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As discussed at the Ocean Spray / BCCGA Winter Workshop on Feb. 4, 2004, dearness scale has been found on cranberry vines in Richmond. In early July 2003, scale damage first appeared as small patches of vines with reddened leaves. Infested vines became pale green, dropping lower leaves from the current years' growth. By the end of summer, patches of scale infestation had been found in at least five fields planted with Stevens, Bergman or McFarlin.
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Scales are soft-bodied insects covered above by a thick protective shell or scale, and below by a partial membranous scale. The thick shell of dearness scale resembles a small beige clam shell and is often covered with a white secretion. Female scales are round and globular whereas male scales are longer and flatter. The white waxy coating gets rubbed off during flood harvest but usually remains after dry harvest. On female scales, the skins cast by the two immature stages may be seen as a yellow area on the uppermost point of the shell.
Dearness scale has been reported on cranberry in Massachusetts and in Wisconsin. Its host range includes many perennial plants. Dearness scale is native to North America, and has been found in 24 states, as well as Canada, Cuba and Mexico. In Massachusetts and Wisconsin, dearness scale has one generation per year. The armored females overwinter, and the eggs within them are usually formed in spring. Crawlers (first stage immatures) are reported to begin hatching from eggs in early June in Wisconsin and mid-June in Massachusetts. Crawlers are bright yellow-orange and tiny: about 1/100 to 3/100 of an inch long (0.25 - 0.33 mm). Crawlers wander or are dispersed by wind, and settle to begin feeding on plant stems within one to three days of hatch. In British Columbia, we suspect that crawlers emerge earlier than in Wisconsin. Crawlers are the stage most susceptible to insecticide treatment. There is evidence of parasitism and predation on dearness scale in British Columbia. Holes made by emerging parasitoids have been found. Some scales showed marks typical of parasitoid egg-laying punctures, and others had grooves that might be made by ladybird beetles. Integrated pest management of dearness scale in British Columbia will attempt to conserve these natural enemies.
| Scale from Wet Harvest Fields |
Group of scale on cranberry vine |
Female scale after flood harvest,
with nymphal skin showing |
Scale with possible ladybird damage |
Scale with 3 parasitoid stings |
Male scale with parasitoid hole |
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| Scale from Dry Harvest Fields |
Group of scale on cranberry vine |
Female scale with nymphal skin
showing |
Two female scales |
Group of scale on cranberry vine |
Photos by Mairi Robertson
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