Weird Weather and Pest Predictions

One of the most common questions that has come up in response to this season's winter weather (or lack thereof) is what effect it will have on pest problems this spring or summer, particularly insect populations.  Below are excerpts of responses given by two Extension experts. 

Larry Caplan, Extension Horticulture Educator in Vanderburgh County addressed this question in a recent newspaper column:

I was asked the other day what effect this strange weather will have on our pest problems this year. That is always a very tough topic for me. I don’t like to make predictions, because there are so many variables that can affect future events, rendering my predictions worthless. Still, there are a few things that I expect will happen this season.

First of all, everything will start happening at least 3 weeks earlier than normal because of the long warm-up we’ve had. Crabgrass germination occurs at about the same time as the forsythia shrub blooms. Usually, we can hold off applying our pre-emergent herbicides until mid to late March; this year, though, some parts of the tri-state may already be too late to get the best preventative control.

Dormant oil is applied to fruit trees to prevent later problems with spider mites. The oil needs to be applied before the trees bud out, otherwise the young leaves will be burned by the chemical. It’s already too late in some places. Likewise, the traditional orchard sprays to control disease and insect attacks should begin as the buds open. Normally, gardeners don’t expect to begin this until late March or early April, but I’ve already seen apple and cherry trees in bloom. Be sure to stop spraying while the flowers are open, so that you don’t hurt any bees that may be out.

The repeated storms of the last few weeks have dumped a lot of moisture on the tri-state. With moist conditions and standing water, we can expect increases in biting midges, mosquitoes, and crane flies. This is what we’ve seen for the last couple of years, which have all been pretty wet.

Warm, moist weather is ideal for fire blight, a bacterial disease that attacks apples, crabapples, and pears. The bacteria usually enters the tree through the flowers, but it can also enter twigs damaged by hail storms. Spraying the antibiotic Streptomycin during bloom and after a hail storm may offer some protection.

If warm weather continues, we may see an earlier emergence of Japanese beetles, eastern tent caterpillars, and other pests, but I don’t believe we’ll see increased numbers. Very few of these insects are killed by severe winters, so I don’t think their survival rate will change much.

And from Dr. Rick Foster, Purdue Extension Entomology Specialist, some points focusing specifically on insect populations:

While some insects, such as flea beetles, are directly impacted by cold winter weather and experience greater survival and higher populations as a result of mild winters such as the one we just experienced, many insect species are very well adapted to winter weather and will survive just fine no matter how cold it is.

Most insects have an amazing ability to reproduce in large numbers and, if spring and summer weather is conducive, will be able to develop to serious population levels no matter how many survived the winter.

Finally, some of our pests overwinter indoors and others overwinter in the South, so our winter weather has little effect on their populations.

The bottom line is that for a few insects, we can definitely expect higher populations, but for many others, we just can’t predict.

As you can see, there is no one answer to this seemingly simple question.  While winter weather conditions have little effect on most insect populations, it is the earlier-than-normal emergence of these insects, as well as weeds and diseases, that will be the most likely effect of our mild winter.  And, as Mr. Caplan adds, this is Indiana, so it could snow this weekend and change everything!