[APWG] wooly adelgids

[Olivia Kwong]

---------- 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