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Options for Grape Berry Moth Management in Ontario Vineyards

Until 2008, grape growers relied primarily on synthetic pyrethroids for management of grape berry moth (GBM). These products are contact nerve poisons that are effective on all larval stages. They are applied around peak male moth flight as indicated by pheromone trap catches. Peak activity usually occurs within 1 week of "upswing" in pheromone trap catches, which is when numbers of male moths start to increase rapidly following sustained flight. Upswing in numbers corresponds to early egg-laying activity by females and subsequent egg-hatch. If you have attended the OFVC in the last few years and have read other articles in this newsletter, you likely know that the biology of GBM makes management a challenge. Maintaining good coverage has always been key to reducing damage.

Two "new" synthetic pyrethroid products are UP-Cyde (same active as Ripcord) and Perm-UP (same active as Pounce). Pyrethroids have a short period of effectiveness (7 days, less if daytime temperatures are higher than 25 C) so will likely have to be applied more than once per generation. Other "old" products registered for use include the OPs Guthion, Diazinon and Imidan, and the carbamate Sevin. Sevin is not commonly used because of residue problems (by LCBO standards) if it is applied after the bunch close stage. Guthion/Sniper has an extended re-entry period of 28 days, precluding any hand work or other activity in the vineyard. Imidan has a 14-day re-entry / pre-harvest period.

Fortunately, two new products were made available for use in vineyards in 2008: Delegate (Dow AgroSciences) and Altacor (DuPont Crop Protection).

• Delegate belongs to Group 5 of insecticides, the same group as Success. It is a nerve poison, but works in a different way than OP's or pyrethroids. Delegate works primarily by ingestion. Delegate has longer residual activity than Success, another Group 5 insecticide that is registered for GBM management. While Delegate and Success are labeled for suppression of GBM, in AAFC field trials, they provided control comparable to commercial standards. Delegate is not recommended for third generation of GBM. For Delegate, the PHI is 7 days and the REI is 12 hours.
• Altacor is a Group 28 compound. Products in this group have a different mode of action from other insecticides that affect the insect nervous system because it affects the muscles of the insect. Once the larva eats the insecticide, it stops feeding almost immediately and dies within a few days. The PHI is 14 days and the REI is 12 hours.

Altacor and Delegate (and Success) work primarily by ingestion against GBM and therefore must be eaten by the insect to achieve rapid knockdown of the pest. They are most effective on young larvae. Therefore, they will be most effective if applied after egg deposition but before the larvae exit the eggs. Because the products must be consumed, the timing is a lot more critical than it was for the older contact products. Altacor and Delegate should be applied earlier than more conventional products, and before peak flight of GBM occurs. A combination of regional and site-specific trap catches and degree day accumulations will be used to help time these products.

Another thing to consider is that since these new products must be eaten by the target pest, coverage is critical. GBM eggs are laid on the berries and the only thing outside the berry that the emerging larva eats is the "shell" of its egg when it exits - it spits out the bites of berry skin before it enters the berry. In order to ensure they ingest a lethal dose of insecticide, excellent coverage is required. Make sure to apply the products at recommended rates and with sufficient water volumes.

There are several benefits to using these new products.

1. They are from new chemical families that are different from pyrethroids, OPs and carbamates, so they are useful rotation partners for resistance management. This is particularly important in preserving pyrethroids for pre-pick sprays, as they have the shortest pre-harvest interval.
   
2. Very rainfast. Altacor and Delegate are absorbed into the waxy layer of plant tissues and are not removed with rainfall about 1 hr after spraying.
   
3. Not affected by temperature. The effectiveness of pyrethroids is significantly reduced with temperatures greater than 26 C while Altacor and Delgate work consistently regardless of temperature.
   
4. Long residual activity. The interval between sprays of Altacor or Delegate is 10-14 days while that for pyrethroids is 7 days. Fewer sprays of these newer products will be required; in fact, depending on trap catches, a single application may take care of an entire generation.
   Short re-entry period. The re-entry period for Altacor and Delegate is 12 hours.

Our suggested strategy for integrating these products is to use Altacor for second generation, Delegate for third generation and reserve pyrethroids for pre-pick sprays. As other insecticides that will replace synthetic pyrethroids become registered for use in grape in the (hopefully) near future, our recommendations for managing GBM will change - so stay tuned!

The alternative to juggling insecticide timings is to use mating disruption. Mating disruption works best when used in an area-wide program; a minimum of 2 ha is required but larger blocks are recommended. Isomate-GBM Plus is effective for 150 days. It should be applied prior to moth emergence in the spring (immediate pre-bloom, flower cluster with floret separation). In areas where large sources of mated females may migrate into the vineyard (areas with significant wild grape, poorly managed adjacent sites), supplemental insecticides may be required along border rows.

The following table summarizes the cost of a single treatment per ha based on the manufacturer's suggested retail price.

The pyrethroid insecticides are useful to cover the pre-pick period since they have such a short pre-harvest interval and also provide control of lady beetles. But they are also vulnerable to the development of resistance. While more expensive, rotation with one of the new products that are available is an investment in keeping the pyrethroids for when we need them most. Mating disruption appears expensive if looked at this technology only in terms of the cost per ha. However, at least some of this cost is compensated for by not having to worry about spray timing, no re-entry interval, no pesticide residues, no pre-harvest interval, fewer non-target effects and long-term resistance management.