Codling Moth Monitoring Tips in Walnuts

Codling moth can look benign, above, but do serious damage. (Photo: UC Statewide IPM Project)

It is important to understand how mating disruption affects the ability to monitor codling moth in walnut orchards under mating disruption (MD) as well as in orchards in proximity to MD.

Researchers are currently investigating just how far-reaching the impacts of mating disruption are to nearby non-MD blocks. Pheromone-only trapping methods will certainly be impacted in MD blocks, and can be affected in nearby non-MD environments — without the added benefit of substantial disruption, and thus population and damage reduction. Other monitoring methods are necessary in and near MD orchards to effectively manage codling moth populations.

 

Damage from a codling moth feeding is seen walnut which was cut open. (Photo: UC Statewide IPM Project)

Disruption of sexual communication in moths is thought to function by the following broad types of behavioral mechanisms, and combinations of the two mechanisms:

 

Therefore, pheromone traps predominantly track only male activity.

Successful MD will shut down pheromone traps to zero or very low male catches relative to non-MD environments. In a MD orchard, you will want to monitor pheromone-only traps to gauge this measure of MD effectiveness. However, it is also critical to be able to track flights and relative population abundance to determine if supplemental insecticide treatments are necessary, and to properly time the applications.

The Suterra aerosol is trade-named “Suterra CheckMate Puffer CM.” (Photo: Suterra)

Fortunately, there are options available for monitoring CM in/near MD that can overcome trap shutdown by (1) incorporating non-pheromone based lures to trap males, females, or both sexes; and (2) employing additional surveillance methods (non-trap-based) to gauge pest pressure and inform treatment decisions.

Combination Lures
Both female and male moths respond to pear ester. This is available in the CM-DA combo lure, which (contains codlemone, the codling moth pheromone, plus pear ester, a plant volatile-based kairomone). Traps baited with these lures should be used in orchards under MD in addition to pheromone- only traps (baited with 1X or L2 lures), necessary to detect trap shutdown as a proxy for efficacy of the MD treatment. If you are concerned with the performance of pheromone-only CM traps in non-MD orchards, consider adding some CM-DA traps, particularly if you suspect you are in proximity to an MD block that is affecting your pheromone trap catches.

Another option is the three-way lure (CM-DA combo plus acetic acid, AA). Think of this as a “‘super-charged”’ lure, which can provide more robust capture in terms of numbers of males and females (in both MD and non-MD orchards).

With both the CM-DA and CM-DA+AA lures, be cautious in your evaluation of trap numbers. Numbers may be higher or lower than pheromone trap catch numbers, depending on your particular environment (MD, non-MD, near MD), and may not directly correlate with the same moths/trap/night thresholds you are accustomed to.

Non-Trapping Methods
These surveillance methods involve in-season damage/population estimates via dropped nut counts and canopy counts looking for strikes (visible as small chimneys of frass at the CM entry point). These monitoring methods can and should be incorporated into your IPM program to aid in treatment decisions, regardless of presence of MD and the trap-lure combination you are using.

More information and details regarding these monitoring and treatment options for codling moth are available online in the University of California IPM Guidelines.

Best Practices For Trapping/Monitoring
Some thoughts on best practices for lure-based trapping, and monitoring in general:

The Pacific Biocontrol aerosol is trade-named “Isomate CM Mist.” (Photo: Pacific Biocontrol)

 

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