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Controlling This Pest Is A Sticky Situation

Stephanie Klunk, Communications Specialist: UC Statewide Integrated Pest Management Program

A heavily infested hackberry leaf with the honeydew produced by the aphids dripping from the tip. Photo: andrew lawson

First found in Florida and Georgia in the late 1990's, the Asian hackberry woolly aphid spread rapidly across the south and into California, showing up on Chinese hackberry trees in many Sacramento Valley cities in 2002.

Identifying The Problem

Hackberry woolly aphids secrete pale bluish or white wax over their bodies. These fuzzy masses are each about 1/10 inch or less in diameter. This waxy covering usually obscures the insect's gray, green, or yellow body. Winged forms have distinct black borders along the forewing veins. Their antennae have alternating dark and light bands.

The fuzzy white insects found on the tops and bottoms of leaves produces a sticky liquid to drip on anything and everything beneath them.This sugar excretion not only draws ants and other pests, it often produces a black mold on affected surfaces. While large populations of aphids do not kill the trees, the increasing amount of the sticky substance produced has become a major nuisance in many urban and landscape settings.

Realizing the concern over the growing problem, scientists set out to find ways for landscape superintendents to eliminate the pests, while still preserving the trees and areas around them. Through their testing, they found a way to both save money and time through applying a specific amount of insecticide to control the aphid.

A close up of the winged adult aphid showing the characteristic dark banding on the wings and the alternating light and dark bands on the antennae. Photo: Jack Kelly Clark

Targeted Testing

Entomologist Andrew Lawson, Plant Sciences, California State University, Fresno, and Pam Geisel, now University of California Statewide Master Gardener Coordinator, found that applying treatments of systemic imidacloprid in the spring after aphid populations are established is effective on well irrigated trees.

Study results indicate that soil injections of imidacloprid (Merit 2F, Bayer Environmental Sciences) applied three weeks after trees leaf out, when aphid infestations can be confirmed, are as effective as applications made before bud break when treatments may be applied unnecessarily to trees without infestations.

Treatments can be applied after populations have been confirmed through monitoring, checking leaf samples and using water sensitive cards to measure honeydew are reliable monitoring methods to determine the number of aphids present. Users can then see if the aphid population is high enough to require insecticide treatment.

Researchers monitored aphid and predator populations for three seasons. Aphid densities were found to be highest in the spring and fall, with lower densities during the mid-summer months. No treatments should be conducted during fall, because hackberry leaves drop naturally.

Imidacloprid treatments are applied as a systemic insecticide; it is taken up by the roots and spreads through all the tissues of the plant. The material may be mixed in a bucket of water and poured around the trunk, or injected into the soil using special equipment that places it 6 inches below the soil surface.

Both application methods have been shown to be equally effective.In addition, soil injections of imidacloprid (Merit 2F, Bayer Environmental Sciences) at one eighth of the low label rate (0.0125 oz/ inch DBH or 0.002675 oz AI/inch DBH) were shown to be as effective at reducing aphid populations as treatments applied at the regular low label rate (0.1 oz/ inch DBH or 0.0214 oz AI/inch DBH). Rate refinement allows users to reduce the cost of application by decreasing the amount of material required for pest control.

Sustainable Solution

Lawson and Geisel took the initial steps to find a long-term, sustainable solution to controlling the hackberry aphid. With Kent Daane, UC Cooperative Extension specialist in biological control at UC Berkeley, they have contacted cooperators in China, and a foreign exploration trip is planned to search for natural enemies that may eventually be imported to help control the aphids.

This two-year project supplied municipalities, agencies, and landscape superintendents with important information that will be used by for years to come.Through their research, scientists were able give a full picture of the lifecycle, monitoring and eventually accomplished their goal of controlling of the hackberry aphid.

Tree Bands, such as this one made by BugBarrier, are an effective chemical free alternative for the control of gypsy moth caterpillars and cankerworms, preventing the bugs from climbing up trees and causing damage.

Chemical Free Tree Bands Effective In Eliminating Climbing Insects

For Landscape Superintendents looking for alternatives to applying chemicals to their trees, tree bands provide a pesticide-free way to stop and contain a number of climbing insects.

Unlike burlap bands used in years past, new designs are becoming increasingly effective, clean and easy to install and remove. They not only stop voracious gypsy moth caterpillars from crawling back into trees, bands are also effective against spring and fall cankerworm, winter moths, forest tent caterpillars and other pests.

As the caterpillars eat a tree's leaves, they expose themselves to the sun's heat and predators. To survive, gypsy moths crawl down the tree to the cool shelter of the tree base or ground. Cankerworm and winter moth larvae come down the tree to pupate in the ground. After emerging from the ground and mating, the flightless females climb up the tree to lay their eggs. The tree band works by allowing these bugs to crawl down the trees, but catches them as they return at dusk. They are stopped by the fiber and, as they attempt to go around the barrier, get caught on the adhesive band.

A major innovation of newer bands is the adhesive facing the tree as opposed to away from it, where it can collect leaves, and bug carcasses. Not only is this debris unsightly, it also creates bridges for the bugs to cross, rendering the band useless. Consisting of a dense, flexible fiber barrier and an adhesive film barrier, the band's fiber is wrapped around the tree trunk to fill bark crevices.

While many cases call for the use of chemicals and insecticides, tree bands offer an environmentally pleasing alternative that may actually save you money and man-hours.

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May 19, 2019, 8:28 am PDT

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