This article, written by Extension post-doctoral researcher Anthony Hanson and Extension entomologist Robert Koch, was originally posted in Minnesota Crop News . On January 31, 2019, most of Minnesota had morning lows near or below -30°F (Figure 1). Cold winters help prevent many potential pest insects from establishing here or requires species that cannot survive our winters like potato leaf hopper or black cutworm to migrate up from southern states. Extreme cold can also knock back species that are established here. Figure 1. Morning lows on Jan. 31, 2019; U.S. National Phenology Network: www.usanpn.org.