Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu
The recent very wet and cool temperatures we have had over the last two weeks have resulted in several fields of early planted cantaloupe and watermelon having seed corn maggot infestations. Seed corn maggots (SCM) overwinter in the soil as a maggot inside a brown case. In March and April small, grayish-brown flies emerge. Adult flies are most active from 10 a.m. – 2 p.m. and are inactive at night, in strong winds and when temperatures are below 50o F or above 80o F. Eggs are oviposited in soils with decaying plant material or manure. The adults are also attracted to the media around the roots of transplants and to germinating seeds. That is why fields that have been fumigated can still have problems with SCM. SCM flies are often found dead stuck to vegetation during periods of warm wet weather. These flies have been infected by a fungus, but the infection rate is rarely enough to reduce the SCM population and stop infestations. Soil temperatures two inches deep in the planting hole that are at or above 70o F reduce SCM egg laying and larval survival. If soil temperatures are above 70o F at planting but fall below this level for several days in a row, SCM adults will begin to oviposit eggs at the base of transplants. When wilted transplants are inspected in the field, maggots are often not found (they have already pupated), but their tell-tale damage can be seen as a hollowed out stem or root held together by a few strands of plant material. The use of treated seed gives only marginal control of SCM. Replacing dead transplants is the only solution after SCMs kill a plant.