Winter zapped some Mid-South pests

The 2002-2003 winter has provided much of the Delta with day-after-day of below freezing temperatures. While these bitter cold temperatures aren't very conducive to outdoor recreation, they could ultimately benefit the area's cash-strapped farmers come this spring.

That may be especially important considering the amount of pest-harboring crop residue left in water-saturated fields as a result of Tropical Storm Isidore and Hurricane Lili last fall.

“While crop residue provides habitat for overwintering insects, the cold temperatures we've experienced in recent weeks will go much farther in reducing insect populations this spring,” says Charles Ed Snipes, Extension cotton specialist at Delta Research and Extension Center in Stoneville, Miss.

According to the Delta Research and Extension Weather and GIS Data Center in Stoneville, Miss., weather station readings between Dec. 1, 2002 and Feb. 25, 2003 recorded winter temperatures below freezing for 37 days in Stoneville, Miss.

Those frigid statistics should prove to be good news for the boll weevil eradication effort.

Gordon Andrews, an entomologist at Delta Research and Extension Center in Stoneville, Miss., says previous lab studies have shown that overwintering boll weevils often die if subjected to a minimum of six continuous hours of below freezing temperatures. “We've seen that this year so we should have a pretty good mortality of weevils this year.”

It's generally believed that constant temperatures below either 5 F with low humidity, or below 20 F with high humidity, will drastically reduce some insect populations, particularly boll weevils. “Temperatures below 20 degrees for 24 hours or longer are quite detrimental to boll weevils,” Andrew says. “Those temperature levels are ambient temperatures, which means it may have to be even colder to kill pests over-wintering in piles of leaves or underground.”

Aubrey Harris, an entomologist at the Delta Research and Extension Center in Stoneville, Miss., and consultant for the eradication program, says he expects the Delta's boll weevil eradication effort to benefit greatly from the 2002-2003 winter.

Some insects, like the boll weevil, are fairly sensitive to over-wintering conditions. Hard freezes for long periods of time, and growers could see massive mortality of those insects.

Delta growers could also see fewer armyworms this spring due to below freezing temperatures. However, reducing spring and summer armyworm populations has more to do with how cold it gets in South Texas and Florida and less to do with Mid-South thermometer readings. Armyworms do not overwinter in the Delta, but the colder it gets farther south of us, the further they will stay away from us this spring, according to area entomologists.

While the cold winter weather bodes well for a spring with fewer armyworms and boll weevils, the same may not hold true for other insects, such as plant bugs, budworms and bollworms.

Because plant bugs are able to successfully overwinter in Canada where it is much colder, the winter weather the Delta has experienced will do little to reduce plant bug populations, according to Blake Layton, an entomologist at Mississippi State University in Starkville, Miss.

Budworms and bollworms are also likely to have survived the below freezing temperatures this winter. “While there is the possibility budworms and bollworms could be affected by the cold winter weather, it's not likely because they are pretty well insulated in the soil,” he says.

A warm wet spring could also limit the effects of a massive winter pest mortality, because many insects can build up to high numbers in a short amount of time given the right environmental conditions and spring host plants.

Among those insects affected more by early spring weather conditions than by the winter cold are thrips and aphids. “The low temperatures have little effect on these insects unless their host plants fail to green-up in the early spring due to cold early-spring temperatures,” Layton says.

Another insect that will likely be found in large numbers throughout the Delta this spring, despite the cold winter temperatures, is the mosquito. Mosquitoes can survive just about everywhere, including in the arctic tundra where hard freezes can persist two to three feet down in the soil.

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