Embrace the Cold: It is Likely to Restrict Some Pest Species Populations
Figure 1. Abundance of grey garden slugs, shown here attacking newly emerged soybeans, can be limited by cold winter temperatures (Photo by Sarah Frame, Penn State Extension).
The current cold spell might be hard to appreciate, but it is likely to help limit some pest populations, which I hope can lift your spirits and help you to better enjoy the cold. Cold winters are known to restrict populations of some pest species, including bean leaf beetle, cereal leaf beetle, and slugs (Figure 1). If recent cold conditions persist, populations of these pest species are likely to be lower than usual come spring, but there is no guarantee. Survival of slugs, for instance, is also influenced by the amount of snow on the ground because higher amounts of snow insulate slugs against colder temperatures. The ultimate outcome, therefore, will be difficult to predict, but at least the current winter appears to be colder than last year's, which was quite mild and allowed large populations of slugs to survive the winter and inflict heavier damage on some crops, including soybeans.
For most pest species, however, the influence of cold winter temperatures and lots of snow is likely to be minor. Many pest species are well adapted to living in our climate, whereas others visit only for the growing season and do not get to experience our winter. For instance, many insect pest species that can cause economic damage in Pennsylvania (e.g., potato leaf hopper, black cutworm, armyworms) are migratory and come to Pennsylvania from southern states where they spend the winter. Our local weather, therefore, will not influence their survival at all; it is their local overwintering conditions further south that matter.
For pest species that have been established in our region more recently, we have a relatively poor understanding of the influence of winter temperatures on their populations. Brown marmorated stink bug, for example, seems to have higher mortality the colder it gets, but the quality of their overwintering sites influences their survival. If stink bugs can find just the right overwintering spot that keeps them cold but not too cold, they will probably make it through the winter.
The bottom line is that it is difficult to predict the future. When spring arrives, growers will need to rely on regular bouts of scouting to understand local pest populations and determine which species, if any, threaten their fields. But in the meantime, as you bundle up against the cold, please join me in hoping that the cold weather continues so at least slug populations will be lower than they were last year!
