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Rappelling from rooftops, chewing tree leaves: How to combat the spongy moth caterpillar

 The larvae of lymantria dispar or spongy moth are hungry caterpillars that eat nonstop and can decimate tree leaves.
Evgeniy Andreev/Getty Images/iStockphoto
The larvae of lymantria dispar or spongy moth are hungry caterpillars that eat nonstop and can decimate tree leaves.

Rappelling down from the rooftops like Tom Cruise in a Mission Impossible movie, lymantria dispar, known as the spongy moth caterpillar, are HUNGRY.

This spring in our region, we're seeing the larvae by the millions, its seems, defoliating trees.

The caterpillar invasion is happening again this year, because the naturally occurring fungus that has controlled them for years wasn't able to eradicate them, due to an overly dry spring.

These small black caterpillars are busy munching away on everything from oak and apple and plum trees to blueberry bushes, even witch hazel plants.

You may see them climbing tree trunks or clinging to the sides of your house and sheds or you may notice the countless holes in all the newly-unfurled leaves on your trees.

Learn more about spongy moths on VPR's Vermont Edition episode: They're baaaack: Spongy moth caterpillars return with new name, same drama.

Unfortunately, it's only going to get worse as they grow and their appetites grow with them.

Don't despair! Even if you have large trees that are getting defoliated, as long as the tree is healthy, it will come back again.

And the entire cycle with the spongy moths will also run its course within a year or so.

Though, instead of waiting for nature and fungus and the hopes of a wetter spring to help eradicate the spongy moths, there are some things you can do.

A couple of different methods for small-scale operations can work if you are treating just a couple of trees. For instance, if you have a recently-planted small tree or shrub, you'll want to protect it.

The first technique is one that you can add to your morning routine: wake up, stretch, make coffee then grab a bowl of soapy water!

Then head out to the affected trees and handpick the caterpillars right off the leaves and drop them into the bowl. The soapy water will kill the caterpillars.

You might want to wear gloves for this method, as some people can get a rash from the hairs on the caterpillars.

A less labor-intensive way to combat the critters is to spray bacillus thuringiensis or BT. It is an organic spray that kills anything in the lepidopteraor caterpillar family.

Because it is deadly to caterpillars, take caution when using it, because you only want to target the spongy moth caterpillars.

Plan to spray in the evening when the weather is calm and spray the underside of the leaves. The caterpillars will munch on the treated leaves and that will kill them after a few days.

On a bigger scale, if you have several trees, hand-picking caterpillars would become a full-time and futile job.

Instead, try the duct tape method. Use a regular hardware store roll of duct tape but wrap it around your tree trunks so the sticky side is facing out. This helps catch caterpillars as they go up and down the trunk. From there, you pick them off and kill them in the soapy water.

Use the same method but with burlap fabric wrapped around the tree. Create a fold in the fabric that the critters will become entangled in, then dispose of them.

The task may feel daunting and like a losing battle but keep this thought in mind as you pick or spray - Your plants and trees will most likely survive the caterpillar onslaught.

Q: I live in the Northeast Kingdom between Zone Three and Four and I'd like to plant perennial ornamental grasses. Do you have any recommendations for grasses that thrive really well in colder climates? - Westerly, in East Burke

A: Here a couple of suggestions for grasses that are hardy to Zone Three, to be on the safe side!

One of the simplest to grow is northern sea oats. It grows a couple feet tall and has flowers that resemble dried oats. This one also makes a great cut flower. Do take heed if you plant northern sea oats, as they self-sow pretty readily.

If you're looking for something a little bit bigger, try a native grass like Big Bluestem. This will grow to three or four feet tall with beautiful bluish stems and nice flowers. There's even a smaller version, called Little Bluestem.

One more tall, hearty grass variety is silver grass or miscanthus that will grow four to five feet, even up to six feet.

Q: I grew delicious microgreens under my new grow light this winter, and I loved them so much, I want to continue through the spring and summer. I've harvested my first batch of microgreens and I'm wondering if I can reuse that soil or if I should replace it with new potting soil? Or could I recharge the existing soil with some compost? - Kim, in South Burlington

A: You can reuse that soil at least once, especially if your microgreens didn't have any diseases on them.

Your instinct to refresh it by adding a little bit more potting soil after a couple of uses is a good one.

Then, add the old soil to a no-dig garden bed where it can benefit in your garden in another way.

All Things Gardening is powered by you, the listener! Send your gardening questions and conundrums and Charlie may answer them in upcoming episodes. You can also leave a voicemail with your gardening question by calling VPR at (802) 655-9451.

Hear All Things Gardening during Weekend Edition Sunday with VPR host Mary Engisch, Sunday mornings at 9:35.

Have questions, comments or tips?Send us a messageor get in touch by tweeting us @vprnet.

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Copyright 2022 Vermont Public Radio. To see more, visit Vermont Public Radio.

Mary Engisch
Charlie Nardozzi is a regional Emmy® Award winning garden writer, speaker, radio, and television personality. He has worked for more than 30 years bringing expert information to home gardeners.

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