[APWG] wooly adelgids
Olivia Kwong
plant at plantconservation.org
Tue Jul 25 16:31:49 CDT 2006
---------- Forwarded message ----------
From: Tom McAvoy <tmcavoy at vt.edu>
Date: Tue, 25 Jul 2006 10:15:00 -0400
Subject: Re: wooly adelgids
Since 2000 we (Dept. of Entomology, Virginia Tech, hemlock woolly adelgid
group) have worked on managing HWA at Mt. Lake. Mt. Lake (elev. 4,000') is
one of only two natural lakes in Va. It is surrounded by hundreds of
hemlocks, many up to 40 - 45 " dbh. HWA began infesting these trees in
1999. Releases of Sasajiscymnus tsugae (Coleoptera: Cocinellidae)
(formerly Pseudoscymnus tsugae) were made in 1999. Several were found in
2000 but none since. No impact on HWA could be attributed to this species
at Mt. Lake. Recovery of this species at release sites from North
Carolina to Massachusetts have been rare. As far as I know Sasajiscymnus
tsugae is no longer being released. A new bio control agent Laricobius
nigrinus (Coleoptera: Derodontidae) shows more promise since it has been
found 1- 2 years after release. This species is not available for general
public release.
Since 2001 we have treated hemlocks using soil injection (Kioritz) and
stem injection (Mauget) of imidacloprid (Merit). Stem injection is more
expense since it is more labor intensive than soil injection. Stem
injection was used on trees near open water or springs to avoid ground
water contamination. We have treated ~380 trees. As of 2005, 10% of the
treated trees have died while 23% of the untreated trees have died. We
have not treated since 2004 due the decline and nearly complete absence of
HWA in this area. HWA normally declines 2-3 years after the initial
infestation due to the decline in tree health and was exasperated by the
drought from 2000 - 2003. However, this year there has been a slight
increase in HWA around Mt. Lake. Trees should be treated as soon as you
find HWA. If you can save the tress during the first year or two of the
initial infestation you have a better chance of saving trees.
The area surrounding Mt. Lake is very rocking with the water table fairly
close to the surface. As stated on the Merit label do not exceed 0.4 lb of
active ingredient per acre. If the area is rocky and the water table is
close to the surface I'd suggest using stem injection on trees within 50
yards of open water or springs. Especially if the soil is low in organic
matter since imidacloprid binds with organic matter which reduces
migration in the soil. So the more the organic matter the less chance of
movement.
Imidacloprid has saved a significant number of trees at Mt. Lake.
The cost of imidacloprid has recently increased substantially.
Tom McAvoy
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