaves (Figure 6). Examine 5 leaves (leaves 3-7 from base of shoot)/shoot on 5 different shoots at each location. If a threshold of 5 nymphs/leaf is reached then an insecticide application is recommended.
Late August – The scouting protocol at this time follows the same procedure as the July sampling. However, the threshold for the August sampling period is 10 nymphs/leaf before an insecticide application is recommended.
Based on scouting data, if an insecticide application becomes necessary during the season, there are a number of options available. Consult the “2017 New York and Pennsylvania Pest Management Guidelines for Grapes” (6) for a list of insecticides which are effective for grape leafhopper management.
Shoot and leaf removal practices conducted in many wine grape vineyards may reduce leafhopper population levels, if the removed leaves are harboring nymphs of this pest. In addition, these practices will open up the canopy for better spray penetration.
A number of predators (e.g., spiders, green lacewings, lady beetles, etc.) and egg parasitoids (Anagrus species) which occur in vineyards contribute to reducing leafhopper population levels (7). Therefore conserving these beneficial insects, by avoiding unnecessary applications of broad spectrum contact insecticides, is advised. Good weed control in the vineyard and the prevention of overgrown areas around the vineyard will also reduce leafhopper overwintering sites.
- Martinson, T. E. and T. J. Dennehy. Varietal Preferences of Erythroneura Leafhoppers (Homoptera: Cicadellidae) Feeding on Grapes in New York. Environ. Entomol. 24:550-558 (1995). https://academic.oup.com/ee/article/24/3/550/2394852/Varietal-Preferences-of-Erythroneura-Leafhoppers
- Grape Leafhopper. Grape Insect IPM Insect Identification Sheet No. 4 (1984). NYS. Ag. Exp. Station, Cornell University. https://ecommons.cornell.edu/bitstream/handle/1813/43102/grape-leafhopper-FS-NYSIPM.pdf?sequence=1&isAllowed=y
- Leaf- Stippling Leafhoppers (Ontario GrapeIPM). Ontario Ministry of Agriculture Food & Rural Affairs, Canada http://www.omafra.gov.on.ca/IPM/english/grapes/insects/ls-leafhoppers.html
- Martinson, T. E., et al. Impact of Feeding Injury by Eastern Grape Leafhopper (Homoptera:Cicadellidae) on Yield and Juice Quality of Concord Grape. Am. J. Enol. Vitic., 48:291-302 (1997). http://www.ajevonline.org/content/ajev/48/3/291.full.pdf
- Martinson, T. E., et al. Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper. New York’s Food and Life Sci. Bull. 138. 10 pp. (1991). http://nysipm.cornell.edu/publications/grapeman/files/risk.pdf
- Weigle, T. H., and A. J. Muza. 2017. “2017 New York and Pennsylvania Pest Management Guidelines for Grapes”. Cornell and Penn State Extension. 150 pp. https://store.cornell.edu/p-197039-2017-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx
- Williams, L., III, and T. E. Martinson. 2000. Colonization of New York Vineyards by Anagrus spp. (Hymenoptera:Mymaridae): Overwintering Biology, Within-Vineyard Distribution of Wasps, and Parasitism of Grape Leafhopper, Erythroneura spp. (Homoptera: Cicadellidae), Eggs. Biol. Control 18:136-146. https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=43140&content=PDF
By: Andy Muza, Penn State Extension – Erie County
As the season begins, growers should be prepared to manage a serious pest which can cause substantial economic losses. The grape berry moth (GBM) is a prevalent pest of grapes throughout Pennsylvania and the eastern United States. The larval stage feeds on berries and causes yield losses due to consumption and shelling of berries and by providing entry sites for fungi that can cause cluster rots.
I consider management of this pest to be a three phase process which includes: 1) PRE –TREATMENT Phase; 2) TREATMENT Phase; 3) POST – TREATMENT Phase.
1) PRE-TREATMENT PHASE
Follow maintenance procedures outlined in your sprayer manual. Check pump, hoses, filters, nozzles, etc. to be sure that everything is in good working order before your first pesticide application. Also practice routine sprayer maintenance during the season such as lubrication of bearings and cleaning and flushing of the sprayer after each use.
