Ask an Arborist: “Why do I have White Moths All Over My Trees?!”

As professional arborists, we often get asked “why do I have white moths all over my trees?” Here’s the answer.

At this point most homeowners are familiar with LDD (Lymantria dispar dispar) moth (formerly known as Gypsy Moth), but for those that are not, here is the answer to the above common question. It is a regular inquiry, and we want to make sure you have the answers you need.

What is it?

LDD Moth is an invasive pest that attacks a wide range of trees, including Oak, Maple, Birch, as well as certain deciduous trees. In some years, this pest can reach outbreak levels and many trees can be defoliated completely in summer. Adding to this dramatic effect is the raining debris of caterpillar droppings, followed by swarms of white moths in late summer. The overall experience can be quite distressing for tree owners.

When are they active?

The egg masses are visible on tree trunks and branches from late summer through the following spring. Caterpillars emerge in April and can be observed feeding through June. This is the stage of development that causes defoliation.

Pupation can be seen between June and July. This is followed by the swarms of white moths in July and August.

Is it a severe problem?

Healthy trees can withstand the damage and defoliation caused by LDD Moth. Populations rise and fall over the years, with some years being worse than others. Although unsightly, the health risk to host trees is relatively low.

Repeated defoliation in peak years can become more serious. With leaves being the ‘food factories’ for trees, a prolonged period of defoliation year after year can start to affect overall health and vigour. In some areas in the GTHA, populations have been high for several years and tree health has decreased which can be a cause for concern. Municipalities, including Mississauga, are considering aerial sprays for the 2022 season to help control populations for both public and private trees.

What can you do?

Managing LDD Moth infestations is multifaceted. Destroying egg masses will reduce the overall population of moths for the next season. Egg masses can be carefully scraped off and destroyed. Dispose of the eggs in soapy water, or by burning. Egg masses can still hatch from the ground, so disposal is key.

Once eggs hatch, burlap skirts installed around tree trunks provide a place for caterpillars to hide from the heat of the day. Collect the sheltering caterpillars and dispose of in the same way as the egg masses.

What can Maple Hill do?

Most egg masses will be high in the canopy and removing these can be dangerous without the proper training and equipment. Maple Hill can access the parts of the canopy that are out of reach and safely remove the eggs, either through rope access or using aerial bucket trucks.

Biological controls can be provided to reduce LDD Moth population. These options can be quite cost-effective and successful. These include TreeAzin Injections for larger trees and/or BTK sprays for small to medium-sized trees.

Long-term health and vitality is critical for trees surviving repeated pest attacks. Improving the cultural conditions for host trees is integral.

Maple Hill can provide deep root Compost Tea applications to tree soils to improve organic nutrient content. We can further improve site conditions by the addition of well-composted, high organic content wood chip mulches.

Both these strategies help to provide trees with the best possible growing conditions, and in turn the best pest tolerance. Remember a healthy tree is a happy tree!

Traditional fertilizers can also be applied as needed for short-term encouragement of new leaf development.

During pupation, pheromone traps can be installed to capture male moths and reduce egg fertilization. Typically, males hatch before females, so there is a brief period after hatch where traps can be highly effective. It is important to have the traps up before the moths emerge, but they can be effective later in the season to capture swarms of moths around outdoor areas. Please contact us as soon as possible to reserve your trap from the 2022 season. Stock will be limited.

Are there other options?

Any Integrated Pest Management program begins with monitoring. Late winter or early spring inspections can allow us to predict the degree of infestation by surveying egg masses. One or more of the above services may be recommended based on the egg masses present on your trees.

Maple Hill also offers our clients monitoring through our Tree Management Program. With two annual inspections of the complete property, pest and disease issues can be identified early and addressed, as necessary. The inspections also provide detailed information about pruning needs, general tree health, and identify future tree care requirements to help you better plan and budget for any needed maintenance of your property trees.

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