Spruce spider mites
During examination of white spruce branches for spruce budworm on May 19th
, numerous specimens of spruce spider mites were discovered on the new
shoots. The spruce spider mite, Oligonychus ununquis, can be a serious
problem in windbreak and other landscape conifers. Most conifer leaf
mites overwinter as eggs under the bud scales and can produce three or
more generations per year. They usually prefer the older needles.
Damage to needles occurs by adult mites sucking plant juices causing tissues
to rupture and dry up. Branches appear grayish due to the mottled
needles. The webs, formed during extensive feeding, collect dirt
and dust on the foliage; this might be your first clue to a mite infestation.
Warm, dry periods followed by moist, cool conditions favor the buildup
of large populations of spider mites. Reproduction drops off during
the summer months, so there is usually a fall and spring defoliation cycle
to cause concern. Many pesticides are available for control of mites.
Horticultural oils applied two to three times during the early spring or
late fall, seven to ten days apart are recommended to control mite populations.
Spruce budworm degree days
OOPS! Let's try this again. The table in the last Newsletter
was in degrees Celsius rather than degrees Fahrenheit. The author
claims ?temporary mislocation?, apparently he was confused about which
side of the Canadian border he was on. Here's the corrected version.
|Accumulated spruce budworm degree days
|Peak stages of insect development||Balsam fir||White spruce|
|2nd instar||192 F||197F|
|Base temperature = 46 F.|
Starting date = March 1.