Imidacloprid Application  

TOPIC: Soil injection vs. root drench for HWA

== 1 of 2 ==
Date: Wed, Dec 12 2007 4:33 am
From: Andrew Joslin

I have a basic question about administering imidadcloprid to treat
HWA. I've talked to an arborist with pesticide certification about
doing this and mentioned the soil injection technique used by Will.
They say: "you mean root drenching?" I just want to be sure that
there is a difference. Root drench sounds different than soil
injection. Same or different?


Andrew Joslin
Jamaica Plain, MA

== 2 of 2 ==
Date: Wed, Dec 12 2007 7:27 am
From: James Parton


I did not know they were a predatory beetle native to the US. The ones
I have read about are of Asian origin.

James P.

TOPIC: Soil injection vs. root drench for HWA

== 1 of 3 ==
Date: Thurs, Dec 13 2007 12:31 pm
From: "Brandon Gallagher"

I've been away from my desk for over a week so I apologize if this has already been answered.

Soil injection involves special equipment that literally injects the product into the soil using pressure. There are different types soil injectors, some high volume some low volume. Our company has developed a system that accurately injects 250ml of solution per shot then keeps track of the number of shots so you can put in any volume of solution required. Most soil injectors can be run off of a backpack unit or tank system. You can see what I mean at (has a fancy video!)

Soil drenching is simply pouring the solution at the base of the tree, either into a moat around the tree or just right onto the soil surface. Equipment is usually just a mixing reservoir and maybe a hand trowel.
Hopefully this clears up the two terms.

Brandon Gallagher Watson
Plant Healthcare Specialist
ISA Certified Arborist MN-4086A

Rainbow Treecare Scientific Advancements
2239 Edgewood Ave S
Minneapolis, MN 55426

== 2 of 3 ==
Date: Thurs, Dec 13 2007 3:35 pm
From: Andrew Joslin

Thanks for the clarification Brandon. I've seen some hand pump units
that looked good for carrying into the woods. Soil injection looks
like it would disturb the roots near the surface less (no digging)
and perhaps provide more effective delivery. Obviously root drench is
less equipment intensive. Any pro or cons regarding effectiveness for
either method?

Andrew Joslin
Jamaica Plain, MA

== 3 of 3 ==
Date: Thurs, Dec 13 2007 3:50 pm
From: "Will Blozan"


I exclusively use the Kiotitz handheld injectors. They can be calibrated, no
hoses to drag, very sturdy and easy to use. They are disproportionately
expensive for what they are but well worth the investment of ~$250-400
depending on where you get it. The reservoir is small (3L) but we just carry
a jug of mixed water and chemical with us through the woods. Each jug will
treat 240-480 diameter inches of hemlock before needing to be refilled.


TOPIC: "Waterless Imidacloprid"

== 1 of 2 ==
Date: Thurs, Dec 13 2007 2:28 pm

Imidacloprid applied as a soil injection or soil drench is applied as a wettable powder dispersed in water. It remains a powder after application and only goes into solution very slowly. That's why the trees take it up so slowly and why it lasts so long.
The most difficult thing about treating hemlocks is getting the water to the trees. Carrying gallons of water up steep slopes covered with rhododendron can be an ordeal. And what if water just isn't available?

Why can't imidacloprid be applied dry? I'm thinking that a person could dig up a bucket full of soil then mix in the appropriate amount of imidacloprid then work that in to the top couple inches of soil around the tree. Let mother nature supply the water. This would probably do best on trees that weren't already in severe decline. I doubt anyone has ever tried this but it would be an easy experiment to set up.

We have a big job ahead of us here in Tennessee and at least a little while to plan for it. Applying "Waterless Imidacloprid" would make the job vastly easier.

Any thoughts


== 2 of 2 ==
Date: Thurs, Dec 13 2007 3:45 pm
From: "Will Blozan"


Bayer makes a pelletized version of imidacloprid, "Core Tech", soon to be
released. It is being tried at the Biltmore Estate and a row of trees next
door to me. So far no results after several months, even on 1" diameter
trees. It is supposed to take LONGER to get into the tree than the powdered
version. It may be appropriate for trees in excellent vigor as a preemptive
strike. Unfortunately, the folks writing the label made the dosage rate
linear as with the powder so larger trees will be underdosed.

It is not yet labeled for forestry use as far as I know, and the field
trials are being conducted under a research partnership with Bayer (for
which I signed up). The product has been available for years but not labeled
for treating hemlocks.


TOPIC: "Waterless Imidacloprid"

== 1 of 2 ==
Date: Fri, Dec 14 2007 6:16 am
From: pabigtrees

Will, ENTS

I read that the solution works better if injected below the duff layer
as imidicloprid binds to organic matter and slows the uptake to the
tree? What is your field experience with this? I agree it is a pain
in the a$$ to haul a delivery system out to the trees. When you Bill
and I were in NC at Bill's cabin, you poured some on the base of a
small tree there. Is that acceptable for larger trees? I am guessing
it is less effective? Hope all is well!


== 2 of 2 ==
Date: Fri, Dec 14 2007 6:47 am
From: "Will Blozan"


Good question. Most studies I've read and observed field results don't
indicate a difference between soil injection or drenching or powdered
imidacloprid. In both cases, the solution (actually mostly a suspension) has
to be placed under the litter layer since imidacploprid photo-degrades
rapidly. The first hemlocks I treated in 2002 were just this year retreated
for the first time. They were soil drenched (topically, no moat) and the
smallest was 28" diameter. At this time just the lower vigor, shaded
branches appear to be reinfested and the trees look awesome. 5 years!

The affinity of imidacloprid to organic matter is well documented, and so
should never be applied in sandy, gravely soil lacking organic material
(which would be really weird if you are under a hemlock).

