Trees offer many benefits to the community, so it is important to keep them healthy and understand the pests and diseases that threaten them. Review the list below to learn about the current tree pests and diseases in Kingston.

On this page: 

• Spongy Moth Infestation
• Tree Pests
• Tree Diseases

Spongy Moth Infestation

The Spongy Moth - previously referred to as Lymantria Dispar Dispar or Gypsy Moth – is a non-native species that originated in Europe. The first detection of this invasive caterpillar in Ontario was found in 1969, while extensive defoliation (where leaves have been eaten) did not happen until 1981. This invasive pest defoliates trees, prevents new growth, and stresses trees, making them more susceptible to damage from secondary pests, drought, and poor growing conditions. Spongy Moth outbreaks happen in cycles, often occurring every seven to 10 years, with outbreaks lasting three to five years.

As a food source, Spongy Moths prefer oaks, but the moths will lay eggs on, and the caterpillars will eat, a variety of both Deciduous and coniferous trees. When the caterpillars hatch in the spring, they will climb upwards in search of leaves. Left untouched, a tree can be defoliated as one single caterpillar will eat in the range of 1 square meter of foliage in its life cycle. A single or double year of defoliation will not likely kill a deciduous tree (broadleaf) on its, the contribution of draught additional pests and diseases can cause enough stress to impact leaf production the following year. Multiple years of defoliation can cause long-term health effects to an individual or stand of trees. However, a healthy tree will produce a second flush of leaves in the same year it has been defoliated. You can assist your tree by ensuring it is watered during periods of drought during the peak times of defoliation to ensure stored resources are not depleted.

Coniferous trees are not a preferred species of the Spongy Moth but when preferred resources are depleted, or during peak infestations, they will be infested. Once defoliated they will not recover, by growing new needles. Typically, you notice stripped branches starting at the base of the tree progressing upward.

City of Kingston Action Plan

Currently, the City of Kingston is doing moth density surveys at 20 separate locations within the city’s urban boundary. This information will help us determine population spikes throughout the city and assist in determining management strategies. We will not be aerial spraying at this time.

Trees at Risk

• Oak (Quercus)
• Basswood (Tillia)
• Norway Maple (specifically Crimson King cultivars)
• Birch (Betula)
• Elm (Ulmus)
• Poplar species (Populus)
• Sugar maple (Acer saccharum)
• American beech (Fagus grandifolia)
• Eastern white pine (Pinus strobus)
• Balsam fir (Abies)
• Colorado blue spruce (Picea pungens).

Characteristics

• Mature larvae are 50 mm long, dark coloured, hairy, with a double row of five pairs blue spots, followed by a double row of six pairs red spots, down the back.
• Male moths are light brown and slender-bodied, while females are white and heavy-bodied and cannot fly.

Natural controls

Natural predators and pathogens are curbing the outbreak of Spongy moth in North America.

• Nuclear polyhedrosis virus (NPV) – is a viral infection that is known to kill Spongy Moth larvae once the virus builds in population. This virus can spread quickly from infected larvae to non-infected larvae, which kills them. One can see the affects of this virus working by noting dead larvae hanging on a tree in an upside-down “V”.
• Entomophaga maimaiga – is a fungus that is known to cause Spongy Moth populations to collapse. Cool, wet conditions provide a favourable environment for this fungus to spread. Dead larvae that appear brittle and are hanging vertically along tree trunks is a sign that this fungus has killed Spongy Moth larvae.
• Predation and parasitism – a species of wasp called Ooencyrtus kuvanae is known to infect Spongy Moth eggs and can reduce Spongy Moth populations the cocoons of the parasitoid wasp resemble uncooked grains of rice. Birds, mammals, and other insects are known to prey on the Spongy Moth.
• Cold weather – Long periods of extreme cold (−20 degrees Celsius) can kill overwintering larvae in exposed egg masses.

Life Cycle and Protecting Trees

Follow the steps below to help protect your trees from the invasive Spongy moth caterpillar.

