Unwanted pest in the garden

There is an unwanted visitor showing up on many tomato plants, and this visitor has invited all of his friends. Spider mites are able to cause a lot of damage in a very small amount of time, especially to tomato plants.

These mites are not a six legged insect, but rather an eight legged arachnid. Most spider mites have the ability to produce fine silk webbing. These plant wreckers are very tiny, being less than 1/50 inch (0.4 mm) long when adults. So spotting them in the garden may be quite tricky to the untrained eye.

Most commonly found on the underside of leaves, the mites may create fine webbing that appears as dust or dirt. Not all will produce a web, so it is best to be aware and recognize the damage. Many species of spider mites exist, ranging from the two-spotted spider mite to the spruce spider mite. However, the damage done will look the same.

The tiny mouthparts of the pest are designed to pierce individual plant cells and remove the green colored contents. Left behind is a leaf surface that is mottled with tiny yellow or white speckles. As these speckles appear in greater number, the entire leaf will take on a yellow or bronze cast. As the leaf loses all of its 'juices' to the spider mite, it will eventually turn brown and become crispy. In severe infestations the entire plant may be defoliated and die. If mites are suspected, samples may be brought to your county OSU Extension Service for a free diagnosis.

All spider mites go through the same stages of development. Adult females lay their eggs on host plants. The eggs will hatch after several days into the first stage, called larva. Larvae are born with only three pairs of legs. They will go through two molting stages before the adult stage is achieved. The fourth pair of legs comes after the first molt.

Syringing may be helpful in controlling these pests. This technique is done by applying a forceful stream of water to knock spider mites off the host plant. This may be done several times a week until control is achieved. It is best to spray the plants early in the morning.

Horticultural soaps are also useful, especially when the control is needed on vegetable plants. To make your own soap solution, try mixing 2 to 4 tablespoons of dishwashing detergent and 5 tablespoons of vegetable oil per gallon of water. If the population of mites is too far gone for the syringing or soap solution to work, there are miticides available. As always, read the label to be certain what you are using is safe for use on edible crops.

8/4/08
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Date: 7/28/08

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