Several species of spider mites thrive in our gardens and on our houseplants, causing general plant decline for days or weeks before we detect their presence. Learn to recognize these tiny pests, and then use a combination of biological, spray, and cultural controls to eradicate them from your garden.
To the unaided eye, spider mites are nearly invisible, appearing as red, brown, or greenish dots as small as the period at the end of this sentence. As spider mites proliferate, the organic gardener can observe their damage, which occurs as brown or grayish leaves, which may appear speckled or drop off entirely.
Be suspicious of ailing plants with webbing, as sometimes unsuspecting gardeners mistake spider mite webbing for beneficial spider webs. If your spider mite problem has progressed to the point where you can see webbing encasing your plants’ leaves, the infestation is severe.
Several natural predators control spider mite populations, including ladybugs, pirate bugs, predatory thrips, and predatory mites. You can purchase ladybugs or predatory mites from the Phytoseiidae family to release in your garden if your beneficial predator population is low. If you have a hose-end attachment with a misting feature, use this in conjunction with the beneficial insect release to encourage your predators to remain in your garden.
Spider mites are a member of the arachnid, or spider family, and as such require special sprays that target this family of pests. A common problem among gardeners using conventional pesticides is the use of chemical sprays that kill the beneficial predators of mites, but leave the pests untouched.
Organic gardeners can choose from horticultural oils, sulfur powder, or insect soap to control spider mites. If you choose horticultural oil, make sure you choose a lightweight summer formula, and not the viscous formula used as dormant oil. Use insect soap with caution, as it can burn tender foliage in the hottest summer months that support mite outbreaks. Sulfur powder is a wise choice if your garden suffers from fungal diseases, as sulfur controls garden fungus as well as spider mites.
Spider mites appreciate dry, dusty conditions, and they will exploit the stressed conditions of poorly irrigated plants by feeding on plant sap and relying on arid conditions to wick away their excretions. Dry weather also discourages beneficial insects, which allows spider mites to multiply unchecked.
If you notice the beginnings of spider mite webbing on your plants, blast them off with a strong jet of water from your rain wand. Spider mite webs protect them from predators and function as a nursery for eggs, so blasting them away disrupts their life cycle. If your houseplants show evidence of a spider mite infestation, you can place them in the shower with you each day for a healing rinse.