2022 Note: It has been decided by the Entomology Society of Canada that the new common name for LDD/Gypsy moth is now Spongy Moth. Visit their website for more information. In future, MLF will refer to this moth as the Spongy Moth.

The Invasive Species Centre has a wealth of informative fact sheets and papers on their website at https://invasivespeciescentre.ca/invasive-species/invasive-species-resources/

We wanted to share these fact sheets about the Spongy Moth (Lymantria dispar dispar/LDD moth, formerly known as European Gypsy Moth) and management practices, since May and June are when we see those spongy moth caterpillars on maples and other trees.

Species Fact Sheet PDF

Species FAQ PDF

Timely excerpts from these resources:

IMPACT of the Spongy Moth:

• A single Spongy Moth caterpillar can eat one square metre of leaves in a season
• Repeated defoliation makes trees susceptible to other pests and diseases, and can eventually lead to tree death
• Defoliation in orchards can increase vulnerability to agricultural pests and diseases and can negatively impact farm stock
• Loss of species in natural areas can affect biodiversity and forest wildlife

How to manage Spongy Moth Caterpillars

(April through June):

BIOLOGICAL CONTROL

For private homeowners, BTK (Bacillus thuringiensis kurstaki) is available for purchase from local hardware stores to use against spongy moths. This biopesticide can be applied by a registered pesticide application company or by homeowners who have carefully read application instructions. BTK is a product that affects the digestive system of caterpillars and should only be applied between May and early June, when spongy moths are still in the larval (caterpillar) stage. Two spray applications are usually required for effective control. Application of BTK after mid-June is not an effective way to manage spongy moths.

On a larger scale (multiple properties or a forested area), Btk should only be applied by a professional pesticide application company and is most effective when supported by a team of landowners, landowners’ association, or municipality looking to manage spongy moths.

Spongy moth populations are also affected by a number of pests, including mice, birds, wasps, and a specific fungus and virus. The fungus and virus are believed to be the reasons spongy moth populations crash for ten or more years.

BURLAP/ TRAPPING

Caterpillars can be successfully trapped using burlap. Start by wrapping a 45 cm (18 in) wide strip around the tree at chest height. Tie a string around the centre and fold the top portion down to form a skirt, with the string acting as a belt. Pick off the caterpillars daily and dispose of them (see hand removal above).

2022 Note: It has been decided by the Entomology Society of Canada that the new common name for LDD/Gypsy moth is now Spongy Moth. Visit their website for more information. In future, MLF will refer to this moth as the Spongy Moth.

This year has seen a rise in the number of Spongy Moths (Lymantria dispar dispar / LDD / European Gypsy Moths) and caterpillars, which affect native maple trees as well as other species. In areas with severe outbreaks, “trees and shrubs are completely defoliated over large areas; despite the trees’ ability to produce a new crop of leaves over the summer, the damage causes significant growth loss” (https://www.ontario.ca/page/lymantria-dispar-dispar-ldd-moth)

One effective way to reduce the spread of this invasive pest is to collect and destroy their egg masses before they hatch.

The Invasive Species Centre and Eastern Ontario Model Forest are currently running a contest to encourage residents to remove Spongy moth egg masses from their trees. They hope to limit the spread of the destructive caterpillars and moths by working together to collect 500 or more egg masses across Ontario. There are even prizes being offered as incentive to collect as many as possible!

NOTE: Egg Masses can be removed any time from August through the fall and winter to mid-April. Scraping in the Fall after the leaves have fallen may make it easier to see the egg masses.

Find out more and enter the contest here: www.invasivespeciescentre.ca/take-action/edrr-network/european-gypsy-moth-egg-scraping-contest/

Learn more about the Spongy Moth and how to manage this pest by watching this webinar:  

https://www.youtube.com/watch?v=A70AoBORNQ4

This article is a follow up to Carl Mansfield, tree consultant for MLF farm visit on September 7, 2019.  On June 22, 2020,  Deb Pella Keen, Executive Director, MLF visited the MLF farm with Ken Jewett, founder of MLF.   We again observed the Lymantria dispar dispar or LDD moth (also known as European Gypsy Moth) larvae feeding on several trees, and one unusual host tree, a larch. Digging in the internet we found some interesting information on LDD moths.  There are now two known species of LD moth invaders in North America: the LDD moth introduced to Canada over 130 years ago and now the Lymantria dispar asiatica / LDA (aka Asian Gypsy Moth) which while not known to be established in Canada, was first recorded in 1991 in North American at the port in Vancouver, BC according to the US Department of Agriculture (see PDF).

2022 Note: It has been decided by the Entomology Society of Canada that the new common name for LDD/Gypsy moth is now Spongy Moth. Visit their website for more information. In future, MLF will refer to this moth as the Spongy Moth.

