2021 is proving to be a devastating year for our trees thanks to the destructive European LDD moth (Lymantria dispar dispar), also known by its common name, Gypsy moth. This invasive species feeds mostly on oak trees but is also found on other hardwoods, such as maple, birch, poplar and willow, and – during particularly bad years such as this – white pines. Its population is known to surge every six or seven years, and during these outbreak years, the caterpillars – or larvae – are seen everywhere, and have been known to completely defoliate trees, weakening them and making them more susceptible to disease and other insects.
For some effective natural solutions to these pests, scroll down the page. For more general information click here.
*In an effort to use inclusive language, Environment Council is transitioning away from the term "Gypsy moth" and will instead use the term LDD moth going forward.
The LDD moth has four developmental stages: egg, larva, pupa (see image), and adult (moth). LDD moth eggs hatch between late April and mid-May. The larvae feed on the leaves of a variety of trees, most notably oak trees, for approximately seven weeks from late May to early or mid-July. Then they enter the one to two week pupa phase during which they appear dormant though inside their cocoon great changes are taking place. Adult moths emerge in mid- to late July and into August. Adult LDD moths don't feed. They live only for a couple of weeks and for the sole purpose of reproducing. Males may mate multiple times, but females produce just one silky egg sack filled with between 600 and 1,000 eggs. They deposit these on sides of buildings, in eaves, and under flaps of bark. This is the time to destroy them, if possible buy scraping the sacks off tress and other surfaces and into buckets of soapy water.
To watch a video demonstrating the removal of egg sacks, click here.
Photo by Tina Warren
LDD Moth Lifecycle Chart
Understanding the life cycle of the LDD moth and the timing of its various life stages will help to determine the best control method at any time during its development.
Oil + Water: An Effective Natural Solution
An ideal time to reduce or eradicate your LDD moth population is before the eggs hatch between the end of April and mid-May – meaning the window for spraying the egg masses is between late August and the end of April.
Ston(e)y Lake cottagers Reid Brownscombe and Jennifer Darling (Acting Environment Steward, Juniper Point Cottage Owners' Association) have tested a treatment they report is particularly effective at destroying egg masses before they hatch. Here, they describe the method and equipment required, and the satisfying results. Thank you, Reid and Jennifer!
Jennifer reports that: "This past winter I was contacted by Reid Brownscombe who discussed a vegetable oil spray option that he used for the Gypsy Moth egg masses. On doing some research, I was unable to find any scholarly articles that gave evidence to the method being effective. With Reid’s consent, I collected 10 sprayed egg masses and 10 unsprayed egg masses then hatched them in my home. From my control group (10 unsprayed masses) I had 100% hatch rate with a total of 3700 caterpillars (all ready to munch on our trees). From the sprayed egg masses I had 0% hatching. While this study is low in power, I believe it gives enough evidence to the effectiveness of Reid’s methods. There is still time to smother the egg masses with the oil mixture. For those who want to proceed, I would encourage you to do so as soon as possible. Basically, the oil mixture deprives the developing caterpillars of oxygen and kills them, by spot spraying them we can avoid smothering any beneficial insects. Hatching will commence within the month and hopefully we may be able to lessen the load."
1. A backpack sprayer from Home Hardware or Home Depot. While it’s a bit cumbersome, it will deal with nests up to twenty feet above the ground. Holding up to 4 gallons, it will deal with a lot of nests. Home Hardware may have to order it in, which can take a couple of weeks.
2. Vegetable oil.
3. Rain suit and gloves.
4. A COVID-like full face shield, preferable to the mask and goggles pictured here.
A very good time to attack Gypsy Moths is in their nesting phase. Each nest contains between 500 and 1,000 eggs. Each nest killed is a good step.
The challenges of dealing with a major infestation in cottage country are many: nests can be too high to scrape, tree bark can be too awkward to easily scrape nests from, and the sheer number of nests and nesting spots can be overwhelming.
I spent a lot of time last summer investigating how to deal with the infestation on our two acres, and the larger 18 acre Island we’re on. I settled on the following approach as the most effective way to deal with the nests.
