Viticultural considerations during bloom and early fruit development
In this week’s blog, you will find updates and information from several of our authors with an emphasis on disease and insect management and vine nutrient status.
Bloom and early fruit set disease management
By Bryan Hed, Department of Plant Pathology and Environmental Microbiology, Penn State Extension
Well, the 2018 season has gone from 0 to 100 mph over the past four weeks, and grapevine shoots are currently growing at a rate of at least an inch a day. Trying to keep grape tissue protected with pesticide sprays can be a bit of a challenge when canopies double or triple in size each week. However, now it’s time for the most critical fungicide applications of the season; the immediate pre and post-bloom sprays. This is your annual reminder. Fruit ($$) of all grape varieties are most vulnerable to infection from all the major fungal diseases at this time (black rot, Phomopsis, powdery and downy mildew), and in many places across Pennsylvania the previous 4 weeks have been warmer and wetter than average; the perfect setup for fungal disease development on fruit. There’s no more critical time to “spare no expense” than immediately before bloom to about 2 weeks (juice grapes) to 4 weeks (wine grapes) after bloom. Use best materials, apply for best coverage, and allow no more than 10-14 days between these next 2 to 3 sprays. At this time, do not rely on materials that we know are slipping in efficacy, or have already slipped in efficacy, due to the development of resistance in many parts of the East (ie, strobilurins and sterol inhibitors).
When I hear from growers that have experienced problems with fungal fruit infection in the past, breaches in disease control are most often traced to the period of grapevine development around bloom. Some common mistakes include: i) use of the wrong materials (there was resistance to what they used, their mix didn’t cover all diseases, their choice of materials wasn’t very effective, etc), ii) stretching of spray intervals (more than 10-14 days between the immediate pre and post bloom spray), iii) less than optimal coverage (canopies were too dense, canopy management was lacking, sprayers weren’t adjusted for maximum coverage, etc), iv) taking a vacation from farming during this period of time (all of the above?).
If you’re growing bunch rot susceptible wine varieties, fruit-zone leaf removal around or shortly after bloom, can improve coverage and create a fruit-zone environment that is less favorable for the growth of fungal pathogens (For more detailed information see: Early season grapevine canopy management, Part II: Early leaf removal). Strict pre-bloom sucker control can delay the rise of diseases like downy mildew and black rot that emanate from the vineyard floor. Pre-bloom shoot thinning, while shoots can be easily removed by hand, will not only balance canopies with yield but also improve the efficacy and value of fruit protection sprays. Proper weed control/maintenance of row middles and cover crop height can reduce humidity in the vineyard and improve drying time of plant surfaces after rainfall. Integrating these cultural practices into your pre-bloom crop management plan will greatly assist your fungicide applications toward maximizing fruit disease control during bloom.
For more details on the various diseases and how to deal with them during this critical fruit protection period, you may find it convenient to check out previous posts from April 7 and June 16, 2017:
Insect updates on Grape Berry Moth and Spotted Lanternfly
By Jody Timer, Entomology, Lake Erie Grape Research and Extension Station
Grape Berry Moth (GBM): The first grape berry moth for the season usually appear at about 150 degree days from January 1st. This year, in the Lake Erie Grape growing region, we had a late spring which resulted in a later-than-usual emergence of GBM (around May 15th). The emergence occurred much earlier for the growers in the Southeastern portion of the state. The research we have done in the past indicates that spraying for GBM prior to the first full generation (not this emerging generation) is more effective and will not adversely affect yields at harvest. So this generation, which starts to peak at wild grape bloom and continues for about 10 days, does not in most cases need to be sprayed. Wild grape bloom in the Lake Erie Grape growing region occurred around May 30th, it was as early as May 13th in the southeastern regions of PA. Wild grape bloom is used as the biofix for the NEWA system to start accumulating degree days. This system uses the GBM phenology model to recommend optimal spray timings for GBM http://newa.cornell.edu. It is important that you keep track of when wild bloom occurred in your area to allow the model to precisely track the GBM phenology. If you missed the wild bloom date, the NEWA system will calculate wild bloom for your area based on historical data. The best way to determine infestation of your vineyard is to scout for damage. This generation of GBM produces webbing on the flowers and clusters. This webbing, although harder to scout for than later berry damage, is a good indication of severity in the ensuing generations. If your vineyard has high GBM consider spraying more often during the upcoming generations. Grape berry moth can cause considerable damage to vineyards through berry damage and late season rots.