Although in many ways similar to the LDD, the discovery of the LDA moth in Canada has raised new concerns. According to Health Canada, the LDA prefers coniferous trees, is better adapted to colder climates, and the female is able to fly longer distances. These traits make the LDA moth a serious threat to Canadian forests.

The spread of the LDD moth has been largely attributed to the movement of firewood, as well as outdoor recreational and household articles.  Knowing how to detect, report and manage LDD moth could significantly reduce and limit the spread of LDD moths to new areas.  So if you find LDD moth larvae (caterpillars) this summer, do your part for citizen science and download this app (EDDMapS Ontario) and report your finding. 

EDDMapS is a web-based mapping system for documenting invasive species and pest distribution. It was developed by the Center for Invasive Species and Ecosystem Health at the University of Georgia, and since its launch in 2005 has now expanded to include the entire US and Canada. As of June 2020, EDDMapS had over 4.9 million records.

We did our part in reporting our finding of LD moth larvae at the MLF farm and while it is highly unlikely (we certainly hope!) that the moth we found was an LDA, it is important that we all learn more about these destructive invasive species.

For more information on LD moths in Canada and how you can control and prevent their spread see these links:

• forestinvasives.ca/Meet-the-Species/Insects/European-Gypsy-Moth
• www.canada.ca/en/health-canada/services/pest-control-tips/gypsy-moths.html

In the later fall and winter, when other food sources are scarce, voles, mice and rabbits eat the bark and underlying tissue of young trees. Voles frequently girdle a tree by removing a continuous strip of bark and cambium around the circumference of the tree, usually within 30 cm of the base of the tree. Trees do not recover from this girdling and usually die during the following year.

Some commercially available repellents used by fruit growers can effectively  discourage voles, rabbits and deer from feeding on trees. SKOOT and other brand name repellents contain Thiram, a distasteful but harmless fungicide that discourages animals from taking a second bite. With a paint-like consistency, the repellent can be painted onto the tree’s bark from below the original soil line to a height of 150-175 cm to discourage deer browsing, and feeding by rabbits and voles.

Before applying the fungicide, the bark mulch and a few centimetres of soil is removed from the base of the tree to allow the property manager to paint the trunk of the tree from below soil level to a height of 150-175 cm with the repellent to discourage feeding by voles, rabbits and deer.

Ensure complete coverage when applying the repellent and follow the  package directions.

Where there is a known threat of vole and rabbit damage, a galvanized hardware cloth cylinder with a 6-8 mm square mesh can be set in place around the base of the tree and buried to a depth of 5 cm into the soil.

The soil and mulch is then returned to its original form and depth, covering a few cm of the painted trunk at the base of the tree before three 15-20 cm wire staples are used to fix the cylinder in place, centrally around the trunk of the tree. Short pieces of poly-coated wire secure the cylinder to a 125 cm stake, driven at least 25 cm into the soil.

Individual Tree Wraps and Tree Guards may be more effective where vole and rabbit damage is concerned, in areas where there is a low deer population and minimal risk deer browsing.

Rabbits and voles gnaw the bark of young trees, consuming the outer and inner bark, exposing the inner wood. If the chewing extends more than half way around the trunk, the tree may not survive.

Protect the tree by wrapping a soft, flexible plastic tree wrap around the trunk. Starting at the bottom, bury at least 5 cm of the wrap below soil line and work your way upward. Be sure to wrap beyond the typical snow line. Remove the wrap in the spring.

In areas where deer may be a problem from browsing or rubbing their antlers against the tree trunk, use a tree guard 100-125 cm in length.

Tree guards also offer some protection from winter sunscald

Many different tree wraps and protectors are available from garden centers and farm supply outlets. A flexible plastic tree wrap is shown above on the left. A ventilated, corrugated tree guard is shown on its right.  We used both of these tree protectors to protect the native maples that were planted recently. Both installations include the use of a hardware cloth cylinder supported by a sturdy stake.

More information available at:

Protecting Trees from Animal Damage: http://www.agr.gc.ca/eng/science-and-innovation/agricultural-practices/agroforestry/diseases-and-pests/protecting-trees-from-animal-damage/?id=1198877618448

Newly planted trees (those planted within the past three years) require regular watering and care throughout the annual growing season. The first few years are the most critical to their long term survival and growth.

A 200-250 cm sugar maple sapling that was planted as a bare root tree in mid-May 2018. Note the hardwood mulch placed around the base of tree and the tree-watering bag set in place. The bag capacity is 65-70L when full with a draining time of  6-8 hours, but the bag content can be reduced when used for watering smaller sized trees.

Deep watering to a depth of 30-40 cm keeps the tree’s root zone moist (but not wet) and encourages rapid root regeneration that is essential to the tree’s reestablishment in its new environment.

MLF’s woodlot manager, Mike Fisher has been watering the 200-250 cm sugar maple saplings regularly, partially filling the tree-watering-bags with  40-45 L of water weekly. The trees were watered more frequently during the hot dry weather we experienced in June and July. The water soaks into the soil over a period of 4-6 hours, saturating the tree’s root zone.

