Bug Scout 1979
Rains Reduce Borers
(Tom Turpin, Entomologist, Purdue University)
Who said we should scout this field before that little ol' cloud got here?
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December 1979

Cornborer larvae aren't very good swimmers!  That explains why first-brood cornborer populations in 1979 were high in some areas and low in others.
The areas with high infestations had very little rainfall in late June and early July when cornborer moths were laying eggs.  Rains elsewhere reduced the population to very low levels.  Young larvae that don't drown are frequently knocked to the ground by rainfall and can't return to the plant.

Some corn growers treated for borers based on damage estimates made before the rain.  It's not likely the treatments were needed.

Most cornborer damage thresholds are based on percentage of plants with leaf feeding plus the presence of live borers.  Leaf feeding by young larvae is an indication of a potential cornborer problem.  However, the real damage is caused by larger borers and many factors, like rainfall, can cause mortality.

Treating for cornborers without looking for live larvae is like shutting the barn door after the horse is gone.  


by Tom Turpin, Entomologist, Purdue University

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