Invasive Pests in Caldwell County

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Invasive pests are a real problem in Caldwell County. These invasive pests can be insects, plants, plant diseases, and animals. Invasive pests are are not part of our natural ecosystem. The problems they cause varies, but the underlying issue is these invasive creatures have no natural enemies to keep their populations in check. This allows them to build up in large numbers and cause considerable damage.

There are many invasive insects in Caldwell County. A few that come to mind are, Japanese beetles, Asian lady beetles, ambrosia beetles, varroa mites, tracheal mites, kudzu bugs, brown marmorated stink bugs, and the hemlock woolly adelgid.

The hemlock woolly adelgid is an invasive insects that feeds on eastern hemlock trees (Tsuga canadensis). This insect is a small (1/32 inch), reddish-purple, aphid-like insect that covers itself with a white, fluffy secretion. Their mouthparts are thread-like and about 1/16 inch long and used to suck sap. Sucking sap from young twigs retards or prevents tree growth and causes needles to turn grayish-green and drop prematurely. The loss of new shoots and needles is detrimental to a tree’s health. In two or three growing season these insects may cause the tree to lose its needles and die.

The eggs of these insects are hidden within the small, white, fluffy secretion. When the eggs hatch, the adelgid crawlers move about looking for a good place to feed. Once these crawlers settle, they soon secrete the white fluffy “wool” that completely covers their body. Like aphids, adelgids are parthenogenetic.

white fluff (adelgi) on tree

The puffy white blobs at the base of these hemlock needles are an invasive insect called the hemlock woolly adelgid.

This means they are all females and reproduce without males. In fact, there are no male hemlock woolly adelgids.

The hemlock woolly adelgid was first reported in North Carolina in 1995. State surveys indicate the hemlock woolly adelgid is now in all counties where there are eastern hemlock. I first noticed the insect in Caldwell County in 2007. Infested hemlocks become covered with dirty white globs of cottony puffs. Infested trees defoliate prematurely and eventually die. Natural stands of hemlock are at greatest risk. Landscape plantings should be treated when infested.

The hemlock woolly adelgid is a difficult insect to control because of the fluffy white secretion that protects this insect from pesticides and potential enemies. A good time to target control is October when the second generation begins to develop. Control can also be effective now, in the late winter and early spring, when first generation crawlers are active. Insecticidal soap and horticultural oil sprays are effective when the entire plant can be sprayed. This approach causes minimal harm to natural predators and parasites. It is an effective control for hemlock hedges.

There is a natural enemy of the hemlock woolly adelgid that has been released in North Carolina and is showing promise of controlling this invasive insect. Using insecticidal soap and horticultural oil is an effective way to treat for the adelgid without harming this predator.

Control for larger trees can be achieved with Merit or other insecticides with the active ingredient imidacloprid. This insecticide can be applied at a soil drench, which is taken up by the root system and sent throughout the plant. This product can also be injected into the tree where it is also sent throughout the vascular system of tree and kills the feeding adelgid.

For additional information about hemlock woolly adelgid, visit http://caldwell.ces.ncsu.edu or contact the Caldwell Extension Center.

Written By

Photo of Seth NagySeth NagyCounty Extension Director (828) 757-1290 seth_nagy@ncsu.eduCaldwell County, North Carolina
Posted on May 4, 2015
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