• Timing. It seems the only restriction is to wait until the weather is consistently above 4c. I don’t know if that’s average, high or low, but in winter the nests go into hibernation of some type. So wait until after the cold, but well before they hatch. You can also apply it in the fall, until the 4c temperature limit.
• Mixture. In the backpack tank, mix 50% water and 50% vegetable oil. Add to that a small amount of emulsifier. This is crucial. It will ensure the water and oil stay mixed. I used only a tablespoon or so in a full 4 gallon tank. Any normal dish washing soap should work. I used Dawn. An option is to mix in some food colouring as a way of knowing which nests have been dealt with
• Spraying. The objective is to thoroughly soak the nests with the mixture. It will suffocate the eggs in the nest. The backpack sprayer comes with a few different nozzles. I used a tight one that, to my delight, blasted the nests apart. While this was highly satisfying, it is neither effective nor recommended.
Before going after the nests I tested the nozzles, backpack, pumping process and soaking process with just water. It was a well spent 20 minutes.
As you soak a nest, the colour will change from “wheat” to a much darker shade. Food colouring helps, but even without it, the colour change is noticeable. When the tank is fully pressurized, you can control the exit pressure with the trigger on the wand, which keeps you from blasting the nests apart.
You’ll figure out how close, or far away, you can stand. Keep the tank pressurized, which is easily done with the built in pump. Spraying very high requires lots of pressure, and the spray back will cover your face shield. I found one horizontal branch with 50 nests, 10 feet above the ground. It was very satisfying.
Inevitably, the mixture will splash back on you. It’s messy. Maybe I was just sloppy. Most important: WEAR THE FACESHIELD. Keep the mixture out of your eyes. It will coat the rain suit and gloves. Keep your boots tucked in to your rain suit pants to minimize the hazards of deer ticks and wasp nests.
The mixture is environmentally friendly, being vegetable oil. There is a commercial brand available (Golden Pest Spray Oil), but it is much more expensive and is 95% vegetable oil. The remaining 5%, I believe, is emulsifier.
It’s a satisfying way to spend some time in the woods. The trees have a certain “shine” to them afterwards, in spots, but it’s satisfying to know the number of Gypsy Moths you’ve dealt with.
If you’ve only got a couple of low nests, the same approach works with just a handheld plastic sprayer/mister. Or scrape them into a bucket and soak them thoroughly in soapy water. Even 1 nest this year may yield a huge number of nests next year.
Gypsy Moth caterpillars prefer hardwoods but will go after Pine Trees, too, and with catastrophic impact. They bite the base of a needle, which causes the needle to drop off. Unlike hardwoods, Pines can’t re-grow their needles, and a substantial Gypsy Moth feeding will weaken a Pine tree irreversibly.
I know I didn’t get every nest. I’m guessing I got 95% of them. Some where too high but, hopefully, being up high, the winter cold killed some of them. Some nests, I just didn’t see.
– Reid Brownscombe
How to Get Rid of LDD Moths
Some natural, simple solutions
Make your own spray
There are several recipes combining soap, oil and water that EC members have been using to good effect. But here's one that incorporates essential oils that scientists have been testing specifically for use against LDD moths:
2 cups of water
1 cup castile soap (Dr. Bronner's makes a good one)
15 drops EACH of nutmeg, thyme and rosemary essential oils
These oils are toxic to the LDDs and will kill them shortly after contact.
Using burlap or any kind of fabric (our EC vice chair John has been using old sheets on his trees effectively) wrap your tree, using a piece of twine at the middle of the wrap. Then fold the top half of the wrap down over the twine to create a cool, dark place for the larvae and moths to gather. Once the moths have collected, remove the band and drop it into a bucket of soapy water. This will kill the larvae and moths. Rinse. Repeat. Click here to watch a demonstration of tree wrapping.
This method is effective during the caterpillar/larva stage and also the adult moth stage. The female moths don't fly so you can trap and dispose of them in soapy water before they lay their eggs.
Here's a solution with a dual benefit: using a high-powered hose, such as a pressure washer or a fire hose, to spray the caterpillars and moths out of the trees and then do away with them once they hit the ground. Yes, we're talking squishing them. Not only will you be destroying the LDDs you'll be giving your trees a much-needed drink at the same time.