Foiled the nasties: gypsy moth caterpillars, that is

I don't like dealing with pests and hate to spray anything, so mostly I tend to choose plants that are reputed to be pest-free. But, of course, when you're a gardener nothing is guaranteed, except that you will be plagued with all sorts of problems now and then.

This year one of the worries was a heavy gypsy moth caterpillar infestation. These beasties are voracious eaters that can defoliate entire forests, something we experienced in the early '90s, when we spent a lot of time in Ontario cottage country.

In previous years, we kept them under control by removing them from tree trunks, but this season, the caterpillar population has exploded.

Since we've been gardening here, we must have planted something in the range of 40 to 50 deciduous trees, mostly maples, oaks and ashes. When we checked the trees last week, there were so many caterpillars that we had to make a decision: to spray or not to spray.

The spray in question is the biological insecticide Bacillus thuringiensis subspecies kurstaki (Btk), a natural bacterial insecticide that works against gypsy moths.

The key thing is that Btk must be eaten by the caterpillars when they're very young, just as they start to feed. After they take it in, they get sick, stop feeding and eventually die. The great thing about Btk is that spiders, birds and bees are not affected at all, and neither are people or pets.

The indicator plant for the right time to apply Btk is bridal wreath spirea in bloom. If you don't spray at the right time, you may as well not bother. Btk isn't effective when the caterpillars are big (like the ones in the picture, above).

So we sprayed early last week with a backpack sprayer. It's hard work holding the spray nozzle above your head. Luckily, our trees are still young - 15 to 20 feet tall - and the spray reached the leaves of the lower part branches where most of the caterpillars were. My husband had to spell me off halfway through when my arm got sore.

Today, I looked at all of the trees and, tada, there were very few caterpillars. The ones I found I scraped off and killed if I could reach them. So the upshot of our spraying is that our trees get to keep their leaves this season. My arm was sore for a day or two after the effort, but it was worth it.

If you have gypsy moth caterpillars and the Btk spray window has closed, there are still things you can do:

• pick caterpillars off leaves and soak them in a pail of soapy water
• place sticky bands on tree trunks, where the caterpillers rest during the day (they feed mostly at night)
• tie burlap wraps around tree trunks and then collect and destroy the caterpillars

More information about gypsy moth caterpillars.

Featured comment:

Anonymous said...
We live in the Poconos in Northeastern PA. These disgusting gypsy moth caterpillars have literally invaded our area. Our houses are "moving/crawling structures". The caterpillars have even eaten the evergreens down to sticks. Our brilliant politicians have decided it was expensive to spray the BT and comments were "they will be gone in a few weeks". We are hostages in our own homes. Backyard picnics, graduation parties, swimming in pools, none existent in our area.
Our beautiful landscape has been eaten alive and hopefully will recover. Our area is known for the beauty, which is now nonexistent.
Thanks PA politicians for keeping our area safe. Spending our tax dollars wisely isn't a concern of yours.
Creepy-Crawly Disgusted Pennsylvanian

Gypsy moth coming - get ready to do battle

Over the winter, as I walked the golf course across the road I saw lots and lots of gypsy moth egg masses - so many that I began to scrape them off the trees. Beautiful old burr oaks had dozens of egg masses, most of them so high I couldn't reach them. So I wasn't too surprised to see this headline in the local paper today: Gypsy moth invasion predicted.

I had noticed the gypsy moth caterpillar population building up over the past several years. We've managed to keep them from doing too much damage to our trees by getting rid of the egg masses and killing the caterpillars (mostly squishing them - rubber gloves help!).

The map shows the area of gypsy moth infestation in eastern North America. The gypsy moth caterpillars build over a number of years to the point where they can defoliate entire forests. I remember this happening in the late '80s and the early '90s. The infestation usually isn't fatal, but the trees then have to use up a lot of energy to grow a second set of leaves, and if they're stressed by heat and drought as well, they can die. (So, if you can, do water your trees during drought to keep them healthy.)

After a massive infestation, predator populations rise, and the gypsy moth population collapses. Then we can breathe a sigh of relief for a few years - usually about a decade.

Here's what you can do to control gypsy moth on your property:

• Right now, look at all of your trees, scrape and destroy egg masses to reduce the number of caterpillars during the season. Don't just scrape onto the ground, instead burn them or soak them in kerosene or soapy water. The picture at the right shows you what they look like.

• Watch for small caterpillars in late spring. A garden hose has enough water pressure to knock them off the leaves and tree trunks and kill them, especially when they are very small.

• Wrap a piece of burlap cloth that's folded in half lengthwise around tree trunks. Caterpillars feed at night and they crawl into the burlap fold to escape the heat during the day. Collect and destroy caterpillars each afternoon. An insecticidal soap spray also kills them. You can squish them if you're not too squeamish, or hand pick and drown them in a bucket of soapy water.

• Trap male moths by hanging pheromone (sex hormone) traps on the trees. These traps act as decoys and prevent male moths from mating with female moths.

• In severe infestations, apply the biological insecticide Bacillus thurigiensis kurtsaki (Btk). This kills the caterpillars, but is only effective when they're quite small. The best time to apply Btk is when the bridal wreath spirea shrub is in bloom.

For more information: The U.S. Department of Agriculture Forest Service has an informative and well illustrated website about gypsy moth and a list of trees that are most affected.