Hemlock Woolly Adelgid is a destructive pest. It has severely affected the eastern and Carolina hemlock trees in the United States. The adelgid feeds on the sap of the hemlock trees and deprives them of nutrition and water. Severe infestation can lead to accelerated needle drop, branch dieback, and death of trees. Once you notice cottony tufts clinging to the underside of the needles, contact your nearby pest control company to find out suitable control options.

Hemlock woolly adelgid

Hemlock woolly adelgid

Here are some popular hemlock woolly adelgid control options that your pest control company may suggest you:

Insecticidal Spray

If your trees are 30 feet or less in height, you can try spraying them with insecticidal soaps and horticultural oils. You can also try adelgid specific insecticidal sprays available with your nearby gardening store.

Things to keep in mind while trying the spraying method:

  • The spraying process will be effective only when the adelgids do not have their protective cover (i.e. white cottony tufts) on them. This happens only when the eggs are just hatched i.e. March and April for the winter generation and September and October for summer generation.
  • This spray is a contact insecticide and therefore, it must be sprayed on the trees thoroughly. Any part that is not sprayed thoroughly can offer shelter to the adelgids. So, make sure you spray the foliage, twigs, and branches until they are completely drenched.
  • The insecticidal or horticultural sprays do not leave any residue behind. Therefore, you need to apply them several times.
  • Garden spray will work for small ornamental trees, whereas, you will require power sprayers for large trees.
  • Sprays must not be used on windy or rainy days and during late spring when there is new growth seen on the trees. If they get washed away, they may contaminate the water sources.
  • To avoid any damage caused to trees, pets, birds, and tree-friendly soil organisms, please read the label carefully before trying the product.

Soil Treatment

Spraying can be risky as you will have to climb up the trees to make sure they are completely drenched with the insecticidal spray. Moreover, if the coverage is not thorough, the surviving hemlock woolly adelgid will reinfest the trees. Soil treatment is a safer hemlock woolly adelgid control method.

There are three ways of soil treatment:

  • Soil drenching: In this method, a specific amount of insecticide is diluted with water and applied to the soil surface. You can create small holes in the soil around the base of the trees and pour the diluted insecticidal solution into the holes. The roots will absorb the solution and transport them to the needle base. Once the adelgids suck the insecticidal solution, they will die. The diluted solution should be applied to moist soil to ensure good penetration.
  • Soil injection: Instead of applying the insecticidal solution on the soil, you can inject it using soil injectors. Injection ensures good penetration and good placement of insecticide. The better the penetration and placement, the more the solution will be absorbed.
  • Trunk injection: If your trees are near water bodies, there are high chances that the insecticidal solution will get washed away and contaminate the water. To avoid this, you can try injecting the solution directly into the trunk of the trees. This method is, however, not recommended unless there is no other alternative. Injections can cause severe tree wounding and may cause death. Trunk injections should be applied by professional arborists.

Biological Control

The biological hemlock woolly adelgid control methods are not as effective as chemical methods. Adelgids don’t have any known parasitoid that can help control their population. A few species of beetles may help curb their population but it is a very long-term process and is not suitable if the infestation is severe. Further, biological control is not recommended for homeowners. The beetles may escape from the initial release site or may pose a threat to people and pets. They are, however, found to be effective for controlling adelgid population in large forest land where insecticides cannot be used.

Chemical hemlock woolly adelgid control methods are risky and should be carried out by professional arborists/pest control companies. Contact your nearby tree services company to find out how they can help you.



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