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What is it?
Cabbage loopers are small green, striped worms which are known as trichoplusia ni. These green worms attack lettuce plants and can be extremely damaging to the lettuce crop. Trichoplusia ni will also attack the many plants in the cabbage family. Those cabbage family plants which are susceptible to trichoplusia ni cabbage loopers include broccoli, brussels sprouts, cauliflower, chinese cabbage, collards, kale, kohlrabi and of course the common cabbage.
What does it look like?
Cabbage loopers are known as trichoplusia ni, and should not be confused with imported cabbage worms, pieris rapae. These two worms are often linked together under the common name cabbage worms, however it is very rare that pieris rapae attacks lettuce plants. Typically, infestations of either sort of cabbage worm will present themselves in the form of irregular roundish holes in the leaves. The holes may appear chewed or may have smoother edges. After noticing the holes, you may also see green worms on the lettuce plants which can grow in size up to 1.5 inches long and usually the cabbage loopers have lighter green or white stripes down the center of their backs. You may also note large clumps of green or brown pellets among and on the leaves of the lettuce plants, where the cabbage loopers have left excrement in the wake of their feeding on the lettuce leaves and heads of the lettuce plants. If cabbage loopers have infested the heads of your lettuce plants, you may also note the presence of tunnels in the plants when trichoplusia ni infestation occurs.
How does it manifest?
Adult female cabbage loopers lay their eggs throughout the growing season, which then emerge as the small green, striped cabbage looper worms and begin feeding. Mature cabbage loopers are brownish moths and often lay pale green eggs which are hard to see on the leaves of the lettuce plants because of their color. Because of the extended life cycles of trichoplusia ni and the ability of these small green worms and adult brown moths to create many generations in a growing season, cabbage loopers may be present from early spring until late fall and may even be present year round in the warmer climates of the southern United States. As such, trichoplusia ni can be an extremely devestating worm to your lettuce plants and other susceptible plants such as those in the cabbage family to the vegetable gardener.
What can you do about it?
Cabbage loopers can be controlled with a variety of insecticides. As soon as you note damage from trichoplusia ni, you should treat the affected plants with an insecticide containing diazinon, carbaryl, pyrethrins, rotenone and even some insecticidal soaps are created specifically for use against cabbage loopers which attack lettuce plants. While the worms are still small, they can also be killed off with a biological control such as bacillus thuringiensis. For as long as you can still find cabbage looper worms on your lettuce plants, you should repeat the chosen treatment in weekly intervals. However, you need to stop applying insecticide 3 days prior to harvest. Also, post-harvest you will need to remove any leftover or excess lettuce plant debris so that hidden pupae may be destroyed.
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