Calibration of Sprayer
Sprayers should be calibrated early in the season well before any insecticide or fungicide spraying is required. Calibration of sprayers ensures that the appropriate amount of spray material is being applied where it is needed to manage pests. The sprayer should be calibrated in the vineyard under conditions in which the sprayer will be operated. Ideally, sprayers should be calibrated 2-3 times during the season as canopy growth increases.
Classifying a Vineyard Using the GBM Risk Assessment Program
The GBM Risk Assessment Program was developed by Hoffman and Dennehy (Cornell University), (“Bulletin 138, Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper” – http://nysipm.cornell.edu/publications/grapeman/files/risk.pdf). It is a method of classifying vineyard blocks for risk (e.g., High, Low or Intermediate) of receiving damage from grape berry moth. The criteria used for assigning risk include: Value of the varieties being grown; Surrounding Vineyard Habitat; History of GBM injury; Climatic factors related to the region where grapes are being grown.
High Risk Classification
Value of the varieties being grown – if higher value varieties such as Vitis vinifera, many hybrids, or table grapes are being grown then these vineyards should automatically be assigned a High Risk Classification. Therefore most vineyards in Pennsylvania, outside of the Lake Erie Region, should initially be classified as High Risk. This classification can be adjusted later if scouting history reveals that GBM injury is consistently low at your vineyard site.
Surrounding Vineyard Habitat – if wooded edges or hedgerows/weedy areas are present around vineyards.
History of GBM injury – if scouting reveals that damage is often above 6% cluster damage in July and /or above 15 % cluster damage (2% berry damage) at harvest. These injury levels were developed with processed juice grape varieties in mind and injury levels may be lower for varieties that command a higher value/ton.
Climatic factors related to the region – if a region has prolonged winter snow cover or mild winter temperatures.
Low Risk Classification
Value of the varieties being grown – if lower value varieties (e.g., juice grapes) are being grown.
Surrounding Vineyard Habitat – if no wooded edges or hedgerows/weedy areas are present around vineyards.
History of GBM injury – if vineyards seldom have problems with GBM. The history of GBM injury for each site is acquired by maintaining scouting records of vineyards over the years.
Climatic factors related to the region – if permanent snow cover is rare and site is prone to severe winter temperatures.
Intermediate Risk Classification – is a catch all classification. If it isn’t High or Low risk then site is classified as Intermediate risk.
Life cycle and description of GBM
Knowledge about the life cycle and ability to identify the pest and injury caused is important for successful management. Moths emerge from the overwintering pupal stage in spring. Emergence in Erie County, Pa. occurs in late May but in other areas of the state this may occur 2 -3 weeks earlier. These moths are small (about 6 mm), brownish with grey-blue coloration at the base of wings (Figure 1). Unless pheromone traps are used it is unlikely that moths will be observed. Adults are active around dusk and have a distinctive zig zag pattern in flight. Mated females lay eggs singly on flower clusters or berries. Eggs are very small (< 1mm), scale-like and whitish, opaque (Figure 2). Due to their size, eggs are difficult to observe without a hand lens. Early in the season larvae hatching from eggs will web together small berries to feed. However, when berries reach about 5 – 7 mm in size, larvae will bore directly into berries to feed. Newly hatched larvae are tiny with white bodies and black head capsules. Later stages are brownish to purple in coloration (Figure 3). Upon completing development larvae exit berries and either drop to the ground to pupate in leaf litter or some will pupate in the canopy in a semicircular leaf flap. Pupae which are encased in leaf sections are light brown to greenish in coloration (5 mm). Leaves with pupae will remain underneath the trellis if there is poor weed control or will be moved by the wind and collect along wood edges, or in brushy areas. Adults will emerge from pupae to begin the next generation. There are usually 3 – 4 generations of GBM per year in Pennsylvania, depending on temperatures during the growing season.
Regular scouting throughout the season (at least weekly) is critical in determining if and where applications should be applied for GBM. A scouting protocol for GBM is described in “Bulletin 138, Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper” .
