Friday, July 4, 2008

Landscape and Nursery - Cottony Scales

Three species of cottony scales often infest plants in our area and now is the best time to control them. The following is information on cottony scales and their control.

Collectively, we refer to them as the “cottony” scales because of their long, white egg sacs. Here's an I.D. hint to separate them check the host range and egg laying site. Cottony maple scale (Pulvinaria innumerablis) occurs on several plants, but particularly on silver maple and hickory. The 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. The crawler period in our area peaked at approximately 1388 GDD. Cottony maple leaf scale (Pulvinaria acericola) occurs on many plants, but is most often observed on maples, dogwoods, black gum, and Pieris. Adults and egg masses are found all over the plant, but usually 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 P. innumerablis, 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. Peak crawler stage for this scale was 830 GDD in our area.

Many predators and parasites feed on these scales; they are often controlled by them. However, they have performed well this year due to the mild winter. Dormant oil treatments and foliar treatments directed at the re-migrating females are ineffective crawler treatments are the best option. 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. The use of a spring-applied soil systemic neonictinoid insecticide (i.e. Merit, Safari) is also utilized.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens

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