CANKERWORMS

What is a cankerworm?

Cankerworms are small caterpillars that feed on many different tree species, including elm, Manitoba maple and green ash. The two types of cankerworms that cause damage in Saskatoon are the spring and fall cankerworms. Don’t let the names fool you; spring is when both kinds of cankerworms feed and cause damage.

What do cankerworms look like?

Spring and fall cankerworms look very similar. Mature larvae vary from light green to dark brownish green, and are about 25 mm long.

What is the life cycle of cankerworms?

The two cankerworms have slightly different life cycles. Fall cankerworms lay their eggs on trees in the fall, which hatch in the spring. Spring cankerworms lay their eggs in the early spring. The larvae of spring cankerworms will hatch close to the same time as fall cankerworms, and will feed simultaneously. When feeding is complete, the larvae will descend to the ground using long silk threads. The larvae then burrow into the soil where they pupate and emerge as adults in either the late fall (fall cankerworms) or spring (spring cankerworms).

What can I do to control cankerworms?

The City of Saskatoon does not have a spray program to control cankerworms. To protect your tree from these caterpillars, we recommend that you band your trees. If you are experiencing severe damage to your trees, commercial larvicides are available. The safest product to use is the bacteria, Bacillus thuringiensis var kurstaki, which is usually sold under the trade names Dipel, Thuricide, or BTK.

MOURNINGCLOAK BUTTERFLY

What is a mourningcloak butterfly?

Mourningcloak are fairly large butterflies with a wing span reaching 60-100 mm. Adults are typically purple-black with a border of white or yellow along the outer edge of the wing. The larvae, when fully grown, are approximately 50 mm long, with large spines. The spines look menacing, but they are harmless. The larvae have a speckling of white dots on the body, red legs, and a single row of red dots running down their backs.

What kind of damage is caused by Mourningcloak Butterflies?

Mourningcloak are voracious eaters, devouring the leaves of an entire stem of a tree before moving to the next stem. Groups of feeding larvae consume large amounts of foliage, but typically there are not large numbers of caterpillars. Their preferred hosts are willow and elm trees, but they will also feed on poplar, aspen and birch.

How do I control Mourningcloak?

When feeding larvae are present, small infestations can be pruned from the tree. In situations where pruning is not feasible, the larvae are easily controlled with the larvicide Bacillus thuringiensis var kurstaki, but typically this is not necessary.

TENT CATERPILLAR (FOREST TENT CATERPILLAR)

What is a tent caterpillar?

The larvae are hairy caterpillars with a black stripe and white dots down the back, brown and yellow lines along the sides, and a row of oval blue spots on the sides. In 4 to 6 weeks the caterpillars are fully grown and 45-55mm long. At this time, they begin to wander away in search of protected areas to spin a cocoon. Contrary to their name tent caterpillars do not make a tent but they are easily recognized when they congregate in large numbers on the trunk and branches of trees.

What kind of damage is caused by a tent caterpillar?

Tent caterpillars are major defoliators of green ash not only in Saskatchewan, but throughout most of North America. They are also commonly found feeding on hawthorn, maple, cherry, peach, pear and plum trees. While damage caused by these caterpillars can be extensive, outbreaks in Saskatoon are infrequent. Trees that become defoliated will often recover in the same growing year.

What is the life cycle of a tent caterpillar?

Eggs hatch in the spring and larvae begin feeding on the newly expanded foliage of host trees. During this time, larvae can be seen following one another in straight lines up the main stem and congregating on the host trees. Larvae feed through June and into July then pupate in silken cocoons in folded leaves or other protected spaces. Adults emerge in late July, locate hosts, mate, and lay eggs. Egg masses are deposited around small twigs of host trees and are often concentrated on trees near well-lit urban areas. The adult moths are nocturnal and are strongly attracted to light. Forest tent caterpillar populations usually cycle, remaining high for 3 to 4 years before dropping to low levels due to harsh weather, predation, disease, and/or starvation.

How can I control tent caterpillars?

