Dogwood borer control in apples
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
The dogwood borer can be a problem in Michigan apple orchards. Dogwood borer adults emerge in mid-June and begin laying eggs over a four to six week period. Initially the dogwood borer larvae feed inside burr knots (adventitious roots) which can develop on the exposed above ground portion of clonal rootstocks. Feeding in the burr knot does little damage to the tree, but feeding can continue below the bark where it is much more destructive and may eventually girdle the tree.
Burr knots are aggregations of partially developed root initials that usually occur in clusters at or below the graft union. Reddish frass on the surface of a burr knot is a visible sign of infestation. Burr knots are fibrous and permit entry of some insecticides such that larvae are readily exposed to a lethal dose while still within the plant tissue. The larvae can be controlled with trunk applications of Lorsban 4E at a rate of 1.5 quarts per 100 gallons of water. The larvae can also be controlled with trunk applications of Lorsban 50 WP at the rate of three pounds per 100 gallons, or Lorsban 75 WG at two pounds per 100 gallons of water. This must be applied directly to the trunk from a distance of no more than four feet using low volume handgun or shielded spray equipment. Do not allow spray to contact foliage or fruit. A single spray timed for the peak egg hatch in late June to mid-July will provide good control.
A new insecticide from the neonictinoid class, Assail 30SG, is now labeled for dogwood borer control. It should be applied at eight ounces per acre after moth emergence, to coincide with dogwood borer egg laying, followed by a second trunk spray 14 - 21 days later.
Dr. Wise's work is funded in part by MSU's AgBioResearch.