2012 22.1 Raspberry Crown Borer Research in Skagit Valley

Blue Heron Farm is about forty miles east of Interstate 5 in the upper Skagit Valley. Nearby along State Route 20, there is a continuous forty mile stretch of wild Himalayan blackberries which can harbor any number of transferable berry pests, as well as pest predators. During pruning season two winters ago, Schwartz began to see evidence of the Raspberry Crown Borer working its way through an older raspberry planting.

Normal preventative measures for Raspberry Crown Borer include pruning out old raspberry canes as close to ground level as possible. In addition, some growers remove and burn the older canes to destroy first-year larvae. Schwartz had planned to remove her older raspberry block because the variety was not as well adapted to the higher temperatures found that far east of I-5. During last winter’s pruning, the Raspberry Crown Borer infestation became apparent, with most of the best canes infested. Though raspberries had been grown on the farm for nearly thirty years, the rapid rate of infestation will likely force a stop to production.

The Raspberry Crown Borer is the larva of a medium-sized moth that closely resembles a wasp. From August through September, the females lay single red eggs on the underside of the leaves along the leaf margins. Eggs are laid on the leaves within the top two to three feet of the primocanes and are barely visible to the naked eye. By late September, the eggs hatch and the larva crawls down the cane to below the soil surface and burrows into the plant. Safe from all harm, including most insecticides, the larva feeds inside the base of the cane for up to two years before pupating and emerging as an adult.

The farm sent out a plea for help on a few listserves for anyone with experience dealing with this pest organically and was contacted by graduate student Carolyn Teasdale from Simon Fraser University. Teasdale is evaluating the use of pheromone lures in sticky traps to capture the male moths. She had been setting traps in twenty Fraser Valley raspberry fields and five Washington State fields when she responded to the email. Teasdale hopes to correlate the number of moths caught in traps with the presence of eggs in the field to develop a monitoring tool for this pest.

Towards the end of July, Teasdale came out to the farm, set up a couple of traps, and gave Schwartz instructions for changing the lures and counting the adults caught in the trap. She showed how to extend the life of the sticky trap by pressing the sides together and then pulling them apart several times to redistribute the sticky substance around the trap. The first traps caught no moths because the maturation of the moth was delayed by about two weeks due to the cold, wet spring and summer. By the end of the third week, over 25 moths had been caught in each trap. By the second week of September, the traps were only catching a few male moths, and that’s when Teasdale returned to the farm to look for eggs.

Teasdale and Schwartz found many eggs on the raspberries, several of which had hatched. Teasdale also observed something she hadn’t seen before. Borer eggs are normally a distinctive red color, but some 20-30% of the eggs were black. It’s possible these black eggs were indicative of a parasitoid in the population.

The recorded results were:

  • 83% of canes were infested with eggs
  • 26% of eggs had hatched as of October 6, 2011
  • 28% of eggs were black instead of red in color, possibly indicating that the eggs had been parasitized

One possible strategy in fighting the Raspberry Crown Borer could be to cut the top third of the plant off after the females lay eggs and before the eggs hatch in October. This would be similar to pruning without weaving the canes and would require good vigor in the best canes.

Teasdale’s research on this pest continues, and a full report of her research has been submitted to the Washington Red Raspberry Commission and can be downloaded here: http://www.red-raspberry.org/info/2011-A.pdf

Tags: Blue Heron Farms, Carolyn Teasdale, Crown Borer, Moth, Pest Management, Pests, Raspberry, Research, Simon Fraser University, Skagit Valley, Sticky Trap