Grape Pests Updates – Spring 2016

By: Jody Timer

As a new grape season approaches, you all may be asking yourselves, “What is going to be my biggest headache this season?” As far as insects go, I would have to answer, as always, the grape berry moth (GBM).  In this blog I would like to touch on the most recent research regarding the grape berry moth, as well as, other insects to scout for in your vineyards in the early part of the growing season.

The last two growing seasons, growers expected to see a dramatic decline in GBM populations, due to the harsh winters and record breaking cold. The opposite scenario occurred when greater than average GBM infestations materialized.  So, what can we expect from this growing season?  The winter of 2015-2016 was mild, the spring started off warm, and then April slowed down the accumulation of degree days. The total accumulation of degree days for this season is only slightly ahead last season’s and is forecasted to catch up in the next week to within two days, with average temperatures throughout the rest of May.  With our current research, we aim to enhance the temperature-based phenology model to provide more detailed recommendations.  We are researching ways to optimize the timing of generation-specific interventions, thereby providing prevention of economic damage of subsequent generations. The number of generations of grape berry moth has been increasing from the traditional three generations per year to four plus. First, and most obvious, adding generations increases the overall attack potential. Second, and largely ignored, adding generations may increase the developmental asynchrony of the population. Given the already narrow time-window of vulnerable life stages, and changes in current and future insecticides, such developmental asynchrony increases the risk that late-season generations will require more than one insecticidal application to achieve control below industry-mandated economic thresholds.

The timing of chemical control of GBM is particularly challenging because the stages most vulnerable to insecticidal applications reside inside the berry for the majority of their life cycles. The result is an extremely narrow management window. (See http://newa.cornell.edu/index.php?page=berry-moth for the online forecasting tool for your growing regions). The early season developmental synchrony in GBM is caused by the relatively synchronous forcing of diapause, as adults emerge from diapausing pupae in late spring. Later in the season the generations become less and less synchronized and the peaks of emergence become blurred.  We are exploring the correlation with GBM spring emergence (DD) and the timing of wild grape bloom and the resulting asynchrony of the subsequent generations. Presently the wild grape bloom is used as the biofix for the NEWA GBM phenology forecast model. We expect GBM developmental synchrony to be dependent on multiple factors, most importantly, the rate of emergence in the spring. Our research is exploring the possibility that the closer the GBM spring emergence coincides with grape bloom the greater the survivorship of the first generation of GBM. Consequently, a large first generation emergence would result in subsequent generations, all of which would emerge in the presences of suitable hosts, exponentially proliferating. For example, in the Lake Erie grape growing region the wild grape bloom usually occurs around the first week in June and the GBM peak in emergence occurs around the end of May.  However, if we experience a very warm spring and the GBM emerge sooner than the wild grape blooms, they will emerge with no suitable host and less of them will survive. Such enhanced models will allow for more adaptive generation-specific protocols of management, and could include novel control strategies.  According to this model, we are expecting another heavy infestation of grape berry moth this year.

Early Season Insects:

Grape Flea Beetle– also known as the steely beetle. These beetles are small (3/16”) and metallic blue in color. Beetles overwinter in the adult stage and emerge as grape buds begin to swell, with one generation per year.  This beetle primarily attacks buds of wild and cultivated grapevines.  They are one of the first insect pests to appear in the vineyards in the spring. The most significant injury caused by this pest is due to adults feeding on swollen grape buds, often destroying the developing bud. They have the potential of causing considerable damage under the right conditions; specifically when we get a prolonged swollen bud stage. Look for damage from steely beetle along the edges of the vineyard. By about 1/2” growth the threat of economic loss from this pest is over. Infestations are worse on wooded edges. They get their name from their ability to jump.

Climbing Cutworms: There are several species of cutworm larvae feed on grape buds during the swell stage. The injury to buds can be confused with grape flea beetle damage. The moths are night flyers and the larvae are night feeders. Both stages hide during the day. Larvae have a brown to gray coloration with darker stripes or dots along the body, and are 30-36 mm long. Vineyards with weed cover under the trellis and areas with sandy soils are at greater risk for injury. The greatest economic injury occurs during bud swell in the spring. Scout frequently during this time.

3 – 12 INCH SHOOT GROWTH

Banded Grape Bug and/or Lygocoris inconspicuous – both of these insects have piercing and sucking type mouthparts. Banded grape bug nymphs have antennae with black and white bands, green/brown bodies and are <1/2”. Lygocoris inconspicuous nymphs are slightly smaller with light green antennae (no bands) and light green bodies. Nymphs (immature stage) of both insects feed on developing flower clusters by piercing florets, pedicels and rachises. Begin scouting when shoots are 3 – 5” in length and continue until shoots are at least 12”. See scouting video, below – Banded Grape Bug LERGPvids:

Grape Phylloxera (leaf form)Grape Phylloxera. Grape phylloxera is an aphid-like insect with a complex life-cycle that causes feeding galls on either roots or leaves. The life cycle is different for the foliar and root forms of this insect. The root form is the more destructive of the 2 forms but is managed by grafting susceptible varieties to phylloxera resistant/tolerant rootstocks. Leaf galls are in the shape of pouches or and can contain several adults and hundreds of eggs or immature stages. Root galls are swellings on the root, sometimes showing a hook shape where the phylloxera feed at the elbow of the hook. At high densities, leaf galls can cause reduced photosynthesis. Root galls likely reduce root growth, the uptake of nutrients and water, and can create sites for invasion of pathogenic fungi. There is a wide range in susceptibility of grape varieties to both gall types. Begin scouting early in the season. Galls may become evident as soon as the 3-5 leaf stage so carefully examine the undersides of terminal leaves for warty looking, green to reddish growths. An insecticide application can be applied when first galls are forming. The most reliable method to determine if crawlers are active is to cut galls open and observe for presence of nymphs. Crawlers are extremely small so a good hand lens is needed.

Phylloxera Nymphs (Crawlers) Photo From: http://www.virginiafruit.ento.vt.edu/phylloxera.html

Phylloxera Nymphs (Crawlers) Photo From: http://www.virginiafruit.ento.vt.edu/phylloxera.html

Additional Insect Pests – During this time period a number of other insects (i.e., grape plume moth, grapevine epimenus, 8 – spotted forester, tumid/tomato gallmaker, grape cane gallmaker, and grape cane girdler) may also be present in the vineyard. Although injury from these insects may look alarming, damage is usually cosmetic and insecticide applications are rarely needed.

For more detailed information, please see: Andy Muza’s blog last spring: Grape Insect Pests to Watch for from: Bud Swell through Immediate Pre-Bloom Stages

Fact sheets on grape insect pests can be found at the following sites: Please click on the links below for more fact sheets specifically on insect pests found in the vineyard.

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