Pheromone traps provide another tool in fight against LBAM

A control program for light brown apple moth based on pheromone mating disruption looks like it can help even organic growers meet the zero tolerance established by the U.S. Department of Agriculture for this quarantined pest.

Pheromone ties placed at a very high rate of 300 per acre prevent the light brown apple moth from mating, by flooding the field with the odor the males use to locate the females.

"It works. You get about 300 pheromone ties an acre out there and you don't see any LBAM out there because they can't find each other to mate," said Mark Bolda, University of California Cooperative Extension farm advisor in the Watsonville office.

Bolda and former UC Davis postdoctoral entomology researcher Hillary Thomas did large-scale trials of the pheromone ties in organic strawberry fields outside Watsonville that had been infested with the pest. The results were dramatic, as control with this organically approved method looked every bit as good as could be achieved with conventional treatments.

"In caneberries and strawberries we feel the fields are large enough for mating disruption to work. I think when you see the numbers, you're going to agree," Bolda said.

Pheromone ties were placed in four different eight-acre strawberry fields at a rate of 300 ties per acre on June 15. Two weeks later LBAM monitoring traps placed in each of these four fields, and in nearby fields without pheromones, were examined and the results were impressive.

In three of the pheromone fields there were no LBAM at all, and in the fourth field only one solitary moth was trapped. But in the nearby plots without pheromones, the traps caught between 23 and 42 of the pests.

Four months later the effectiveness of the pheromones looked even better, according to Bolda, because the fields with pheromones still had no LBAM while the fields without pheromones had steadily increasing populations.

Although the pheromone ties can last from four to six months, researchers strongly recommend replacing them sooner than every four months in order to maintain mating disruption.

The ties can easily be twisted around the trellises used to support raspberries and blackberries.

For strawberries, the recommended method of keeping the ties in place is to twist each one around a chopstick, and then put the chopstick in the ground.

"Twist ties should be placed all across the production field and distributed at an even rate. At a minimum, twist ties should be placed down every other row of the strawberry field at an even spacing between each tie to arrive at the recommended per acre rate. If possible, it is suggested to place twist ties as far out as the edges of the field or slightly farther where possible, to reduce the probability of a mated female moth flying in from external sources," Bolda said.

The program begins with vigilant monitoring for LBAM, using both pheromone traps and visual inspection.

"Leafrollers may be identified using timed visual inspections or pheromone traps. Where any levels of LBAM are detected, available management tactics include pheromone mating disruption, insecticide use and cultural management techniques such as vacuuming and manual removal of leafrollers. Natural biological control by wasps has also been observed and may play a more central role in its control with time," Bolda said.

Although no insecticides were used in the recent Watsonville strawberry study, researchers recommended augmenting the pheromone ties with an insecticide application at the beginning of the season.

"The use of twist ties should be supplemented with the use of insecticides where possible, to reduce the probability of an in-field light brown apple moth find. This also has the added benefit of targeting similar looking leafroller species, such as orange tortrix or garden tortrix. Since leafroller populations are lower in the spring, it is recommended to take initiative at this point in time by commencing a program of pesticide application. This is especially true for producers of organic strawberries, since the selection and efficacy of materials available is quite limited," Bolda said.

Strawberry growers have the advantage of a very long harvest season, during which workers walk past every foot of the field a few times every week. Training workers to identify and remove leafrollers is another important part of an LBAM control program.

"Considering that crews are passing over every foot of strawberry row at least three times a week during the harvest season, they can be very effective in reducing LBAM and other leafroller numbers. It is worth noting that LBAM larval infestations tend to be clustered, so the presence of leaf webbing on one plant means that it is likely that there could more webbed leaves nearby," Bolda said.

Because there is zero tolerance for LBAM, Bolda recommended continuing the traps through the colder months in order to maintain continuous control of the pest.

During the winter, when there is little foliage on many blackberry and raspberry varieties, "there is still LBAM moth activity on the Central Coast and fields will benefit from having mating disruption deployed. Likewise for strawberry growers, especially organic growers, it is a very good idea to maintain or replace the twist ties in their fields going into a second year of production," Bolda said.

Light brown apple moth was first discovered in California in the Berkeley area in 2007. In 2009 it was found in blackberries and raspberries in the Watsonville area, and in 2010 it was found in strawberries in the Watsonville area. The California Department of Food and Agriculture has decided that eradication of LBAM is not possible in the Pajaro Valley, but the zero tolerance standard remains in effect as part of the attempt to contain the pest to quarantined areas.

"It is generally not an economic problem but it is a regulated pest. Inspectors work in the coolers and look for larvae in the fruit. If they find it in the cooler, 15 inspectors show up in the field and if they find light brown apple moth they shut the field down," Bolda said.

Because discovery of even a solitary, two-millimeter worm hiding under the calyx of a single strawberry is grounds for shutting down the entire field, the control standard is extremely high.

"Our threshold is zero and that's a challenge, especially in organic fields," Bolda said.

(Bob Johnson is a reporter in Magalia. He may be contacted at bjohn11135@aol.com.)