I want to share one of the best web sites I’ve found that describes insects with excellent photos of pests that attack cannabis: http://vegipm.tamu.edu/imageindex.html

Spider Mites

Identify: The spider mite is the most common pest found on indoor plants and causes the most problems. Mites have eight legs and are classified as spiders. To the untrained naked eye, they are hard to spot. Spider mites appear as tiny specks on leaf undersides; however, signs of feeding– yellowish-white spots, stippling–on the tops of leaves are easy to see. Careful inspection reveals tiny spider webs–easily seen when misted with water–on stems and under leaves as infestations progress. A magnifying glass helps identify mites and their translucent eggs.

Damage: Mites suck life-giving sap from plants, causing overall vigor loss and stunting. Leaves are pocked with suck-hole marks and yellow from failure to produce chlorophyll. They lose partial to full function, and leaves turn yellow and drop. Once a plant is overrun with spider mites the infestation progresses rapidly. Severe cases cause plant death.

Controls: Cleanliness and good air circulation: This is the most important first step to spider mite control. Keep the grow room and tools spotless and disinfected. Mother plants often have spider mites. Spray mothers regularly with miticides, including once three days before taking cuttings. Once mite infestations get out of control I recommend the entire grow room be cleaned out and disinfected with a pesticide and 5 percent bleach solution.

Cultural and physical control: Spider mites thrive in a dry climate and reproduce every five days in temperatures above 80°F (27° C). Create a hostile environment by lowering the temperature to 60°F (16°C) and spray foliage, especially under leaves, with a jet of cold water. Spraying literally blasts them off the leaves as well as increasing humidity; it will slow their reproductive cycle and you will have a chance to kill them before they do much damage. Manual removal works for small populations and wash leaves individually in between two sponges. Avoid infecting other plants with contaminated hands or sponges.

Spider mites cause stippling, small spots, on the top of leaves. Remove leaves with 50 percent or more damage.

Remove damaged leaves and throw away, making sure insects and eggs do not reenter the garden. If mites have attacked only one or two plants, destroy the infected plants to stop the spread of mites.

Biological: Predators.  Predatory mites work best when there are only a few spider mites. Introduce predators as soon as spider mites are seen on vegetative growth, and release them every month thereafter. This gives predators a chance to keep up with mites. When spider mites have infested a garden, the predatory mites cannot eat them fast enough to solve the problem.  Predators are available commercially. When properly applied and reared, predatory spider mites work very well, but predators eat a limited number of mites a day. The fungus, Hirsutella thompsonii, trade name Mycar®, kills spider mites.

Sprays: Homemade sprays often lack the strength to kill infestations but work as a deterrent by repelling mites. Popular homemade sprays include Dr. Bonner’s Soap, garlic, hot pepper, citrus oil, and liquid seaweed comos. If these sprays do not deter spider mites after four to five applications, switch to a stronger spray: neem oil, pyrethrum, horticultural oil, or nicotine sulfate, cinnamaldehyde. Insecticidal soap does a fair job of controlling mites. Usually two or three applications at five to ten day intervals will do the trick.

Pyrethrum (aerosol) is the best natural miticide! Apply two to three applications at five to ten day intervals. Pyrethrum is the best control for spider mites. Spider mites should be gone after two or three applications at five to ten day intervals, providing sanitary preventative conditions are maintained. Eggs hatch in five to ten days. The second spraying will kill the newly hatched eggs and the remaining adults. The third and subsequent applications will kill any new spider mites, but mites soon develop a resistance to synthetic pyrethrum.  Neem oil works great!

  Heavy-duty chemical miticides are available but are not recommended on plants that will be consumed by humans. If using any chemical miticide, be sure it is a contact poison and not systemic.

Progressive control measures for Spider mites:

Cleanliness — Clean room daily, disinfect tools, do not introduce new pests into the garden on clothes, no animal visits, etc.

Create hostile environment — Humidity, temperature, water spray.

Create barriers — Smear Tanglefoot™ around pot lips, stems, drying lines. 

Dip cuttings and vegetative plants —Dip small plants in pyrethrum, horticultural oil, neem oil. 

Spray — Apply pyrethrum or neem oil; use strong miticides only if necessary. Rotate sprays so mites do not develop immunity.

* Excerpted from “Chapter 14 – Pests and Diseases” Marijuana Horticulture: the Indoor/Outdoor Medical Grower’s Bible, by J. Cervantes, 512 color pages, 1120 color photos and illustrations, glossary, index, $24.95.