The willow leafminer is a small gray moth that is native to North America and has caused extensive damage to willow trees across Alberta.
What are the Risks?
Caterpillars of the moth feed on willow leaves and thereby cause extensive damage which appears as dead and discoloured blotches on the upper surface of leaves. Damaged parts affect plant nutrition and growth, and may eventually lead to branch death.
In 2011, an outbreak within Alberta caused the damage of many willow strands.
What to Look For
The willow leafminer is a small gray moth and causes premature drop of damaged leaves. Damaged leaves have a reddish-brown colour and is found to be hollow because either a caterpillar (flat, pale and yellowish) or its droppings will be between the upper and lower layers of the leaves.
Mature caterpillars make a cellophane-like cocoon that is generally located on the upper surface of the leaf. Here, the caterpillar will enter into a transition stage where the moth can develop.
Prevention
Keeping your willow healthy and vigorous will help to mitigate the impact of the leafminer. Other methods include:
- Apply fertilizer in springtime;
- Water during draught conditions; and
- Use leafminer resistant varieties.