Friday, June 19, 2009

Landscape - Cottony Scales

Cottony scales are common in Delaware landscapes. The following is more information on the subject.

Cottony scales get their name from long, white egg sacspresent now. They all cause sooty mold and isolated branch dieback. For ID check the host range and egg laying site.

Cottony maple scale (Pulvinaria innumerablis) occurs on several plants, but particularly silver maple and hickory. Adults and eggs are almost always found on stems and branches, with crawlers settling on leaves for the summer until they migrate back to the stems to overwinter as female scales. Crawler peak is 1388 GDD.

Cottony maple leaf scale (Pulvinaria acericola) occurs on many plants, but most often on maples, dogwoods, black gum, and Pieris. Adults and egg masses are found all over the plant, but mostly on the leaves. They migrate twice after the crawler stage once back to the twigs in the fall and then from the twigs to the leaves in the spring. It is often confused with cottony maple scale (above) or maple mealybug (Phenacoccus acericola), which does not injure plants as severely as cottony maple leaf scale.

Cottony camellia/taxus scale (Chloropulvinaria floccifera) occurs on hollies, sweet box, Cephalotaxus, and its namesake hosts. Like cottony maple scale, it has two migrations per year and the adult females dry up and die after laying eggs leaving only the cottony egg mass on the leaf. Egg hatch from a single mass can take place over 6 weeks. Crawler peak is 830 GDD.

Many predators and parasites feed on these scales; and provide some control. Crawler treatments are the best option as hort. oil in the dormant stage and foliar treatments directed at the remigrating females are ineffective. For cottony camellia/taxus scale, two treatments of horticultural oil at ½ egg hatch and complete egg hatch (~3-4 weeks later) provides the best control with minimum impact on natural enemies. Spring-applied soil systemic neonictinoid insecticides (i.e. Merit, Safari) are also often utilized.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens

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