September to April: Remove egg masses

The egg mass is a fuzzy tan/beige coloured flattened blob, about 2 to 2.5 cm (3/4 of an inch) wide and slightly longer. The egg mass will have dark brown spots – known as pupae and they too should be removed if you find them – at this time of year, they are probably empty. These masses should be removed and destroyed to prevent and control population growth; as each egg mass can hold 100-1000 eggs.

Why wait until the fall to remove the egg masses? Beginning now and into August and September, look for “pinholes” on the egg masses, evidence that they have been parasitized by a tiny, non-stinging wasp. If you can, wait to remove or destroy egg masses until after leaf fall or the first hard frost to allow this beneficial wasp an opportunity to build up its numbers.

To remove the egg masses:

• Locate egg masses on trees of all species, in the tree trunk and crevices, and ground up to crown, along branches, under rocks, lawn furniture, decks, houses, firewood piles, recreational vehicles etc.
• Place a container below the egg mass
• Use a scraper tool to scrape off the egg mass into the container
• Place the scrapped egg masses into a bucket of soapy water.
• Leave the egg masses soaking in the bucket for a day or two to destroy them.
• Be sure to collect all the eggs, as any that fall to the ground will survive.
• The best practice is to wait until the tree has lost its leaves in the fall to make identification easier.

Do not use a pressure washer, a hose, or spray bottle to remove the eggs, this will cause dispersion and the eggs will likely survive.

Late April - May: Tape trees

During the early spring (late April – May) when conditions allow, eggs hatch and larvae spread in search of trees to feed on foliage (leaves). At this state, you will see holes centred in the leaf. At the beginning of the life cycles, feeding occurs during the day, however, as a caterpillar matures feeding can occur overnight when temperatures are cooler. One will find them feeding on the edges of the leaf and will find more Spongy Moth caterpillars in the lower parts of a tree during the day when temps are high which makes it easier to handpick.

Caterpillar larvae will emerge from the egg masses during this time. They will begin looking for food, these tiny caterpillars will find a tree and crawl up to the canopy to begin feeding. You may see caterpillars hanging from silk lines dangling from trees or other hard surfaces, they do this as a mode of ‘transportation’, taking advantage of the wind to be moved from tree to tree and may fall to the ground during this time. Tape can be applied to the tree trunk to prevent caterpillars from reaching the top.

• Sticky traps can be installed on host species
• Using durable tape, create a barrier of 5 – 10cm around the trunk of the tree at chest height, be mindful not to damage trees with thin bark such as Birch.
• Ensure that the tape is tight to the bark and does not allow the larvae to pass under it.
• Caterpillars will stage at the tape barrier and may not try to cross, remove any staged caterpillars by picking or scraping and dispose of in soapy water. Smaller caterpillars will be caught by the sticky surface.
• Carefully collect them every day and shake into a detergent and water solution and leave them for two days until they are dead. The long hairs on the caterpillar contain histamines that can cause allergic reactions so wear gloves if you think you will contact the caterpillars.
• Remove the tape in July to prevent any damage to the tree trunk.
• Most effective on young smaller trees.

Mid-May: Spraying

If you are able to, in mid-May when the caterpillars are still small and vigorously eating is the ideal time to apply insecticides that include the bacterial compound BTk (Bacillus thuringiensis kurstaki) which occurs naturally in soils. Btk is very specific and only activates in insect stomachs with low/no acid (alkaline environments). It produces a toxic protein that breaks down stomach walls. The insect usually dies within two to five days.

Facts about Btk:

• It does not affect adult moths and butterflies – it only affects newly hatched caterpillars feeding on plant material at the time the spray is used
• It does not affect other insects, honeybees, fish, birds, or mammals
• It does not work in the stomach acid of humans and other animals

Feeding typically is completed by mid-July

Mid-May - August: Place burlap

Once the caterpillars are established actively eating and larger in size, they will move down the tree trunk to seek shelter from heat and predators. Placing burlap around the tree trunk will entice caterpillars to rest there. These caterpillars can then be easily removed and destroyed.

