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It Mite Still Be The Problem
by Tom Mugridge

Q:I have a problem with 3 dwarf Alberta spruces. All three have bare spots where needles have gone brown and fallen off (mostly on the bottom of the trees). Also, even the green needles on all three are a sickly green, not a dark green. These three spruces are next to each other in their own planting bed. They are about 2.5 years old.

The problem was originally confined to 1 tree but now all three exhibit it. I have looked for spider mites but have found none. Finally two other spruces are planted in a separate bed in the front of the house. These exhibit no problem.

A: As I read your description of your troubles, the first thing that came to mind was, indeed, spider mites. However, you state you were unable to find any. I still think you have a spider mite problem, but the spider mites had done their damage and were gone at the time you checked for them. I think the two unaffected ones have been lucky enough to be yet undiscovered by spider mites, hence their good appearance.

Generally, there are 2 types of mites that find dwarf Alberta spruces tasty - the spruce spider mite and the two-spotted mite. The spruce spider mite is a cool-season mite - it likes spring and early fall temperatures. The two-spotted mite likes hot, dry summer temps. As such, it is possible for both types to be effecting your Alberta spruces at different times from spring into early fall.

The best way to check for spider mites is to dislodge them by sharply rapping some branches above a white sheet of paper. Wait 10 seconds, carefully tip off any plant debris, then smear the paper with the back of your hand.

Look for greenish streaks - these are spider mites. They're small - about the size of the period at the end of this sentence. They move very slowly - if you see some larger, fast-moving insects, they're probably not spider mites, and quite possibly are predators.

Spider mite control can be difficult at best. We're sometimes dealing with hundreds of thousands of these pests at one time. Normally, a horticultural oil application in spring will start controlling them, but dwarf Alberta spruces are sensitive to even the best oils, so I would not recommend using it.

Instead, try a miticide (or an insecticide, if it's labeled for spider mite control) when you detect the adults. Repeat as needed but only for a few times, as you may actually aid the spider mites by killing off their predators with the same application you're doing to try to kill the mites! Don't forget -- ALWAYS follow the directions on the chemical label.

You can also dislodge spider mites with a direct stream of water from your water hose. This knocks them off the plant, and they have a hard time getting back on (periods of heavy rainfall accomplish the same thing). This may help you reduce the amount of chemicals you use to try to gain control.

If you're still stumped, I recommend contacting a local professional. He or she will be able to help you address these concerns.


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Tom Mugridge




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