- Author: Mark Bolda
Blackberry growers in the Pajaro Valley should be aware that there are substantial numbers of light brown apple moth (LBAM) larvae active in many fields right now. The photos below outline what this pest looks like and what it is doing right now in our blackberry fields.
In the photographed field, there were on the order of 7-9 leafrolls per two feet of hedge in the heaviest infested areas and in excess of 80% of the leafrollers sampled in the photographed field were identified as having a very high likelihood of being LBAM. This is very concerning, since under the current quarantine enforced by the USDA, the presence of any leafroller in a field can be cause for significant delay of harvest much less outright field closure if an LBAM is found.
While clearly not the level of devastating 100% loss of harvest caused by field closure for a positive LBAM find, LBAM itself is also capable of causing some damage. As one can see from the photos below, damage ranges from incidental feeding on flowers resulting in blemished (thus unmarketable) fruit to heavier feeding causing abortion of entire laterals and the subsequent loss of fruiting potential there. In the field photographed below there was damage of some sort to one of every sixteen fruiting laterals.
Anecdotally, it appears that growers who kept up with changing out pheromone based twist ties every four to six months have very low populations of LBAM suspect leafrolls, while those who allowed pheromone coverage to expire before putting up a fresh set are tending to have heavier, in some cases very heavy, larval infestations. If one is not going to be using pheromone based twist ties through the entire year, it is at least a good idea to put out a few pheromone traps to find out when adult males are starting to fly and looking to mate so as to better target use of mating disruption techniques.
As it seems many of the larvae being discovered currently are in the fourth to late instar stage (½ to ¾ inches in length), applications of Bacillus thuriengiensis formulations will not prove to be very effective. Better materials are the spinosyns, one of which (Entrust) is registered for use in organic fields, and bifenthrin (hard on beneficials though). Addition of a good surfactant is always a good idea to break spray water surface tension to facilitate movement of material into even the tightliest wound leafroll.
There are several insecticides mentioned for control of light brown apple moth in this article. Before using any insecticides, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.