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Bagworms, Webworms, and Caterpillars
Friday
September 23rd and Saturday the 24th; Illinois 2005 Master Gardener
Conference at Collinsville, IL (just outside St. Louis, MO)
Mike will host an organic gardening Q & A workshop from 3:30 to 5
pm on Friday and 8:30 to 10am on Saturday, sign books and generally do
the major out-of-town schmooze thing at this 3 day (Thurs-Sat) event.
To register, call Monica David in the Illinois Master Gardener Office
at 217-265-5256 or email her at modavid@uiuc.edu,
or use this form: http://www.extension.uiuc.edu/mg/training/2005%20conf%20registration.pdf
REGISTER BY AUGUST 25TH TO AVOID A $25 LATE FEE
Bagworms, Webworms and Other
Caterpillar Pests
Q. Help! A beautiful blue
spruce in my front yard is being eaten by bagworms. We have been
pulling the bags off as we find them, but every day there is another
new crop. What can I do to get rid of these ‘worms’ and save my blue
spruce?
---Mary in
Winchester, KY
Mike: Two of the evergreens at my parents' house have bagworms high up.
These trees are very tall (one is a good 70ft), so I can't remove the
bags manually. I can rent an industrial sprayer that reaches 100ft, but
I don't want to use chemicals. Is there anything non-toxic I can spray
to get rid of them?
---A.J. in
Montgomery County, PA
Mike: …my Leyland Cyprus have it pretty bad, and a lot of the bags are
too high to reach.
---David in
Southern Maryland (near Washington, DC)
Mike--Two of my arborvitae are absolutely writhing with bagworms. I've
never seen them here before, but recognized them from an infestation I
saw on junipers in Knoxville many summers ago. They have half-killed
one huge tree already. What can I do?
---Ruth in
Medford, NJ
Mike: I have a honey locust tree infested with webworms. I have tried
to control them with dormant oil spray in March and in the summer with
Sevin. Unfortunately the little suckers return every year. Is there a
systemic or organic treatment for this ‘worm’? I don't want to spray
the poor birds who are living in this tree, and I really want to stay
away from those dreaded
pesticides.
---Elaine in
Doylestown, PA
Mike: The honey locust in our back yard is annually devastated by tiny
caterpillars that enrobe themselves in a tent of silk and dead leaves.
The tree is 25 feet high, so I can't reach it with an aerosol. We have
tried to avoid using toxins to control pests, and I think the diameter
of the tree is too small (about 7") to pound or drill in the capsules I
found in a garden store. Milky spore has controlled our Japanese
beetles very well, but doesn’t seem to have any effect on these bugs.
---Jay in
Phoenixville, Pa
A. The pests may be different,
but the solution is the same—whether the unwanted home-builder in
question is:
a. a tent-pitching
tree-eater like the Fall webworms we’re currently seeing (hairy,
inch-long caterpillars that become large pure white moths);
b. the tent caterpillars who built their big ugly
communal nests in trees back in the Spring (big, two-inch long, mostly
black caterpillars that become reddish-yellow moths);
c. this year’s big nuisance, bag worms, whose small,
individual nests look a lot like pine cones (a great camouflage, as
these pests mostly attack evergreens, where the natural-looking ‘bags’
often go undetected; here’s a link to a Univ. of Delaware bulletin
showing the nests: ( http://ag.udel.edu/extension/horticulture/pdf/ent/ent-04.pdf);
or
d. any other pest caterpillar—including ones that
DON’T make nests or attack trees.
That solution is not milky spore, which only affects Japanese beetle
grubs in the soil. Or dormant oil, which is great at smothering pests
that spend their winter on tree bark, but no help against ones who
spend the winter down in the soil or deep inside a protective nest. Or
a highly toxic insecticide like Sevin (that’s more of a threat to you
and those poor birdies than to any pest.) Or systemic pesticide
capsules pounded into the ground or trunk to poison the poor tree’s sap
(the use of which is hardly ‘avoiding toxins’, by the way…).
