Beating the Bugs
by VCE Agent Kirsten Conrad
The information here was originally published in a monthly column on pest control in Between the Rows – A Guide to Vegetable Gardening published by VCE in collaboration with MGNV.
Don’t miss Kirsten’s in depth online class:
What’s Eating My [Cucumbers, Tomatoes, Eggplant, Beans, Squash]? :
Insect Pest Management for the Vegetable Garden
Pests of Cabbage, Kale, and Collards
The pests of this group of plants are a worthy challenge to our skills as gardeners. There is nothing more disheartening than to see the cloud of little white moths that swarm up from an infestation of whiteflies. These plants are also attacked by aphids, cabbage loopers, cabbage worms, harlequin bugs, and flea beetles on an annual basis.
Aphids, sometimes called plant lice, are generalists and are pests on many different kinds of vegetable crops. These sap sucking insects come in many different colors, but all will cause disfigurement of the leaf and developing buds, reduce vigor of the plants, and produce excrement—“honeydew”—that may cause sooty mold to grow. Their piercing sucking mouthparts remove sap and cause stunting, puckering, and yellowing of plant tissue.
The good news is that they are easy to control and many chemicals are registered for use to kill aphids. Soapy water will knock them down, and there are many beneficial predators that will help you out. Be on the lookout for the aphids that are parasitized by Trichogramma wasps. These aphid mummies host a developing wasp larvae, and if blown up, aphids are present. Take care with your control efforts; you don’t want to remove the helpers from your garden.
Many organic products will give you good control over aphids, but you will have to alternate your products for continuing infestations. Oils and soaps give good control, as do azadirachtin, Beauveria bassiana, hot pepper wax, and insecticidal soaps. Kaolin clay, neem, and pyrethrins will also give good control.
Cabbage loopers are little, voracious pale green, white striped caterpillars up to 1 ½ inch long that can cause big damage to leaves of all brassica family plants. Larger caterpillars may also eat their way into cabbage heads with the damage looking very similar to that of the cabbage worms.
Several generations of cabbage loopers can occur each year. Handpicking caterpillars off plants and tilling under the soil will help reduce the numbers of active loopers and overwintering pupae.
Imported Cabbage Worms & Cross-Striped Cabbage Worms
The imported cabbage worm is velvety green with very faint yellow stripes and fine hairs that feeds on the underside of leaves. This familiar white butterfly can be seen in daytime fluttering around cole crop fields. Each forewing has a dark border and one or two round black spots. Eggs are laid singly on the underside or top of leaves, about 1/8 inch in length, light green, and slightly elongated, standing upright.
The caterpillar, called imported cabbage worm, is gray-green, slightly fuzzy, and sluggish. The chrysalis (pupa) will be green or brown, smooth with three pointed ridges on its back, and attached to a leaf.
Cross-striped cabbage worms lay their eggs in batches (3 to 25) rather than singly. Egg batches are yellow, flattened, and attached to the lower leaf surfaces. Larvae grow to 3/4 inch long in 2 to 3 weeks.
The caterpillars are light bluish-gray on top and green underneath, with numerous black bands across their backs and a yellow line down each side. There are 2 to 3 generations per year and are most injurious to late season plantings.
Organic controls for both imported and cross-striped cabbage worms include the use of biological agents like Bacillus thuringiensis and parasitic wasps (Hyposoter, Copidosoma, and Trichogramma) that can be released to attack these larvae. Organic controls for both cabbage loopers and imported cabbage worm include Beauvaria bassiana, azadirachtin, Bacillus thuriengiensis, kaolin clay, insecticidal soap, neem oil, spinosad, and pyrethins.
Best practices for control also include removal of larvae and pupal cases and thorough end-of-season garden sanitation.
Harlequin bugs are early pests of brassica plants that overwinter inside plants left in the garden. The colorful, 9.5 mm-long insect goes through six instar stages. It causes significant damage to many kinds of plants by sucking sap from leaves. The injury is similar in appearance to that caused by other stink bugs and by leaf-footed bugs.
Organic controls include pyrethrins, which can be applied up to day of harvest, as well as several registered chemicals. Cultural controls include removal of garden debris, adjacent weeds, and overwintering crop plants.
Flea beetles emerge from the soil in early spring to chew holes in the leaves, mate, and lay eggs near the soil line. Its larvae feed on roots and pupate into adults in 2-3 weeks. They will chew many small holes in leaves, and can severely damage young plants.There are multiple generations per year.
Control these with crop rotation, fall tilling of debris into the soil, and using a row cover of floating fabric.Registered chemicals are available for control, but making sure that all plant debris is removed from the garden and the soil plowed or tilled under will reduce the overwintering population.
Organic controls for serious infestations consist of dusting with diatomaceous earth or rotenone. Azadirachtin, kaolin clay, and pyrethrins are also considered effective in preventing or limiting flea beetle numbers.
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