Turf Logic - Plant Health Care Program

Pest of the Month

Hemlock Wooly Adelgid

It was a beautiful summer afternoon, and I was enjoying a barbeque at my best friend Bryan's house. As a reached in to the cooler for another beverage I happened to glance up at his gigantic Hemlock hedge, what I saw gave me pause. His huge hedge that had been planted to give his small yard some privacy was covered in a swath of white about two feet wide. "Dude!"I exclaimed with a mouth full of ground chuck. "You've got Hemlock Wooly Adelgid!"

Hemlock Wooly Adelgid (HWA) is an introduced insect species from Asia. The insect itself is barely visible to the naked eye, but its telltale signs are unmistakable even from a distance. Bryan's hedge looked as though a freak summer snow squall had popped up, localized around his hedge, and blown snow into a neat little band across its face. The "snow" was in fact a waxy secretion that the insect produces to protect itself from predation and desiccation. The waxy secretion is the wooly in Hemlock wooly Adelgid.

HWA is a member of the insect order homoptera whose members include aphids and scale insects. Like all members of this order they have straw-like piercing/sucking mouth parts that they insert into the tissue of host plants to withdraw the vital nutrients that flow just below the tissue surface. HWA has a strange and some what complicated life cycle. In the early spring females lay eggs along the branches and needles, when the eggs hatch the immature insects called crawlers find a suitable location on a needle and settle down to feed. The immatures feed until mid-July when they become dormant. In mid-October the insects come out of dormancy and begin to feed again. They are active throughout the winter.

Well, Bryan could have scarcely cared less about his burgeoning insect problem until the following spring. The very next year we were again in Bryan�s back yard and again the HWA presence was plainly visible, but now instead of a white swath across his hedge there was a brown streak of dead branches running the length of his hedge. The adelgid had killed the branches of the hedge at eye level giving us a decidedly unattractive view into the interior of his once beautiful hedge. Needless to say I was soon in Bryan employ.

What is the morel of this cautionary tale? The morel is that pests can rapidly become a problem if they are not dealt with quickly and correctly. Had Bryan acted decisively his hedge would have remained pristine, and his neighbors would have been spared the site of Bryan in his bathrobe every morning. The real irony of this story is that although HWA is a serious problem in the landscape and can kill hemlocks, it can be effectively controlled using some of the best and safest products available. Both horticultural soaps and oils work well on HWA. Oils and soaps are great because they are not chemical pesticides; they control pests by so-called mechanical means. Oil achieves control by surrounding tiny insects like Hemlock wooly adelgid in a bead of oil. Adelgid are so small that they can not escape the bead and suffocate. Larger insects like ladybugs are unaffected. Soap works by drying out small soft bodied insects, the desiccation is so sever that it is fatal.

The most important part of treating a pest outbreak is to understand the pest. As Sun Tzu said �know thy enemy as thy know thy self�. Know what it is, why it hurts your plant, when it is vulnerable and most importantly know how to control it while doing minimal damage to the environment and other insects. Armed with these intellectual weapons pests like the Hemlock wooly adelgid can be effectively managed.