University of Maryland Extension

High Tunnel Tomatoes with Mite Infestations

Dr. Gerald Brust, IPM Vegetable Specialist

June 2013

This week I saw several high tunnel tomatoes with moderate to severe two-spotted spider mite (TSSM) Tetranychus urticae infestations (Fig. 1). These pests vary in color from white to yellow to red. Mites feed by sucking sap from the plant causing small white stippling marks on the top surface of the leaf (Fig. 2). This damage may look like other problems early on and because the mites are difficult to see on the underside of the leaf at this stage of damage their build-up can go unnoticed. The feeding damage then progresses to yellowing, wilting, browning, and eventual death of the leaves or whole plant. They occur in the highest numbers on the undersides of leaves, but when their populations get very high they can move to the top-side of a leaf or onto tomato fruit. In most of the HTs there were only 1 or 2 cultivars (out of anywhere from 4-7) that the mites were found on in heavy numbers. Growers need to be sure to check all the different varieties of tomatoes they are growing for mite infestations.

The warm, dry conditions in a high tunnel favor rapid mite development and reproduction, which enables them to complete a generation in as little as 5 to 7 days. Heavily infested leaves may be covered with very fine, irregular webs in which mites and eggs can be found (Fig. 3). Once the spider mites begin to make these webs they are even more difficult to control. This is because the mites hide under the protective layer of webbing making it that much more difficult to get spray coverage to the underside of the tomato leaf. For a heavy infestation, one miticide application usually will have to be followed by another about 7-10 days later to be sure all the adults, immatures and eggs are controlled. Check the Commercial Vegetable Production Recommendations Guide for miticides.

Fig. 1 HT tomatoes with a severe TSSM infestation

Fig. 2 Early TSSM feeding causes white stippling (specks) on tomato leaf.

Fig. 3 TSSM webbing on tomato leaflet. Dark specks are TSSMs

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