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Green Speak

Horticulture topics from gardens to lawns and then some.

Mild Winters and the Pests of Summer


So far the winter of 2015-2016 has been unseasonably mild. Many gardeners speculate what this means for our next growing season and the pest insects we love to hate.

The past two winters beheld a new term for most of us living in North America – polar vortex. Residents in Central Illinois saw first-hand the effects of severe freezing temperatures of -20°F to -30°F. One such result was the steep decline of Japanese beetles. (Though, this past year the calls I did receive were localized pockets where they remained as numerous as ever.)

With the mild temperatures this winter, should we expect overwhelming numbers of garden pests? Will we be able to see the plants from the aphids? Will there be mosquitoes the size of hawks!?

Not likely, says Extension entomologist, Dr. Phil Nixon. During the winter months, insects enter diapause (similar to hibernation.) During diapause insects are rather impervious to cold temperatures above the minus 20 degree Fahrenheit mark. So whether it is 40°F or 10°F, it doesn't matter much to the insect.

What causes the highest mortality in insects is spring weather. During a particularly damp spring, fungal organisms run rampant plaguing insects of all types.

Dr. Phil Nixon notes that even though our winter weather may be conducive to pest insects it is also helpful for our predator and parasitic beneficial insects.

Should this mild weather trend continue to spring, emergence time for many insects (i.e. Emerald ash borer) will be ahead by a few days to weeks. You can monitor certain insect emergence by tracking the growing degree days. http://www.isws.illinois.edu/warm/cropdata/

On winter days that get above 50°F you may see mosquitoes, flies and even butterflies like the mourning cloak butterfly. After a few weeks of diapause, some insects are able to become active (reanimate) when temperatures reach a certain threshold and will become quiescent (inactive) when temperatures fall below that threshold.

We still have two months of winter ahead of us, so keep your heavy coats on hand. Hopefully, we will get our taste of winter to make summer worth the sweat.



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