Updated: Apr 21
By Opuntia - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2580261
It's no secret that South and Central Ontario trees got hammered by Gypsy Moth last year. It was a terrible year for defoliating trees, and the little munching pests were so aggressive that not only did they eat away at their favoured hosts ( oaks, maples, birch.) - but they even expanded into chewing coniferous trees such as pines and cedar.
I recall being in Albion Hills Conservation Area, and the Gypsy Moth had infected a stand of Cedars. The Cedar Trees were obviously stressed, and the foliage of the trees were curled inward. Unlike Deciduous Trees, which can 're-leaf' mid-summer, defoliated coniferous trees are much more susceptible to Gypsy Moth infestation. They cannot recover lost needles, and thus lose significant photosynthetic capacity as a result.
Origins of Gypsy Moth
Firstly, they are not a native bug. Like many things, they Gypsy Moth was introduced during a poorly thought out scheme, about 150 years ago, to establish a Silk Industry in North America. Etienne Leopold Trouvelot was a French astronomer, artist and amateur entomologist who immigrated to the United States in the 1850's. He brought the Gypsy Moth to his home in Medford, Massachusetts where, much to his astonishment, the little critters escaped. Soon after, Trouvelot decided to give up his entomological endeavours and focus on painting stars.
How Bad Could They Be?
Gypsy Moth outbreaks have occurred since the late eighteen-hundreds, with nearly $1 Billion Dollars in damages inflicted by these pests since then. They defoliate and often kill what would otherwise be healthy trees, and compound the stresses of climate change on large-tract native forests and urban forests. The caterpillars can even cause Gypsy Moth Rash to susceptible individuals, a very uncomfortable rash that presents itself similar to Poison Ivy.
In other words, "Damn you, Gypsy Moth!!"
Like many invasive insects, the Gypsy Moth has few natural enemies. The white-footed mouse (Permyscus leocopus) has taken up the mantle, to some extent and although it consumers ALOT of Gypsy Moth caterpillars, it's not enough to make up for the booming populations during the outbreaks.
So, what can I do?
That's a good question. There is no pan-continental solution to eradicating this pest, and your backyard success (or failure) is going to rely on your (and your neighbour's) efforts. Control of Gypsy Moth generally occurs because their numbers become so high that they simply collapse due to starvation, or a viral pathogen infects them and spreads throughout the population. The good news is that these peak-populations of Gypsy Moth only occur about every 30 years, and they last only about 2-5 years, depending on various factors. However, there are certainly some chemical controls that can be deployed in your backyard to control Gypsy Moth:
Aim to Eradicate These
First, you have to identify the nests. These straw colored nests can hold thousands of eggs. They can be located throughout the tree branches in the winter, but they tend to be more concentrated on the trunk. This is enemy number one- knock out these nests, and you begin to eradicate a lot of these little munchers...
Dormant Oil (but be CAREFUL...)
A pre-hatching application of dormant oil spray on the infected trees is one method. Generally, a 1% oil/emulsifier to water is adequate (please read manufacturers instructions), but care has to be taken not to injure the trees with over-application. This can be done by adhering to the proper concentration, and by visually identifying the cocoons and targeting them specifically, rather than the entire tree.
Btk (Bacillus thuringiensis, or the little soil bacteria that could...)
Btk Spray is based an organic spray derived from the Bacillus thuringiensis bacteria. Basically, what Btk spray does is coat the trees/foliage with protein shards that, if consumed, essentially cause internal injuries that kill the feeding caterpillars. Gypsy Moth only feed when they are in their caterpillar stage, so timing is crucial. Furthermore, Btk spray degrades rapidly in sunlight. It is best to observe the trees, and apply Bt ATK spray to the entire leaf canopy of the host tree(s) at day 7 and day 14 after hatching. Concentration of Btk-to-Water will vary and, as always, it is important to follow the MSDS and the manufacturers instructions for rates, PPE...etc.
Mixing Molasses (appx 2.5% tank) can dramatically increase uptake and improve control.
Pray for Cold
Perhaps one of the best controls for Gypsy Moth infestation is extreme cold weather. Extended period of temperatures < -9.3 degrees Celsius, or a short cold snap < -23 degrees Celsius will wipe out many Gypsy Moth nests and eggs. So far, this winter has been mild and the Great Lakes have seen less ice than at any time in the last 50 years.
That's not great news. Nonetheless, hope springs eternal and we are not yet into February. Let's hope Old Man Winter takes a good swipe for us, and spare us all a Spring Gypsy Mothapocalypse.
Ascents Tree Service has qualified Pesticide Applicators that can assist you with your efforts against Gypsy Moth. Give us a call in the Spring, and we'll see if we can help. But, really, pray for cold...