Grape Berry Moth: Answers to questions you should be asking about this native pest
By: Andy Muza, Penn State Extension – Erie County
In Erie County, Pennsylvania, grape growers are more than familiar with the perennial, insect pest known as grape berry moth (GBM). However, as more vineyards are being planted throughout PA, growers in other areas of the state may be unaware of the threat that this destructive insect poses to grapes. Therefore, in this blog I will be discussing grape berry moth (GBM) by answering questions that a grower should ask if they are unfamiliar with this pest.
1) What is Grape Berry moth and why should I be concerned about this pest?
GBM is an insect in the Order: Lepidoptera (moths and butterflies) and Family:Tortricidae. It is native to the eastern U.S. and has evolved with wild grapes (e.g., Vitis riparia). GBM larvae feed on berries of grapevines which are spread throughout eastern woodlands. As commercial vineyards are being planted in counties across the state this insect will readily take advantage of the newly available food sources. Grape Grape berry moth is considered a serious pest of grapes throughout all of the eastern U.S. GBM larvae feed directly on berries causing yield loss due to: consumption of berries; berry shelling; and crop rejection due to contamination. In addition, feeding injury provides entry points for fungi (e.g., Botrytis) and bacteria which can cause cluster rots.
2) How do I identify grape berry moth and what is the life cycle?
GBM HAS FOUR LIFE STAGES: EGG, LARVA, PUPA AND ADULT
Egg – Laid singly on berries; very small (< 1mm); whitish, opaque; flat, oval, scale-like. Hatch in 3 – 8 days (temperature dependent).
Larva – 4 larval stages; Newly hatched – tiny, creamy white with dark head capsule; Later stages – greenish to purple coloration (10 mm).
Pupa – Light brown to greenish coloration (5 mm). Pupae encased in leaf sections which are easily moved by wind to wood edges, trashy areas.
Adult – Small moth (about 6 mm); brown coloration; base of wings grey- blue; brown patches at tips of wings. Moths active at dusk and fly in a zig zag pattern.
LIFE CYCLE This pest has 3-4 generations/year in PA, depending on seasonal temperatures. This insect overwinters in the pupal stage in plant debris on the vineyard floor or in protected sites, such as wooded areas, where leaf debris has collected. The adults emerge in spring (late May in Erie County, Pa.), mate, and females lay eggs on flower clusters and berries. Larvae hatch and web together small berries (early in the season) and feed, or bore into berries (at about 5 – 7 mm in size). Larvae exit berries after completing feeding and either: cut a semicircular flap in a leaf to pupate in the canopy; or drop to the ground and pupate in leaf litter. Adults emerge and continue this cycle for several generations throughout the season.
Grape Berry Moth Fact Sheets containing additional pictures of life stages, injury and life cycle information can be obtained at the following sites: NY IPM Program; Grapes.msu.edu; Mid-Atlantic Vineyards Grape IPM; and Ontario GrapeIPM.
3) How do I know if GBM is present and causing problems in my vineyard?
Indicators of potential GBM problems include: Feeding injury (small holes) in berries, shelling of berries, rotting clusters.
Scouting Regular scouting throughout the season is a critical component of GBM management and will reveal if this pest is present in the vineyard. A scouting protocol and assigning a GBM risk rating is outlined in “Bulletin 138, Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper”
When scouting, pay particular attention to areas most susceptible to infestations such as: border rows near woods, overgrown areas, tree lines, or any protected areas around the vineyard where leaf debris might collect.
Since other disease causing organisms may also cause injuries similar to GBM damage, examine clusters closely. What to look for: webbing in clusters; berries with holes, splits or dark tunneling underneath berry skin; reddish or brown discoloration of berries; presence of larva and/or frass in injured berries. Observation of eggs can be difficult due their small size so a hand lens is useful. Positioning clusters towards the sunlight as they are examined will aid in revealing eggs. Practice is required to acclimate your eyes for observation of eggs.
Map vineyards and keep records – Make 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 population levels can be monitored using commercially available pheromone traps. Monitoring traps are baited with small rubber lures impregnated with GBM female sex pheromone for attracting male moths. Pheromone traps can be used as a scouting tool to indicate flight periods and can provide an idea of population levels at your vineyard site. However, trap data are not used for timing of spray applications due to ambiguity concerning correlation of capture numbers and berry injury levels. Monitoring traps are available at Great Lakes IPM, Inc. and Scentry Biologicals, Inc.
