European Corn Borer

The European Corn Borer was never thought to be considered a pest of hops until modern small scale growers began experimenting with growing hops.  Since it's discovery in 1917, the borer has progressed westward across the U.S. to the Rockies and into Canada.  The female is a light yellowish brown color with dark, irregular, wavy bands across the wings. The male is slightly smaller and has a darker color.  


The moth lays its eggs on the stalk of corn plants (or hops in this case) and once hatched, the caterpillar (Fig. 1) bores into the stem (Fig. 2) and feeds on the inside of the plant tissue.  This weakens the central stalk and causes it to collapse, killing the upper portion of the plant.


What makes this pest more difficult to control, is that it has the ability to overwinter in its larval stage and re-emerge the following spring as temperatures warm.  Controls for this pest are difficult once the larvae enter the plant stalk/stem.  Many corn growers have been using genetically modified corn that produces a protein that kills the caterpillar, but resistance continually builds and the modification must continually be adjusted.   


For hops growers, controls for this pest are extremely limited since most known pesticides are only registered for use on corn and not hops.  Pyrethroids may be effective, but only until the caterpillar enters the leaf tissue.  Once this happens, pesticides cannot contact the caterpillars and control is near impossible.

Corn Borer In Stalk

Corn Borer Entry Hole

Corn Borer Entry Hole

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Fig. 1

Corn Borer Entry Hole

Corn Borer Entry Hole

Corn Borer Entry Hole

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Fig. 2