Home gardeners and commercial organic gardeners often experience heavy insect damage on winter vegetables such as turnips, bok choy, cabbage and other brassica crops. Both fall and spring crops are subject to insect damage. Sometimes unprotected crops are so heavily damaged they just can’t be harvested or sold.
Such brassica crops are often attacked by caterpillar pests: diamondback moths, cabbage loopers, imported cabbageworms, cross-striped cabbageworms, and more, and caterpillars often cause heavy damage to brassica crops. But yellowmargined leaf beetles (YLB) are another pest to be aware of, and YLBs alone, or in combination with vegetable weevils, can easily wreck a brassica crop without any help from caterpillars. These are non-native insects, but they have been here since late 1940s and now occur throughout the Southeast.
Adult yellowmargined leaf beetles are about 1/5 inches long and are mostly black with a light, yellow-colored border around the outer edges of the wing covers. The dark-colored larvae are about 1/4 inches long when fully-grown and are shaped like Colorado potato beetle larvae. This is a cool season pest. YLBs aestivate during the summer.
Both adults and larvae feed on leaves and heavy infestations cause extensive damage, resulting in lacy, skeletonized leaves. But even low to moderate infestations can make produce less attractive or reduce marketability due to fecal contamination and unsightly holes in leaves. Because these small pests often feed on the undersides of leaves and/or in plant crowns, light infestations are easy to overlook. But these little beetles are fairly easy to find if you get down on your knees and look carefully. Check for larvae and adults, and while you are done there be sure to look for vegetable weevils and caterpillar pests as well.
Control: Yellowmargined leaf beetles can be controlled with timely sprays of zeta-cypermethrin (GardenTech product) or spinosad (Bonide, Fertilome and Monterey products). Spray thoroughly so spray reaches the bases of the leaves and crowns of plants where larvae often feed. To avoid heavy damage, spray early in the crop’s development, as soon as you notice the first larvae or adults. This is especially important with cabbage, as dead beetles tend to accumulate in leaf crevices after being controlled.
Both products have a 1-day pre-harvest interval on turnips, mustard, bok choy and other brassicas, but always check these details for yourself before spraying. Some formulations of spinosad are approved for organic gardening. These treatments will also control vegetable weevils, which often occur in combination with YLB. Spinosad is the better choice if you are also concerned about diamondback moth and other caterpillar pests—and you probably should be. See Extension Publication 2347, Insect Pests in the Home Vegetable Garden, for more information.
Commercial organic producers can use Entrust, which also contains spinosad and is approved for organic vegetable production. Conventional commercial vegetable producers have access to a wide range of effective products and often treat early in the crop grow cycle for other pests, which is why they tend to have fewer problems with YLB.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
Mississippi State University is an equal opportunity institution.
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