This protocol recommends selecting four different areas in your vineyard to be sampled during each scouting event. Two different areas should be checked in the interior of the vineyard and two different areas along the exterior (border) portions of the vineyard. At each of the four sampling sites, randomly select 5 vines and examine 10 clusters/vine for GBM injury. Determine separate injury levels (# injured clusters/100 clusters = % injured clusters) for the interior and exterior portions of the vineyard. It is important to keep separate injury levels for the interior and exterior areas because border areas near woodlines/hedgerows will usually have higher levels of injury. Therefore, border areas may need an insecticide application while interior areas may not.
When scouting early in the season look for webbing in the clusters (Figure 4). Until berries are large enough to enter, larvae will web together multiple berries and feed from inside webbing sites. Some varieties (e.g., Concord) may exhibit a distinct reddening of portions of the berry if injury occurs before veraison (Figure 5) while other varieties do not (Figure 6). Later in the season look for holes, splits, webbing or dark tunneling underneath berry skin (Figure 7). If injured berries are broken open then larvae may be found.
Map vineyards and keep scouting records – Develop detailed maps of your vineyards and surrounding topography. Keep records of GBM injury levels for each scouting date and vineyard sections checked. These records will provide a GBM history per site.
Pheromone Traps – GBM flight periods can be monitored using commercially available pheromone traps (Figure 8). Traps and pheromone caps can be purchased from a number of sources such as at Great Lakes IPM, Inc. and Scentry Biologicals, Inc. Monitoring traps are baited with small rubber lures impregnated with GBM female sex pheromone for attracting male moths. Pheromone traps may provide an idea of population levels at your vineyard site and can be used as a scouting tool to indicate flight periods. However, trap data are not used for timing of spray applications due to ambiguity concerning correlation of capture numbers and berry injury levels.
Cultural practices are integral for any integrated pest management program. Therefore, maintain good weed control under the trellis. Poor weed management resulting in excessive vegetation under the vines can harbor grape berry moth (GBM) pupae.
Viticultural practices that promote a more open, less dense canopy resulting in better exposure of clusters to sunlight (e.g., shoot thinning, leaf removal, judicious use of nitrogen) will not only improve quality of fruit but will enable better spray coverage.
Vineyard area maintenance such as preventing overgrown, weedy areas around the vineyard will reduce overwintering sites for GBM pupae. If possible, removal of wild grapevines near the vineyard will decrease potential reservoir sites.
2) TREATMENT PHASE
To accurately time insecticide applications it is recommended that the Grape Berry Moth Degree-Day Model be used. The GBM DD Model is a temperature-driven developmental model developed by Tobin and Saunders at Penn State. This model is incorporated into Cornell’s Network for Environmental and Weather Applications (NEWA). Collaborative research at Penn State, Cornell and Michigan State Universities has shown that use of this developmental model can improve GBM management. For a comprehensive explanation concerning the development and use of this forecasting model consult “Focus on Females Provides New Insights for Grape Berry Moth Management” , Issue 14, May 2013.
Use of the GBM DD Model:
- CHECK the NEWA weather station closest to your vineyard. There are a number of NEWA weather stations located throughout Pennsylvania. However, the majority of vineyards outside Erie County, PA will probably not be close enough (i.e., within a few miles) to a NEWA station for this option to be useful. But you can still use the GBM DD Model by recording daily maximum and minimum temperature data on your own. Options include either purchasing a max/min thermometer or weather station for your site. The RainWise AgroMET & IP-100 Package http://www.rainwise.com/ is the authorized choice for participation into the NEWA network.
- MONITOR and RECORD the date of wild grape bloom (i.e., when approximately 50% of flowers open) for each vineyard site. Research has shown that egg laying by females that emerge in the spring (first generation) is closely associated with bloom of wild grapevines. Therefore, the majority of eggs from this generation are laid on wild grape clusters and not in cultivated vineyards. NOTE: If using a NEWA site then enter the date of wild grape bloom into the model. If you do not record a wild grape bloom date for your site then the model does provide an estimated date for the weather station that is used.
- TRACK GBM degree days using a NEWA station closest to your vineyard site OR keep a running total throughout the season of GBM degree days [(Daily MAX + MIN Temperatures)/2) – 47.14 F] starting on the recorded date of wild grape bloom.
- SCOUT to determine injury levels.
- SPRAY (if needed) as close to the designated degree day timings as possible.
