Woolly Adelgids Vs. Horticultural Oils

Hemlock woolly adelgid - WikipediaMost of us have heard of Aphids, but many have no clue what an Adelgid is. Adelgid are essentially the conifer version of an Aphid. They use a sucking mouthpart to rob conifers of essential moisture and nutrients the tree needs to thrive and survive. This causes Hemlocks to slowly deteriorate. One of the most detrimental Adelgid is the Woolly Adelgid that specifically attacks Hemlock trees. To identify an infestation of Woolly Adelgids, one can look on the underside of Hemlock bows for a ‘woolly’ like substance. This woolly texture is the secretions of the Adelgids that keeps them protected and allows them to complete their lifecycles to continue to spread along the tree or within a forest/landscape.

Unfortunately, there is no known native predator to these Adelgids. However, treatment methods for Woolly Adelgids range from systematic insecticides, basal trunk sprays, insecticide cover spray and horticultural oils and insecticidal soaps. For this article we would like to focus on the use of horticultural oils and its effectiveness towards controlling the spread of Woolly Adelgids.

The great news about Horticultural oils is its non-toxic and a great option for homeowners to apply safely and effectively. Horticultural oils are an effective control for most soft bodied insects like Adelgids. The oils are capable of dissolving the waxy protectant the Adelgids secrete, therefore allowing the oils to contact the insect and suffocate the Adelgids along with deteriorating their cellular membranes. The oils need to be applied in the spring and/or fall during temperatures between 45 degrees F – 75 degrees F along with application time being in the evening when the sun is not able to magnify on the oils and burn the trees needles.

Some obstacles to using horticulture oils are the size of the tree/trees and the required multiple applications for effective aDamoil Insecticidend long term control. Smaller trees can easily be sprayed by the homeowner and multiple applications are typically easy. However, once a tree reaches larger mature sizes or the homeowner is dealing with a large population of trees, the applications can become overwhelming or outside of the homeowners capability. For small to medium size trees, homeowners can use a Pump & Spray applicator, but once the tree population or tree size if too extravagant for the homeowner, a larger commercial sprayer will have to be utilized by a professional.

Thankfully, we have many options to protect our Hemlock trees from these life sucking Adelgids. It is in our hands as industry professionals and homeowners to do our part to slow the spread of this pest. Whenever a Hemlock is purchased from a Nursery, it is our responsibility to ensure a healthy and uninfected tree is being added to the landscape or forest to ensure the health of existing Hemlocks and conifers.

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