Pest Update: Cabbage Maggot

Thursday, May 16, 2024


With the warm weather finally arriving, it's important to pay attention to when insect pests will become active so that control measures can be implemented. 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 growing degree day perspective, emergence begins around 161 Growing Degree Days (GDD) at a base of 4°C, with peak flight occurring around 250 GDD for the first generation of cabbage maggot. As of Thursday May 16, 2024, 172 GDD (base 4°C) have accumulated in Brooklyn Corner. If you would like to check how many GDD have accumulated in your area go to Perennia’s Farm Data Tools website. Once there, you can make a free account and access the Farm Weather tool. From the Farm Weather tool map, select a station close to you, which will bring up the GDD calculator as well as current weather condition at that station.

Cabbage maggot feeding on roots. 
Other Delia species, Delia platura (seedcorn maggot), Delia antigua (onion maggot) and Delia florilega (bean seed maggot) are also on the move in the Valley. 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.