Gypsy moth update: friendly fungus at work

According to the Integrated Pest Management newsletter from Michigan State University, a friendly fungus called Entomophaga maimaiga is expected to slow down gypsy moth infestations next season:

"This fungus infects caterpillars, turning them into a mushroom in about a week. Fortunately, Entomophaga maimaiga is very host specific and only infects gypsy moth and not any other animals. The caterpillars die facing head down, the bodies becoming shriveled and rubbery in a few days. Eventually the dark-brown to black mushrooms, still in the shape of a shriveled caterpillar, fall to the ground around the base of the trees. In each mushroom are thousands of spores that will infect gypsy moth caterpillars next spring. When young caterpillars become infected next spring, they will die quickly, turn into mushrooms and sporulate immediately during wet weather, infecting other caterpillars. It is in this way that the fungus can spread quickly through a forest, infecting most of the gypsy moth caterpillars. The fungus in large caterpillar-mushrooms that are present now will not sporulate until next May when the next batch of gypsy moth larvae are active.

The outbreaks of gypsy moth that we are seeing around the state at this time may be due to two or three relatively dry springs in a row. Entomophaga cannot sporulate and infect caterpillars under dry weather conditions. However, the wet spring and early summer that we have had so far this year has allowed Entomophaga to spread quickly."

So how can you tell if the fungus is in your area? Here's what the MSU report says to look for:

"Take a look at the oak, birch, poplar or other infested trees on your property. You may find many dead caterpillars (mushrooms) on the trunks. If Entomophaga is active in your area, the gypsy moth population will naturally decline, so you may not see nearly as many caterpillars next year or the year after."

When I checked my trees recently, I saw exactly what they describe. Good news indeed. This fungus proliferates during moister, cooler conditions. (Though we are still a bit on the dry side, we've had more rain and cooler temperatures than last summer.)

For more information, see the newsletter and download a PowerPoint presentation on this fungus.

© Yvonne Cunnington, Country Gardener

Gypsy moth spraying: the question of the season

Gypsy moth egg masses on a young maple in my neighborhood
A few weeks ago I put an article about gypsy moth caterpillars up on my gardening website. Today I received this email from a reader in Oakville, Ontario:

I am interested in your article about the gypsy moth! We in Oakville have learned that some of our lovely forest areas are to be sprayed with Btk in May.

I was interested in your comments that this infestation doesn't last and in a few years is not present in that particular area where it was a problem. I would really appreciate any more thoughts you may have about this as my question to our local officials was to be: "What happens if you do nothing?" Thank you in advance for any information you may have for us.

This was my reply:

Thanks for contacting me about this issue, which is going to be of great interest and concern this summer. I have noticed that all the big oaks and maples at the local golf course across the road from me are covered in egg masses. If nothing is done, they are going to lose all their leaves this season.

We hand sprayed our own trees with Btk last May (they are not very large as yet, about 15 to 20 feet tall), and the control we got was amazing. I did a visual inspection of the deciduous trees on my property last week, and I found only two egg masses.

You are very fortunate that Oakville is willing to spray Btk in May. It is a safe, natural and effective control. It's true that the populations do crash after they get really bad, even if you don't spray Btk.

However, doing nothing this year could seriously endanger trees because they have been very stressed by almost a decade of drought, culminating in the worst drought in 49 years last year. If stressed trees get defoliated by the caterpillars, they will be in serious danger of further decline, and you could see a lot of large trees dying in Oakville in the next few years.

I would support spraying. It's a small price to pay for all the environmental and quality-of-life benefits of shade trees. Everything is a trade-off, but I believe the trees need us to help them now. With the drought stresses they have endured over the past decade, trees in southern Ontario don't have a lot of reserves. I hope that helps in deciding to support spraying.

The U.S. Department of Agriculture Forest Service has an excellent gypsy moth education website, from which the following information is taken:

The Effects of Defoliation on Trees

The effects of defoliation depend primarily on the amount of foliage that is removed, the condition of the tree at the time it is defoliated, the number of consecutive defoliations, available soil moisture, and the species of host.

If less than 50 percent of their crown is defoliated, most hardwoods will experience only a slight reduction (or loss) in radial growth.

If more than 50 percent of their crown is defoliated, most hardwoods will refoliate or produce a second flush of foliage by midsummer (figs. 11, 12). Healthy trees can usually withstand one or two consecutive defoliations of greater than 50 percent. Trees that have been weakened by previous defoliation or been subjected to other stresses such as drought are frequently killed after a single defoliation of more than 50 percent. (My emphasis, as this is the current situation of trees in southern Ontario.)

The entire article can be found here.
© Yvonne Cunnington, Country Gardener

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.