Seedling Problems

The University of Maryland Extension statement on advising for commercial or backyard cannabis growers.

The unusually warm winter and early spring we have had up to now has allowed large populations of seed and root maggots to invade our vegetable fields. Some farms have been hit particularly hard in their onion, bean, pea or radish crops this season by maggots. These maggots include seedcorn maggot Delia platura (SCM), onion maggot Delia antiqua (OM) and cabbage maggot Delia radicum (CM). All three species overwinter in the soil as a maggot inside a brown pupal case (fig. 1). In March and April small, grayish-brown flies (fig. 2) emerge, which are usually SCM or CM, OM flies usually peak 2-3 weeks later. Adult flies are most active from 10 a.m. – 2 p.m. and are inactive at night, in strong winds or when temperatures are below 50o F or above 80o F. Adults live 2-4 weeks and females lay hundreds of eggs.