There has been a proliferation of insect activity this spring. It seems the extra moisture has benefited more than just our plants. In the Broomfield Xeriscape Demonstration Garden, we are seeing two insects that aren't typically present on healthy trees: Woolly apple aphids and hawthorn mealybugs.
These two insects are somewhat similar in appearance. Both produce a protective white waxy coating, and because of this, both can be difficult to control with contact insecticides. Luckily the damage they cause is mainly aesthetic, especially on older, established trees.
Woolly apple aphids affect both apples and crabapples. They appear as small cottony masses at the base of twigs and suckers, around pruning wounds and on cankers. They produce waxy filaments that give them a fuzzy appearance.
Though chemical controls are rarely warranted, because there are many beneficial insects that keep populations in check, the sticky honeydew produced by these sap-feeding insects can become a nuisance. Black sooty mold could grow on the honeydew and can detract from the appearance of the tree.
Since they are protected by a waxy coating, systemic insecticides provide the best results. Systemic insecticides come in spray forms or soil drenches that are translocated in tree sap. Insects are injured through feeding activity.
Hawthorn mealybugs also are protected by a waxy coating, though they don't produce the same thread-like filaments seen with woolly apple aphids, and have more of a powdery appearance. They also are sap feeders and severe infestations can weaken the tree and cause dieback of twigs and branches.
Like woolly apple aphids, hawthorn mealybugs are controlled by several beneficial insects, including three species of ladybeetles and the larvae of lacewings. Chemical controls might be warranted if infestations are significant enough to weaken the tree or if, like woolly apple aphids, honeydew and sooty mold become a problem.
Young nymphs of mealybugs are mobile crawlers. Insecticide applications can be timed to correspond with this more vulnerable stage, controlling them before they settle down and develop the coating that protects them from contact insecticides as adults. Call a certified arborist to schedule appropriately timed crawler sprays. Soil drenches containing imidacloprid can be effective. Somewhat less effective are dormant oil sprays applied in late winter or early spring.
Though some of the insect problems we're seeing this year seem to be worse than usual, it is important to remember populations are often kept in check by natural enemies. When deciding to use a pesticide, make sure applications are appropriately timed and the correct insecticide is used. If you have questions about insect control or any other garden-related topics, call the Broomfield Master Gardener Helpline at 303-464-5554.
Colorado State University Extension in the City and County of Broomfield provides unbiased, research-based information about 4-H youth development, family and consumer issues, gardening, horticulture and natural resources. As part of a nationwide system, Extension brings the research and resources of the university to the community. The Broomfield County Extension office is at 1 DesCombes Drive, Broomfield, 80020. For information, call 720-887-2286.