Stressed plants attract pest insects. This fourth successive drought year with mandated urban watering restrictions will really stress our plants. We also have had another weather condition that favors pest insect proliferation; mild temperatures this last winter that did not fall low enough to kill off overwintering pest insects or destroy their eggs. Pest insect populations will undoubtedly increase this summer growing season. We’ll need to be very conscientious in monitoring for pest insects, eradicating their breeding and hiding places, and acting to reduce their populations before they get out of hand.
Sucking insects including whiteflies, mealybugs, scale, red spider mites and aphids can be controlled if not eliminated by using lesser toxic methods including washing insects off plants (aphids and red spider mites), putting out sticky traps (whiteflies), applying insecticidal soaps and spraying horticultural oils (immature scale in May). Check the undersides of leaves regularly for whiteflies and for red spider mite webbing. Aphids and scale insects excrete a sticky substance (“honeydew”) that can be seen on leaf surfaces and underneath infested plants and trees. Mealybugs hide in the crevices between leaf and twig joints.
The populations of chewing insects like hoplia beetles, snails and slugs, cutworms, budworms and other caterpillars can be be reduced by handpicking (snails and tomato hornworms), creating barriers (cutworms), applying iron phosphate baits (near snail and slug hiding places) and by applying Bt or Bacillus thuringiensis at the first signs of budworm or caterpillar damage (round holes in leaves, small black droppings on leaves).
Two fairly recent pest insect arrivals, bagrada bugs and leaffooted bugs, are piercing/sucking stink bugs. Both use their piercing mouthpieces to suck juices from plant tissues; the digestive enzyme released when bagrada bugs feed creates lesions and stippling that causes leaves to wilt and die. Leaffooted bugs create the most damage when they feed on fruits and nuts.
Insecticides have little effect on adult bagrada and leaffooted bugs. Early detection and, if necessary, using chemical pesticides to destroy egg masses and nymphs will be more effective. Just remember that applications of broad spectrum insecticides will also kill beneficial insects (and pollinators) and disrupt the natural balance in your garden.
Some ways to battle the bugs: Clean up weedy areas where adults and eggs overwinter; remove host plants for bagrada bugs including sweet alyssum and other members of the cole and mustard plant families; use row covers; handpick (wear gloves; they stink) or vacuum, beat or shake off bugs; and destroy egg masses on the undersides of leaves.
Note: The Clovis Botanical Garden will host its annual Spring into your Garden Festival Saturday, March 28 from 9 a.m-2 p.m. Experts will provide tips on drought-tolerant gardening and the plant sale will feature waterwise and California native plants. Garden presentations will begin on the hour starting at 10 a.m.
The garden is at 945 N. Clovis Ave. by Dry Creek Park. There is a $5 donation; Botanical Garden members enter free.