2020 is proving to be a big year in the Kawarthas for the destructive European gypsy moth (Lymantria dispar dispar), an invasive species that feeds mostly on oak trees but is also found on other hardwoods, such as maple, birch, poplar and willow, and – during particularly bad years – 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. If these pests are an issue on your property, please do not spray pesticides or insecticides as these chemicals are often highly toxic as carcinogens, endocrine disrupters and attack the central nervous system of many animals including humans. A good natural remedy: mix equal parts water, soap and vegetable oil in a spray bottle. (EC members have had good success with this method.) Scroll down for more safe, natural solutions.
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The gypsy moth has four developmental stages: egg, larva, pupa (see image), and adult (moth). Gypsy 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 gypsy 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.
To watch a video demonstrating the removal of egg sacks, click here.
Photo by Tina Warren
OR NOT TO SPRAY
This is a question that arises frequently. "Can't we do an aerial spray to wipe out the gypsy moth?" Indeed, it isn't difficult to find an insecticide that will kill the Gypsy moth on contact. The most popular one is called Bacillus thuringiensis kurstaki – or BTK – and it's labelled in stores as "biological" and "safe." Sounds like an easy and appealing solution. However, there are a number of reasons to steer clear of BTK. The jury is out as to whether or not it's safe to use around humans, there's a risk of cross-contamination (BTK is often sprayed in conjunction with other chemicals), and some scientists believe that spraying will prolong the natural GM cycle. Most importantly, BTK is not gypsy-moth specific. In other words, it doesn't discriminate and will kill all caterpillars, moths and butterflies on contact and has been reported to harm the bee population, too. (You can read about that here.) Fortunately, it isn't necessary. There are some very effective, safe solutions that will manage an infestation nicely. Read on.
Rid your trees of gypsy moths with these natural, simple remedies
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 gypsy 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 GMs 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 GMs to gather. Once the GMs have collected, remove the band and drop it into a bucket of soapy water. This will kill the GMs. 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 GMs 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 GMs you'll be giving your trees a much-needed drink at the same time.