I have a question about the timing of spraying woolly adelgid on hemlocks...

Asked April 25, 2014, 1:31 PM EDT

I have a question about the timing of spraying woolly adelgid on hemlocks with horticultural oil. Because I have conflicting information, I just spoke with Pat at the Maryland Home & Garden Information Center, and she said that I need to have the issue resolved by a specialist, preferably Mary Kay Malinoski. (I do not want to use imidicloprid due to possible harm to pollinators from flowers blooming near the hemlocks.) The timing conflict is this: John Davis, a horticulturalist at Bartlett Tree Experts, e-mailed me that "The Bartlett Research lab recommends 2 treatments for Woolly Adelgid when using oil. First in spring (early-mid may) and again in winter/dormant season. We should do may and then again either late fall or late winter depending on weather." However, your website at http://extension.umd.edu/learn/hemlock-woolly-adelgid-hg2 says, "A dormant rate of horticultural oil may be applied in February or early March before egg laying begins to kill adult females. Sprays are not effective when egg masses are present, usually late March through early June. After all of the eggs have hatched and crawlers are present, by mid-June, a thorough spray with a summer rate of horticultural oil or insecticidal soap will give good control." So, should I have Bartlett spray my trees before May 15, or around June 15? Also, when should Bartlett apply the dormant application? Also, is the warm-weather application at 1% horticultural oil, and the dormant application at 2%? Thanks for your help. Judy Fulton Baltimore County Resident and Howard County Master Gardener

Baltimore County Maryland

1 Response

Spray a summer rate 2% of horticultural oil after all of the eggs have hatched and crawlers are present usually by mid-June.

You can spray a dormant rate 4% of horticultural oil from November to early March before eggs are laid. See our publication for more information http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG2%20Hemlock%20Wool...