Identification
The cabbage moth, also known as the diamondback moth, is a small, slender insect with a wingspan of 12-15 mm. Adults have light brown or gray wings with distinctive diamond-shaped markings along the back. Larvae are pale green, about 8-12 mm long, and have a tapered body. These moths are found worldwide, particularly in temperate and tropical regions where brassica crops are grown.
Lifecycle & Reproduction
Cabbage moths undergo complete metamorphosis, progressing through egg, larval, pupal, and adult stages. Females lay up to 300 eggs on the undersides of leaves. The eggs hatch within 3-5 days, and larvae feed on foliage for about two weeks before pupating. The pupal stage lasts 5-10 days, after which adults emerge. In warm climates, multiple generations occur per year.
Habits, Diet & Behavior
Larvae are highly destructive, feeding on leaves, stems, and developing flower buds. They create irregular holes in foliage and often skeletonize leaves by consuming only the leaf tissue between veins. Adults are nocturnal and weak fliers, often fluttering when disturbed. The larvae move in a characteristic wriggling motion when touched.
Where You’ll Find Them / Typical Locations
Cabbage moths and their larvae are commonly found on brassica crops, including cabbage, broccoli, cauliflower, kale, and mustard greens. Infestations are most severe in agricultural fields, gardens, and greenhouses. Eggs and larvae are primarily located on the undersides of leaves.
Threats & Danger
Cabbage moth larvae cause severe defoliation, reducing crop yields and plant vigor. Heavy infestations can destroy seedlings and severely impact commercial and home gardens. Additionally, their feeding damage creates entry points for bacterial and fungal infections, further weakening plants.
Prevention
- Rotate crops to reduce population buildup.
- Use floating row covers to prevent egg-laying on plants.
- Encourage natural predators like parasitic wasps and ground beetles.
- Handpick larvae and destroy affected leaves to limit infestations.
- Maintain plant health through proper fertilization and watering.
Signs of Infestation
- Small, irregular holes in leaves.
- Skeletonized leaves with only veins remaining.
- Presence of small green larvae on leaf undersides.
- Silk webbing and frass (larval droppings) on plant surfaces.
- Increased moth activity in the evening.
How to Get Rid of It
- Apply Bacillus thuringiensis (Bt) to target larvae effectively.
- Use neem oil or insecticidal soaps to deter feeding.
- Introduce biological controls such as predatory wasps.
- Use pheromone traps to monitor and reduce adult populations.
- For severe infestations, apply selective insecticides labeled for cabbage moth control.