
Grape scale, Diaspidiotus uvae (Comstock)
This is taken primarily from an extension
bulletin
by D. G. Pfeiffer & P. B. Schultz, entitled "Major Insect and Mite
Pests of Grape in Virginia" (Va. Coop. Ext. Serv. 444-567 (1986))
Grape scale is related to the more widely known San
Jose scale and is similar in many respects. One important
difference
is that grape is the only host on which grape scale is economically
important.
It has also been reported on sycamore, hickory, and Ampelopsis
(a
vine related to Vitis). The other major difference between this
species and San Jose scale is the number of generations per year; two
in
the former and three in the latter (Zimmer (1912) reported a single
generation;
Johnson et al. (1999) a second). Grape scale is widely distributed in
the
eastern states, from Florida through New Jersey.
Immature scales overwinter on the grape trunks
and
resume development in the spring. In May or June (June 16 at Roanoke in
1983), crawlers disperse from the maternal scales. After wandering for
24-48 hours, the crawlers settle, begin to feed, and secrete their
scale
coverings. There are two nymphal instars, that remain under their scale
coverings. The females never move from their sites; but, when the males
are mature in the spring they leave their scales, fly to the females,
and
mate. The male flight period is of short duration.
Adult scales are whitish in color and may create
whitish patches on vine trunks when colonies are present. Vigorous
vines
are less severely affected. Grape scales seldom reach damaging numbers
in commercial vineyards, although in the early years of this century
important
damage was reported. This species may be seen most frequently on
backyard
vines.
Johnson et al. (1999) recommended a dormant oil
spray,
and timing a spray of diazinon or carbaryl with degree days against
crawlers,
at 274 and 550 degree days above 10 degrees C (493 and 990 DD above a
base
of 50 degrees F).
Additional references:
Johnson, D. T., B. A. Lewis & J. D. Whitehead.
1999. Grape scale (Homoptera: Diaspididae) biology and management. J.
Entomol.
Sci. 34: 161-170.
Zimmer, J. F. 1912. The grape scale (Aspidiotus
uvae Comst.). U.S. Dept. Agric., Div. Entomol. Bull. 97: 115-124.
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