Spotted Lanternfly (Lycorma delicatula): This new invasive insect was first discovered in Bucks County in 2014, the affected area was placed under quarantine to prevent the movement of the insect and its egg masses. Prior to its discovery in the fall of 2014, the spotted lanternfly had not been found in the United States. This fall, when the adults were flying and laying eggs, the quarantine area saw considerable increases and movements of the population. As a result, the quarantine area has been expanded to include all of the counties in southeastern PA. There has also been a colony found in Virginia. Spotted lanternfly host plants including fruit trees, ornamentals, hardwood trees, and grapevines. These insects are exhibiting a preference for tree of heaven (Ailanthus altissima) and vines including grapevines. Spotted lanternfly has the potential to cause substantial damage. Some have estimated potential crop losses, which includes Pennsylvania apples, grapes, and hardwoods, at $18 billion dollars. While feeding on and damaging their host plants, spotted lanternfly also ejects a liquid called honeydew which causes sooty mold and attracts secondary insect pests. Spotted lanternfly overwinter as egg masses, which are small (about 1-4”) and greyish white. They somewhat resemble a dirt splatter.
The first nymphs began to hatch in late April or May and complete four instars. These nymphs are 4-9 mm long and wingless with black with white spots. The fourth instar develops red patches, and then emerge into adults in late summer. This time of the season it is important to scout for egg masses, which although hatched, would indicate an infestation in your area. The black and white nymph stage will be present now.
There is a team of state, federal, and local public officials, academic researchers, and extension personnel working on the problems dealing with this insect. It is important to report findings of spotted lanternfly is you are not in the quarantine area. The website: https://extension.psu.edu/spotted-lanternfly as well as the PDA website has important information on this insect and includes numbers to call if you find insects outside of the quarantine area.
Assessing vine nutrient status
By Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science
Proper vine nutrient management is crucial for the vineyard longevity, as it helps ensure adequate vegetative growth, fruit set and growth, and optimum wine quality. While some nutrients up-taken by the vine are recycled through fallen-leaves decomposition, the majority of nutrients leave the vineyard in harvested fruit, pruned-wood material (if the brushes are not chopped and left in the vineyard), or through leaching and runoff. Assessing vine nutrient status should be a routine practice and used not just to confirm a suspected nutrient deficiency.
To determine vine nutrient status in an established vineyard, plant tissue nutrient concentration should be analyzed at bloom and/or later in the season around véraison. A soil test is useful and can provide clarification, but has limited benefit. It will indicate relative nutrient availability, but it does not tell what and how much the vines absorb.
What type of tissue to collect for nutrient analyses
There is a long-standing debate about what leaf tissue (blade, petiole, or the whole leaf) best reflects vine nutrient status and correlates to nutrient requirements for optimum vine growth, yield, and fruit composition. However, in the eastern US, the sufficiency range (or target value) of each nutrient concentration is only defined for petiole tissue.
When to collect grapevine petiole samples for nutrient analyses
Collecting a petiole sample at both bloom and véraison and having it analyzed will provide meaningful insight when developing a nutrient management plan. For example, if you noticed visual symptoms of nutrient deficiency in the previous growing season (Figure 1), a nutrient test at bloom will help determine if there is an actual deficiency, and you will be able to correct it in a timely manner (1). Nutrient concentrations in leaf tissue tend to be more stable as the season progresses, so taking a sample at véraison is typically recommended compared to taking samples at bloom, especially for routine analysis (1).
How to collect grape leaf tissues for nutrient analyses
A comprehensive and illustrated guideline on how to collect whole leaf samples (which can also be used for petiole sampling) is on page 12 of the Vineyard nutrient management in Washington State extension bulletin. Be sure to sample each variety separately and to collect 50 large petioles or 100 small ones per variety.
