WEBWORMS ON PANICLE HYDRANGEAS
In July,
I wrote about webworms (Hyphantria cunea)
on panicle hydrangeas. For the
past several weeks, the second
generation has been active in my neck of the woods. And boy, are they active!
It seems every day they form new webs where none were the previous day. That
will continue through October or until the first killing frost. Ugly doesn’t come
close to what the plant looks like when these beasties are at work.
WEBWORM LIFE CYCLE
Webworms are the larvae
from moth eggs that were laid on the underside of foliage. The pupae survive
the winter in a cocoon beneath ground litter and soil, and emerge the following
year. The cycle begins anew as they mate and lay their eggs on the undersides
of leaves. Once the larvae hatch (in about a week), they spin their web over
the foliage so they can begin feeding. As you can conclude, fall clean up is
key to prevention next year.
HOW TO TREAT WEBWORMS
You can simply cut off the stem with the web on it. Put it in the trash, not the compost. However,
if you’re like me, you want as many flowers as possible. In that case, fix the
problem surgically. Break open the web and expose the worms to make a tasty
meal for your birds. Or you can snip off and dispose of the damaged leaves,
preserving your flower at the tip of the stem. Then look around: it’s likely
you have webworms on other plants. It’s known to be active on over 100 plant
species. I found them on my crabapples and redbuds. If the webs are too high to
reach, use a long handled tool like a pole pruner, rake or broom to break open
those webs.
INSECTICIDE TREATMENTS
If you
must apply an insecticide, the one to use once you open the nest is Bacillus thuringiensis subspecies kurstaki (Btk), not Spinosad. Like most
organic products, it is ineffective when it dries and only works on contact
with the caterpillar: it must be ingested. You can’t spray preventively; you
must target the caterpillar in the moment. Btk is the treatment that works on members of the
moth family. Keep in mind that although Btk is an organic treatment, it is
lethal to all caterpillars, including those that turn into butterflies. Just
another reason to use a mechanical approach. But
if the caterpillars are gone by the time you get to the nest, forget the Btk:
the insecticide is useless. I prefer not to use an insecticide regardless. It’s
low tech all the way for me.
The
season is late so the impact of webworms on your plant is mostly
cosmetic. But your plant has been stressed so treat it well until it goes
dormant, making sure it gets watered if you have a dry fall. Do not fertilize but
feel free to add compost - that's always a good thing.
Regardless of where you
find webworms, GET RID OF THEM!
UPCOMING PUBLIC HYDRANGEA TALKS
If you find yourself on Cape Cod this month (maybe you’re thinking about a trip
there?), why not attend the Cape Cod Hydrangea Society meeting? I’ll be speaking
to this illustrious group about The Magic Of Rebloomers.
DATE: Saturday, September 28, 10 a.m. Harwich
Community Center 100 Oak St , Harwich ,
MA 02645
Hope to see you there!
