Give Codling Moth A Virus

Many apple growers continue to do battle with codling moth (CM) and Oriental fruit moth (OFM). While they may rely on insecticides as their principal control tool, more and more growers are also adding sex pheromone mating disruption to their management toolbox.

Despite the loss of some valuable insecticides due to the Food Quality Protection Act (FQPA) and the development of insecticide resistance, the toolbox for the control of the internal fruit-feeding complex continues to expand each year. Among the many new tools available is a naturally occurring virus that was identified in 1964 in Mexico on infected CM larvae. Because of its high selectivity toward this pest, it is called the codling moth granulovirus (CpGV).

Each CpGV particle is naturally microencapsulated within a protein occlusion body (OB). In order for the virus to be effective, the OBs must be ingested by the larva. It only takes a couple of these OBs to cause death in a young larva. The virus rapidly penetrates the gut lining, causing the virus to replicate numerous copies of itself, which then rapidly spread to other organs within the larva. This multiplication causes the larva to stop feeding within a few days, becoming sluggish and discolored as the virus moves throughout the body of the insect. Upon death, the larva “melts,� spreading billions of the viral OBs that can be ingested by other CM larvae. Each OB is capable of causing a new infection within other newly hatched larvae.

Tools And Timing

In Pennsylvania, there are two products that are currently available for use by fruit growers, Cyd-X (Advan LLC, formerly Certis USA) and Carpovirusine (Arysta LifeScience). The label use rate for Cyd-X is 1 to 6 fluid ounces per acre and the label rate for Carpovirusine is 6.8 to 13.5 fluid ounces per acre. Both products can be used right up to the day of harvest and they both have a four-hour re-entry window. These products are certified for use in organic orchards.

We have been researching both products during the last few years and have achieved much success in substantially reducing CM populations, especially where CpGV was integrated with some form of sex pheromone mating disruption. However, before using a CpGV product, there are a number of important points to understand:

• The virus must be ingested by the larva, thus timing and coverage are extremely critical.
• The virus breaks down rapidly in an orchard environment, thus spray intervals should not be stretched for more than seven to nine days.
• The feeding larva causes some injury to the fruit, commonly referred to as a “sting,� before the virus eventually kills the larva.

Since CpGV is most active against young larvae and these larvae usually penetrate the fruit within 24 hours of hatching, it is very important to have the virus present when egg hatch begins. If CpGV is intended as the primary control tactic for CM, then the first application should be timed to coincide with the beginning of egg hatch. Depending upon the length of the egg hatch period, a total of three to five applications will be necessary. Since the virus rapidly breaks down in the orchard environment, it is our experience that frequent applications of a lower rate is a better approach than high rates that are applied at longer spray intervals.

The CpGV must replicate itself within the larva in order to be effective, thus allowing the larva to continue to feed for a few days and causing some shallow feeding damage to fruit. If growers are trying to decide when to use a CpGV product, they may want to restrict their use of a CpGV product to the first generation. If stings or even some deep entries do occur, these fruit often fall from the tree or can be thinned off. In addition, at this time of the season, the fruit on the tree are still small and canopy volume is still not complete, thus allowing more thorough coverage of the fruit.

CpGV products are compatible with most fungicides and insecticides sprayed on apples. However, since CpGV is sensitive to high alkaline conditions, it should not be mixed with copper fungicides or lime sulfur. In addition, it is recommended to use a buffer to neutralize the spray mix if the pH is above 9 or below 5.

Since UV light can rapidly break down the virus particles, it is also recommended that growers avoid applying the virus during periods of intense sunlight conditions. Also, if rain is forecast, wait until after the rain period to make the application.