Hemlock Woolly Adelgid

Asked July 12, 2013, 5:55 PM EDT

I want to put Merit into the root system of about 15 hemlock trees varying in height 20' to 70'. I understand late September is the best time to treat. I've been told it takes 6 weeks to work its way into the tree. So, should I place this treatment about the 2nd week of August? Is this the best thing to do?

Lackawanna County Pennsylvania

1 Response

I would suggest waiting until mid September to apply the Merit. Below is some additional information.
On trees that are too large to spray and trees that are not within 25 feet of surface water a soil treatment works best. The product of choice is imidacloprid. This product is sold as: Merit 75WP, Zenith, and Bayer Advanced Garden Tree and Shrub Insect Control. With each of these products application is as follows: Mix with water and apply the appropriate amount in a circle one foot away from the tree trunk and 4 inches deep. Works best if soil is wet, however, avoid times when a very hard rain is expected within the next two days. Can apply in the spring or fall. May not have to retreat for 2 – 3 years. Annual scouting to determine the need for re treatment is suggested. Trees that are already under additional stress from other problems may not survive. Determination of product rate will be based on tree diameter at breast height (4′ from ground) or the circumference of the tree at breast height.