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(News article for December 2020)
Brassica is a genus of plants in the mustard, or Brassicaceae, family that includes mustard greens, cabbage, broccoli, collard greens, kale, kohlrabi, turnips, cauliflower, and others. Brassicas are easy to grow but are subject to some insect pests that you should know about. The most common pest I see on brassicas are caterpillars (worms). Worms usually chew holes in the leaves. Holes may be big or small depending on the size of the worm. Worm frass, or feces, is another telltale sign that worms are feasting on your plants.
Flea beetles and aphids are other common pests of brassicas. Flea beetles chew very small holes in the leaves while aphids suck sap from the plant. Aphids usually cause leaf yellowing, yellow spots, or shriveling. You may find sooty mold, a black mold that develops on insect honeydew excretions, on plants where aphids are present.
Scout your plants for insects early and often. If you catch infestations early, you will not need to use as many chemicals later, when the plants are closer to harvest. Check the underside of leaves for insects and look for other signs like leaf shriveling, yellow spots, and insect frass.
I recommend a permethrin spray to control brassica insects. Bonide Eight is easy to find at your local co-op or garden center and the label gives a 1-day pre-harvest interval for greens and other brassicas. With a 1-day pre-harvest interval you should wait 24 hours after spraying to pick and eat from the plants. Sevin is another good insecticide for brassicas. Multiple applications may be necessary to control the insects. Organic options include BT (Bacillus thuringiensis) for caterpillars, and insecticidal soaps. Follow the label directions with any insecticide.
Jessie Hoover is a County Agent with the LSU AgCenter covering horticulture in East Feliciana, West Feliciana, and St. Helena parishes. For more information on these or related topics contact Jessie at 225-683-3101 or visit the LSU AgCenter Website.
Leaf shriveling due to aphid feeding. Photo by: Whitney Cranshaw, Colorado State University, Bugwood.org
Holes in cabbage plant due to worm feeding. Photo by: Whitney Cranshaw, Colorado State University, Bugwood.org