David Owens, Extension Entomologist, owensd@udel.edu
Now is the time to prepare greenhouses for the 2021 planting season. Pests such as thrips and spider mites overwinter on weeds growing in the greenhouse or on weeds along the outside of the greenhouse. Now is the time to remove these weeds. Spider mites are going to start shutting down their feeding to prepare for overwintering. They start changing in color to an orange color, and these orange overwintering mites are also harder to kill. Keep them from overwintering in or near your greenhouse by treating weeds. Chickweed and henbit are good winter food sources and are germinating now. In 2020, many watermelon fields had unusually early and severe spider mite infestations, and this can probably be traced back to the greenhouse. Also use the winter as an opportunity to make repairs to covers and screens to prevent moths and aphids from entering in the spring.