The model recommends an insecticide treatment in high and possibly intermediate risk sites when: 810 GBM degree days are accumulated for the second generation; 1620 GBM degree days for the third generation; and 2430 GBM degree days (if harvest has not yet occurred) in years that a fourth generation occurs. Insecticides such as Intrepid, Altacor, and Delegate are suggested for these timings.
If using broad spectrum contact insecticides (e.g., pyrethroids) then applications should be delayed about 100 GBM degree days for each generation (i.e., 910, 1720, 2530 GBM degree days).
Insecticide Choices/Application Practices
There are numerous insecticides effective for GBM which are registered for use in Pennsylvania. Consult the 2017 New York and Pennsylvania Pest Management Guidelines for Grapes (https://store.cornell.edu/p-197039-2017-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx).
Rotate insecticides with different modes of action into your GBM spray program to prevent/delay insecticide resistance. Read the label to determine if a spray adjuvant and/or pH adjustment to spray water is required. Also, incorporate more selective insecticides (e.g., Intrepid, Altacor, Delegate) into your spray program which will aid in conserving natural enemies.
Good spray coverage on clusters is critical. Therefore, spray every row and use appropriate gallonage, speed, pressure, and nozzles for good cluster coverage as the size of the canopy increases throughout the season.
3) POST-TREATMENT PHASE
Evaluate efficacy of applications
Don’t assume that because an insecticide was applied that GBM was controlled. After an insecticide application check areas that were sprayed to determine the effectiveness of the application. High Risk sites in Erie County, PA have benefited from back to back applications (about 10 days apart) per generation due to extremely high population levels at these sites.
Continue to Scout
Monitoring your vineyard(s) not only for GBM but also for other insects, diseases and weeds should continue through harvest.
Keep Accurate Records
Accurate records should be kept each season for: scouting (e.g., dates, pests observed, vineyard location where observed, injury levels); pesticide applications (e.g., pesticides used, rates/acre, gallons/acre applied, etc.) and weather data.
Re – examine management practices
At the end of the season, especially if GBM was not adequately controlled, re – examine management practices by reviewing your records. A few factors to consider that contribute to poor control include: Inadequate Spray Coverage; Inaccurate Spray Timing; Too Few Applications; and Choice of Insecticides.
Change/Fine Tune management practices
The results of re-examining your practices may reveal flaws in your management strategy. If flaws are identified then be prepared to make the necessary changes in the future. Fine tuning your pest management strategy is an ongoing process which should evolve as long as you continue to farm.
By: Jody Timer, Research Technologist
The brown marmorated stink bug (BMSB), Halyomorpha halys (Stal) is an invasive species that has become a major pest in the eastern United States. This pest originally became a sizable problem in Mid-Atlantic vineyards, including southwestern Pennsylvania, during the 2010 growing season and continues to be a large-scale problem. The Lake Erie grape belt is the largest Concord grape growing region in the world. The recent appearance of the brown marmorated stink bug in Lake Erie vineyards has the potential to become problematic. After the mild winter of 2015-2016, the numbers of BMSB in this area began to increase rapidly. This winter, frequent complaints have been received from homeowner concerning the presence of BMSB in their houses.
BMSB have been found in both grape foliage and grape clusters; they seek the moisture, sugar, and warmth on the inside the clusters (especially overnight) and they often migrate to the cluster’s interior close to harvest. This makes the possibility of BMSB inside the cluster very likely when these grapes are mechanically harvested and transported to the processor.
All BMSB life stages (5 instars) have been observed in vineyards indicating that grapes are a suitable crop for BMSB development, and all stages have been found to cause direct damage to grapes (Bernon 2004). At the Lake Erie Grape Laboratory, we have maintained an adult BMSB colony on a diet of Concord grapes with no apparent development problems. It has also been estimated that the presence of 5 BMSB per grape cluster may lead to 37% loss in grape yield as a result of BMSB damage (Smith et al. 2014). With the yearly increase of numbers of BMSB in the Pennsylvania vineyards, the possibility of BMSB tainting the juice produced in this area is becoming a primary concern to processors, growers, marketers, and consumers.
