Planning for Grape Berry Moth in August
By: Jody Timer
Lake Erie Regional Grape Research and Extension Center
The grape berry moth, Paralobesia viteana, (GBM) is, by far, the most destructive insect pest in the Eastern vineyards of the United States. Often the damage from these insects goes unnoticed until late in the season, which makes controlling them, and the damage that they cause, difficult.
This blog will be a brief overview of the grape berry moth’s life cycle, what to scout for, and some suggestions on how to control their infestations.
GBM has three, and often four, generations a year with larval infestation in vineyards increasing from generation to generation. These numerous generations contribute not only to their ability to be so ruinous, but also to their ability to build up a resistance to insecticides. The GBM overwinters in the pupae stage. The adults emerge in the spring from overwintered leaf litter and debris that gets blown from the vineyards to protected sites.
The mated females oviposit on developing buds, flower clusters, or grape berries. Upon hatching, 1st instars burrow into the grape and feed. There are four larval instars, and larvae fully develop in approximately 10-13 days. Typical loss of berries is due to GBM larva feeding internally, but additional significant losses can occur as a consequence of fruit rots brought on by this pestiferous insects’ damage to berries. The damage can extend to entire clusters resulting in major crop losses. Once the larva enters the berry, they are protected from insecticides.
Compounding these management decisions are the late season generation’s infestations in recent years that have caught growers unaware, resulting in additional crop losses. Growers need reliable and effective methods for assessing risk from GBM, and precise control options in many regions, to avoid significant economic damage. One tool, originally developed in the in the 1970s and 1980s, is a trap baited with synthetic sex pheromone. Unfortunately, the pheromone-based lure, as currently employed, is useful for indicating the first flight of overwintered male GBM, but cannot out-compete the female GBM in the vineyard. This causes the captures to be sporadic and consequently makes detecting the spray timings for subsequent generations difficult. A grape berry moth model was developed by Tobin et al. (2001) and was incorporated into Cornell’s NEWA website http://newa.cornell.edu. This website uses the wild grape bloom in a particular area as the starting point for degree day calculation. Once the wild grape bloom date is entered the website will give the growing degree day accumulation in your area, and spray timing recommendations.
According to the Grape Berry Moth Model found on the NEWA website, we are past, at, or rapidly approaching, the 1720 DD timeframe in the southeastern part of the state. The northwestern part of the state will have another 10 days at least, but scouting should be started now. When scouting for GBM, make sure to separate the berries. GBM tend to lay their eggs in- between berries which often makes their holes hard to detect. The 1720 DD timeframe is when contact insecticides should be applied for GBM in high risk vineyards and in low- and intermediate-risk vineyards where scouting showed damaged clusters above the 15% threshold. The best way to use the model would be to plug in the wild grape bloom date that you know for your region. The location and wild grape bloom date can make a significant difference in spray timing. If you do not know the wild bloom date, the model calculates one for your region. The GBM DD Model provides the optimum timing for an insecticide application. However, the decision to apply an insecticide should depend on scouting data and history of GBM injury at the site. (http://lergp.cce.cornell.edu/submission.php?id=69&crumb=ipm|ipm) contains a table listing the modes of actions of insecticides used, and which insecticides have shown efficacy, in New York and Pennsylvania vineyards.
|Tobin, P.C., S. Nagarkatti, and M.C. Saunders. 2001. Modeling development in grape berry moth (Lepidoptera: Tortricidae). Environ. Entomol. 30: 692-699.|