Cottony Maple Scale Diagnostic Guide
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.
Trees at Risk
Silver maple is the preferred host, but cottony maple scale can also be found on red maple, boxelder, alder, hackberry, dogwood, hawthorn, beech, osage orange, apple, mulberry, sycamore, poplar, peach, plum, pear, oak, black locust, willow, linden and elm trees.
Signs of Damage
- Cottony maple scale can produce large amounts of honeydew which leads to sooty mold.
- Premature loss of foliage may occur with heavy infestations.
- Branch and twig 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 1/4” to 1/2” in length and are visible in late spring to early summer.
- Adults emerge and mate as the leaves begin expansion in the spring.
- 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.
- One generation per year.
Dormant oil applications are a good option, especially if soil applications of Xytect™ or Transtect™ have not been previously applied. Xytect™ and Transtect ™soil applications must be timed to ensure high dosage levels are within the tree at the time of the first generation crawler hatch and feeding. Arborists should use foliar sprays only for immediate activity against crawlers or use dormant sprays for management of overwintering females on twigs.
Tree Injection using Xytect 10%
Dosage: 1 mL/in DBH for trees 2 - 10 in DBH 1.5 mL/in DBH for trees 10 - 36 in DBH 2 mL/in DBH for trees 36 in DBH and above. For heavier infestation and/or more resistant insects, use 1.5 mL or 2 mL rates on trees having a DBH >1 in. Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding Re-Treatment: Annually
Properly timed soil applications of Xytect™ or Transtect™ will work extremely well for most soft scales. Use foliar sprays for immediate activity against crawlers or for management of overwintering females on twigs with dormant sprays.
A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org