Insects produce small, volatile molecules that may be imparted to juice and wine during crush. Humans are able to detect these molecules at extremely low concentrations. For example, 2-isopropyl-3-methoxypyrazine (IPMP) from Multicolored ladybeetles (ladybug taint) is detectable at 0.30 ng/L concentrations in Concord grape juice (Pickering et al. 2008). BMSB have a distinctive odor which has been described as green, cilantro-like, which may or may not be off-putting within grape juice aroma. BMSBs produce taint associated compounds as allomones, alarm pheromones, aggregation pheromones, and kairomones. These compounds are mainly released from the dorsal abdominal glands in nymphs and paired metathoracic glands in adults (Baldwin et al. 2014). When BMSBs are crushed along with grape clusters, release of these compounds could potentially taint in the juice.
Multidimensional gas chromatography mass spectrometry (MDGC-MS) analysis of stressed BMSB, adults and nymphs, has been used to identify more than 39 compounds. The volatile compounds in the taint are tridecane, dodecane, trans-2-decenal and trans-2-undecen-1-ol. Tridecane and trans-2-decenal together constitute at least 70% of BMSB taint (Baldwin et al. 2014; Solomon 2013). Trans-2-decenal, is the major irritant and is believed to be responsible for the potent stink odor from BMSB. However, being an extremely unstable compound it can easily break down, and its degradation products lack the distinctive BMSB odor (Baldwin et al. 2014). When trans-2-decenal was added to red wine (Pinot Noir) the morning of testing, the detection threshold was in the low microgram per liter (ug/L) range (Mohekar et al 2015). However, because trans-2-decenal is unstable, this may not reflect what happens when juice is processed and stored. Joe Fiola from University of Maryland, reported that while 5-10 BMSB per 25 pound lug of white grapes imparted a perceptible taint in raw juice for up to four months in some cases, the taint was not perceptible in the wine after fermentation (Fiola 2011). Mohekar and colleagues, from Oregon State, reported that trans-2-decenal, has a detection threshold in the ug/L range in Pinot Noir wines, and was able to be detected by tasters (Mohekar et al 2016).
Informal sensory testing with the on-site staff was performed at the Lake Erie Regional Grape Research laboratory. Small batches of grape juice were produced using a residential Kitchen Aid® juicer, and increasing numbers of BMSB were added. Batches of juice containing the equivalent of 0, 2, 10, and 25 BMSB per lug (~35 lbs. of Concord grapes) were tasted raw and after high-temperature, short-time pasteurization (HTST) by five staff members. In blinded triangle tests (2 blanks and 1 spiked sample), 5 of 5 individuals correctly identify the spiked sample of the 25 BMSB/lug juice (both raw and pasteurized); for the 10 BMSB sample, 4 of 5 correctly identified the spike in raw juice, and 5 of 5 identified the spiked sample for the pasteurized juice. The following month the pasteurized juice was re-tasted by 10 individuals and similar results were obtained. These tests suggest 25 BMSB/lug are sufficient to induce a perceivable flavor change in Concord grape juice. Following this testing, a set of samples were processed at the Food Science laboratory of Penn State, using industrially relevant methods (equivalent to Welch’s Corporation processing techniques), to assess if the odor-causing compounds secreted by BMSB were stable enough to transfer through the juicing, processing, pasteurization, and storing of grape juice and therefore cause it to be rejected by consumers. Large scale sensory tests were then run with regular grape juice consumers to quantify rejection thresholds for BMSB-spiked, processed grape juice.
Grape clusters, with varying amounts of BMSB (0, 4, 8, 16, 24, and 32 BMSB, per 35 lbs), were crushed and destemmed; the juice was pasteurized, clarified and blended. Following storage for 8 weeks (2 months after initial processing), sensory testing was performed with grape juice consumers in the controlled sensory testing facility to determine rejection thresholds for different levels of BMSB. Sensory testing was then repeated 8 weeks later (4 months after initial processing).
Despite the use of BMSB levels that clearly caused a noticeable change in the flavor of processed juice in pilot testing, we were unable to find a level of BMSB that caused rejection in consumers following processing and storage at either time point.
