Homeowners in West Virginia may have noticed two pests on their yellow poplar trees this year – tuliptree scale and yellow poplar weevil. Neither insect is likely to kill trees, but tuliptree scale can cause a severe shower of sticky “honeydew.”
“We have received numerous calls of yellow poplar trees dripping sticky sap over everything. Heavy scale populations are responsible for this problem,” said Commissioner of Agriculture Gus R. Douglass.
Extreme infestations can cause branch dieback and mortality in trees of up to five inches in diameter. Stressed trees increase tuliptree scale populations, so promoting plant health through proper watering, fertilization and site improvements will decrease the likelihood of heavy scale infestation. However, over-fertilization can also increase buildup of scale.
“The tuliptree scale has many natural enemies, but these predators are not capable of keeping the tuliptree scale at sub-outbreak levels all the time,” said West Virginia Department of Agriculture (WVDA) Forest Entomologist Tim Tomon. “If needed, yard trees may be treated to help control tuliptree scale.”
The honeydew is actually the excrement of the female insects after feeding on tree sap, he added. The substance is sugary and can attract ants and wasps. A black mold grows where the honeydew has landed if it is not washed away.
Stressed trees increase tuliptree scale populations. Promoting plant health through proper watering, fertilization and site improvements will decrease the likelihood of heavy scale infestation. Over-fertilization can also increase buildup of scale.
Horticultural oils can be used to control scale. This is effective against the stage that overwinters. Therefore, it must be done in early spring after danger of freezing has passed, but before the tree is putting on new growth.
Registered contact insecticides can only be used against the crawlers of tuliptree scale. This is the stage that hatches out of the eggs and is present from mid-August to mid-September. Contact insecticides that can be used for this include malathion and carbaryl, but check others for effectiveness against scales. More than one application may be needed.
Systemic insecticides, such as imidacloprid, are also effective when applied as a soil drench or soil injection. These are applied to the soil around the base of the tree, and are taken up by the roots. They can technically be applied anytime the ground is not frozen or waterlogged. However, fall applications are recommended. In addition, sufficient soil moisture usually increases the effectiveness, so some irrigation prior to application may be necessary.
The insect is called a “scale” because it has a soft covering that resembles miniature turtle shells, particularly when a number of them are clumped together. Colors can vary greatly from grey/green to pink/orange mottled with black.
The yellow poplar weevil is less of a pest, although it causes unsightly holes on the leaves of yellow poplar. The adults feed and make holes in early spring. By late spring, mating and egg-laying have occurred, and larvae feed within the leaf tissues, which can cause browning or a scorched appearance in that portion of the leaf. Some loss of leaves may occur, but should not harm an otherwise healthy yellow poplar tree.
For more information, contact the WVDA’s Plant Industries Division at 304-558-2212.
WVDA’s Plant Industries Division