Spider mites are the bane of marijuana growers. Mites are not insects, but arachnids, the same family as spiders. They have eight legs. Your garden is probably infested with two spotted mites. When looking through a loop or magnifying glass, two black spots are visible on the pest’s back. Gardens are also infrequently infested with the red spider mite.
Spider mites are about the size of a poppy seed. They insert a tube into the plant and suck out its juices. Indoors, where they are not combating nature’s challenges, mites multiply quickly and overwhelm gardens. Mites lay eggs after they mature, about two weeks after hatching. The females lay thousands of eggs over their lifetime. They hatch in about three days.
Mites inhabit the underside of the leaf and are not readily apparent. The first indication of their presence is usually the sight of tiny brown spots circled by small yellow areas. These areas indicate sites where mites have used their proboscises to puncture the leaf surface and suck the plant’s sweet juices. As the population increases they begin to build webs and can be seen commuting from one feeding area to the next.
If only one plant or one section of a plant seems to be infected or if a plant is much more infected than the others in the garden, wrap it in a plastic bag to prevent infecting the other plants as you remove it from the garden.
If your plants are growing vegetatively you have quite a few options. First you can wash them with a moderately vigorous spray to knock down the mite population. This will help the plants by lessening their loss of vital juices. Prepare a spray with a teaspoon of real soap such as Dr. Bronner’s peppermint or eucalyptus liquid soap per gallon of water, or spray with Safer’s horticultural soap to help dislodge and suffocate the pests. Mites are found on the underside of the leaves and must be sprayed there. If the plants are small or easy to handle it might be easier to dip them in the soapy water. Spraying can remove most but not all the mites, and it doesn’t remove the eggs.
A small mite infection left unchecked is a temporary condition. So it is unwise to go into flowering with infected plants. The problem is that after the plants are one third of the way through flowering, two to three weeks, you want to avoid spraying with water or soapy water to wash off the suckers.
Mites must be eliminated before forcing or when they attack plants in the early stages of flowering. If not they will multiply with disastrous results. The skimpy buds will be low quality and covered with dead mites. It’s not an enjoyable smoke.
Spraying can be used to control mites through the vegetative stage and for the first two or three weeks of flowering. However, other means must be used to get the plants to the zero tolerance level. By far the easiest method is to use an acceptable miticide.
There are several commercial miticides that can be used early in the season to kill mites.
Pyrethrum has been used to kill mites. It is a natural pesticide produced by a close relative of the chrysanthemum. The problem with using it is that many races of mites have developed immunity to it. However, it is the first miticide you should try.
Cinnamite comes as a concentrate that is diluted and sprayed on the plants. It contains a miticide derived from cinnamon oil. It is very safe and is rated least hazardous. It is quite effective but it doesn’t kill the eggs. It should be used every three days for two weeks to make sure all the mites are killed soon after they hatch. It is a contact spray so plants should be dipped or sprayed on the leaf undersides. It is also effective against powdery mildew.
Neem oil is a natural miticide derived from the nuts of the Neem tree, which is found in India. It is a mite repellent as well, so some gardeners use it as a prophylactic, spraying it on a weekly basis. I mix neem oil with Cinnamite to eliminate small infections. Cinnamite and neem oil are also used against powdery mildew.
For growers who distrust anything commercial, try an ?herbal tea? that acts as a miticide. To each quart of water use a tablespoon each of ground cinnamon, ground clove and 2 tablespoons of ground Italian seasoning. Heat the mixture until it starts to simmer, then turn off the heat. Add 2 tablespoons crushed fresh garlic when the water cools to warm. Let the tea sit until it cools. Strain and save the water using a cloth or coffee filter. Add a few drops of liquid soap or dishwashing liquid to the water. It is ready to be sprayed on the leaf undersides. After spraying the mites off with water, spray it on the leaf undersides. It will eliminate the mites if it is sprayed every three days after the wash. Within two weeks the mites will probably be gone.
Avid is a miticide registered for ornamental plants. Its active ingredient is abamectin, a derivative of a toxin originally found in soil bacteria. Avid is not registered for use on vegetables except in certain restricted situations. Other brands of abamectin such as AgriMek by Syngenta are registered for a wide range of crops. The AgriMek label calls for a minimum of a seven day wait between application and harvest. I wouldn’t use marijuana if I knew it was treated with this pesticide during the last few weeks of flowering.
Some gardeners have reported success controlling mites using predatory mites or other predators. These carnivorous mites reach an equilibrium with the herbivorous mites, keeping damage to a bare minimum. I have tried introducing mixed species of predatory mites a few times but have never been satisfied with the results. They did not get the problem under control. However, they can work and some gardeners swear by them. I probably didn’t provide them with the right conditions. There are also other predators that eat mites, but I have no experience using them.
Ultimately, the solution to the mite problem and the pest problem in general is to prevent the garden from becoming infected. Following certain simple rules will help:
Wear freshly washed clothes or change into a garden outfit when going into the garden.
Never work outdoors, especially in a garden or other vegetative or turf area right before working in your indoor garden.
Pests are frequently carried in on shoes. Do like Mr. Rogers and change your footwear before you enter the garden.
Don’t use outdoor soil, tools or containers in the indoor garden
If a plant is to be introduced to the garden, first do a close examination and then put it in quarantine for five or six days. Examine it closely, especially the underside of leaves, before placing it in the garden.
Close up any unfiltered airways or holes through which plant pests might enter. Make sure that air intake from outside is filtered.
Readers with grow questions (or answers) should send them to Ed at: Ask Ed, PMB 147, 530 Divisadero St, San Francisco, CA 94117, USA.
You can also email Ed at [email protected] and send queries via his website at www.ask-ed.net.
All featured questions will be rewarded with a copy of Ed’s book, The Big Book of Buds.
Sorry, Ed cannot send personal replies to your questions.