The safe, sane—and highly effective—solution is to prune off any ‘bags’
and/or tent-like nests you can reach, and then spray the old original
form of Bacillus thuringiensis on the rest of the tree while the
caterpillars in question are actively eating (which is right now in
most locales for bagworms and Fall webworms). Don’t worry about that
panic-inducing name—most people just call this organic pest killer by
its initials: “Bt”, with a letter added at the end to indicate what
strain or variety it is. There are currently three different Bts, each
affecting a different type of insect pest. The one that stops
caterpillars—ALL caterpillars, by the way, not just ones that build
little homes in your trees—is the kurstaki strain, “BTK”.
One of the oldest, most effective, and easiest to find tools in the
organic arsenal (its been in use for close to 40 years), BTK is a
naturally occurring soil bacteria that just happens to be deadly to
caterpillars. It’s available from Gardens
Alive and other natural gardening product suppliers, and at most
garden centers (retail brand names include Dipel and Thuricide;
ingredient labels should say ‘Bt’ or BTK). Don’t be surprised if a
store keeper thinks it IS a chemical; BTK is used by lots of farmers to
protect their sweet corn from tip-eating earworms, often without their
knowing its one of those high-faluttin’ organic things!
When pest caterpillars chew on Bt sprayed leaves, their stomachs stop
working and they soon die. Bt has NO effect if you spray it while
they’re not eating, like in the winter—they must be actively feeding.
And Bt is one of the safest things you can use. It will not harm you,
your pets, earthworms, or beneficial insects. Birds could eat
caterpillars that just ingested Bt and the birds would not be harmed.
You won’t even hurt the caterpillars of pretty butterflies when you use
Bt, because those caterpillars are feeding on weedy looking plants in
the wild, not your tree leaves. (The only butterfly caterpillars that
do appear in any kind of garden situation feed on carrots and parsley
plants.)
And like we said earlier, Bt will work on ANY pest caterpillar that’s
actively feeding—cabbage lopers, tomato hornworms (what IS it with
these ‘worm’ monikers for pest caterpillars? If I were an earthworm I’d
sue!), those nasty little ones that eat rose buds—ANY caterpillar; just
spray it on the leaves they’re eating and they will soon be daid.
Back to the ones causing tree troubles: As AJ notes in his email, you
can rent an industrial sprayer or use a pressure washer to get the Bt
up into tall trees. Flush the sprayer several times first to make sure
there aren’t any soap or herbicide resides in there. And remember—you
have to spray when your specific caterpillar is out and feeding. If you
can’t tell for sure, contact your local county extension office;
they’ll know when the pests are actively feasting in your locale.
And finally, insect pests prefer weakened plants; you can greatly
lessen the chance of infestation by treating your trees right. Don’t
use chemical fertilizers. Don’t prune without being sure of what you’re
doing (pruning in the Fall, for instance, is ALWAYS wrong). Don’t mulch
with wood chips or shredded bark. Never pile any mulch up against the
trunk, and never mulch more than an inch or two thick; those ‘mounded’
trees are doomed.
In addition, always try and plant new trees and shrubs in the Fall or
very early Spring; summer plantings have very little chance of ever
being healthy. And no matter when you plant, keep young trees well
watered until they are very well established.
You Bet Your Garden Question of the Week ©2005
Mike McGrath
Helpful
Products From Gardens Alive!
Catch those nasty leaf hungry Caterpillars with these organic products.
Green
Step Caterpillar Control
Green Step is an effective, all-natural Bt formulation in a liquid
concentrate. paralyzes caterpillars, resulting in their death from
starvation.
Bulls-EyeTM
Bioinsecticide
Stops damage almost immediately.
Bulls-Eye is highly effective against many types of leaf-eating
caterpillars, as well as leafminers, thrips, Colorado potato beetles
and even fire ants. Use it on garden crops, fruits, lawn grass and
ornamentals.
On-Gard!™
Tree and Plant Protector
Blocks crawling pests. Easier to use and more effective than sticky
barriers, which require frequent re-application. Cutworms, slugs,
snails and caterpillars can't reach On-Gard-protected trees and tender
transplants.
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