Spider Mites

In the summer months, I'm Having Mitemares...

They're back! Just what you don't want to find on your bonsai or greenhouse plants.

Spider mites. Most species will attack deciduous trees and shrubs but the spruce spider might prefers conifers and is especially damaging to spruces. Its damage can continue throughout winter. Drought stressed plants are especially affected, be it forests, agricultual corn, alfalfa or nursery plants. Increasing humidty, by spraying or irrigating more often will help; more on that later.



In CA, we used cygon and kelthane primarily; the former is not for sale for the home gardener. Malathion used with Safer Oil, or a soybean activated surfacatant such as 'Preference.' , sticking agent (wetting compound) worked to a lesser degree. Some people used Basic H as that wetting agent. Here in WA. State I ended up using wettable Orthene, which is a rather toxic chemical and would have to be ordered on line, as it is not sold for retail use. Neem oil is a potential possible alternative, but my experiences with it have been less than positive on all soil born insects.

None of these insecticides will ever eliminate the pests for slowly but surely, the survivors build up a resistance to whatever you use. Therefore, a careful and well-documented rotation of chemicals should be used. Washing the plant down, even using a pressure hose on say Alberta spruce, will dislodge the adult and young, but will not dislodge the eggs. Safer oil or other oil-based formulas should be used. Those eggs will hatch in a month or less, so the treatment should be done again. This battle will continue throughout the summer months.

There are biological controls, which might be tested. There are predacious mites which feed on these and it is something to investigate. The gamble is this, during their usage or test one cannot use any chemical at all. They are even more sensitive than the mites you are trying to eliminate and will be wiped out very quickly. If they do not do the job, your plants may be seriously damaged by lack of chemical or other treatments.Source one.

Source two being Nature's Control. I would further caution all who would buy such Predatory mites that even "safer" insecticids such as the Pyrethryn family should not be used. Although Pyrethryn like Nicotine sulfate breaks down quickly, most of them are encapsulated to make the product a slow time release. This causes it to be effective for two weeks and though weakened enough not to work on the pests, it remains strong enough to kill off the Hired help.

Systemics may also provide a solution, but technically speaking cannot be recommended unless so labeled. That said, I used a granular turf product and have used it sparingly on Orchids and Cactus to control root mealybugs. It is not so labeled, but I suspect that it might also be used to control weevil and other grub insects in Bonsai. If this is a potential problem for you, I would consider applying some of it beginning in July.

Arbico Organics is one source for predatory insects. I tried to put a link to their site, but it would not work. You will have to google them.

I also found this to be a informative article. Do read

© 2009 Herb Senft