Summer options for dogwood borer management

Dogwood borer trap catches are beginning in orchards with a history of problems with this pest. However, adult emergence will continue through to early September with peak flight typically occurring mid-July. During this time, females lay eggs on the surface of burr knot formations, pruning cuts, cankers, and wounded bark, after which the larvae use as entry points to bore into the tissue to begin feeding.

If pheromone traps have not been placed in the problem orchard yet, these need to be installed as soon as possible since adult flight has begun. Four traps per site, placed in low scaffold limbs, are recommended. Use a minimum distance of 50 m between traps, and monitor twice a week. Record the number of adults captured - graphing the results - to identify peak flight time. This information can be used to time trunk applications of a registered insecticide.

This season, the labels for Altacor, Delegate WG and Rimon 10 EC have been expanded to include control of dogwood borer in apples (see table). Rimon 10 EC is an insect growth regulator (IGR) that must be absorbed by eggs or ingested by larvae to be fully effective. The optimal timing for this product is around 25-75% egg laying, or approximately peak flight. Delegate WG and Altacor must be ingested by the larva in order to work; therefore it must be applied at the beginning of egg hatch, or a few weeks following peak flight. With all products, a repeat application 14 days later is recommended.

Comments:

• Do not exceed 2,000L water/ha.
• Max. 2 applications at a 14 day interval.
• Apply as a trunk drench with a handgun or backpack sprayer, directed particularly to graft union and any pruning cuts. Thorough coverage is essential.

* Can also be applied in the spring targeting larvae preparing to pupate OR post harvest (autumn) as a curative spray (single application only)

An alternative management option for dogwood borer next year is the recently registered mating disruption product, Isomate DWB. Dispensers (250-375 dispensers/ha) should be applied before adult borer emergence, or approximately the end of May. Researchers from Rutgers and Cornell University feel that Isomate DWB can adequately control light to medium dogwood borer infestations and give equal control to trunk drenches after multiple years of use.

However, the best way of avoiding dogwood borer infestations is to prevent burr knot development. If possible:

• Select rootstocks with a lower tendency for burr knot formation to reduce attractiveness to borers. Rootstocks particularly susceptible to burr knot formation - and attack by borers - are M9, M26 and Mark.
• Use wire mesh mouse guards rather than solid guards. Borers prefer shaded, protected habitat. Solid guard restrict air circulation and prevent bark hardening, pre-disposing the tree to winter injury and providing good borer egg laying sites.
• Apply white latex paint to trunk to deter egg laying and, if applied thick enough, suffocate borers already in the wood.
• Keep in mind frequent use of NAA may increase the development of burr knots.
• Mound soil around the rootstock in established plantings where the graft union is close to the ground. If this is not possible, keep the area around the tree weed-free to avoid shade and high humidity.