The cottony maple scale (Pulvinaria innumerabilis) is one of the largest and most conspicuous scale insects in this country. Its favored host is maple trees, although it has been found on a number of other species as well. Females are inconspicuous and overwinter on twigs, and in the spring they rapidly grow and produce their characteristic white egg sac. Damage comes from crawlers that appear in June and July when they migrate to the undersides of leaves, insert their mouthparts in or near the veins, and withdraw sap from the plant. Heavy infestations may kill weakened trees and cause branch dieback in healthy trees. Large amounts of honeydew are produced which eventually cause the leaves to be covered with grayish/black colored sooty mold. The sooty mold reduces the aesthetic features of maples and honeydew can become a nuisance as it coats patios, decks, and vehicles.
Females grow rapidly in spring and produce hundreds of eggs. Eggs hatch in early summer and young scales migrate to the leaves. Xytect and Transtect soil applications must be timed to ensure high titer levels are within the tree at the time of the first generation crawler hatch and feeding. Arborists should use foliar sprays for immediate activity against crawlers or for management of overwintering females on twigs with dormant sprays. Xytect 10% as a tree injection treatment for trees that cannot be treated with foliar sprays or other systemic options.
Other Treatment Practices
- Promote health and vigor with proper irrigation, mulching, proper pruning and prescription based fertilization practices.
- Adequate water is a key factor in maintaining stress free plants. A slow, deep watering event once every few weeks during dry conditions will help maintain soil moisture levels and minimize stress.
- Mulch is very beneficial for all trees because it reduces competition with turf and moderates soil temperature and moisture levels. The addition of 3 inches of wood chips or shredded bark under the drip line can have a very beneficial effect by holding in moisture and promoting healthy fibrous roots.
- Cambistat can be also be used to promote tree health and reduce the incidence and severity of stress mediated diseases and insect problems on trees growing in urban areas.
Xytect and Transtect will provide a high level of control of all soft scales. Arborists should use foliar sprays for immediate activity against crawlers or for management of overwintering females on twigs with dormant sprays. Properly timed soil applications of Xytect or Transtect will work extremely well for most soft scales.
Females grow rapidly in spring and produce hundreds of eggs. Eggs hatch in early summer and young scales migrate to the leaves. Scales mature in late summer and after mating females return to twigs and branches for the winter making dormant oil applications a good option, especially if soil applications of Xytect or Transtect have not been previously applied.
Oils should not be used on Japanese or sugar maples.
Signs of Damage
- Cottony maple scale can produce large amounts of honeydew which can eventually be covered with sooty mold
- Premature loss of foliage may occur with heavy infestations
- Branch dieback may occur with heavy infestations
- Mature females can be found on undersides of leaves near veins, and may reach 5mm in length
- Mature females look like popcorn strung along the twigs
- White egg sacs may be ¼” to 1/2” in length and are visible in late spring to early summer
Photo: Eugene E. Nelson, Bugwood.org
Photo: Nancy Gregory
University of Delaware, Bugwood.org
Trees At Risk
- Silver maple –preferred host (Acer saccharinum),
- Red maple (A. rubrum)
- Boxelder (A. negundo)
- Alder (Alnus)
- Hackberry (Celtis)
- Dogwood (Cornus)
- Hawthorn (Crataegus)
- Beech (Fagus)
- Osage orange (Maclurapomifera)
- Apple (Malus)
- Mulberry (Morus)
- Sycamore (Platanus)
- Poplar (Populus)
- Peach, plum (Prunus)
- Pear (Pyrus)
- Oak (Quercus)
- Black locust (Robinia pseudoacacia)
- Willow (Salix)
- Linden (Tilia)
- Elm (Ulmus)
- Females grow rapidly in spring and produce hundreds of eggs.
- Adults emerge and mate as the leaves begin expansion in the spring.
- Eggs hatch in late spring-early summer(802-1265GDD)and young scales migrate to the leaves.
- Scales mature in late summer.
- One generation per year.
Insects that Feed on Trees and Shrubs. Johnson and Lyon
Ohio State University Extension Fact Sheet
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.