How to Control Spider Mites

Spring is here! Flowers! Gardens! All the wonderful things we associate with good weather are coming!

So are the spider mites.

These vampire little pests typically hang out on the undersides of plant leaves draining the plant of vital juices. They’re not picky; they’ll attack indoor and outdoor gardens, making a mess of everything.

We have your back! Read on for some organic methods of how to control spider mites.

What are Spider Mites?

First, they are not true insects. They’re a type of arachnid, like spider, scorpions and ticks. The adults are either pale or reddish-brown, oval-shaped, and extremely tiny. At about 1/50th of an inch, they’re about as small as a period at the end of a sentence. The immature mites look like the adults only they’re smaller still.

Spider mites love hot, dry conditions and thrive in places in which their natural predators have been eliminated by pesticides. There is actually species of spider mites that feed on the spider mites that eat plants. They are colonizers, usually on the underside of leaves, and, just like vampires, bite the leaves and suck out the juices. These bites look like light dots and, as they continue to feed, the leaves yellow, dry up and fall off.

Larger colonies often display fine webs. Most houseplants, trees, ornamental flowers, and fruits & veggies such as melons, strawberries, bean, tomatoes and eggplant can host a colony. This list is only a small example of the plants spider mites love. To make matters worse, spider mites are windsurfers. They ride their webbing far and wide going wherever the winds take them. That makes containment and disposal very important.

Life Cycle

Most spider mites spend their winters as eggs on their host plants. When warmer weather comes, the eggs hatch and small six-legged larvae start feeding. A few days later, they find shelter on their host and molt into their first nymphal stage. These nymphs are eight-legged and molt twice more before maturing into adults.

Females lay as many as 300 eggs over a couple weeks after they mate. If conditions are right (hot, dry weather), spider mites go from egg to adult in about five days. Several generations overlap each other each year.

Damage

The only ways to tell if you have a spider mite infestation is by finding either the tight webs that are created under the leaves and along the stems of the host plants or by visible leaf damage in the form of tiny spot or stipplings. Leaves may change color, curl up, and drop off. Otherwise, spider mites are almost to small to be seen with the naked eye.

The University of California Agricultural and Natural Resources division’s Integrated Pest Management website says the following about the damage mites cause:

  • Annual vegetable crops such as squash, melons, and watermelons can have smaller yields or sunburned fruits due to leave loss.
  • Sugar peas, beans, and other pod veggies suffer direct damage if the pods are attacked.
  • Ornamentals suffer mainly aesthetically, but if the colonies are large enough, the plants may die. Spider mites are also huge pests in field-grown roses.

Control

The best way to control spider mites is with organic means and not just because it’s more environmentally sound. Spider mites can quickly develop resistance to some pesticides, rendering them ineffective. The pesticides also kill off the mites’ less resistant natural predators.

Here’s a handy how-to to help you with your spider mite problem:

  • Prune any infested parts (leaves, stems, etc.) well beyond the webbing. Throw these bits in the trash; do NOT compost them. Owning a sharp, built-to-last pruner is a must for any green thumb or even newbie-gardener. We recommend Corona or Felco pruners.
  • If a plant is overrun with spider mites, pull it and trash it to keep the mites from spreading.
  • Wash plants with a strong stream of water to reduce the infestation.
  • Buy beneficial insects. Ladybugs, lacewings, and predatory mites are spider mites’ natural predators. This works best with small- to medium-sized infestations.
  • If you have no choice, use a least-toxic, short-lived pesticide for large infestations. Follow this with a release of predatory mites to keep the colonies under control.
  • You can spot treat heavily infested leaves with neem oil, botanical insecticides, or organic insecticidal soap such as the kind made by Safer.
  • Apply horticultural oil to the leaves of fruit trees either early in the season or late in the fall to get rid of overwintering eggs.
  • Hose off plants once or twice at mid-season to eliminate dust. Dusty leaves, branches, and fruit invite mites; dust-free foliage is an easy preventative.
  • Properly water trees and garden plants. Water stress makes both more susceptible to spider mite infestations.
  • Water stress makes both trees and garden plants more susceptible to mite infestations. Make sure your plants are properly watered.

Repeat treatments are always a good idea due to the spider mites’ accelerated development, especially during egg laying season and warmer weather. The eggs and larvae have to be dealt with otherwise the infestation will continue. Leaf shines and washes also help control and prevent infestations.