Submitted by Brandy Brabham
WVU Extension Agent
A number of calls have come in recently about yellow (tulip) poplar trees exerting sticky black substance covering the trees and surrounding ground as well as damage to leaves.
It appears that two different insects are causing these problems. The popular trees are plagued with high numbers of soft-bodied insects known as scale.
The first is the tuliptree scale. Tuliptree scale is a type of soft scale that attacks primarily yellow poplar and magnolia trees. These insects have one generation per year and are generally found on twigs and branches where they feed on the vascular system of the tree.
Damage symptoms can include yellowing of leaves, premature leaf drop, and branch dieback. They also produce copious amounts of sugary liquid called honeydew, which can promote the growth of sooty mold, a black colored fungus.
In the first stage of growth for the scale, or the nymph stage, they appear dark red and about 0.5 mm long. At this stage, they are known as crawlers because they have functional legs, which can be used to move over plant surfaces to find feeding spots. Once settled, they attach themselves to the plant and do not move. Females are pinkish orange with mottled black. They give the limbs of a tree a warty appearance. Each female is able to produce 3,000 crawlers of several weeks.
The second insect is the yellow poplar weevil. These weevils also have one generation per year and will feed on the leaves of yellow poplar, sassafras, sweetbay, and magnolia trees. Larval stages mine through leaves feeding between the lower and upper leave surfaces while adults feed primarily on the lower leaf tissues.
Larval activity occurs primarily in late May and June while adults are active in the spring during egg-laying and again in late June and July when new adults emerge. Damage symptoms include brown inflated mines or discolored spots that give the leaves a burned appearance.
Although damage from these insects can be unsightly, established trees in the landscape are generally able to withstand some feeding pressure.
Numerous species of predatory and parasitic insects will generally keep these insects under control most years. However, natural enemies are usually not present in high enough numbers to provide sufficient control during outbreaks seasons like this year. Where populations of these insects are extremely high chemical control may be warranted.
Control of tuliptree scale is often difficult, because immobile scales will produce a waxy covering that offers protection from many insecticide sprays. For this reason, chemical control of tulip tree scale is most effective in late August to September when crawlers are active.
Foliar applied broad spectrum insecticides containing acephate, carbaryl, imidacloprid, malathion, or permethrin can be used to control crawlers. However, these materials can also kill the scale's natural enemies responsible for lasting control in the landscape.
Biorational, or low impact materials such as horticultural oil, insecticidal soap, or pyriproxifen can be used in place of these products as a foliar treatment.
Where trees are too tall to maintain adequate spray coverage to infested branches, soil-applied systemic insecticides containing imidacloprid can be a good option. Systemic insecticides applied during the fall will generally provide the most effective control for the following spring.
For yellow popular weevil, foliar applied insecticides containing acephate or carbaryl may be used to target adults. Unfortunately, we are beyond the point where systemic insecticides would be effective for control of larval weevils.
- Article developed in collaboration with WVU Extension Entomologist Dr. Daniel Frank and WVU-Roane County Extension Service Summer Intern, Nikki Randolph.
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