How to Get Rid of Spider Mites Effectively (Complete Guide)
Spider mites are tiny sucking pests that can quickly wreak havoc on indoor and outdoor gardens. Many species of the spider mite (family: Tetranychidae) are common in North America and attack both indoor and outdoor plants. They can be especially destructive in greenhouses.
Interestingly, spider mites are not true insects, but are classed as a type of arachnid, making them relatives of spiders, ticks, and scorpions.
Adults are reddish brown or pale in color, oval-shaped, and very small (1/50 inch long) – about the size of the period at the end of this sentence. Immature stages resemble the adults except only smaller.
Mites live in colonies, mostly on the underside of leaves, and feed by piercing leaf tissue and sucking up plant fluids. Feeding marks show up as light dots on the leaves. As feeding continues, the leaves turn yellow and may dry up and drop off.
Spider mites are most common in hot, dry conditions, especially where their natural enemies have been killed off by insecticide use. Some of the many species common in North America are predators of the plant-feeding mites, which make up the vast majority. They are also very prolific, which is why heavy infestations often build up unnoticed before plants begin to show damage.
Large populations are often accompanied by fine webbing. Host plants are many and include strawberries, melons, beans, tomatoes, eggplant, ornamental flowers, trees, and most houseplants.
In this article, we’ll share everything you need to know about spider mites, including how to identify and prevent their damage, and how to get rid of them effectively.
What are Spider Mites?
Spider mites (Tetranychus urticae) are one of the most common pests in gardens. They are smaller than the head of a pin, which makes them hard to spot.
Due to their eight legs, rather than six, these bugs are classified as arachnids (related to spiders) rather than insects. Most spider mites have the ability to produce fine silk webbing.
There are over 1600 species of spider mites, with two-spotted spider mite and the red spider mite being the most common in the United States. Their colors can range from red, green, yellow, orange, to even brown.
The twospotted spider mite (Tetranychus urticae) is orange in color with two dark spots on the sides. It also happens to be the main culprit in houseplants and greenhouse infestations as well as most ornamental plants.
Spider mites come out to eat plants when the weather warms up in the spring. This can cause plants to become sensitive to disease and other issues. Spider mites have a fast rate of reproduction, and each female lays hundreds of eggs.
Life Cycle of a Spider Mite
Most mite species overwinter as eggs on the leaves and bark of host plants.
In early spring, as temperatures warm, tiny six-legged larvae begin hatching and feed for a few days before seeking shelter where they molt into the first nymphal stage. Nymphs have eight legs and pass through two more molts before becoming mature adults.
After mating, females continuously produce as many as 300 eggs over a couple of weeks. Hot, dry weather favors rapid development of these pests. During such conditions, the time it takes to pass from egg to adult may occur in as little as 5 days.
There are several overlapping generations per year.
Note: Spider mites are wind surfers. They disperse over wide areas riding their webbing on the breezes. Careful containment and disposal of infested plants is crucial.
Damage Caused by Spider Mites
Spider mites are tough to spot with the naked eye, which allows them to pass into our gardens without notice. They use their piercing-sucking mouthparts to feed on sap from plant cells on the underside of leaves.
Large infestations cause visible damage. Leaves first show patterns of tiny yellow spots or stipplings. They may change color, curl, and fall off. Certain plants, like azalea, may even develop distorted leaves and flowers due to this damage.
The mites’ activity is visible in the tight webs that are formed under leaves and along stems. Often, these signs and symptoms can be confused with drought stress.
The University of California Agricultural and Natural Resources division’s Integrated Pest Management website says the following about the damage mites cause:
- On annual vegetable crops — such as squash, melons, and watermelons — loss of leaves can have a significant impact on yield and lead to sunburning.
- On crops such as sugar peas and beans, where pods are attacked, spider mites can cause direct damage.
- On ornamentals, mites are primarily an aesthetic concern, but they can kill plants if populations become very high on annual plants. Spider mites are also important pests of field-grown roses.
How to Spot and Prevent Spider Mite Damage
One of the best ways to protect your plants is to check them regularly. A 10x hand lens will make this much easier. Every 3-5 days, check your plants and see if there are any leaves with white or yellow spots on them.
If you find any, check the underside of the leaf with the 10x hand lens. If you see webbing or mites, you will need to treat the plant.
If you don’t have a magnifying glass, you can also place a white sheet of paper under the plant leaves and tap the leaf sharply. The spider mites will tumble off the leaf and onto the paper.
If you discover spider mites while examining plants, it is best to isolate the plant away from other plants so the spider mites do not spread. If this is not possible, then immediate treatment of the mites is necessary to avoid a major infestation in your garden plants.
Heavily-infested plants will probably not recover, so removing them and placing them in the trash may be your best option. Do not place the plant in a compost pile.
How to Control and Get Rid of Spider Mites
Chemical pesticide use actually encourages the spread of spider mites by killing the beneficial insects that prey on them.
Mites are also known to develop quick resistance to various pesticides. For these reasons, it’s important to control mites with effective natural and organic methods.
Prune Your Plants
Prune leaves, stems, and other infested parts of plants well past any webbing and discard them in the trash (and not in compost piles). Don’t be hesitant to pull entire plants to prevent the mites from spreading to its neighbors.
Water Plants Properly
It’s also important to keep in mind that water stress makes both trees and garden plants more susceptible to mite infestations. Make sure your plants are properly watered.
Spray with Water
Use the Bug Blaster to wash plants with a strong stream of water and reduce pest numbers.
Plus, dust on leaves, branches, and fruit encourages mites. A mid-season hosing (or two!) to remove dust from trees is a worthwhile preventative.
Release Beneficial Insects
Commercially available beneficial insects, such as ladybugs, lacewing, and predatory mites are important natural enemies. For best results, make releases when pest levels are low to medium.
Use Horticultural Oils
Insecticidal soaps or botanical insecticides can be used to spot treat heavily infested areas. On fruit trees, horticultural oil should be applied early in the season or late in the fall to destroy overwintering eggs.
Mix Pure Neem Oil with Coco-Wet and apply every 3-5 days to kill pest eggs indoors and interrupt the reproductive cycle. Make sure to spray all plant parts, including the undersides of leaves. Do NOT apply when temperatures exceed 90˚F and wait at least six hours before turning lights on.
Nuke Em, a relatively new organic insecticide containing food-grade ingredients, works fast and kills most indoor gardening pests at the egg, larvae, or adult stage. Best of all, it does this without leaving a residue on the leaves that can impact flavor.
BotaniGard ES is another highly effective biological insecticide that you can consider using. It contains Beauveria bassiana, an entomopathogenic fungus that attacks a long list of troublesome crop pests – even resistant strains! Weekly applications can prevent insect population explosions and provide protection equal to or better than conventional chemical pesticides.
Tip: Management strategies must take into account the fast development time of this pest, especially during warm weather when eggs are laid continuously. Just targeting the adults will do little good if eggs and larvae survive. Repeat treatments are almost always necessary. The use of leaf shines and washes helps control and prevent further infestations.