California walnut growers are again battling the codling moth, but this spring they have a new type of lure to augment their trapping.
The kairomone, also known as DA2313, is an attractant made from the essence of pear. It draws both male and female codling moths (CM), whereas a synthetic pheromone, in duplicating a female scent, “calls” only males. It does not attract other moth species found in walnut orchards.
Pheromone traps, using various lures, have been in use for more than a quarter-century, and the counts of male CM caught in the sticky traps are used for calculating effective timing of insecticide sprays.
Pheromone trapping took much of the guesswork out of control of CM larvae, which damage developing walnuts and create a port for entry of Aspergillus fungi causing harmful aflatoxin in the nuts.
In describing various strategies and materials for CM control at the recent Tri-County Walnut Day at Visalia, Bob VanSteenwyk, Extension entomologist at the University of California, Berkeley, recommended walnut growers become accustomed to using kairomone traps along with standard pheromone traps in their orchard monitoring for CM.
The kairomone was discovered by USDA scientists in California and Washington and has been researched by USDA and University of California entomologists for the past four years.
Their Walnut Marketing Board-supported trials in Central Valley orchards of several walnut varieties confirmed that kairomone traps yield more reliable information than male-oriented pheromone traps.
Heading up the studies is Doug Light, research entomologist with USDA's Agricultural Research Service at Albany, Calif. “Pheromone-based monitoring systems,” he said, “present a great potential for error in estimating egg hatch based on male capture in pheromone traps and related interpretation of degree-day accumulation models.”
Light said he and other entomologists will be working with growers and pest control advisors for the next couple of years to develop confidence in kairomone trapping.
He said more exact timing of insecticide sprays with CM hatches has become crucial in view of regulations requiring less toxic chemicals with shorter residual action.
Counts of trapped females give a better indication of emergence and density of larvae and potential damage. The males migrate farther than females, and since the kairomone is active over a shorter range than pheromones, counts made with it are relevant only to the specific, trapped orchard.
Pheromone trapping typically shows “A” and “B” peaks in first-generation CM male captures. The two peaks vary by orchard and year and must be interpreted.
Kairomone trapping, on the other hand, allows for a “direct monitoring of female flight activities, including biofix-emergence, flight intensity and pattern, and assessment of the degree and frequency of female mating,” Light said.
Acting independently from conventional pheromones, the kairomone shows CM activity even in orchards already under mating disruption with pheromone dispensers.
The commercial kairomone lure, said to be less expensive than pheromones and active for eight weeks, was developed under a partnership agreement between USDA and Trece, Inc. of Salinas, Calif.
It is marketed as PHEROCON, DA Kairomone by Trece in kits of polyvinyl dispensers with instructions on trap deployment. Information on the product is available at (831) 758-0204.
Another speaker at the walnut day, Don Thomson, a Seattle-based consultant on pheromone technology, in an analysis of codling moth control, said pheromones should not be used against high, or even moderate, populations of CM and do not replace close monitoring of walnuts for CM damage.
Use as supplement
“Use pheromones as a supplement to insecticides to reduce populations. That could be done full-season with Isomate or a puffer dispenser or for a generation or peak with sprayable pheromones.”
“Think of this technology as a powerful tool to manipulate codling moth behavior, as opposed to a control strategy like you had with methyl parathion.
“Some of the most effective programs use pheromones, managed properly, plus judicious use of pesticides, to take populations to a very low level,” he said.
Thomson, a consultant for 3M Canada, said data on the release rate, ultra-violet stability, and rain-fastness should be considered when selecting a pheromone product, particularly the sprayable types.
A common question is how to determine if mating disruption techniques are working in an orchard. “Sometimes pheromone traps tell you, sometimes they don't. You cannot hang your hat on pheromone traps to assess the efficacy of mating disruption.”
He said growers should use pheromones, and the new kairomone, cautiously and make certain they are diligent in monitoring both their traps and inspecting orchards for CM strikes.