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Need to know series: Spider Mites

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In the indoor grow world over the past couple of months the rise in pesticide sales always rises of course especially around spring and summer. The arrays of questions asked about numerous pests are not only varied but most are geared up to eradication. These need to know articles will be based on the basics we should all know when dealing with certain aspects of indoor growing. This article will be on the problem of spider mites, their biology, their life cycle and how to deter and kill any current infestations.

The two spotted spider mite.

Photograph by Eric Erbe, USDA. Digital colorization by Chris Pooley, USDA. Courtesy of University of Florida.

Spider mites are members of the Acari (mite) family Tetranychidae, which includes about over a thousand different species. They tend to live on the undersides of plants leaves. When your grow room is truly infested they may spin protective silk webs all over your plants. In fact spider mites are mites were named just that due to their ability to produce webbing. Unfortunately the webbing is not the damaging part but they feed by piercing leaf tissue and sucking up the plant fluids. As the spider mites continue to feed, the leaves turn yellow, and may dry up and drop off.
Large populations of spider mites are usually accompanied by fine webbing. Host plants for spider mites are many and include strawberries, melons, beans, tomatoes, eggplant, ornamental flowers, trees and most houseplants. Bearing this in mind the indoor grower has to be extra careful when in their outdoor garden, in the park or even literally brushing past a bush etc.
Spider mites lay many eggs that stick to your plants leaves and body. A mature female mite is capable of laying several hundred eggs in its life cycle.

Drawn by Mert Ucin

After hatching, the yet to be mites go through a larva stage and two nymph stages, before becoming a sexually mature adult please see diagram. The lengths of the growth development will vary by species and environment, usually from 1 - 3 weeks. A hot and dry environment will cause a much faster growth within a mite’s growth and reproduction rate.
Spider mites are tiny and are almost too small to be seen by eye. So painstakingly check your plants on a regular basis and introduce these weekly checks as a part of your new ongoing spider mite prevention regime.
Spider mites attack a wide variety of plants, but the cool weather mites focus on broad-leafed evergreens and conifers. So bear those types of plants, along with herbs too.
Now controlling and eradicating these guys is easier said than done but you do have 2 options: One is chemical, using toxic pesticides and harmful sprays, the other is organically.
Chemical pesticide used 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.

Webbing produced by twospotted spider mites

Photograph by University of Florida.

Now there are some chemical pesticides that will not be so damaging, but you must do your research and if in doubt ask your local grow shop or just pop into Go Grow Hydroponics in Edgware HA8 5EF and ask us.
Organic methods work fine as well but you will need to vary your attacks and use your products accordingly.
There are many home made brews you can try out for yourself. Please bear in mind that we always advise to foliar spray plants during lights off.

Soap & Water Spray
Simply add 5 tbsp liquid dish detergent to 1 litres of water. Repeated sprayings will be required to kill the mites. While spraying, ensure that you do use it on the undersides of the leaves. You may require multiple applications depending on how well you can cover each individual leaf of the plant. Make sure to rinse off the leaves with plain water 20 minutes after spraying in order to prevent the soap from clogging up the stomata on the plants leaves.
Chilli Bang Spray
2-3 Garlic Bulbs, 6 large or 12 small hot chilli Peppers or 1-2 tbsp hot chilli powder, 1 tbsp Vegetable Oil, 1 tsp Natural Liquid Detergent or Soap, 7 cups Water. Shake vigorously and sieve contents through a pair of tights and pour into sprayer and apply. Wait and after 20 minutes re-spray your plants with clean water.
Alky Spray
This spray requires alcohol but not from the drinks cabinet but actual rubbing alcohol. It consists of one part rubbing alcohol and one part water in equal measure. Rubbing alcohol is poisonous; it will kill the mites on contact. But no need to worry as it evaporates quickly and thus will do little damage to your plant. Make sure to use the spray on the entire plant.
Bakers Spray
Half a cup of baking soda, 1 cup vinegar, 3 tbsp lemon juice, 2 drops washing up liquid, mix and dilute with plain water to just over a litre. Wait and after 20 minutes re-spray your plants with clean water.
Predatory Mites
These mites do not feed on plants but on other plant damaging mites and are used regularly within the gardening world. There are a few types of predatory mites, but for spider mites we offer gardeners either Spidex - Phytoseiulus persimilis or Spical - Amblyseius californicus. Both types are very good at tackling the problem with no spraying after you release your predatory mites.
Companion Plants
This method of control is more preventative than cure or a mite killing method. Companion growing is all about growing plants that deter pests and insects next to plants that cannot. The list below is of simple plants you can grow next to nearly anything to ward of pests indoor or outdoor.
Garlic – Deters: aphids, cowpea curculio, flea beetles, Japanese beetles, Mexican been leaf beetles, root maggots, spider mites and squash vine borers
Onion – Deters: bean leaf beetle, cabbage loppers, carrot flies, flea beetles, harlequin bugs, mice, rabbits, spider mites
Dill – Deters: aphids, cabbage moths and spider mites
Fennel – Deters: aphids, slugs, snails and spider mites
Coriander/Cilantro – Deters: aphids and spider mites
Chives – Deters: aphids, Japanese beetles and spider mites
Cloves – Deters: spider mites
Well there you have it, a low down of what you really NEED TO KNOW about Spider mites. Any questions please come and visit us at the shop. Unit 1 Mill Yard Industrial Estate, Columbia Avenue, Edgware HA8 5EF.