Above: Asian Wooly Hackberry Aphids and sooty mold are seen on a wooden fence. // AMY DISMUKES
By AMY DISMUKES
THEY’RE BACK … and making a real mess of things!
The Asian woolly hackberry aphid (Shivaphis celti), rightly named for the waxy, woolly coat they sport, is making a comeback in many areas of Middle Tennessee.
An uninvited guest from the East, the Asian woolly hackberry aphid (AWHA) infests the hackberry tree and other Celtis species, including sugarberry. Because both sugarberry and hackberry are both common trees in Tennessee, the AWHA has become a major nuisance.
WHY? This aphid is a serious pest due to its ability to produce copious amounts of honeydew. Honeydew is a sweet, sticky liquid that plant-sucking insects excrete as they suck plant ‘sap’ and indicates an infestation may be in the works. Honeydew creates a sticky mess on any surface below the infested tree, be it plant, furniture, sidewalk or auto, and provides a surface for sooty mold to adhere and grow.
HOW? Sooty mold refers to multiple species of non-plant pathogenic fungi that are present in the everyday environment. Although sooty molds don’t infect plants, they reduce the plant’s photosynthetic ability by coating the leaf surface in a black soot.
Leaves coated in sooty mold will often drop early, ensuing panic of tree death among homeowners. Funny enough, no long-term damage has been observed, even after years of infestation, so insecticides are not required for survival, but are applied when honeydew/sooty mold become are intolerable.
LIFE? In general, aphid populations vary from year to year and are hard to predict, with the weather being a major factor. Without control efforts or help from our beneficial predator friends, AWHA populations build rapidly, resulting in more and more honeydew, making sooty mold most visible in the fall months of the year. AWHA overwinters as eggs, permitting winter survival and resurgence in the spring, when conditions become favorable.
CONTROL? As always, healthy plants are less prone to attack so utilize some cultural controls to make your hackberry happy … appropriate soil moisture, avoid compaction or root disturbance and no fertilizers unless a nutrient deficiency has deficiency has been identified. A hard spray of water can also assist in aphid detachment. Just be mindful of pressure as you don’t want to blast the foliage off the tree.
Biological. The convergent and multicolored Asian lady beetle(s), syrphid fly and
lacewing larvae, all love to snack on aphids. Sadly, natural enemies do not always
provide adequate biological control.
Chemical. Know it before you go it. Decrease user error resulting in (1) lack of effective control and/or (2) negative environmental impact by following the product label.
Insecticides can have unintended effects.
If trees are small enough and can be safely sprayed, complete coverage of the
foliage with a non-residual, contact insecticide can provide some control.
Examples include BONIDE Horticultural Oil, Safer Brand Insect Killing Soap
Concentrate II, etc. With a very low toxicity, non-residuals pose minimal harm.
Multiple applications are required for control due to reproductive abilities.
Systemic insecticides are another option. The insecticide is absorbed by a part of
the tree (roots or bark) and moved (translocated) throughout the tree, to leaves
or other plant parts. Systemic neonics for use on landscape plants include:
imidacloprid (Bayer Advanced 12 Month Tree & Shrub Insect Control Landscape Formula, BONIDE Annual Tree & Shrub Insect Control Concentrate) and dinotefuran (Green Light Tree & Shrub Insect Control with Safari 2G, etc.). No treatments should be conducted currently because trees will soon begin dropping leaves. Because systemics can translocate into flowers and have negative effects on natural enemies and pollinators, NEVER apply to any plant in bloom.
Broad-spectrum residual foliar sprays can persist for weeks, are highly toxic to
natural enemies and pollinators and are not recommended for aphid control in
the landscape. Examples include: carbamates (carbaryl or Sevin), organophosphates (malathion), and pyrethroids (bifenthrin, fluvalinate,
With some simple observation, a little honeydew monitoring and a proactive mindset, you too can control an Asian woolly hackberry infestation situation before it all begins!
For more information, contact your local county extension agent.
“A Home Grown Tradition” is written by Amy Dismukes. Amy is the UT/ TSU Horticulture Extension Agent for Williamson County, Tennessee and is a graduate of Auburn University, where she received a Bachelor of Liberal Arts, a Bachelor of Science in Horticulture and a Master of Agriculture in Plant Pathology & Entomology. She provides educational training for both homeowner and commercial clientele regarding issues concerning horticulture, conducts site visits throughout the county to diagnose and resolve issues with insects, plant diseases, soil and weeds, and is a frequent guest speaker for professional, garden and horticultural associations and commercial pesticide workshops/conferences. Amy also coordinates the Williamson County Master Gardener Program. Please email any questions or concerns to Amy at firstname.lastname@example.org.
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