4) How do I manage Grape Berry Moth?
CULTURAL PRACTICES Maintain good weed control under the trellis. Poor weed management resulting in excessive vegetation under the vines can harbor GBM pupae. Viticultural practices that promote a more open, less dense canopy resulting in better exposure of clusters to sunlight (e.g., judicious use of nitrogen, shoot and leaf removal) will not only improve quality of fruit but will enable better spray coverage. Vineyard Vineyard area maintenance such as preventing overgrown, trashy areas around the vineyard will reduce overwintering sites for GBM. Removal of wild grapevines near the vineyard will decrease potential reservoir sites.
GRAPE BERRY MOTH DEGREE-DAY MODEL
The temperature-driven developmental model for GBM was developed by Tobin and Saunders and is now incorporated into Cornell’s Network for Environmental and Weather Applications (NEWA). Currently, many grape growers in the Lake Erie Region have adopted this model to more accurately time insecticide applications for GBM management. Prior to the GBM forecasting model, grape growers in New York and in Erie County, PA used the grape berry moth risk assessment program to time insecticide applications. However, collaborative research at Penn State, Cornell and Michigan State Universities has shown that timing of insecticide applications using the GBM degree-day model results in less injury compared with the grape berry moth risk assessment protocol ( “Focus on Females Provides New Insights for Grape Berry Moth Management” , Issue 14, May 2013 ).
(I highly recommend reading this article by Saunders, Isaacs and Loeb which provides an excellent background concerning the development and explanation on use of this forecasting model).
Use of this developmental model can improve GBM management. However, to ensure the greatest efficacy a few steps are required:
- Check the NEWA weather station closest to your vineyard. If a weather station is not located close enough to your vineyard site then you will have to record temperature data on your own and follow the procedure outlined in “Focus on Females Provides New Insights for Grape Berry Moth Management” .
- Monitor and record the date of wild grape bloom (i.e., when approximately 50% of flowers open) for each site and enter these dates into the model. If you do not record a wild grape bloom date for your site then the model will provide an estimated date for the weather station that is used.
- Regularly check the model to track degree days.
- Scout both before and after insecticide applications.
- Incorporate GBM selective insecticides (i.e., Intrepid, Altacor, Belt, Delegate) into your spray program which will also aid in conserving natural enemies. Obtain a copy of the 2015 New York and Pennsylvania Pest Management Guidelines for Grapes . This guideline provides insecticide recommendations and efficacy information for grape berry moth management in Pennsylvania vineyards.
- Spray as close to the designated degree day timings as possible (i.e., the day of or within 1 or 2 days of the recommended date).
- Evaluate efficacy of applications.
It is important to be aware that the model provides the optimum timing for an insecticide treatment. However, the decision to apply an insecticide depends on your scouting data and the history of GBM injury at your site.
SPRAY APPLICATION PRACTICES
Obtaining good spray coverage on clusters is critical. However, this can be a challenging feat, particularly later in the season due to the extent of canopy growth. Therefore, it is important that diligent spray practices are adopted.
- Check equipment for proper working order (Hoses, pumps, nozzles, etc.).
- Calibrate Sprayer – sprayers should be calibrated at a minimum in the beginning of each season. Preferably 2 – 3 times/season as canopy growth increases. Consider using a patternator to check nozzle output and spray cards or fluorescent dye to check spray coverage. Two YouTube videos which are available to assist in calibration of an airblast sprayer for vineyards include: Calibration of Airblast Sprayers for Vineyards: Part 1 – Selecting and Changing Nozzles. U.S. version and Calibration of Airblast Sprayers for Vineyards: Part 2 – Measuring Liquid Flow. U.S. version by Andrew Landers – Cornell University.
- Be Aware of: Pesticide registrations; pesticide preharvest intervals; reentry intervals and pH of water sources. (The pH of water can vary throughout the season depending on source). Adjust pH if necessary according to the pesticide label.
- Use appropriate gallonage, speed, pressure, and nozzles for good cluster coverage as the size of the canopy increases throughout the season.
- Spray Every Row.
- Minimize Spray Drift.