Winter’s Impact on Pests- Del Voight Senior Extension Educator- Penn State Extension
Many pests are impacted by winter’s climate conditions. For the most part, fungus spores are highly resistant to winter conditions but are sensitive to tillage much more than certain weeds and insects. A large amount of insect mortality occurs in winter. Insects perish due to cold temperatures and natural diseases that attack them while they are in the resting stage. Grubs for example, over winter as larvae and many are killed by a pathogen that infects their outer skin, which desiccates the body. Some insects which normally over winter in surface residue (leaves, corn stalks, etc.) and soil many times don't locate themselves deep enough to survive winter and normally will be killed
by cold temperatures. This winter, being mild (?) to date, may cause an increase in the amount of insects that over winter and may bring increased insect pressure next season. On the other hand if the mild weather forced some insects to start growth and the weather turns sharply cold many insects will perish. A lot depends on the temperatures in February, the particular insect, and if snowfall occurs. Snow insulates the soil and will lessen the mortality of insects. For example, Flea Beetle populations will be elevated when February temperatures are mild.
Insect hatches usually occur when the host (preferred food of the insect) is present. If the host is not present in enough quantity to support the insects when they hatch then the insect will die. This is why crop rotation is critical because by rotating the crop (corn, soybean) the insect life cycle is broken and the insect population plummets. For example, the most effective root worm (severe insect pest in corn) control in corn is to rotate to soybeans to break the life cycle. Another example is the recommendation to wait 12 days after killing a field infested with
chickweed or any other spring weed to allow the insects time to die before planting corn to avoid damage to the corn stand. Once the food source is eliminated the cutworms die.
Many species of insects like root worms, and grubs lay eggs in late summer. Last summer the drought certainly impacted the moisture in the soil where the eggs were deposited and may have caused a condition where the eggs desiccated (dried out) and populations could be lower. At this point, it is difficult to tell whether insects are going to be a problem in the summer of 2000 due to the mild winter (so far). One can bet that certain fields will be infested with insects for other reason besides weather such as rotation and tillage system impacts. Entomologists are expecting large populations of brown marmorated stink bugs and soybean aphids. It is wise to begin planning now to manage these pests. Seed treatments in combination with post emergence applications of pyrethroids may prove useful in manageing these pests next season.
The major impact on weeds from winter weather conditions is the competitiveness of winter annuals on perennial crops such as alfalfa and winter annual crops such as winter wheat. This fall was mild and chickweed and henbit populations thrived with ample moisture and cool temperatures. If the winter remains mild wheat and alfalfa fields may need to be sprayed sooner than normal. Wheat growers should be assessing stands before tillering (February) to determine whether a treatment is needed to ensure weeds will not prevent tillering space. In addition, alfalfa fields should be assessed in early March to determine a need for treatment. By understanding the behavior and requirements of pests more effective pest management programs may be developed to lesson our reliance on pesticides and ensure adequate control of pests. The Extension office has fact sheets detailing pests. If you have an unknown insect, disease or weed or just want more information about a pest please visit or call me at the Lebanon Extension Office.