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New York State Hemlock Initiative

Keeping the legacy alive

Hemlock Hedges and Biocontrol Opportunities

Part of the efforts of the New York State Hemlock Initiative is our research into biological control for hemlock woolly adelgid (HWA). We work with predatory insects that rely on HWA as a food source and thus present an opportunity to control and combat HWA without long-term reliance on insecticides. Our focus has been on two biocontrol insects, the beetle Laricobius nigrinus and silver flies of the genus Leucopis. Both have been found to control HWA populations on the West Coast of the United States, and we hope to use them here on the East Coast to prevent further spread of HWA and reduce the size of existing HWA infestations.

Landowners can be especially helpful in our biocontrol research program. While we are working hard in the lab to rear healthy biocontrol insect populations, Laricobius can only be reared in small numbers in captivity. That is why we are asking for the help of those who have hemlock hedges on their properties. These hedges can potentially serve as nursery sites for our biocontrol bugs, providing a valuable resource for hemlock conservation going forward.


Hemlock Hedges

Hedges are an important resource in the rearing of biocontrol populations. Not only are they excellent sources of hemlock habitat for insects, they are also easy to monitor, reach, and harvest biocontrol agents from when it comes time to release the insects at infested forest sites. An ideal hemlock hedge is one that is still healthy but still has an HWA infestation and has low levels of disturbance such as mowing or gardening beneath it. If you have a hemlock hedge that you think could be a potential biocontrol insectary and would like to have us assess its suitability, send us an email at info@nyshemlockinitative.info or send us a letter addressed to NYS Hemlock Initiative, 111 Fernow Hall, Cornell University, Ithaca NY 14850.

[Even if your hedge is not infested, we’d still like to know about it! We will put you on our hedge list and give you updates on HWA in your area. When your hedge becomes infested, let us know and we will see if it is a good fit for our hemlock hedge insectary program.]

To help us understand where HWA is in New York, you can report HWA findings on your property. Find out how to report here.

We also have informational resources for landowners, including  biocontrol monitoring programs, on our website here.

 

Tips for planting your own hemlock hedge:

  • Hemlocks are forest trees, so even in full sun it will take four to seven years to have a tall, full hedge. However, if you buy hemlock saplings that are a little older you can speed up the hedge-growing process.
  • Hemlock trees should be spaced out so they do not crowd each other as they grow. It is a good idea to space trees depending on the size of tree being planted. A row of trees four feet tall should be spaced about three feet apart and will take about five years to fill in. If you are looking for a quicker hedge, however, consider planting eight-foot trees about six feet apart. Keep in mind you can buy taller trees and trim them to the size that works for you.
  • After planting, consider leaving your hemlock hedge to grow and develop for one to three years before major trimming or pruning; this will ensure they have time to become acclimated to their new site and are healthy. If you planted trees that are already your desired height you may want to “pinch the leader” by trimming the tall leading shoot to limit the upwards growth of the hemlock. Don’t worry, this won’t hurt the tree in the long term!
  • Pruning the hedge will be important to retain its size and shape, and create a dense growth habit. It is best to prune in the early spring before buds emerge but you may also prune towards the end of the summer after most of the season’s growth has taken place. Pruning will also keep the bottom of the hemlock hedge or “skirt” filled out instead of the lower branches dying off from being shaded from above, as would take place in a forest ecosystem. Consider pruning every year to every other year to maintain the desired size and shape but still allow time for recovery between prunings.
  • Hemlocks will grow in many types of soils but prefer soils that are more acidic (pH 5.6-7.5) and damp. They can also withstand shady or sunny conditions, though full sun will encourage fast growth of your hedge. Hemlocks are found almost everywhere in New York, so yes, your climate will be great for hemlock hedges!

If you have any other questions about hemlock hedges, biocontrols, or hemlock woolly adelgid please do not hesitate to reach out! You may also visit our FAQ page for more information.

Email us: info@nyshemlockintiative.info

Mail us: New York State Hemlock Initiative, 111 Fernow Hall, Cornell University, Ithaca NY 14850

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