Spider mite problems are common on tomatoes in high tunnels in the early summer. Many high-tunnel tomato producers are approaching the end of the high tunnel crop and just beginning to pick field tomatoes. Others may be trying to extend their high-tunnel harvest as long as possible. Besides spider mites, tomato russet mite has been a sporadic problem in high-tunnels and greenhouses.
Mite management begins with regular monitoring in the high tunnel. This is done weekly at a minimum, but preferably at least twice a week. Attention should be given to areas where air enters and leaves the high tunnel or greenhouse. Mites can be found on the upper and lower leaf surface, but are more common on the underside. When populations are high, webbing between plant structures or large numbers at the tips of leaves may be common.Tomato russet mite can cause rapid desiccation of leaves, russeting of the fruit and bronzing of the stem. Producers should watch for any of these symptoms. The foliar damage may be mistaken for herbicide injury or disease. The russet mites are very small and difficult to see even with a hand lens.
If a decision to treat for mites is made, be sure to not use a miticide that is prohibited in the greenhouse. For this use, a high tunnel is considered the same as a greenhouse. A list of those that are prohibited in hightunnels and greenhouses are listed on page 129 of ID-36. If russet mites need to be controlled, Agri-Mek (or a generic version) is the only miticide labeled for russet mites that is approved for use on greenhouse tomatoes.
By Ric Bessin, Extension Entomologist