Diamondback moth on cabbage, broccoli and kale
Bt kills diamondback caterpillars and spares Diadegma, the wasp that does most of the natural control, which is why UF/IFAS calls Bt especially important for this pest. But resistance to Bt occurs in some places. UF/IFAS advises rotating insecticide classes and alternating the kurstaki and aizawai strains, and UMass says the aizawai strain (for example XenTari) usually controls resistant diamondbacks better than older products. If a Bt spray stops working, resistance is one possible cause; resistant strains can arrive on transplants grown in the South.
At a glance
- Damage
- Small holes and translucent "windowpanes" in brassica leaves; damaged growing points
- Type
- Chewing
- Settings
- Field, Garden
- Threshold
- No garden threshold; UMass treats at 35% of young plants or 15–20% from heading, 10–15% for greens
- Ally
- Bacillus thuringiensis kurstaki
- Rate
- Label rate — Thuricide 1–2 tsp per gallon for diamondback moth on broccoli, Brussels sprouts, cabbage, cauliflower, collards, kale, mustard and turnip greens; DiPel DF 0.5–2 lb per acre
How to confirm it
A pale green caterpillar only about 5/16–7/16 inch (8–11 mm) long, pointed at both ends with a forked V at the tail. Touch it and it wriggles violently, backs up, or drops on a silk thread. Look for small holes that leave the upper leaf surface intact as a clear film, and loose, lacy white silk cocoons on the leaves.
Identification, lifecycle, degree days and every control option are on the full Diamondback moth profile. Not sure it is this pest? Answer four questions about the damage.