Time to keep an eye out for cabbage maggot

Monday, May 25, 2020

With a cool start to the spring this year, insect pests have been a little later getting out and about than we would typically see. Now that there are warmer days upon us, it's important to pay attention to when those insect pests will be active so that control measures can be taken in a timely fashion.

Cabbage maggot (Delia radicum) is a particular challenge in brassica crop production. It overwinters in the pupal stage, emerging in the spring, usually coinciding with the bloom of yellow rocket and serviceberry. From a degree day perspective, emergence begins around 161 Degree Days (DD) at a base of 4°C, with peak flight occurring around 250 DD for the first generation of cabbage maggot. As of Friday May 22, 2020, 175 DD (base 4°C) had been accumulated in Kentville. Other Delia species, Delia platura (seedcorn maggot) and Delia florilega (bean seed maggot) are also on the move in the Valley.

Cabbage maggot larvae in soil. Photo UMass Extension.

Once the first generation of adults has emerged in the spring, they take flight and lay their eggs. It is important to know when peak flight is taking place so that you have the opportunity to alter planting times or deploy control measures, such as insect netting, accordingly.  For scouting purposes, eggs can usually be found small clumps on the soil around the base of your seedlings. For more information on cabbage maggot, including concerns about pesticide resistance, check out Perennia’s fact sheets “Cabbage Maggot” and “Chloropyrifos Resistance in Cabbage Maggot”.