Fluffy Maple Leaves? Check for Cottony Maple Leaf Scale!

Red and silver maples can be host to an interesting looking scale insect, the cottony maple leaf scale. Entomologists tend to be on-the-nose when naming things, so unsurprisingly this scale insect specializes in feeding on leaves and, at one point in its life, the female has a cotton ball like appearance. While the cotton stage is the most noticeable stage, it is actually the calm before the storm as this is when the insects are in the egg stage. After this visible stage, they can be difficult to detect and may induce some damage before caught.

Biology

This scale species produces one generation per year. In the spring, males and females will mature into their adult forms. Males are winged in order to fly and mate with females. Females will move from their overwintering sites on maple twigs to the leaves where they will begin laying eggs and eventually die. In late May and early June, their desiccated dead bodies are attached to a long trailing cotton “ovisac,” which is a white, messy bag that contains their eggs.

Inside of each ovisac can be thousands of eggs, which hatch before the end of June. The resulting crawlers, the early nymphal stage that is mobile, will migrate to the veins of leaves and

By the end of summer and start of fall, the scales will migrate to their overwintering spots on twigs. There they will stay and feed until winter and the next spring when they move towards the leaves to begin the cycle anew.

Figure 1: Cottony maple leaf scale females produce conspicuous ovisacs before they perish. These fluffy “bags” are often the first sign people might notice on their infested maple tree. (Photo: Jonathan L. Larson, UK).
Figure 2: In this closeup, an ovisac has been dissected to show some of the many small eggs hidden inside. Each egg has the potential to hatch into a crawler that may become a scale feeding on the plant. (Photo: Jonathan L. Larson, UK).plug their mouthparts in to feed.

Symptoms

Cottony maple leaf scale is a soft scale, which means they can make copious amounts of honeydew during their life. This sticky fecal material is a byproduct of their diet, which consists of sugary material from the host plant. It sticks to the leaves below scales and twigs and branches. Cars and sidewalks below may also be shiny or sticky. Honeydew frequently attracts other insects, who wish to dine on the sugary butt juice, but can also recruit black sooty mold to grow on the plant. The stress of the scale infestation may also induce twig dieback and a thin canopy.

Management

Usually, populations are kept in check by natural enemies, like lady beetles and parasitoid wasps. However, there can be situations where the pest outpaces these beneficial organisms and becomes an issue. In those cases, systemic insecticide applications of imidacloprid or dinotefuran will help to mitigate issues. These would be applied when egg cases are noticed and are most often applied as soil drenches around the base of the tree. If applying to the soil, be sure to move mulch away from the base of the tree before making an application in order to improve efficacy. Some imidacloprid formulations may be applied to the foliage and then be systemically transferred through the tree.

Be careful and follow label directions no matter which method you choose.


By Jonathan L. Larson, Entomology Extension Specialist

Posted in Landscape Trees & Shrubs
%d bloggers like this: