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Saturday, July 7, 2012

Red Spider Mites Worse in Hot Weather!

Ozarks Gardening
Jim Long, Copyright 2012

Have you noticed yellow-splotched leaves on your phlox and petunias? Or on the leaves of grapes, melons, potatoes, tomatoes or other garden plants? It’s likely red spider. They especially like those crops - they really, really like phlox - but they go after over 180 different species of plants.

These tiny creatures aren’t insects, they’re actually more closely related to spiders and ticks. They have eight legs, although you can’t count them unless you use a magnifying glass. An easy way to tell if you have red spiders is to hold a piece of white paper under a leaf and shake the leaf, if you can see what looks like dust, you have mites. Look on the underneath side of the leaf, if you see very tiny webbing, then spider mites are your culprit.

Spider mites feed by sucking out plant juices causing mottled, yellow foliage. Left unchecked they can suck the life out of plants rather quickly. Damage is worse during dry, hot weather when plants are already stressed and mite populations take off like rockets. The mites can be carried on the wind and can spread rapidly to other plants. What can you do?

The worst thing you can do is to use a pesticide! Pesticides kill all the bugs on the plant, including the beneficial insects which are feeding on the spider mites. With the beneficials gone, the unhatched red spider mite eggs hatch and the population explodes, making the problem worse. Some chemical pesticides actually stimulate mite reproduction - so avoid that can of spray.
Hort. Oil Spray is not the same as Dormant Oil.

These little critters thrive in dry conditions. Wash off under the leaves with a spray from a garden hose and they won’t be happy with the moisture. Mulching plants to hold moisture and reduce stress is helpful. So is regular watering the affected plants, with one or two waterings per week. If your infestation is particularly bad, use Horticultural Oil Spray or Insecticidal Soap. Both work. Some gardeners swear a by 1-to-1 solution of rubbing alcohol and water, sprayed under the leaves. The alcohol evaporates quickly and supposedly doesn’t damage plants, however I’m a fan of Insecticidal Soap which is always reliable.

(Note: I sell Horticultural Oil Spray. It's one of the best, organic controls for garden insects and indoor houseplants. $16.95 plus shipping for 1 quart, which makes gallons of spray. Contact me at

Another option is to encourage natural predators (you can order these to increase your beneficial population). Big-eyed bugs, damsel bugs, lacewings, ladybugs and minute pirate bugs all are happy to devour spider mites.

I highly recommend the book, Good Bug, Bad Bug, by Jessica Walliser, from St. Lynn’s Press, which has photos and controls of many garden pests.

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