My Alberta spruce got hit with spider mites in spots. Is there a safe green spray to use to cover these brown areas with?
The Gardener’s Answer
Hello, Patricia in New Jersey: Some plants are more prone to insect problems than others, and Alberta spruce are very susceptible to spider mites. As with any plant material they are more vulnerable to insect and disease issues when they are under stress. If your spruce is not given adequate moisture or sufficient sunlight this could be the reason for spider mite infestation. These mites feed on old growth in the spring and new growth the fall after it has hardened off. The damage from spring feeding does not usually appear until later in the summer while the mites are dormant. Severe infestations can cause foliage discoloration and needle drop. The foliage discoloration is caused by the mites sucking the fluids from the foliage, giving it a speckled appearance. Understanding the life cycle of these mites is important in terms of treatment. In the fall the adult females continue to feed and lay eggs on smaller branches and needles until the first hard frost. In the spring the eggs hatch and they begin to feed until summer arrives and the increased temperatures cause them to go dormant until the cooler temperatures return in the fall, and the cycle continues. Treatment of these mites is one of the more difficult to control as far as pests in the home landscape go, but if you can get the population under control before it becomes a severe infestation you will have more success in terms of treatment. Spraying these mites is going to be most effective while they are active. Putting your hose on a jet setting and spraying the branches a couple times a week during the spring and fall is a reasonable organic option. Otherwise horticultural oil and insecticidal soap are both labeled for use spider mites. Plant-based dormant oils can be used during the fall and early spring to kill the eggs and help suppress future populations. Insecticidal soaps are useful during the warmer months so this would be a good option for you at this point. Lady beetles and lacewings are both biological controls.