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What is it?
There are many plants in the cabbage family, they include broccoli, brussels sprouts, cauliflower, chinese cabbage, collards, kale, kohlrabi and of course the common cabbage. Diamondback moths are harmful to these garden plants when they are in their larvae stage as worms.
What does it look like?
Diamondback moths are known as plutella xylostella. The worms chew small holes and sometimes transparent patches on the leaves of cabbage family plants. The small green worms feed on the undersides of the leaves, and when they do not chew completely through, this is when you may note the transparent sections. The green worms are quite small, and only grow up to about 1/4 inch in length. The worms are also very wriggly, and if you disturb a leaf they are on they will begin to wriggle rapidly and may even fall off the leaf, held to it only be a thin silk-like thread.
How does it manifest?
Each year, the diamondback moth population can increase by two to seven generations so they are able to damage both spring and fall crops. The adult diamondback moths also overwinter beneath fallen plant debris where they form transparent silky cocoons which they attach to the underside of the leaves where they have fed. The adult diamondback moths don’t actually harm the plants, and you will often see them flying around the plants in the evening. They are usually a light gray or brown color. The presence of these moths most likely means that your cabbage family plants have been infested with the worms, which are harmful to the plants.
What can you do about it?
Diamondback moths can be controlled with an insecticidal soap at the first sign of leaf damage when the worms are still young. Pyrethrins applied directly to the leaves may also be productive in destroying young worms. However, be sure to coat the undersides of the leaves with the insecticide or you will be wasting your time. As long as the worms are visible you will need to repeat treatments at intervals of a week. Additionally, make sure that you clean up any fallen plant debris in the fall so that diamondback moths don’t overwinter there and reinfest plants when they emerge in the spring.
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