As the area’s BMSB population increases, this research will be notably important for processor to determine threshold levels at harvest. This research suggest that taint from BMSB at high but realistic doses for the Lake Erie grape-growing region will not influence consumer acceptability. Conversely however, our results may not generalize to smaller producers in the area who make grape juice using exclusively from Concord grapes. Typically, this juice is sold as fresh juice with a limited shelf life. These smaller growers and producers should be aware of the possibility of taint in their juice especially with the increasing numbers of BMSB in the region. Pre-harvest scouting for BMSB should be conducted to determine if a pre-harvest BMSB insecticide spray should be applied.
Baldwin, R.L. IV, A. Zhang, S.W. Fultz, S. Abubeker, C. Harris, E.E. Connor, and D.L. Van Hekken (2014) Hot topic: Brown marmorated stink bug odor compounds do not transfer into milk by feeding bug-contaminated corn silage to lactating dairy cattle. J. Dairy Sci. 97. 1877-1884.
Bernon, G. (2004) Biology of Halyomorpha halys, the brown marmorated stink bug (BMSB) Final Report—USDA APHIS CPHST Project T3P01. USDA APHIS.
Fiola, J.A. (2011) Brown Marmorated Stink Bug (BMSB) Part 3-Fruit Damage and Juice/Wine Taint. Timely Viticulture. University of Maryland extension,
http://www.grapesand fruit.umd.edu. Accessed October, 2016
Mohekar. P. (2016) Brown Marmorated Stink Bug (BMSB), Halyomorpha halys Taint in Wine: Impact on Wine Sensory, Effect of Wine-processing and Management Techniques. Dissertation Oregon State University
Mohekar, P., Tomasino, E., Wiman, N.G., (2015) Defining defensive secretions of brown marmorated stink bug, Halyomorpha halys. Presented at the 2015 Annual Meeting of the Entomological Society of America, Minneapolis, MN
Pfeiffer, D. G., T. C. Leskey and H. J. Burrack, (2012) Threatening the harvest: The threat from three invasive insects in late season vineyards, pp. 449-474. In N. J. Bostanian,
Pfeiffer, D., J. Fiola, B. Lamp, K. Rane, A. Nielsen, D. Polk, B. Petty, D. Ward, M. Saunders, J. Timer, C. Hedstrom, P. Mohekar, N. Wiman, E. Tomasino and V. Walton, (2013) BMSB in Vineyards and Wines. www.stopbmsb.org/stopBMSB/assets/File/Research/BMSB…/Vineyards-Vaughn.pd . Accessed September 2016
Pickering, G.J., Karthik, A., Inglis, D., Sears, M. and K. Ker, (2008). Detection Thresholds for 2-Isopropyl-3-Methoxypyrazine in Concord and Niagara Grape Juice. Journal of Food Science, 73 (6): S262-S266.
Prescott, J., Hayes, J. E., & Byrnes, N. K. (2014). Sensory Science. In N. K. V. Alfen (Ed.), Encyclopedia of Agriculture and Food Systems (pp. 80-101). San Diego: Elsevier.
Smith, J.R., Hesler, S.P., and Loeb, G.M., (2014) Potential Impact of Halyomorpha halys (Hemiptera: Pentatomidae) on Grape Production in the Finger Lakes Region of New York. J. Entomol. Sci. 49, 290–303. doi:10.18474/0749-8004-49.3.290
Solomon, D., D. Dutcher, and T. Raymond, (2013) Characterization of Halyomorpha halys (brown marmorated stink bug) biogenic volatile organic compound emissions and their role in secondary organic aerosol formation. J. Air Waste Manag. Assoc. 1995 63, 1264–1269.
Welch’s Corporation, www.Welch’s.com Accessed August 2016.
By: Andy Muza, Penn State Extension – Erie County
Another harvest will soon be over for grape growers in Pennsylvania and the winter season is fast approaching. Take the time this winter to explore the resources below to prepare for next season’s pest problems.
The following 5 references provide information on identification and management of insect, disease and weed problems in vineyards. I suggest purchasing these items before next season begins. Although the cost will be over $250 it is well worth having these invaluable resources in your viticultural library.
- New York and Pennsylvania Pest Management Guidelines for Grapes: Every commercial grape grower in Pennsylvania should have a copy of the current guidelines. This guideline provides a wealth of information on insect, disease and weed management with pesticide options, rates, and schedules, as well as, a chapter on sprayer technology.
