August 4, 2011 in Washington Voices

Warm, late-summer days sure to bring spider mites, other bugs

Pat Munts
 

The warm days of late summer always bring out the bugs. This year is no exception.

The warmer weather is likely to bring on the spider mites. These are tiny, yellowish, greenish or reddish eight-legged mites that are found most often on the underside of leaves of a number of different plants. The presence of a fine web may be the first clue they are there.

Spider mites feed on plant juices. Hot, dry weather tends to dehydrate them, so they begin feeding even more vigorously on plant juices to make the deficit. If their populations are high enough, this feeding can cause the leaves or needles to become yellowed, a condition called chlorosis. If the infestation is serious, the leaves and needles can be killed.

Look for spider mite webs on the underside of leaves. The leaf bottom may appear to be stippled with tiny holes. The insects themselves will be very tiny and hard to see without a magnifier.

For a very light presence of spider mites, simply spray them off the underside of leaves with a hard spray of water once a week. Insecticidal soaps can be used, but must be applied repeatedly, and have had mixed results. If a plant seems to be prone to mite infestations, consider getting rid of it.

As a last resort use an approved chemical. Remember that when you use a chemical, you can also kill beneficial insects that may be preying on the spider mites. Spray both sides of the leaves thoroughly. If the infested plant is large, consider calling a professional who will have the equipment to reach high branches.

Aphids are having a field day this year. Their sticky honeydew is glazing everything from leaves and plants to cars, lawn furniture and anything else it gets on. Aphids are tiny, pear-shaped, soft-bodied insects with long slender mouth parts they use to pierce tender plant stems and leaves to feed on the sap. They may be green, yellow, brown, red, or black and may have a waxy or wooly appearance. Aphids are distinguished by a pair of tube-shaped cornicles that project out the back of their bodies.

In small numbers, aphids do not cause much damage. When populations become large, however, their feeding can cause curling, yellowing, and disfigurement of leaves and stunted growth in new shoots. The honeydew left from their feeding often turns black with sooty mold fungus. Ants sometimes tend aphids to harvest the honeydew as food.

Small infestations of aphids can be controlled with a hard blast of water every few days. This knocks them off the plant and breaks their lifecycle. For large infestations, be patient and let predator insects like parasitic wasps, lady beetle larvae and adults, lacewing larvae and syrphid fly larvae gobble them up. Predators are always present in the environment. Use chemicals only as a last resort and remember they will also kill the predator insects, and that may lead to an even bigger aphid problem.


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