The Hemlock Wooly Adelgid

Another drought! Yes, here we go again. As if the summer of 1998 wasn’t enough, summer of 1999 has begun much the same. So, break out the hoses, don the appropriate sun bonnet and out we go.

Trees and shrubs respond to drought in different ways. Sometimes they will actually shut down their systems in an effort to conserve water. This can be very stressful and will affect the food-producing portion of the plant. When this happens a plant gives off signals that it may be in trouble, giving rise to opportunistic insects waiting for this situation to occur. Insects will seek out plants that are in a stressful environment and one of our common trees, Hemlock, has fallen prey to one of these insects.

The Care of Trees has received numerous phone calls this year from clients seeking help in controlling intolerable levels of, Hemlock Woolly Adelgid. The difficult part of this situation is that this introduced pest is present no matter what the environmental conditions. This insect will bother Hemlocks in the best of years, making drought stricken years even more perilous for this tree.

I thought it timely to go over some facts about Woolly Adelgids and assure everyone that there are ways to treat this pest.

What do these little critters look like? You will see a white woolly substance on the small branches between the needles. The young “crawlers” will emerge from this waxy substance and begin to feed on sap which is drawn from twigs through sucking mouthparts. Adelgids can kill healthy trees in as little as two to four years. Early detection is critical while populations are low and little foliage injury is evident. Scientists tell us that these insects can be controlled at any time of the year, by using horticultural oils, soaps and other insecticides. Treating the young crawler stage in summer is very effective with the use of oils. A fall soil injection of a particular insecticide also works well. This product remains in the soil for the winter and is then taken up into the tree in the spring. When the insect pierces the needles it ingests the product and dies. Remember, the white woolly substance will remain on the tree for quite a while. If the waxy residue can be removed from twigs without leaving a stain, the Adelgids have dried and are no longer alive.

The proper treatment of this insect is crucial with timing being the key. Check your hemlocks regularly, especially smaller tree that are more easily treated. Aerial spraying is more difficult the larger the tree becomes. If we remain in a drought condition try giving your hemlock one to two inches of water per week to bolster the tree’s health. High nitrogen fertilization programs should be avoided if trees are infested with Adgelid. Keep your trees mulched if possible to retain moisture.

Keeping our trees healthy during times of stress can be difficult. Anything we can do to help them along will last into the future. If you have any questions about Woolly Adelgids or any other critters you think you may have, let me know. I will be happy to send you any of our ‘Focus Sheets” on insects or diseases, I’m always here to lend a hand. Have a great summer!

Copyright 2005 by Peter Deahl. All rights reserved.

 
Back to Articles
The Pruning School 16 Berkeley Court Sterling, Virginia 20165