Grape Berry Moth – A Serious Pest of Table Grapes in Pennsylvania

Grape Berry Moth – A Serious Pest of Table Grapes in Pennsylvania

 

It is native to the eastern United States 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.

 

GBM is considered a serious pest of grapes throughout Pennsylvania and the eastern U.S. The larval stage feeds on berries and causes yield losses due to: consumption and shelling of berries, and by providing entry sites for fungi (e.g., Botrytis) that can cause cluster rots.

 

 

Usually when I discuss GBM with growers I am referring to management of this pest in juice and wine grape varieties. However, this insect can also cause substantial economic losses in table grape varieties particularly due to the economic value and lower tolerance for injury levels associated with these varieties. But GBM management is basically the same regardless of varieties grown. The caveat is that more insecticide applications are often required but economically justified for higher value varieties (i.e., table and wine grapes). I consider management of this pest to be a three phase process which includes:

 

 

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.

 

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.

 

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. 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.

 

Value of the varieties being grown

If higher value varieties such as table grapes, Vitis vinifera, or hybrids 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.

 

If wooded edges or hedgerows/weedy areas are present around vineyards.

 

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 tolerable injury levels are likely much lower for table grape varieties.

 

If a region has prolonged winter snow cover or mild winter temperatures.

 

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.

 

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.

 

If permanent snow cover is rare and site is prone to severe winter temperatures.

 

Is a catch all classification. If it isn’t High or Low risk then site is classified as Intermediate risk.

 

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.