Hemlock Woolly Adelgid Update

Here is a sneak preview (actually the entire thing) to my October newsletter article:

Grass Clippings…

Hemlock Woolly Adelgid (HWA) Update

Brian J. Stiehler, CGCS

 

Several years ago, I attended a round table discussion regarding the HWA.  The event was hosted by the Jackson-Macon Conservation Alliance.  Being a Turfhead, not an arborist, it was a perfect opportunity for me to learn more about what is happening with this issue.  Since then, I’ve stayed abreast of what is happening and where we are headed.  I am often asked if this is still an issue in Highlands.  The answer unfortunately, is yes.  The reality is the Adelgid is running out of food.  The only remaining hemlocks are those that were treated.  At this point, I will find adelgid on some trees but the destruction of course, is behind us.  

 That original event was attended by a dozen people, with a broad spectrum of interests.  The professor of Entomology from Clemson University attended.  He oversees the lab responsible for breeding the predator beetle; they have already released many in our area.  A gentleman named Patrick Horan attended who is interested in beetles being sold to the private sector.  There were several chemical treatment advocates there as well as a person who advocates only organic treatments.

 

In regards to chemical treatments, there is very good research out there.  One published article from the Connecticut Agricultural Experiment Station say soil treatments are the best approach.  They saw an 80% mortality rate of the HWA compared to the trunk injections which only offered 64% mortality.  Ironically, the trunk injections are the most expensive way to treat a hemlock.  Also, research has been done as far as the leach rates on Imidacloprid (Merit) in the soil.  This product can only move a maximum of 10cm in heavy organic soils…exactly what we have in Highlands.  On the downside, granular Merit is not a good option because heavy rains can wash the product away from the site.  Research is still being done on the longevity of Merit in the tree.  Now, experts recommend treating two years in a row and than monitoring the trees after that.  Finally, it is never too late to start treating!  A hemlock could be 50% defoliated and still replenish its needles.  There is a newer product on the market, known as Safari that does a nice job on trees with infestations.  We have been using both products at Highlands CC.

 
Foliar sprays can also be effective on small trees and hedges.  April and late October are the best times to spray!  Timing is critical with this approach.  Merit is a systemic approach while contact insecticides kill the HWA it touches.  Therefore, they (HWA) need to be active in order for foliar sprays (including organics) to be effective.  

Another interesting discussion was the topic of the predator beetle.  Over the past several years, Clemson University has released thousands of beetles in our area which comprises Greenville to Gainesville to Highlands down to Walhalla.  At this point, it is difficult to monitor the success of these beetles.  However, researchers have found both mating pairs and larva in the field.  This means there is some success.  Recently, there has been a private lab established in Asheville, which sells the predator beetle.  You must purchase a minimum of 1,000 beetles at $2.29/beetle.  Initially, it doesn’t sound too bad but Clemson University releases 2,000 beetles per tree.  Granted, they release them in Hemlock corridors, hoping the beetle spreads to other trees.  The so called “rate” of beetles needed per tree to combat the issue is still unknown.  Today, this approach has never really taken off.  There are too many unknowns and the success rate would take too long to determine.      

I hope this helps you understand where we are with this issue.  On the golf course, we have treated most hemlocks the past several years and we monitor and treat more as needed.  It is an unfortunate problem in our area and once again, our climate doesn’t help.  In northern climates, the extreme cold winters eliminate the HWA over the winter.  In Highlands, the climate is so ideal (mild winters) that the HWA can reproduce twice a year…not just once!  Keep treating and keep learning!