For Release May 30, 2000
Spider Mites, A Tiny Pest that Can Cause Big Problems
by Chuck Otte, Geary County Extension Agent
I had been waiting for them. Warmer and drier than normal weather almost always brings them out. They should be here. I thought I was starting to see evidence of them by mid month. Finally, last week, the calls started coming in. Evergreen trees and shrubs were all of a sudden going off color. In just a matter of days, plants were turning yellowish, grayish or just an off green color. The spider mites had arrived!
Spider mites are not a true insect, they have too many legs. They are more closely related to ticks or better yet, chiggers. There are many different species of mites that we will find on ornamental plants. We usually just lump them all together as spider mites. Mites are very small. They are easily overlooked if you are just looking for a pest, so we usually look for the damage. Mites have very high reproductive rates, so problems literally can explode in just a few days.
The have a piercing/sucking mouthpart so they donít devour the foliage, they just suck the sap out of the plant. The miteís saliva also creates a toxic effect in the plant which compounds the damage. Mites usually prefer warm and dry weather. When we have normal, regular spring time showers we seldom see mite problems develop. When we have extended dry spells without typical, wind driven rainstorms, we expect to see spider mite problems.
If you are looking for spider mites start looking for the telltale signs. Plants going off color is one good symptom. Upon closer inspection you will usually find lots of little yellowish dots or a stippling effect. If the damage isnít stopped, the foliage will die. Mites will also create a very fine webbing on the leaves. Sometimes you can hold a piece of paper under the foliage and tap the leaves onto the paper. If you see a lot of tiny dots that start to move, you have mites! One of the real treatment problems is that mites prefer to feed on the undersides of the leaves. The easiest way to spray a plant is on the leaf surfaces. This doesnít do any good when the mites are under the leaves.
While mites will feed on virtually any plant species, they seem to be attracted to evergreen plants first. The damage that I have been seeing this spring has been on junipers (cedars) and blue spruces. The denser foliage may be more attractive than everything else early in the season. They can be very damaging since these evergreens can not generate new growth like deciduous plants can. I have also been finding some mite damage on yews this spring also. In gardens, I look for spiders mites first on tomatoes, beans and eggplant. While they will feed on any number of plants, these tend to be the first choice of dining for the mite clan.
Mites are fed upon by predatory insects but sometimes the cycle gets out of whack, like right now. In yards and gardens mite problems can develop when the insecticide sevin is used extensively. Sevin kills many of the predatory insects but does not kill mites very well. Using a rotation of insecticides, when warranted for other problems, is a better choice to reduce insect population explosions.
When you spray for mites, use a lot of water and be sure to spray up under the leaves. If there is a lot of webbing make sure the spray penetrates the webbing. Since most sprays do not kill the eggs, successive sprayings every three to four days may be necessary. The following products will all control mites, just make sure that they are labeled for the plants you are treating. Kelthane is the first choice for mite control in ornamentals, but most kelthane products are no longer labeled for use in gardens. Other mite control pesticides include: diazinon, Malathion, dursban and insecticidal soaps. Read and follow all label directions and precautions.
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