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 the Kirsten’s in depth online class:
What’s Eating My [Cucumbers, Tomatoes, Eggplant, Beans, Squash]? :
Insect Pest Management for the Vegetable Garden
Pests of Beans, Peas, and other Legumes
April in the garden brings warmer temperatures and the pleasure of seeing earlier sowing of peas mature and start to climb up their supports and of getting the soil ready for first plantings of beans. You can select from garden pea, snow pea (flat edible pods), or snap pea (edible pods) varieties. All are cool season crops that prefer a soil acidity of pH 6.5 or higher and soil temperatures that are in the 65-70°F range. The lengthening days of spring favor flower and pod development. Because these are such early season crops, damage to peas are often done by rabbits and animals looking for some spring greens. Insect problems on peas are rare, but aphids, cowpea curculios, and grasshoppers can do damage in some years.
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.
Cowpea curculio is a small non-flying insect that feeds on the seeds inside the pod. About 5 mm in length, the adult is a black weevil that is a major pest in southern states. In gardens where this pest has appeared, crop rotation and using spinosad (an organic insecticide) is effective at controlling this insect.
Grasshoppers will feed on anything that is available but are uncommon in urban areas. Ragged damage from their chewing mouthparts can destroy crops; using a row cover will exclude these hoppers from your peas. Otherwise, organic controls, including insecticidal soap, pyrethrins, and azadirachtin can be applied up to the day of harvest.
Seed corn maggots, also called root maggots, are small fly larvae that feed on decaying plant material. Infested crops may be stunted and show poor germination. A granular insecticide can be used at the time of planting, but cultural control is best—including the use of raised beds, which have warmer soil that promotes quick germination and rapid growth.
Corn earworms grow to 1 inch in length and have an orange/brown head, but their color can vary from brown and pink or yellow to black. These worms feed on all parts of the plant. To control these, handpick them off the plants and use pyrethrins and spinosad for organic control.
Mexican Bean Beetle
The most serious insect pest of beans is the Mexican bean beetle that damages pods and leaves that can be skeletonized by their feeding. Yellow eggs are laid in clusters of 40 or more. The adults are 1/4 inch long copper colored, oval bugs with 16 spots. The 1/3 inch long larvae are orange/yellow and appear fuzzy or spiny. They appear in June and July and remain active for the rest of the year.
One tactic is to plant beans very early and harvest them before the beetles become active in July. Beneficial predatory insects include assassin bugs and a parasitic wasp. Treatment with registered Insecticides is recommended and organic products like pyrethrins can also get good results.
Sanitation can reduce populations and removal of infested plants after harvest is recommended.
For general information on growing beans, see this VCE publication: Beans by Diane Relf and and Alan McDaniel.