As I write this article (February), here in Raleigh, North Carolina, we are experiencing freezing sleet, and we’ve had nighttime temperatures in the lower teens for a couple of days. This is relatively cold for a fire ant!
So what is this going to mean in terms of turf insect pests to us in the so-called transition zone and in the Southeast this spring and summer when we complain about the heat and humidity? I get asked this question every winter at virtually every talk I give or workshop I teach. If the week of the meeting or conference has been warm, everyone will ask if the warm winter is going to result in more insect problems in the summer. If the weather has been cold, the questions will focus on the potential lack of insect pests due to the cold winter.
These are all good questions. Insects can be susceptible to extremes in temperatures, and the fact that they are cold-blooded means their activity is affected by the temperature. So extreme winter conditions can impact their populations. The question then becomes – by how much?
Insects are remarkable creatures and can tolerate a wide range of environmental conditions and still come back strong. They are capable of shutting down many of their normal activities, such as feeding and reproduction, to survive. It’s one of the reasons why insects are found literally everywhere on the planet and seem to be present almost each and every year. They are tough and resilient. Insects such as billbugs, chinch bugs and annual bluegrass weevils generate their own “antifreeze” to protect them against cold weather extremes. Insects are very well-adapted to whatever Mother Nature throws at them.
Grubs stay snug and warm
Even so, an extended cold spell in the winter may affect some insect species. Fire ants at their most northern range, such as in Virginia, might take a hard hit this winter. They are pushing the limits of their range, and really cold winter temperatures may reduce their abundance this spring.
However, most of our white grub species simply hunker down a bit deeper in the soil when conditions get tough. Snug under the insulation of a blanket of snow over the turf, they really don’t know what the winter is like. The record snow in the Northeast is just what any “thinking” insect would have ordered to help it overwinter successfully.
In the South, where snow is uncommon, the insulation from the cold is often absent, but at the same time, the soil temperatures are typically much warmer than what is observed in the northern range for these grubs.
What about insects that overwinter in various forms such as caterpillars or pupae? The black cutworm is an example of an insect that might appear to be susceptible to a cold, cold winter. However, the insect has adapted to environments throughout its range and is able to become a problem throughout the country. Since there is a lack of consistently cold nighttime temperatures during the winter in Florida, for example, the cutworm can overwinter as larvae and pupae. Throughout the southern half of its range, perhaps as far north as Tennessee, this pest can overwinter as a pupae. North of that imaginary boundary, the cutworm does not overwinter, but rather has to migrate north each and every year to infest turfgrass.
Watch out for delayed arrivals
So cutworms will cause turf managers problems throughout the U.S., of that I am certain. What might happen, however, is that if the cold winter results in them surviving in a suppressed range, perhaps only in the far south, then the cutworms from that point northward arrive a bit later in the spring than normal. They will likely still be a problem, but perhaps a few weeks later than normal. Also, spring storms that disperse the black cutworm moths into new areas may impact cutworms more than the winter weather.
The fall armyworm is a pest that seems to have increased in importance over the past 10 to 15 years, especially east of the Mississippi River. However, the winter weather usually doesn’t play too much of a role in the outbreaks that occur in the summer and fall. This is a somewhat tropical insect and even in a warm winter it is restricted to overwintering in Florida and right along the Gulf Coast. Migrating populations that begin their journey from warm climates and move north in the summer usually cause the problems every year.
Again, spring and summer storms often disperse the moths north each year and result in more fall armyworm problems in the summer and fall. Drought is a factor, as well. During a summer dry spell, fall armyworms turn up in irrigated turf. It’s rarely just one aspect of the weather the results in insect pest outbreaks.
One area that entomologists don’t fully understand is the impact of cold temperatures on the various natural enemies that help keep insect pests in check. We do not have sufficient knowledge for most of these turf systems to answer that question.
Yes, pests will be here
The only way to accurately tell if the winter was above or below normal is with good weather data. Even this might not tell you much about potential effects on insect populations. One week of record cold temperatures on insects not protected by snow cover might have a detrimental impact on pests even though the rest of the winter was warmer than normal.
So the answer to the question about the impact of the cold winter weather on insect pests often ends up being answered something like this: “Well it depends” or “I’m not real sure.” This is probably where most entomologists that I know stand on this issue this spring. I’ve been doing this job for more than 30 years, and one thing I know for sure is that the insects will find a way to cause problems.
If you think 2015 will be a year with few insect problems, I would not encourage you to bet too much money on that prediction. In my opinion, the weather in the spring plays a much bigger role in determining the timing and severity of our insect problems. The local conditions, including precipitation, storms and temperatures that lead to an early or late spring, will play an important role in determining the insect challenges we face in 2015.
This is true for mole crickets, fire ants, white grubs, fall armyworms, chinch bugs and other pests. The biggest factors affecting insect abundance are those that take place once the weather is warmer and the insects are active. So pay attention this spring!
COVER PHOTO: RICK BRANDENBURG