A number of homeowners have expressed concern over yellow (tulip) poplar trees. They have noticed a sticky, black substance covering the trees and surrounding ground as well as damage to leaves. Two different insects can cause these problems: Tuliptree scale and yellow- poplar weevil.
About Yellow Poplar Tree Pests
Tuliptree scale is a type of soft scale that attacks primarily yellow poplar and
magnolia trees. These insects, which have one generation per year, are generally
found on twigs and branches where they feed on the tree’s vascular system. The
first nymphal instar or immature stage of the scale is called a crawler because
it has functional legs, which are used to move over plant surfaces to find a feeding
spot. Once settled, they attach themselves to the plant and do not move. Damage
symptoms include yellowing of leaves, premature leaf drop and branch dieback. These
pests also produce copious amounts of a sugary liquid called honeydew, which can
promote the growth of sooty mold, a fungus causing the sticky, black appearance.
Yellow-poplar weevil. These weevils also have one generation per year; they will feed on the leaves of yellow poplar, sassafras, sweetbay and magnolia trees. Larval stages mine through leaves, feeding between the lower and upper leaf surfaces. Adults feed primarily on the lower leaf tissues. Larval activity occurs primarily in late May and June; adults are active in the spring during egg laying season 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. Many species of predatory and parasitic insects will generally keep these insects under control most years. However, natural enemies usually are not present in high enough numbers to provide sufficient control during certain outbreaks such as this year’s. Where populations of these insects are extremely high, chemical control may be warranted.
Note that tuliptree scale is often difficult to control with chemicals because immobile scales will produce a waxy covering that offers protection from many insecticide sprays. For this reason, chemical control of tuliptree 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 during this time.
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 on infested branches, soil-applied systemic insecticides containing imidacloprid can be a good option. Systemic insecticides applied during the fall will generally provide effective control during the following spring season.
For the yellow-popular weevil, foliar-applied insecticides containing acephate or
carbaryl may be used to target adults.
Author: Daniel Frank, WVU Extension Service Entomology Specialist
Last Reviewed: May 23, 2017