During the fall or spring, do visual inspections of smaller branches for egg masses, and remove them. A high pressure hose can be used to kill larvae when they congregate on the trunk. Bacillus thuringiensis var. kustaki can be used to destroy feeding larvae. For this treatment to be effective, spraying must be done when caterpillars are outside of the tents and feeding.

SAWFLIES

What are sawflies?

Don’t let the name fool you, sawflies are not actually a type of fly. The larvae are more similar to caterpillar and feed on many different plants. The name sawfly comes from the saw-like apparatus used by the females to cut into needles as they lay their eggs. The yellowheaded spruce sawfly is common in Saskatoon. The larvae of this insect are green with a yellow-brown head and when finished feeding can be 30mm long.

What kind of damage is caused by Sawflies?

Many sawflies feed on leaves or form abnormal growths, known as galls. The yellowheaded spruce sawfly feeds on spruce needles. Most trees experience only minor damage from feeding, however extended feeding on young trees over several years can result in tree mortality.

What can I do to control sawflies?

Keep your trees well watered, fertilize each spring and prune regularly to keep them as healthy as possible to resist attack from this insect. Similar to forest tent caterpillar a high pressured water hose can be used to remove larvae from the tree.

SPRUCE BUDWORM

What is spruce budworm?

The spruce budworm is one of the most important conifer defoliators in North America. In Saskatchewan, its principle hosts are balsam fir and spruce. Young larvae of the spruce budworm are small (2mm) and light yellow in colour. Developing through six larval stages, a mature larva will be approximately 25mm long with a greenish brown body and a dark brown or black shiny head. Adults are small (20-25mm wingspan) brown coloured moths.

What kind of damage is caused by spruce budworm?

As with many defoliators it is not the insect itself that is most noticeable but the damage that is caused. Damage by spruce budworm occurs early in the spring when larval feeding on newly developing needles damage the developing buds. As the larva grows, needles are severed at the base and left hanging in a thin silken web. The severed needles turn brown, giving the defoliated tree a scorched appearance. 

What is the life cycle of the spruce budworm?

In late June and into July, adults emerge and lay eggs in clusters on needles. Newly hatched larvae will begin to migrate to the centre of the tree where they spin silken tents and over winter in a dormant state. In the spring when they break dormancy, larvae prefer to feed on new buds of male flowers or on the previous year’s needles if this floral tissue is absent. The larvae then bore into developing bud tissue where they continue to feed until the food source is depleted. When the larvae have completed feeding, they tie the bud tips together with silken threads and pupate. Adults emerge after about 10 days to repeat the cycle.

How do I control spruce budworms?

The safest and most effective means of controlling spruce budworm is by spraying larvae with Bacillus thuringiensis var. kurstaki.

TUSSOCK MOTH

What is a tussock moth?

There are numerous species of insects that are commonly referred to as “tussock moths”. The moniker is due to the presence of dense clusters of hairs on the larvae. Some species are major defoliators of hardwood and softwood, particularly in forest stands, while others are of minor importance. In Saskatoon we have numerous tussock moths, including the yellow spotted tussock moth (photo). Of particular concern is the gypsy moth.

What kind of damage is caused by the tussock moth?

Tussock moths are foliage feeders. Damage initially appears as shot holes in the leaves, and then as the larvae grow and continue to feed, they consume leaves from the margins, eventually consuming entire leaves.

How do I control tussock moth?

Control can normally be achieved through removal of larvae by hand. As a last resort, tussock moths can be controlled using Bacillus thuringiensis var kurstaki.

 

 

 

WEBWORM (FALL WEBWORM)

What is a fall webworm?

The fall webworm is a caterpillar that feeds on all types of shade trees. There are two species of webworm, the red headed and the black headed.

What kind of damage do webworms do?

The larvae spin unsightly webs, starting at the tips of the branches and slowly extending down the branch towards the trunk. The larvae feed on the foliage enclosed by their web. As leaves are usually eaten late in the season when the tree is finished growing, the damage to the host plant is primarily aesthetic. The health of the tree is not usually at risk.

What can I do to control webworms?

When infestations are at low levels, cutting the tents from the trees is sufficient. Using a larvicide such as Bacillus thuringiensis var kurstaki is an option, but once the webs are formed, the application of larvicides is ineffective.