Tuesday, September 23, 2008

Landscape and Nursery - Cool Season Mites

The following is information on cool season mites in the landscape. These mites will be more active now with the reduced temperatures.


As temperatures consistently return to the 60's and 70's during the next few weeks, spruce spider mite and southern red mite activity will increase. Spruce spider mites feed on fir, arborvitae, spruce, Douglas-fir, and other conifers, feeding on older foliage first. Spruce spider mites are olivedark red with reddish-yellow legs and two reddish eye spots with a pale stripe down the back (visible with a microscope). Spruce spider mites start feeding in the fall around 2301 3957 [3094 peak] GDD and continues until there is a hard frost. In the summer, damage appears as bleaching, yellowing, stippling or bronzing of the needles. Damage visible on trees in summer is from intensive fall feeding.

Southern red mites feed on a wide variety of plants including azaleas, camellias, hollies, clethra, juniper, elaeagnus, hibiscus, photinia and rose. Nymphs and adults are active starting around 2401 3584 [3034 peak] GDD and 1913 3518 [2933 peak] GDD respectively. This mite has a dark reddish to brown abdomen with a pinkish to red cephalothorax and a pale mid-stripe. It feeds on the lower leaf surface but during high populations may be found on upper surfaces. Damaged leaves may be brown to gray and drop prematurely.

Monitor with a clipboard and a white sheet of paper, looking for dots the size of periods. Watch for predatory mites and small lady beetles; both are predators of the spruce spider mite and should be conserved. Miticides available for control include hexythiazox (Hexygon, Savy), bifenazate (Floramite), abamectin (Avid) and others. Research has shown bifenthrin (Talstar) can cause mite 'resurgences' because natural enemies are killed; thus mite eggs are able to hatch without threat of predators.

Information from Dr. Brian Kunkel, Ornamental IPM Specialist, UD

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