The Mamestra brassicae is a typical parasite of various plants. It particularly damages cabbage crops, as the common name, cabbage moth, suggests. If not promptly removed from the crops, this moth can lead to the death of the plant and, consequently, crop loss. Fortunately, you can mitigate the presence of this formidable leaf-eating insect using organic farming-approved remedies.
Let’s get to know it better and see how to eliminate it from your crops.
Identification and Description of the Cabbage Moth
Mamestra brassicae is an insect belonging to the order Lepidoptera, family Noctuidae. It is very similar, in terms of damage, to the tomato hornworm and the large cabbage white. As an adult, this moth appears as a beautiful butterfly with a wingspan of up to 45 mm. It has both forewings and hindwings. The forewings have a gray-brown color with white and black marbled patterns. The hindwings have a uniform grayish color.
The larvae of this species measure an average of 40 to 45 mm. When young, they are greenish in color, but as adults, they turn gray-green. They can be recognized by their yellowish belly and a dark longitudinal stripe along the back.
Which Plants Does the Cabbage Moth Target?
This cabbage moth prefers vegetables from the Brassicaceae or Cruciferae botanical family. This includes cabbage plants, such as cauliflower, broccoli, cabbage, cabbage head, Brussels sprouts, black cabbage, and Romanesco broccoli. However, it does not disdain other crops such as tomatoes, Swiss chard, potatoes, bell peppers, sunflowers, hemp, apple trees, and pear trees.
What Damage Does the Cabbage Moth Cause?
The damage to crops by the cabbage moth is caused by its larval stages. The larvae are equipped with a powerful chewing apparatus that allows them to feed on and erode leaves. They are highly voracious and mainly act at night, so we only notice the damage during the day. This damage can also extend to the stems, especially the tender ones, where the larvae of Mamestra brassicae create deep tunnels. Extensive infestations can easily lead to the death of the plant or its deterioration. Remember that leaves are essential for the photosynthetic activity of plants. Naturally, young plants are the most vulnerable.
Life Cycle of Mamestra brassicae
Mamestra brassicae overwinters in the soil as a pupa. Adult moths reappear in April or May, where they mate and begin laying eggs under the leaves. Each batch of eggs consists of dozens of eggs. The larvae hatch from June onwards and immediately begin their feeding activity by consuming the leaves. Leaf erosion occurs exclusively at night, while during the day, they retreat into the soil. After 1 or 2 months (depending on the environment), they reach full maturity and pupate in the soil, a few centimeters deep. Usually, in July, there is a new emergence of adult cabbage moths (the second generation), whose larvae are active from August. These larvae overwinter.
How to Eliminate the Cabbage Moth from Cabbages
There are various techniques to eliminate the dreaded cabbage moth, some of which are mechanical, while others involve the use of organic products.
Mechanical defense against the cabbage moth prevents adult moths from coming into contact with the plants to lay their eggs. To implement this, you can use effective insect nets, creating tunnels under which your cabbage plants can grow. This way, the plants are off-limits to both the moth and other pests like red-legged shield bugs. Another solution is to use electrified traps, similar to those used against mosquitoes during the summer. These traps are very effective against the cabbage moth since it is a nocturnal insect. You can find these traps here. Simply place them in the areas around your garden, and you’re good to go. Of course, this method requires access to outdoor electricity.
Biological defense against the cabbage moth can be carried out in several ways. The most effective product is undoubtedly Bacillus thuringiensis var. kurstaki, which you can purchase at specialized stores. Bacillus works on the larvae and acts through ingestion, so it’s essential for the larvae to consume the leaves while they are still moist with the product. For this reason, treatments against the cabbage moth should be done in the evening when the sun has already set. Treating with Bacillus during daylight hours is ineffective. Another bio-approved product is azadirachtin, the active ingredient of neem. It is available in various formulations, and if you are looking for it, you can find it here. If you prefer to use a natural macerate, the most effective one against Mamestra brassicae is the macerate of tomato leaves and females.