Saturday, February 10, 2007

Late winter spider mites and spruce aphids

With spring still a month or so off most people are not yet thinking about landscape and garden pests. However, there are two pests that occur on conifers (evergreen trees and shrubs that bear cones such as pine, fir, and spruce and arbovitae) that deserve your attention before spring weather arrives.

Spruce spider mite, Oligonychus ununguis, is the most important spider mite pest of conifers and can severely damage some host plants. If, for example, you've ever seen an Alberta spruce with large patches of dead needles the damage was likely done by spruce spider mites. Spruce spider mite is especially common and damaging on conifers that are drought stressed or, ironically, water logged.

Spruce spider mite spends the winter months as a small reddish egg (below) on branches and needles. These eggs hatch in early spring to become the first generation of plant damaging mites. Look carefully with your hand lens in late winter and you'll see the eggs on infested plants. If you find eggs late winter is a good time to treat this first generation of mites and significantly reduce damage that will otherwise occur by summer.



spruce spider mite eggs on arbovitae

Infested plants can be treated with horticultural oil that will smother overwintering eggs without harming plants. See the spruce spider mite page at 'Bugs for more information.

The second landscape pest to watch for in late winter is spruce aphid. If you've seen spruce trees with missing needles below the branch tips the damage may have been caused by spruce aphid. These tiny aphids start feeding in late winter and disappear by spring when only their damage remains to be found. These aphids can be effectively treated like other aphids with insecticidal soap but treatment must be done in late winter, not summer.

So, get out there and start gardening by looking for these winter garden pests!

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