Where to send the samples
Use a reliable lab in your area that has experience in vineyard tissue testing, and use the same lab each year so that the analysis is consistent. If you are in Pennsylvania you can send your plant tissue sample to the Penn State Agricultural Analytical Services Lab. Please be sure to provide all the information required to interpret the lab results (e.g., type of tissue, time of the year the sample was collected). Lab results will report the concentration of each nutrient analyzed and if its level is low/deficient, sufficient, or too high/excessive. If you need assistance with interpreting your report, contact your local extension for further assistance. You can find the contact information for your local Penn State Country Office by entering your zip code in the search field on this site: bit.ly/2J9yCPr
- Moyer M., Singer S., Hoheisel G., and Davenport J. – Vineyard Nutrient Management in Washington State, EM111e (Bulletin) Washington State University
Comments concerning insect and disease management at this time of the season (Immediate Prebloom – Early Postbloom period)
By Andy Muza, Penn State Extension – Erie County
I’ll begin by stating that every commercial grape grower in Pennsylvania should have a copy of the 2018 New York and Pennsylvania Pest Management Guidelines for Grapes: https://store.cornell.edu/p-201631-2018-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx 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.
Also, monitoring your vineyard(s) at least weekly throughout the season is critical for managing pests. Frequent scouting will alert you to problems developing in the vineyard and provide the information needed to make informed decisions concerning pesticide applications. (You won’t know what’s out there if you’re not).
Diseases – When thinking about disease management the first thing that commonly comes to mind are fungicide applications. However, cultural practices (e.g. shoot thinning, leaf removal in the fruit zone, etc.) are integral components of a disease management strategy and should be used whenever applicable.
As Bryan Hed mentions and deserves repeating, The Immediate Prebloom (just before blossoms open) through early post-bloom/fruit set period is a critical time for managing fruit infections caused by phomopsis, black rot, powdery mildew and downy mildew. Fungicide protection for botrytis on tight – clustered varieties at bloom (when 80 – 90% of caps have fallen) can also be important in wet seasons.
Insects – Two important insect pests that Jody Timer is covering are grape berry moth and spotted lanternfly. (For additional information on grape berry moth see: Three Phases to Managing Grape Berry Moth https://psuwineandgrapes.wordpress.com/2017/04/28/three-phases-to-managing-grape-berry-moth/ and Grape Berry Moth: Answers to questions you should be asking about this native pest https://psuwineandgrapes.wordpress.com/2015/05/15/grape-berry-moth-answers-to-questions-you-should-be-asking-about-this-native-pest/ ).
I will briefly mention 2 of the more widespread, leaf-feeding pests that you are likely to see sometime this season which are grape leafhopper and Japanese beetle.
Grape Leafhopper – There are several species of leafhoppers in the genus Erythroneura that feed on grape foliage. 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. The greatest risk for economic losses due to grape leafhopper feeding occurs during hot, dry years in vineyards with heavy crop loads and high leafhopper populations. In most years, the majority of vineyards in Pennsylvania should not require an insecticide treatment specifically for management of grape leafhopper. However, the decision to apply an insecticide should be based on scouting information and threshold levels. (For more detailed information see: Grape Leafhoppers https://psuwineandgrapes.wordpress.com/2017/06/09/grape-leafhoppers/ ).
Japanese Beetle – Adult beetles feed on over 300 species of plants including grape. They prefer smooth, thinner types of grape leaves which are characteristic of many wine grape varieties (e.g., Chardonnay, Traminette, and Vidal Blanc). Feeding injury, depending on severity, can result in leaves having a skeletonized appearance due to consumption of the soft leaf tissues between veins. Research has shown that grapevines can tolerate a fair amount of leaf area loss without detrimental effects. However, no economic threshold level has been established for leaf injury on grapes caused by Japanese beetle. Since young vineyard blocks, vines in grow tubes and many wine varieties are vulnerable to serious leaf loss by Japanese beetle feeding consistent monitoring is important. (For more detailed information see: Japanese Beetle: A Common Pest in the Vineyard https://psuwineandgrapes.wordpress.com/2016/07/09/japanese-beetle-a-common-pest-in-the-vineyard/).