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.
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| 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”.
