How to Fight European Elm Flea Weevils

By Erin Marissa Russell and Matt Gibson

If you take care of elm trees, you probably already know how important it is to stay vigilant against the European elm flea weevil.This common garden pest can cause unsightly damage to your trees. And when they attack immature trees, the damage from a European elm flea weevil infestation can be dangerous. Although damage from the European elm flea weevil is strictly cosmetic, it can make a tree vulnerable to secondary pathogens or infections that can ultimately kill the tree.

European elm flea weevils strike American elm (Ulmus americana), Asian elm (Ulmus parmifolia), European elm (Ulmus laevis), Siberian elm (Ulmus pumila), smoothleaf elm (Ulmus minor), true Chinese elm (Ulmus parmifolia “True Green”), and elm tree hybrids. The European elm flea weevil prefers Siberian and smoothleaf elms the best of all its possible hosts.

The youngest trees in your orchard or garden are most likely to struggle with infestation by European elm flea weevils. Particularly at risk are newly transplanted trees that have branches near enough to the ground to allow the gardener to take note of the symptoms of infestation. While European elm flea weevils can strike older, more established trees, the damage they deal is less noticeable on the larger surface area of more well developed leaves, and the weevils are unlikely to pose any real health risk to these more mature specimens.

How to Identify European Elm Flea Weevils

If you notice any of the following symptoms affecting the foliage of the trees on your property, there’s a good chance that you are dealing with an infestation of European elm flea weevils. If you are able to spot the larvae or the adults on the foliage of one of your trees, identification can be rather easy. Larvae are legless, and cream-colored. Adults are tiny, one sixteenth of an inch long, reddish-brown, with black heads and black spots on their wing covers. Their thick hind legs are used for jumping when the creatures are disturbed. They are distinguished by their long snouts, which are surprisingly visible, even though the creatures are so tiny.

Foliage of affected trees exhibits brown discoloration. This discoloration is a result of heavy early feeding and may cause leaves to fall of the tree entirely.

From the end of spring to beginning of summer, gardeners may also see leaves that have holes in them that have a pale or faded appearance when viewed from a distance. The holes produced by European elm flea weevils can be differentiated from holes in foliage caused by Japanese beetles because the Japanese beetles consume trees more heavily, resulting in a higher concentration of holes. Also, Japanese beetles do not begin affecting the landscape until a few weeks after the feeding period of the European elm flea weevils has ended.

Holes in foliage that result from European elm flea weevils also have been chewed from the underside of the leaf. That means that the flea weevils will often remove the bottom and middle tissues of the leaf and leave the upper tissues in place, causing a “window pane” appearance to the damage. This look is often temporary, as the upper tissues will usually fall out of the leaf as they dry out.

Damage from European elm flea weevils tends to occur around two significant points in the season. The first point when European elm flea weevil damage is common happens at the beginning of spring when trees just begin to sprout and put out new growth. The second wave of damage continues for longer and starts as summer opens when the new European elm flea weevils appear, continuing throughout the growing season.

As European elm flea weevils feed on leaf tissues, they’re actually tunneling through the plant cells, resulting in meandering tunnels that carve through elm tree leaves. These tunnels look a lot like the damage left behind by leafminers. At the edges of affected leaves, the fine lines of flea weevil tunnels widen into blotch mines.

The foliage of affected trees appears tattered. In addition to the trademark tunnels (similar to those of leafminers) that widen at leaf edges into blotch mines, European elm flea weevils also leave pits near the middle vein of leaves, in which they lay their eggs. The standard amount of leaf tattering that is usual to see on a tree can seem visually similar to the symptoms of damage from European elm flea weevils. However, flea weevil damage will be at its worst early in the season, while leaf tatter will get worse the longer foliage remains on the tree.

How to Prevent European Elm Flea Weevils

Prevention methods for deterring the European elm flea weevil can be even more important than treatment methods, as deterrence can keep problems with the pest from arising in the first place. Prevention methods primarily consist of maintaining a healthy growing environment for the tree and providing plenty of water to keep the tree as healthy as possible. Healthy trees are far less susceptible to flea weevil infestations.

Gardeners can bypass problems with European elm flea weevils by growing only resistant varieties in their gardens. Of American elms, Princeton and Valley Forge have been proven resistant while hybrid varieties that are relatively resistant include Accolade, Emerald Sunshine, and Morton Stalwart. Especially susceptible varieties include Frontier and Holmstead.

The best way to prevent damage to your trees from the European elm flea weevil is to ensure the tree’s overall health. Ensure that your susceptible trees receive plenty of water between what they get from you as the gardener and what nature provides in rainfall. You can maximize the soil’s retention of the water your plants receive by applying a layer of mulch [https://www.gardeningchannel.com/how-to-use-mulch-in-your-garden/] to keep the temperature of the soil up and keep hydration available to tree roots for longer in the soil.

The European elm flea weevil has a few natural predators in the garden, like the predaceous stink bug, parasitic wasps of a few different varieties, and the plant bug. One way that gardeners can work to prevent flea weevil damage to their trees is by attracting beneficial insects to the garden [https://www.gardeningchannel.com/attract-beneficial-insects-garden/].

How to Treat European Elm Flea Weevils

Once European elm flea weevils have started attacking a tree on your property, there are several different ways to treat the issue before cosmetic damage becomes too unsightly. Use the following treatment options to deter the insects from causing too much damage.

Clean the garden before the chill of winter sets in to sweep the ground clear of leaf litter, twigs, and other debris from infected trees. The European elm flea weevils spend their winters just on top of the surface of the soil in material from infected trees or in the trees themselves, which puts the flea weevils perfectly in position to stake their claim in the orchard again the following spring. As you clean the surface of the soil in your garden, pay special attention to raking up dead leaves, twigs, and bark debris that can house European elm flea weevils or other pests.

Because the damage inflicted by European elm flea weevils is purely cosmetic and can be prevented by maintaining good general health for the tree, many gardeners do not focus on treating or preventing the flea weevil damage. Instead, they put their time and energy toward meeting the care preferences of the specific variety of elm trees they own, seeing the damage from European elm flea weevils as a signal that all is not well with the tree’s care.

Some gardeners treat for European elm flea weevils using insecticides applied to the soil. However, these treatments reduce and do not eliminate the threat of damage due to flea weevil infestation. These treatments also must occur at a particular point in the season to be most effective, often in the early spring. Even when insecticide is used, gardeners should choose the appropriate cultural and environmental controls from among those outlined here to roll out in their gardens. Changing the conditions that led to infestation in the first place is the most effective way to make sure your garden stays free of damage from European elm flea weevils.