It’s a year later and the sapling has grown to 20-25 mm stem caliper. The tree-watering-bag is in place, wrapped around the base of the tree and partially filled with water (40-45 L).

Note: This particular tree was planted in a more exposed location and required a stake to keep it upright while it grew new roots to support the tree. The stake will be removed in spring 2020 if the tree is well “anchored”.

On well-drained soils, 40-45 L per 25 mm of stem diameter/week should be enough water. Don’t overfill the bag as too much water can damage the roots by keeping the soil too wet. Water the trees every 4-5 days during hot, dry, drought-like conditions. 

Above: You can also use a DIY tree-watering-bucket,  an economical alternative to the commercial tree-watering-bag that is shown in the background. Capacity of 20 L. Fill twice to provide the 40-45 L required for each watering. Alter the location of the bucket placement relative to the tree trunk by 90 degrees as you water the sapling during the growing season, to encourage uniform root development around the tree. The duct tape flap covers the “fill hole”, preventing small birds from entering the bucket to get a drink.

The consequences of failing to adequately water recently planted maples – drought stressed leaves as the tree slowly dies.

Year four and after:  you can relax a bit on tree watering in later years but be prepared to water during long periods of drought.

It’s been almost two years since we planted some 175-200 cm sugar maple saplings on the Farm. An arborist will recommend  that you wait at least 2-3 years before attempting any pruning but we knew a few of these trees could use our help.

Most deciduous trees and shrubs should be pruned when they are dormant, preferably in the early spring just before growth starts. Maples are an exception to the dormant pruning rule and should be pruned when actively growing in mid-summer. When pruned in early-spring, maples ‘bleed’ excessive amounts of sap. Pruning should not be done too late in the fall either, as wounds will not have time to heal before winter.

Sugar maple sapling, 200-250 cm, shortly after it was planted mid-May 2018. Note uniform branching structure and single, dominant terminal shoot.

Without some guidance, young maples can start to branch out in the wrong direction. Newly planted trees soak up the sun, moisture and nutrients as they regenerate new roots to strengthen and nourish the tree. They often need help finding their way during their formative years.

It’s almost two years later and this young maple needs some pruning. Note the multiple leaders at the top of the tree and imbalance of new growth on the right side of the tree compared to the left. Selective pruning will correct these conditions as shown in the tree below.

We did some light pruning during a recent tree inspection. The goal was to encourage the tree’s leader to grow by trimming competing branches. We began by removing any dead (leafless) or damaged branches. These were few and far between. We prefer to use bypass shears when pruning.

A few trees had many strong branches but lacked a central guiding leader. For these trees, we selected the strongest central branch to be the new leader and shortened the remaining co-dominant branches. Where experienced suggested doing so, a few of the larger competing branches were completely removed as we pruned to reestablish a single, dominant leader. Any new branches that were found growing on the lower parts of the trunk were also removed.

If there were multiple leaders at the top of a tree, we selected the strongest, best of the group and either reduced the competing leaders by 1/3 their length or completely removed them (if doing so did not remove an excessive amount of leaves). 

We limited pruning of these young maples to what was essential and made a note to revisit these trees after the leaves fall in October.

Elsewhere on the farm, we pruned several 60-70 mm caliper trees by removing or shortening branches that had an irregular growth habit. We removed the parts of any branches that were growing toward the center of the tree’s crown or downwards in any fashion and removed the smaller of any branches that rubbed against one another.

We reduced the length of many of the lower branches that will not be part of the permanent canopy of the larger canopy trees. A few we removed completely. We will continue to do this selective pruning as the tree grows. This raises the tree’s canopy (crown) providing clearance under the tree.

Removal of a competing branch within the crown of a young caliper tree. We prefer to use bypass shears for our pruning work.

We reduced the length of most of the lower branches that will not be part of the permanent canopy of these trees.  A few, we removed completely. We will continue to do this selective pruning annually as the trees grow, raising the canopy (crown) until there is at least 1.8- 2.1 m of clear trunk  under the canopy.

We did not apply any tree pruning paint or wound dressing to the cuts. Using these products hinder the maple’s natural heeling process.

• Carl Mansfield, Arboreal Consultant, Maple Leaves Forever

Last summer we visited a landowner who was concerned with the early-fall colour change several of the maples along his laneway displayed. Click here for related story.

Closer examination revealed that property maintenance staff had severely damaged the bark and underlying tissue around the trunk at  the base of the trees, while using a string trimmer to cut the grass close to the trees. This damage cannot be repaired.

We revisited the property a few weeks ago and found that the trees had made an attempt to grow this year. Even with the cool, wet spring, they didn’t have a chance. Within a week’s time, the new leaves withered and turned brown. Without the vascular tissue to transfer nutrients and water from the roots to the emerging leaves, the trees will die.

Keep string trimmers away from your trees. Use mulches to control weeds.