Tomatoes (Solanum lycopersicum) are one of the mainstays of the home vegetable garden, providing a seemingly endless harvest of juicy, nutritious fruits throughout the summer. Little red spiders that appear on tomato plants are spider mites, a common garden pest that depletes vital plant sap from the foliage. If left unchecked, a spider mite infestation can reduce plant vigor and lower yields.
The leaves of a tomato plant infested by spider mites may be curled, distorted or wilted. They may show patches of yellow, appear bleached or covered in fine dots. In some cases, entire leaves may be encased by spider webs and leaves may droop or drop off the plant altogether. Spider mites can be difficult to see with the naked eye and may resemble pepper or dust. Spider mite colors range from green to brown or gray, although most mites turn orange or red as winter approaches.
Spiders are most active in hot, arid conditions, often targeting crops that are water-stressed. Keeping your tomato well irrigated may be enough to prevent the pests from causing serious damage. You can also hose the plant down with a direct stream of water to drown mites and remove webs. If webs are destroyed, egg laying may be delayed. Spraying the foliage also removes dust, which is helpful because dust inhibits beneficial insects that prey on mites.
Mites can also be controlled with mite-specific chemical controls. Only use insecticides made specifically to control spider mites, called miticides or acaricides. Broad range insecticides are not generally effective and may aggravate the situation by killing beneficial insects that otherwise help reduce mite populations. The Missouri Botanical Garden recommends using a miticide containing neem, malathion, bifenthrin, cyfluthrin or kelthane. Apply at 7- to 10-day intervals, following the amount recommended by the label. You may also spray the leaves with a superior, not dormant, horticultural oil. Superior oils are highly refined and cause less harm to plant tissue and may be used year round. Keep all chemical controls out of reach from children and pets.
Tomato plants that are enjoying proper cultural care are less likely to attract mites. Tomatoes require full sunlight and well-draining, rich, moist soil. Wait until daytime temperatures are around 70 to 80 degrees Fahrenheit before planting. Prior to planting, apply 3 pounds of a 5-10-10 fertilizer per 100 square feet to the soil. After planting, supply extra nitrogen fertilizer every month. Clemson Cooperative Extension recommends applying 2 pounds of a 15.5-0-0 calcium nitrate fertilizer per 100 square feet. Alternatively, you can use 2.5 pounds of blood meal per 100 square feet.