The NPS uses soil drench (poured in a shallow trench around the base of the
tree) in the backcountry of the Smokies. I prefer the hand-held soil
injectors since you don't have to disturb the soil around the injection
site, can inject into nurse logs engorged with hemlock roots, and inject
thru the rhododendron. Can you imagine making a trench around a 4 foot
diameter hemlock in dense rhododendron? No thanks! With the injector you
don't even have to go around the entire tree, just stick it thru the mess
and pump it.

Some of the Carolina hemlocks I have treated while rappelling off cliffs in
SC could not have been soil drenched. They are literally growing in pockets
of soil that are dense mats of fine roots and very thin. Tearing into he
root zone to do a trench and drench (on a cliff?) would not only defy
gravity but would likely do significant damage to the confined roots. The
injector tip, on the other hand, penetrates the organic mat and distributes
the solution in four directions in the soil/root matrix clinging to the rock
face. You can trace the roots into other soil patches or nurse logs and
inject there with no more than a 1/2 diameter hole in the soil mat.


TOPIC: Soil injection vs. root drench for HWA

== 1 of 1 ==
Date: Fri, Dec 14 2007 7:28 am
From: "Brandon Gallagher"

As far as the tree is concerned there is no difference in the application methods. So long as the active gets into the zone of application uptake will be the same. Soil injection tends to be faster if you are doing a number of trees at a site whereas drench is just as fast when only treating a few.

With some products, like imidacloprid, a trench for pouring into isn't required so long as you are not on a slope or a soil where it would run off immediately. For products where accurate dosing is more critical, like tree growth regulators, the trench is necessary to ensure the entire dosage gets into the application zone.

Brandon Gallagher Watson
Plant Healthcare Specialist
ISA Certified Arborist MN-4086A

TOPIC: Timing of imidacloprid treament for HWA etc.

== 1 of 4 ==
Date: Fri, Feb 8 2008 2:13 pm
From: "Will Blozan"

Down here I have seen complete HWA kill in 12 weeks on a 12 inch dbh tree
soil treated in late June with the maximum dosage. This is likely
exceptional and the larger trees take agonizingly long to respond, but they


Behalf Of Andrew Joslin
Sent: Friday, February 08, 2008 5:11 PM
Subject: [ENTS] Re: Timing of imidacloprid treament for HWA etc.

Thanks Will. It sounds like spring makes sense to conservatively have a
chance to affect the fall HWA feeding period.

At 04:12 PM 2/8/2008, you wrote:


Very true about the refoliation. I have yet to get a satisfactory answer as
to how those folks heralding the success of the beetles can differentiate
(or substantiate) "natural" refoliation with reduced HWA loads from that
"caused" by the beetles. I have asked two researchers for data and have
received nothing to date.

Soil applications of imidacloprid are really slow to act and I haven't seen
an immediate impact on HWA regardless of season or purported "best" time of
application. It all depends on soil moisture, too.


 On Behalf Of Andrew Joslin
Sent: Friday, February 08, 2008 3:25 PM
Subject: [ENTS] Timing of imidacloprid treament for HWA etc.

Reading the paper* on eastern hemlock terpenoid response to HWA (Adelges
tsugae) gave me a better understanding of the HWA life cycle. This brings up
a question. If HWA starts feeding in October-November what's the best time
of year to treat hemlock systemically with imidacloprid? What's the uptake
interval between soil injection or root drench and optimal levels of
imidacloprid where HWA feeds in the outer twigs?

Knowing that HWA starts feeding in the late fall to take advantage of low
terpenoid levels sheds light on why the southern hemlocks are being hit so
hard. In the northeast U.S. HWA must slow down or stop feeding when very
cold winter temperatures hit. It's possible that in more southern locations
the adelgid can continue feeding through the entire winter causing greater
stress on the tree and greater reproductive productivity for HWA, possibly
creating the explosive population effect seen in southern hemlock forests.
Obviously lack of winter kill of the adelgid in the south is significant
but enhanced winter feeding opportunity may be a big part of the problem.

Which brings me to something else gleaned from the study. The authors noted
that after the HWA population peaks following initial infestation the food
supply is exhausted, extensive needle drop takes away the feeding site. The
HWA population crashes and an opportunity occurs for the tree to refoliate.
Will has mentioned this post infestation flush of new foliage. The small
numbers of HWA remaining then repopulate the tree and start the attack cycle
all over again. It looks like anyone studying beetle or other biological
controls has to be very discerning to separate out post infestation
refoliation caused by inherent HWA population cycles and the actual effects
of biological controls.


== 2 of 4 ==
Date: Fri, Feb 8 2008 2:47 pm
From: Andrew Joslin

Ok, that's very useful info. Give's a baseline for an optimal

== 3 of 4 ==
Date: Fri, Feb 8 2008 2:54 pm
From: "Edward Frank"


In northern areas the growing season is shorter than in southern areas. Does the period of maximum terpinoid production similarly get shorter in northern climates so that the same pattern of spring/low summer/high fall/low is maintained? If it does, does the aestivation period of the HWA become shorter in northern climates to match the period of minimum terpinoid production?

Ed Frank

== 4 of 4 ==
Date: Fri, Feb 8 2008 3:05 pm
From: "Will Blozan"


I am sure there are vast differences in HWA and hemlock "cycles" N vs. S.
Last October, NPS folks found EGGS already laid in the high elevation
hemlock forests in GRSM. This doesn't "normally" happen until late winter
here, and even later up there. They theorize that HWA has no winter dormancy
and only minimal summer aestivation. I have seen crawlers in wet years
through OCTOBER.

No mercy down here!