The two past winters, 2013/2014 and 2014/2015, were harsh with frigid temperatures surging repeatedly deep into the South. The result was a decline in the populations of some migratory pests, like cabbage looper and beet armyworm, which normally appear here during the growing season. So what about 2015/2016, an exceptionally mild winter?
Above average temperatures in the late fall and winter with very little snow cover marks this season. Survivorship of most pest species will likely be good. Some aphid species probably remained active through December and may be common this spring, especially if temperatures are slow to rise. Aphids have a lower developmental temperature threshold than their natural enemies, which gives them an advantage of being active and reproducing at cooler temperatures.
It’s likely that migratory pests will appear in normal or higher than normal numbers because of the mild winter throughout the southern US. The May-June corn earworm flight may be larger this year because of probable increased survivorship of the overwintering pupal stage of the local populations.
More specifically, using insect phenology models available on the NEWA website, http://newa.cornell.edu/index.php?page=station-pages we can predict pest occurrence based on the accumulation of heat units (degree days). For example, the first emergence of cabbage maggot flies is due to occur this week in the Cumberland County area. Growers transplanting early crucifers should take precautions against this fly. Refer to the Commercial Vegetable Production Recommendations for control options.
Predicting what populations levels will be for the pests is difficult in any year. Many factors affect insect mortality through the winter months. Not only just the cold, but the amount of snow cover, insects’ fitness going into the winter diapause (hibernation), how well they are protected, what the early spring weather conditions are coming out of winter, and so on. Each insect species has its own optimal requirements. We’ll see how good these predictions are when revisited in October.
