Managing Mites On Tomato Crops
August 9, 2012 
As the summer heat continues, it is common to see spider mites on commercial and home-grown tomatoes. Heat, drought, water stress, the presence of a large number of weeds, and incorrect use of insecticides can lead to high buildup of mites on tomatoes.
Mites are 1/50 inch in diameter and usually feed on the underside of leaves close to the midrib. There are several species of spider mites and they typically have a short life cycle of seven to eight days. Eggs are attached to the webbing produced by the adults, and the nymphal stages have three pairs of legs (i.e., resembling an insect).
A Two-Spotted Spider Mite Attack
The two-spotted spider mite is a common species on tomatoes in the south and is distinguishable by a pair of dark spots visible through the orange body. The dark spots on spider mites are generally the accumulation of body waste under the skin, hence the newly formed individuals may lack the spots.
Use a hand-lens to directly study the infected parts and ascertain the number of living individuals per leaf where possible as a measure of population pressure. In an outbreak situation, spider mites could easily exceed more than 40 mites per leaf on vegetable crops.
This pest feeds on individual plant cells and causes damage at an astonishing speed when uncontrolled. By the time producers detect an outbreak, spider mites could have already completed several generations.
Due to extensive spider mite feeding, the upper side of tomato leaves may get a speckled appearance or the entire leaf may turn yellow and die.
During a spider mite outbreak, extensive webbing of tomato leaves can be seen along with masses of spider mites at leaf tips as shown in the picture on this page. Adult mites overwinter in crop debris and wild host plants.
This pest typically feeds on tomatoes, eggplants, squash, cucumbers, and other vegetables. The same species can feed on greenhouse crops and destroy produce. Spider mites can also destroy valuable fruit crops such as strawberries, blackberries, and blueberries.
Management And Control Options
As mentioned, spider mites are rapid breeders, hence it is essential to control increasing populations early in the season after correct identification of the species present. Check insecticide/miticide labels before treating an area. Hot-spots of spider mite activity can be targeted in enclosed structures like greenhouses and high tunnels.
Many insecticides like the synthetic pyrethroids and organophosphates commonly used for thrips and worm control can cause a flare up of spider mites by removing predatory mites and other beneficial insects. The dry weather in late summer can also aggravate the situation.
Vegetable producers should assess the need for insecticide sprays and follow some of the cultural practices mentioned here to prevent an outbreak. Here are some miticide options for vegetable producers:
• Abamectin (AgriMek, Syngenta Crop Protection, 8 to 16 fluid ounces per acre): Abamectin is actually a naturally derived substance and serves as a good rescue insecticide. AgriMek contains synthetic abamectin and provides long-term residual control of two-spotted spider mites.
AgriMek also has a locally systemic action or translaminar activity and must be tank-mixed with a surfactant to enable the product to move inside the leaves. Do not apply more than two sequential applications of abamectin to tomatoes to prevent resistance buildup. The postharvest interval on tomatoes is seven days.
• Bifenazate (Acramite, Chemtura, 0.75 to 1 pound per acre): This is a contact poison against two-spotted spider mites with less toxicity to predaceous mites and beneficial arthropods. Acramite is a good knockdown product and also kills the eggs (ovicidal action). Do not make more than one application of bifenazate per season. The postharvest interval on tomatoes is three days.
• Spiromesifen (Oberon, Bayer CropScience, 7 to 8.5 ounces per acre) and fenpyroximate (Portal, Nichino America, 2 pints per acre): These are slow acting contact poisons. Oberon, a lipid biosynthesis inhibitor in insects, may also provide some whitefly control. These products can take up to four days to activate after application and two applications may be necessary to get control of a spider mite outbreak.
Industry sources indicate that fenpyroximate may provide a fast control of spider mites within two days. In some crops, spiromesifen has up to three weeks of residual action, if it is applied prior to spider mite outbreak. Both products have to be applied thoroughly to the leaf surfaces.
• Etoxazol (Zeal, Valent, 2 to 3 ounces per acre): Although Zeal is not labeled for use on tomatoes, it is worth mentioning because it is a new product. Zeal is a growth regulator specific to plant-feeding mites, and it doesn’t harm mite predators. Zeal has translaminar activity like abamectin and kills eggs and nymphs of the two-spotted spider mites plus it sterlizes the adults.
Go to the next page for management tips for organic producers.
For organic growers, maintaining stress-free plants is one of the best ways to prevent spider mite outbreaks from happening in vegetable fields. Here are a few pointers to keep organic fields mite-free:
● Control Weeds: Keep main production areas weed-free and follow basic sanitation practices diligently.
● Watch Your Fields: Scout crops closely and keep records.
● Keep The Pest In One Location: Avoid mowing grasses close to field crops during mid-summer and especially in drought conditions since mowing will help move the pest.
● Use Beneficials: Predatory mites belonging to the genera Amblyseius, Metaseiulus, and Phytoseiulus along with minute pirate bugs and lady beetles have been reported to be effective in controlling mites (release predatory mites ahead of an outbreak so that predators get a chance to establish on crop plants).
● Available Control Products: Insecticidal soap and neem oil have been suggested as possible low-impact environmental-friendly products for mite control. Do not use oil and soaps when it is too hot. Thorough coverage of plants with oils and soaps is essential along with many repeat sprays. Sulfur may also be used, but it can burn certain vegetable crops.
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