Q. Every year my Dwarf Alberta spruces look terrible. Portions are dying off, and there are brown needles all over them. What's going on?
A. It sounds like you're being plagued by spruce spidermites. The spruce spidermites are cool-season mites - they like early spring and fall.
Check for mites by holding a white sheet of paper beneath the branches and rapping them soundly. This will dislodge mites and plant debris onto the paper. Wait 10 seconds, then tip the paper slightly to allow the plant debris to fall off. Then look for things about the size of a grain of pepper (yes, mites are extremely small!) running around.
Take the back of your hand and run it across the paper. You'll find tiny smears - these are squashed spidermites. If you seen green smears, you have the bad mites. If you see red smears, you have the "good" mites that are predators, feeding on the "bad" mites. If there are a lot of red smears, forego treatment to see if the good guys can take care of the bad guys.
If all you see are green smears, take action! Spidermites are extremely good at increasing their numbers. One spidermite can produce 13,000 offspring in just one month, so you don't want to tarry in trying to control them.
Normally, horticultural oil works well on mites, but Dwarf Alberta spruces are sensitive to oil so you should avoid using it. If you have a professional caring for your shrubs, ask him or her to take care of this for you. If you do things on your own, visit your local garden center and ask for a miticide. Follow the label instructions on how much to mix in how much water.
Spray the plant thoroughly - mites hide out in all sorts of places, so you have to do a good job. Check once a week and re-treat as necessary, but don't OVERTREAT! Too many sprays kill off predators, and the predators don't regain in population as fast as the bad guys. 1 or 2 repeat applications should be sufficient.
You can also try just washing the mites off. Direct a stream of water at them from your hose. They spent the winter in an egg on the plant, so they didn't have far to go once they hatched. If you can knock them off the plant with the water, they have a hard time getting back on, so they can't do any damage!
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