Protect your American Elms with Systemic Insecticide

A threat to American elm trees is an infestation from woolly elm aphid colonies. These particular pests are quite small, measuring in a between 2mm and 4mm in length and pear-shaped in appearance. Their most prominent identifiers are white and waxy-looking strands along their bodies, which give them the appearance of being covered with fluffy or cottony wool.

Woolly Elm Aphid Life Cycle

Their life-cycles follow a very specific path, beginning with their eggs infiltrating and spending the winter months in the cracks and crevices in the bark of American elms. Once spring rolls around and the leaves of the elm begin unfolding, the aphid eggs hatch and the aphids begin feeding on the underside of the new leaves. This feeding pattern has two specific outcomes: it first-and-foremost provides nutrients to maturing aphids, but also causes leaves to curl around aphid populations under the leaves, providing protection from natural predators and conventional pesticides.

As summer approaches, the now-mature aphids give birth to an entirely new generation that also begins to feed on the same leaf. The summer months see advanced life-cycle aphids develop wings and leave the protection provided by the distortion of the leaf, in order to locate a new host, which is generally the Siberian, where they give birth to over a dozen young each. These new colonies make their way to the roots of the Siberian to feed and multiply throughout the summer, giving the soil around the root a bluish-purple hue due to a high concentration of waxy secretions produced by the aphids.

With the coming of autumn, the now-winged and fully-mature woolly aphids leave the soil, in order to return to the American elm, where the mating process begins anew, and eggs are once again deposited in the protected crevices and cracks of their original hosts.

Woolly Elm Aphid Damage

Damage to American elm trees is caused by the removal of sap by the feeding patterns of infesting aphids.

On American elms, the damage is solely aesthetic. Woolly elm aphid infestation results in a large number of unsightly swollen and curled leaves which remain on the tree throughout the year; however, there is no permanent damage to the tree itself.

Siberian elm infestations are a different story, however. Due to the fact that the infestation takes place in the root system, it results in reduced strength and fruit production in mature trees. The infestation of Siberian elm has a more serious effect, in that it can cause the death of young plants as immature root systems are attacked and the seedling is deprived of vital nutrients that would enable it to survive.

Woolly Elm Aphid Control

Due to the protection provided by the curl of the leaves surrounding colonies, as well as their own natural waxy secretions, woolly elm aphids are less susceptible to conventional pesticide sprays and horticultural oils. As the best course of action, in this particular case, ArborCare recommends applying systemic insecticide, such as TreeAzin by direct injection into the trunk of the tree.

This process allows the pest control substance to be taken up by the tree, in its sap, and transported throughout the root system, foliage, stems, and branches where the woolly aphid colonies will be feeding.

For more information regarding the consequences of woolly elm aphid infestations, or to inquire about the professional control services of ArborCare licensed arborists, contact us today!

Sources: Agriculture and Agri-Food Canada & University of Minnesota