• Wrap a piece of burlap cloth around the tree trunk
• Tie twine or rope around the center of the burlap (allow for about 30cm of overhang)
• Drape the burlap cloth over the twine or rope. This will create an overhang where caterpillars can go when seeking shelter during the day.
• Check by lifting the overhanging burlap every afternoon and collect any hiding caterpillars.
• Put the caterpillars in a bucket of soapy water for a day or two to destroy them.
• This can also be effective for trapping the nonflying female moth after it has pupated from the caterpillar instar.
• At this time hand-picking adult caterpillars and the pupae is also very effective and easy to do as they are typically coming out of the crowns of the trees when feeding has stopped. (wear nitril gloves to protect skin)

Notes about burlap:

• Place put the burlap or gardening cloth in a bucket with detergent and water and leave it for at least two days.
• The attached pupae and any adult female moths and their eggs will be killed.
• Immerse the tape in a detergent and water solution if it has pupae or eggs attached to it. The detergent helps the water to penetrate the pupal shell, effectively drowning the developing moth.
• DO NOT throw the burlap out in the garbage before the soaking and destruction of live pupae and eggs is complete.
• The females die shortly after laying their eggs, but some can mate more than once so if the females are present on the burlap or tape, make sure they are fully immersed.

Tree Pests

Aphids – the most common species in Kingston are small and green in colour with long antennas. They attack by sucking the sucrose from the leaves of Little Leaf Lindens and Honey Locust species. They excrete a sticky “honeydew” oil-like substance, which can cause the plant to develop a black sooty mold, making the leaves appear dirty and grey. They can be found on the underside of the leaves of affected trees.

Eastern Tent Caterpillar - similar periodic life cycles to the Forest Tent Caterpillar, active through June and July. This caterpillar forms tent-like webs on branch tips and corners of tree limbs. Primary hosts include the Apple and Cherrie species. They are hairy with a brownish-black colouring and light streak down the back with lines along their body that are brown-yellow lines with blue spots. Adult moths are usually reddish-brown in colour.

Emerald Ash Borer (EAB) - the most destructive tree pest currently active in Ontario. It affects all Ash trees except for the Mountain Ash. Larvae feed on the inner bark and outer sapwood, forming ‘s-shaped’ galleries that are white in colour. Adult beetles are metallic green in color and form D shape exit holes in the bark when they emerge in the spring.

European Gypsy Moth - active from April to June and feed on both coniferous and deciduous species. Moths are charcoal grey colour and have a double row of six red dots on the back. Single larvae can eat in excess of 1 square meter of foliage in a season.

Fall Web Worms – active from mid-August through September, this insect forms a large nest up to one metre long at the ends of branches, wrapping around the branches of Ash, Manitoba Maples, and Crabapple species. The webworm is pale yellow and very hairy. Adults are white moths with a wingspan of from 30 to 42 millimetres. Infestations are non-fatal for trees, but aesthetically displeasing.

Forest Tent Caterpillar - periodic pest; populations can last from 3-6 years on 10-12-year cycles. Heavy defoliators in southern Ontario, their primary hosts are Sugar Maple and Red Oak. The caterpillar creates silk mats on trunks and branches where they collect. They are hairy and brown in colour, with a slate-blue stripe along each side and a row of keyhole-shaped white spots along the back. Adults are buff-brown moths with three darker bands across each forewing.

Tree Diseases

Anthracnose –affects Maple, Ash, and Oak species in the early spring when the weather is cool and damp. Hot, dry summers will stop the progression of symptoms. An early browning and/or drying of leaves will occur with the potential for some leaf drop. Small brown dots on the underside of leaves are also likely to occur.

Dutch Elm Disease –has been active in Ontario since 1946 and affects several elm species, spread primarily by beetles. Symptoms present in newly infected trees during early June and are fatal to the tree within three years.

Maple Tar Spot – forms black blotches on Maple leaves and may cause early leaf drop. It is a non-fatal disease, but aesthetically displeasing. Ensuring leaves are cleaned up as they drop in the fall can break the cycle of this disease.