Dr. Ron Smith, an Alabama Cooperative Extension System entomologist, said Alabama has experienced cold winters down through the ages—and insects are still here.
“Most pests have a generation on wild host plants that will help to boost population numbers in the spring, so generally speaking there will be no major decline in numbers,” said Smith.
Notable Cold-Tolerant Insect Pests
The bollworm is a prime example of a species where cold impacts will be insignificant. Bollworms overwinter in the pupa stage in the soil. Smith said even with a cold winter, bollworms will have the entire spring to rebuild numbers on crimson clover and other spring host plants.
Likewise, the brown stinkbug is somewhat cold tolerant. Smith expects it to make up a larger percentage of the stinkbug complex farmers will deal with throughout the growing season.
“The brown stinkbug is a pest of corn, cotton and soybeans,” he said. “Their cold tolerance is significant because these stinkbugs prove harder to control with chemical inputs in the field.”
A Few Exceptions
Though many crop insect pests are not susceptible to cold, Smith said there are a few species with a limited cold weather tolerance that will be affected.
The red banded stinkbug, originally from South America, was documented in 15 south and central Alabama counties in 2017. The new species was a major emerging soybean pest in central and southern Alabama.
“The red banded stinkbug does not tolerate cold at all,” Smith said. “We do not expect to find them anywhere in the upcoming season. The cold will significantly knock back its population.”
Smith said he doesn’t have reason to believe the species will recover until there is a cycle of several mild winters, like the previous two Alabama winters.
Cold impacts on the silverleaf white fly will likely prove most notable, according to Smith.
“Silverleaf white flies took advantage of the mild winters we’ve had during the past few years,” he said. “Cold temperatures will likely have a major effect on suppressing the pest. These would likely recur without the winter cold snap.”
The silverleaf white fly is a key pest, particularly in the Wiregrass. The 20-degree temperatures will kill adults, but not eggs and immatures.
Smith said the species will suffer and die indirectly by the loss of host plants—or removal of food source.
Smith said several crop pests are semi-tropical pests, meaning they overwinter in Central America and on Caribbean Islands. These include fall armyworms, soybean loopers and velvetbean caterpillars.
“We believe that the moths overwinter in warmer climates and return in the spring,” Smith said. “These pests have always done this, therefore fall armyworms, soybean loopers and velvetbean caterpillars are pests farmers routinely deal with.”