Feb 10, 2009

Control Codling Moth Without Organophosphate Sprays

Azinphos-methyl (AZM, Guthion) has been the most-used insecticide in apples since the late 1960s, primarily as a control for apple’s key pest, the codling moth (CM).

However, the decision by EPA to phase out AZM after 2012 signals the end of this product’s use by tree fruit growers. AZM belongs to a class of insecticides, the organophosphates (OP), that has been the primary target of regulatory action by EPA.

EPA has registered several new insecticides that it categorized as reduced-risk and OP alternatives. Successfully replacing AZM requires that growers understand how the new products work (mode of action) and know the codling moth life stage at which each product asserts control.

Creating management programs with OP-alternative products will require a strategic plan that takes advantage of each product’s potential to control multiple pests and optimizes efficacy through precise timing, spray coverage and appropriate tank-mixing of products with different modes of action.

Now is the time to develop a pest management plan that will be in place when AZM is no longer part of the control picture.

Mating disruption

A key to successful codling moth control is to disrupt the life cycle in multiple places. Few OP-alternatives have activity against adult CM; however, mating disruption applied before moths emerge can effectively reduce the number of eggs deposited in the orchard. Using CM mating disruption can be one of the most beneficial IPM decisions a grower can make.

We have observed that, even when CM pressure is high, pheromones plus supplemental insecticides provide better crop protection than relying on insecticides alone. While mating disruption using pheromones represents an additional cost to the grower, it’s a cost that is usually offset by better CM control and a decrease in the number of insecticide applications required to achieve superior crop protection.

Ovicides

Ovicides are insecticides that kill eggs. Traditional CM control programs have focused on control of the CM larvae at egg hatch. Some OP alternatives allow growers to target the egg stage. The insect growth regulators (IGR) – Esteem (pyriproxyfen), Intrepid (methoxyfenozide), Rimon (novaluron) and a newly registered product, Altacor (rynaxypyr) – kill eggs that are deposited on top of orchard residues. Optimal timing for these products is between 75 and 150 CM degree-days (DD). The added value of using IGRs at this time is that they also kill overwintering LR larvae.

Horticultural mineral oil (HMO) is also an ovicide, but acts when applied topically to eggs that have already been deposited. The optimal timing for HMO is just prior to the beginning of the egg-hatch period, 200 DD. Control of CM eggs with HMO is possible with repeat applications (150-200 DD intervals) but this approach can be confounded by the need to use other chemicals early in the season. HMO concentrations of 1 percent are necessary to kill CM eggs. When used as an adjuvant, HMO at 1 percent can improve CM control with the new insecticides. Unlike IGRs, HMO does not provide control of leafroller larvae.

Larvicides

Larvicides are insecticides that kill larvae. CM larvae find and enter the fruit within hours of hatching. OP insecticides kill CM larvae when they crawl across or consume the toxic residues. In contrast, the OP alternatives –– Assail (acetamiprid), Calypso (thiacloprid), Delegate (spinetoram), Altacor, Intrepid and granulovirus – are most effective when the CM larvae consume them. This means efficacy of these products depends on excellent spray coverage of the foliage and fruit.

Traditionally, larvicides have been applied at the very beginning of the CM egg-hatch period (250 DD) and then reapplied based on the expected residual life of the product. However, the use of an IGR to kill CM eggs offers a new approach to control first-generation CM. Destruction of CM eggs by an IGR allows growers to delay insecticide applications that target first-generation larvae.

The CM model predicts that egg hatch begins at approximately 250 DD. Only 12-15 percent of all the first-generation eggs hatch in the first 10 to 15 days (between 250-350 DD). In the next 21 days, 350-650 DD, almost 70 percent of the first generation eggs hatch. After this period, the rate of hatch slows with the final 15 to 20 percent of the first-generation eggs hatching over about a two-week period.

A potential problem with the traditional (250 DD) larvicide application strategy is that the most active residues from the first application are present at a time when relatively few eggs are hatching, and the residues are weakest when the potential for fruit injury is the highest, during the period of peak egg hatch.

An ovicide applied prior to the onset of egg-hatch eliminates eggs that would hatch between 250-350 DD. As a result, the first larvicide application can be delayed until 350 DD. Delaying the first larvicide places the most active residues in the orchard during the most active egg-hatch period.

This strategy also shortens the period of time that control of larvae is necessary. A delayed larvicide application at 350 DD followed by a second application in 14 to17 days should provide control of the first generation. Many of the new insecticides have a shorter residue life than the OP products they are replacing. To help compensate for this and to further optimize their efficacy as larvicides, using a strategy that delays their first application is recommended.

Tank Mixes

Combining two insecticides with different modes of action in the same tank takes advantage of the multiple modes of action of the OP alternatives. A tank mix of an ovicide (Esteem, Intrepid or Rimon) and a larvicide (Assail, Calypso, Delegate, Altacor) can enhance CM control by killing both eggs and larvae with a single application. A key part of this strategy is the application of an ovicide (IGR) prior to egg-hatch, at 75 to 150 DD. A tank mix (ovicide plus larvicide) applied at 350 DD kills eggs that are deposited on top of the ovicide residue and larvae are killed after they hatch and feed on residues of the larvicide.

The combined action of the ovicide and larvicide in the tank mix extends the period of control from this single application to cover the entire first generation under average conditions. Our experience indicates that this strategy is very effective where CM pressure is high.

Summer generation

The same principles described for control of the first CM generation can be used against the second generation. The second CM generation starts at approximately 900 DD when moths begin laying eggs. An IGR (Rimon or Intrepid) can be applied between 1000 to 1200 DD to target CM eggs. If an ovicide (IGR) is not used, then larvicide applications should begin at 1250 DD. Larvicides from any insecticide class not used in the first generation could be used in the second generation. If an IGR was applied at the beginning of the second generation, then growers can delay the first larvicide application until 1350 DD.

Resistance management

Apple growers now have a number of new products available for CM control. The key to conserving the efficacy of these new products is to enact a sound resistance management program. The key principle is to avoid overusing any insecticide and to not use insecticides with the same mode of action against successive generations of a pest.

Mating disruption is an important resistance management tool because its use reduces the need for insecticide input.

In choosing controls to supplement mating disruption, it is important that growers not use insecticides with the same mode of action against successive generations of a pest. For example, Assail, Calypso, Clutch and Provado (in the class of neonicotinyls) have slightly different pest activity profiles but the same mode of action and they should be used in such a way as to avoid exposing successive generations of any pest to their residues.

Early season Provado applications for control aphids will expose first generation CM to the neonicotinyl class of insecticide. Therefore, Assail or Calypso could be used against first generation CM, but should not be used for summer CM control.

The IGRs disrupt normal insect development, but their modes of action are different, making it possible to use these products in rotation with one another without selecting for insecticide resistance. The biological insecticides, oil and granulovirus, are unique in the way they kill pests, and they make good options to use in a product rotation plan where pest pressures are low.

There are several OP-alternative insecticides currently registered that will provide control of CM. Advanced planning will lead to better management decisions in pest control and help to ensure that apple growers will successfully implement the use of new insecticides in their pest management programs.

Remember that good spray coverage is crucial to optimizing efficacy of OP alternatives. Mating disruption, especially as an areawide cooperative effort with neighbors, forms a strong foundation for any pest management program. Plan your OP-alternative transition approach now. For more detailed information regarding concepts discussed here, visit the WSU-TFREC Pest Management Transition Project Web site, http://pmtp.wsu.edu.

Jay Brunner, Mike Doerr and Keith Granger are with Washington State University’s Tree Fruit Research and Extension Center in Wenatchee, Wash.