Cold winter weather is finally here. This is the time of year when we start to speculate on whether the winter weather will be cold enough to kill off troublesome insect pests. I hate to disappoint, but most insects are very well adapted for winter survival. Here in Georgia we are more likely to get insect control from drought than we are from cold weather. So how do insects survive the winter? As the days get shorter and cooler in the fall, insects enter into an inactive state of arrested development called diapause. During the winter an insect's metabolic rate drops to one tenth or less, so it can use stored body fat to survive. Many insects also produce alcohols which act like antifreeze. Their bodies can reach below freezing temperatures without forming cell damaging ice crystals.
In the spring, as temperatures rise, diapause is terminated and insect growth and development return to normal. Even with all of these adaptations, extreme cold and temperature fluctuations can indeed effect insect survival depending on how low the temperature dropped, how long the cold persisted and if snow cover was present. Other factors to consider are microclimates and how protected they are in their hiding places.
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| Aphids overwinter as eggs laid in the buds of woody plants. |
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So where do insects hide during the winter? Insects spend winter in various life stages. Aphids overwinter as eggs laid in the buds of woody plants. Bagworm eggs are safely tucked away inside a bag. Tent caterpillar eggs can be found in a mass on branches. Bean leaf beetles spend winter as adults under loose bark or fallen leaves. Lady bugs congregate under firewood. Japanese beetle grubs hide deep in the soil and some butterflies overwinter as pupae in cocoons or chrysalis. Each insect has its own way of dealing with cold weather and as much as we would like to think that a rough winter will take care of those pesky insects, most will survive.
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| Euonymus and Camellia scale insects in various life stages from adult to young crawlers and eggs. |
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Scale insects are some of the hardest to control. During the winter they can be found on the underside of leaves and on tree branches. Scale insects feed on the leaves or branches of many ornamental plants grown in the landscape. They attach themselves to a plant and feed by sucking fluids through straw-like mouth parts. This can reduce plant growth and vigor.
Scale insects can be divided into two broad categories: armored scale and soft scale. The distinction is important because behavior and management of the two groups are different. Both groups live beneath waxy covers that protect them from predators, parasitoids and pesticides. Armored scales live beneath a waxy cover that is not attached to the adult body. Thus the cover can be removed to reveal the scale insect hidden below. Armored scales typically do not move once they begin to feed and do not produce honeydew. In contrast, soft scales secrete a waxy layer over themselves that cannot be separated from their body. Soft scales move from branches to leaves during their life cycle and they also excrete sugary honeydew. Black sooty mold fungus is often associated with this honeydew.
Armored scale are typically small and inconspicuous. The protective covers often blend well
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Gloomy scales cause the otherwise smooth bark of maples to be rough and dark. |
with plant bark so populations may become very large before being detected or the plant shows noticeable damage. Therefore, scouting is especially important on plant species that are frequently infested by armored scale. Common symptoms of infestation include premature leaf drop and branch dieback. Heavy infestations can kill a tree or shrub. Euonymus scale, Tea scale, Gloomy scale, Obscure scale, and Juniper scale are all examples of armored scale.
When insecticide applications become necessary, dormant oil applications can be made in winter to kill scale on trunks and branches. Otherwise, target the young crawler stage with an all season horticultural oil or a systemic insecticide in the spring and summer.
Scouting for scale insects feeding on the stems of trees and shrubs will be easier during the winter while trees and shrubs are bare. If scale insects are present spray the stems with horticulture or dormant oil according to the instructions on the label. Also look for bagworms and hand remove as many as possible before they hatch out in the spring.
