Q. I have two dwarf Alberta spruce located in the front of my home that are beginning to turn brown. I am worried and wonder if the plant will recover.
A. Everything is a bit out of kilter this year. When overall temperatures are cooler than normal, often things like bloom times and insect emergence become compressed. This is why I am observing spruce spider mite damage already on plants like dwarf Alberta spruce.
Mites are not true insects because they have four pair of legs at maturity, unlike true insects that have three pair of legs. Mites really are true spiders that are usually very tiny and can occur in huge numbers in certain years.
According to Penn State University Extension, the spruce spider mite is considered one of the most destructive spider mites in the United States. Dwarf Alberta spruce is one of this pest's favorite host plants.
This species is sometimes referred to as a cool-season pest. Other mites prefer hot, dry conditions. These warm-season mites can also attack evergreens, burning bush and beans during the summer.
To check to see if you may have mites, place a white sheet of paper under the affected needles and tap the branch sharply.
If you see what appears to be grains of pepper scurrying around on the paper surface, then you have a mite problem. One can also look at the needles with a magnifying glass or hand lens. One can often observe the tiny webs the mites spin, and sometimes observe the little devils crawling around on the needles.
This species damages host plants by sucking plant fluid from needles as they feed. Infested trees at first have a speckled, yellowish appearance, and lack rich green color. After prolonged feeding, needles turn rusty colored and may drop prematurely. Mites usually attack older needles located in the lower and inner parts of the plant.
Damage may spread as the season progresses. This species also produces silken webs on the needles.
Since needles on spruce do not recover from damage by mites, it can be a huge issue on specimen shrubs like Dwarf Alberta spruce. My preferred organic control for mites on Dwarf Albert Spruce is Diatomaceous Earth, which is available online and at most garden centers nowadays. Just dust the needles with a small amount. It does need to be re-applied after a rain. High pressure water sprays on the foliage from time to time between dustings may help to wash mites off the plant.
Products containing pyrethrum may also be used. The organic pesticide Neem also has some activity against mites. But the oil contained in many formulations of Neem may damage needles. Many experts now say that many conventional insecticides used for mite control may just make the problem worse because mite populations tend to rebound to higher levels after their use than if nothing was done at all.
Often, the best we can accomplish is to limit their damage and keep mites under control.
The Plant Medic, written by Ricky Kemery, appears every other Tuesday. Kemery retired as the extension educator for horticulture at the Allen County Purdue Extension Service. To send him a question, email firstname.lastname@example.org.