- A Pocket Guide for Grape IPM Scouting of Grapes in North Central & Eastern U.S.:This pocket reference book is for use while scouting in the vineyard. The guide provides concise information and color photographs on insect/mite pests, natural enemies, diseases and disorders.
- Compendium of Grape Diseases, Disorders, and Pests, Second Edition: This new edition is an expanded version of the original Compendium with 375 photos and drawings and containing updated information about pathogens including additional diseases. The second edition is divided into 4 parts covering: diseases caused by biotic factors (e.g., fungi, bacteria, viruses etc.); disease – like symptoms caused by insects and mites; disorders caused by abiotic factors (e.g., environmental stresses, nutritional disorders, etc.); and fungicides/spray technology.
- Weeds of the Northeast: Described as the first comprehensive weed identification manual available for the Northeast enabling identification of almost 300 common and economically important weeds in the region. The manual contains color photos of vegetative and flowering stages of weeds, as well as, seed photos.
- Wine Grape Production Guide for Eastern North America: A comprehensive reference on all aspects of wine grape production (e.g., varieties, canopy management, nutrient management, etc.) including chapters on disease management, insect and mite pests and vineyard weed management.
Insect and Disease Resources – 2016 articles
Articles from the 2016 season that should be reviewed include:
- 2016 Pre-Bloom Disease Management Review by Bryan Hed, Penn State University
- 2016 Post Bloom Disease Management Review by Bryan Hed, Penn State University
- Late summer/early fall grape disease control; 2016 by Bryan Hed, Penn State University
GRAPE DISEASE CONTROL, 2016 by Wayne F. Wilcox, Cornell University (74 pages). Dr. Wilcox provides comprehensive coverage of relative research and disease management options.
Grape Insect and Mite Pests – 2016 Field Season by Greg Loeb, Cornell University (21 pages). Dr. Loeb provides a thorough review of insect pests that you might see throughout the season in the vineyard. Included are 18 photos of pests/injury along with management guidelines.
Insect and Disease Resources – Web sites
IPM –Grapes (Cornell): Information is available on diseases, insect and mites, weeds, wildlife, organic IPM, spray technology and pesticides.
NYS IPM : Fruit IPM Fact Sheets (Cornell): Fact sheets on diseases and insects on grapes, tree fruit and small fruit. A total of 22 fact sheets pertain to insects and diseases on grapes.
Identifying Grape Insects (Michigan State University): The information on this site is from the previously mentioned resource, A Pocket Guide for Grape IPM Scouting of Grapes in North Central & Eastern U.S. and is categorized by: Pests attacking; buds, leaves, fruit, root, during harvest. Also includes beneficial insects and mites.
Mid Atlantic Vineyards Grape IPM (Virginia Tech): Insect fact sheets categorized by: direct pests – fruit; indirect pests – leaves; trunk and cane feeders; and root feeders.
Ontario Grape IPM: This site provides information on a variety of topics including: insects and mites; diseases and disorders; weeds; herbicide injury; identification keys; etc.
Growing Grapes – Vineyard IPM (eXtension): Articles both in English and Spanish on: insects, diseases, weeds, animal pests and problems not caused by insects or diseases.
Weed Resources – Web sites
New Jersey Weed Gallery (Rutgers): Photos and descriptions of weeds found in New Jersey. Weeds can be viewed by common name, Latin name or thumbnail images.
Weed Identification Guide (Virginia Tech): These pages are intended to aide in the identification of common weeds and weed seedlings found throughout Virginia and the Southeastern U.S. The weed pictures are arranged alphabetically by common name.
UMass Extension Weed Herbarium (University of Massachusetts): Identification notes and color photos of over 500 weeds.
UC-IPM Weed Photo Gallery (University of California): Common names link to pages with weed descriptions and photos often showing several stages of development.
