Insect Notes-June 20, 2017

Bryan Jensen, UW Extension and IPM Program

Armyworms are still being found at treatable levels in some corn fields.  A common scenario has been corn planted after a grass cover crop.  Other possibilities include spring grassy weeds and corn no-tilled into alfalfa sod.  Continue to watch these fields and make special note of larval size.  Once the “worms” reach the 1-1¼ size range there is unlikely to be significant “preventable” damage that would pay for an insecticide and its applications costs.

Black Cutworm calls have slowed down and most of the corn is beyond the stage where damage is likely.  However, late planted corn may still be at risk.  Remember the treatment decision should focus on the potential for damage not based on damage already done.  Once the corn reaches V4 and/or cutworms reach the 6-7 instar stage future damage will be minimal.  A head capsule gauge and table which reflects damage potential vs instar can be found on page 56 of A3646, Pest Management in WI Field Crops.

There haven’t been any reports of significant European corn borer damage yet, however, most of the early planted corn is now at attractive stage and at a stage when larvae can survive (>18 inches extended leaf height).  Spot checking likely fields would be a good idea, especially if significant damage was noticed in the area last year.

Potato leafhoppers may have benefited from the recent hot weather.  Start spot checking established stands.  New seedings require special attention for potato leafhoppers.  These stand do not get the benefit of a short cutting schedule that establish stands receive.

I would expect Japanese beetle adults to be emerging soon.  I have no guesses how heavy populations might be, however, this is one insect pest that may have benefited from our warm winter.  Adult emergence will happen over a period of time so continue to monitor soybeans fields for defoliation and corn when it starts to pollinating.  Adults Japanese beetles are clumped in their distribution so through scouting is needed.  A potential Japanese beetle look-a-like, the rose chafer, has emerged and is commonly found on sandy soils.  Although soybean defoliation is possible, significant economic defoliation is unlikely.

Rose Chafer, Photo credit: Bruce Watt, University of Maine,