By: Jody Timer, Penn State Dept. of Entomology, Lake Erie Regional Wine Research and Extension Center
Research has been conducted recently at the Lake Erie Grape Research and Extension Center, to determine the prevalence of spotted wing Drosophila throughout the Lake Erie grape growing region. Spotted wing Drosophila, Drosophila suzukii, Matsumura (Diptera: Drosophilae) (SWD) is an invasive vinegar fly of East Asian origin, that was recently introduced into the United States. It was first found in California in 2008 and is now found in all major fruit-growing regions of the country including Pennsylvania. It was first discovered in Pennsylvania’s Lake Erie grape growing region in the late fall of 2011. The potential infestation rate of spotted wing Drosophila differs from other vinegar flies because the female possess a serrated ovipositor that cuts into healthy fruit to lay eggs. Consequently, spotted wing Drosophila (SWD) larvae can be found in fruit that is just ripening: https://youtu.be/dPr61VC2gyo
During egg-laying, it is believed that sour rot and fungal disease can also be introduced, further affecting the fruit quality. SWD are thought to overwinter primarily as adult females, and they prefer moderate, cool wet climates similar to the Lake Erie grape belt. Adults live approximately two to nine weeks. During this time, one adult female can lay 100 to 600 eggs in fruit. During peak temperatures, a female can lay more than 100 eggs a day. Such a high reproduction rate indicates the SWDs’ high potential for fruit infestation and their potential for spreading rapidly through a field or a vineyard. Eggs hatch in two hours to three days with the larvae feeding in the fruit for about 3 to 13 days before pupating into adults. Thus, multiple generations occur per year. Drosophila suzukii is now one of the most serious pests of thin-skinned fruits including blueberry, raspberry, cherry, grape, and strawberry. Because this pest is similar in appearance to common vinegar flies, the greatest problems have occurred when populations went unnoticed and thus remained untreated until they caused considerable damage to crops. A good YouTube video on how to identify SWD damage is: https://youtu.be/DLNDnMMfWfs
In our research we sent up 25 traps for SWD though out the region. By harvest SWD were found in all of the traps. They began to attact the grapes at verasion, and by harvest the SWD outnumber the other vinegar flies (fruit flies) in all of the traps. Over the entire season, the percentage of SWD to other vinegar flies caught in our traps over the last three years is approximately 25-30%. We also found numerous SWD in the traps we placed by cherries, strawberries, raspberries, and corn. Females SWD were caught in traps before males and males were caught in the fall after the females. It is believed that the overwintering populations are mostly female.
We then conducted 2 and 4 choice and no-choice test with common wine and juice grape varieties SWD infested all of the grapes we tested. They showed no strong preference for cultivar of grape, color of grape, or brix’s (as long as the variety was past verasion). An interesting side discovery from our research was that SWD does not appear to attack native wild grapes. Even given no other source (no choice testing) it only laid a few eggs on the wild grapes. SWD do attack injured grapes before non-injured.
These vinegar flies become a greater problem the later the grapes are harvested, due to late season rots, which makes the later ripening wine grapes particularly at risk. Although this insect is a concern of juice grape growers, it should be of decided concern to wine grape growers. Besides the problem of late season rots this insect can impart, there is the problem of wine taint. The beneficial aspects of fruit fly infestation of grapes are stated in a TreeHugger article. It states that the fruit fly also helps the wine by carrying yeast on its body on imparting this to the grapes. Saying that the new knowledge about the interaction between fruit flies and yeast “helps us understand why yeasts make interesting aromas, and opens up the possibility of using flies to help find new yeasts.” Matthew Goddard, from the School of Biological Sciences at the University of Auckland, studied the matter. Goddard’s studies found that when fruit flies had a choice of yeasts, they carried the aromatic wine yeast 100 times more – showing that the smell did have an effect. According to LiveScience, they can find wine or fermenting juice from half a mile away. These beneficial effects are decidedly outweighed by the negative effects from fruit fly infestation. The alcohol in the wine softens the fly’s body and it releases a nasty-smelling enzyme into the wine, they can also transmit large Acetobacter populations. Acetobacter can cause of host of other problem with wine making such as acetic acid. SWD is of special concern because of their ability to lay eggs in otherwise healthy fruit. Often the fruit will not look damaged until the larval populations, which have hatched from the internally laid eggs, grow and feed internally on the grape berry till it eventually collapses. This can happen after seemingly healthy fruit has been harvested and sent to wineries.