Tree Pests: Leaf-feeding Pests Japanese Beetles and More

When we look at trees, their canopies, leaves and needles, we see beauty, shade, and, in some cases, protection. For leaf-feeding tree pests, it’s food. And while small infestations may seem innocuous, over time, they can go well beyond cosmetic damage, impacting a tree’s overall health.

Across the Intermountain West and Pacific Northwest, pests like western spruce budworm, sawflies, and leafminers are becoming an increasingly common problem for urban landscapes. We’re even starting to see Japanese beetles in some of these locations.

Understanding how to identify them as well as what damage they can do is an essential part of keeping your trees healthy and thriving.

Quick Links:

• What Are Leaf-Feeding Tree Pests? (Tree Pests Explained)
• Why Leaf-Feeding Tree Pests Are a Growing Problem in the Intermountain West & PNW
• Common Leaf-Feeding Tree Pests in the West
• How Leaf-Feeding Pests Damage Trees
• Trees Most at Risk from Leaf-Feeding Pests
• How to Prevent Leaf-Feeding Tree Pest Problems
• What to Do If You Have Leaf-Feeding Tree Pests

What Are Leaf-Feeding Tree Pests? (Tree Pests Explained)

Leaf-feeding pests are exactly what they sound like: tree pests that feed on leaves or needles. They’re among the most visible pests out there as they attack the tree in a way that’s usually highly noticeable.

They may chew entire leaves, eat the tissue between the veins, or roll, mine, or weave leaves together to protect themselves while they feed, as tent caterpillars do. Leaf-feeding tree pests include: caterpillars and moth larvae, beetles, sawflies, leafminers, grasshoppers, and other defoliators.

What’s not always as visible as the pests or damage is the impact they have on tree health. Because they feed on and destroy the parts of the tree responsible for photosynthesis and energy production, they severely inhibit the tree’s ability to grow and grow healthy.

Why Leaf-Feeding Tree Pests Are a Growing Problem in the Intermountain West & PNW

Most tree pests, including leaf-feeders, are opportunists. That said, while wood-boring pests are likely to look for already weak trees, leaf-feeding pests will feed on healthy trees. This is particularly important out West, where leaf-feeders are becoming more noticeable.

Various environmental stressors, such as drought, heat, urban growing conditions, and extreme weather/temperature fluctuations, reduce a tree’s ability to recover from repeated or frequent defoliation by leaf-feeders.

When we couple stressed trees with favorable conditions that allow pest populations not only to expand but also to remain active for longer periods, we have a potential recipe for disaster. And, the double whammy is that it becomes a compounding problem. Stressed trees struggle to recover, and defoliation by pests creates additional stress and greater susceptibility to tree pests. It has the potential to create a truly vicious cycle.

Common Leaf-Feeding Tree Pests in the West

Certainly, these tree pests existed before changes in climate created a more welcoming environment, so one advantage we have in mitigating their damage is understanding who they are. Further, because not all leaf-feeding pests damage trees in the same way, knowing a little bit about the most common pests and what they do goes a long way.

Western Spruce Budworm

If you have conifers, including Douglas fir, true firs, and spruce rees, then you may have seen the Western spruce budworm. The larvae, which feed on developing buds and new needles, are among the most significant defoliators in conifer-heavy landscapes out West.

How to spot them:

• New growth is brown or thinning
• Silk webs, partially chewed or ragged needles, and small caterpillars on developing buds

Douglas Fir Tussock Moth

Not the moth itself but the larvae will feast on Douglas and true firs. In outbreak years, the defoliation can be severe and result in overall weakening that leaves the tree vulnerable.

How to spot them:

• Fuzzy caterpillars known for their distinctive tufts of hair
• In fir and douglas fir trees, defoliation in patches or an overall thinning canopy

Tent Caterpillars

Among the easiest to recognize based on the dense silk tents they build, tent caterpillars frequently attack deciduous shade trees and fruit trees.

How to spot them:

• Big, dense, white tents formed at branch unions
• Caterpillars, in groups, feeding on the leaves

Fall Webworm

These pests also build tents, much like tent caterpillars. The primary difference? The webworm’s tents are less dense and more loosely woven.

How to spot them:

• Loose webs located at the ends of branches
• Leaves left skeletonized, eaten from the inside out

Leafrollers

These pests also attack deciduous trees by rolling or tying leaves together with “webs.” Unlike tent caterpillars or webworms, their “webs” are found between the leaves rather than creating a tent.

How to spot them:

• Curled, rolled, or even folded leaves held together with silk webbing
• You may find chewed leaves inside the rolled leaves

Elm Leaf Beetle

As the name suggests, they feed largely on elm trees where they destroy the leaves between veins, leaving leaf skeletons. Again, the danger here is repeated infestations which can significantly damage trees and make them more susceptible to drought stress.

How to spot them:

• Lacy or skeletonized leaves
• Olive-green or yellow beetles on the leaves

Cottonwood Leaf Beetle

Feeding mostly on cottonwoods and poplars, especially younger trees, both the adults and larvae will devour the leaves, often causing significant defoliation.

How to spot them:

• In cottonwoods or poplars, ragged holes on the leaves
• Darker larvae and striped adults feeding on leaves

Japanese Beetles

Japanese beetles love ornamental trees, often skeletonizing leaves and damaging the canopy. They are a more recent concern out West.

How to spot them:

• Distinctive metallic green and copper beetles on leaves
• Leaves skeletonized with veins intact

Pine Sawflies

These may, at first, look like caterpillars but that’s the larvae. They feed, in groups, on pine needles and their heavy feeding thins canopies and stresses young and other vulnerable pine trees

How to spot them:

• Large groups of larvae feeding on needles
• Stripped or partially eaten/chewed pine needles

Aspen Leaf and Birch Leafminers

Both create distinctive feeding patterns on leaves that often resemble “mines” or look like racetracks along the upper and lower surfaces of the leaves. While the impact is mostly aesthetic, as with any pest, repeated infections can damage tree health over the long-term.

How to spot them:

• Blotchy or translucent patches on the leaves
• Leaves look scorched or like onion skin toward the end of the season

Western Tiger Moth, Grasshoppers & Other Opportunistic Defoliators

Some of these defoliators are not prone to leaf destroying, they’re considered “generalists” and opportunists. In years where there is an outbreak of pests or disease or even environmental stressors like drought.

How to spot them:

• Keep an eye out in years where drought and environmental stress are taking a toll on trees
• Irregular chewing and damage across leaves and canopies
• Insects will be visible in large numbers during these outbreaks

How Leaf-Feeding Pests Damage Trees

As the name implies, leaf-feeding pests attack the leaves of trees, but don’t make the mistake of thinking this is purely aesthetic. The leaves and needles keep a tree alive by producing energy, so regardless of whether there is complete leaf destruction, skeletonized leaves, mined leaf surfaces, or missing buds and needles, the impact is the same; there is less foliage available to produce energy for the tree.

How Leaf-Feeding Pest Damage Impacts Trees

Let’s look at some damage specifics:

• Reduced photosynthesis: trees rely on their leaves to convert sunlight into energy. Damaged or missing foliage results in less energy for the tree which impacts everything from root function and growth to its ability to defend itself against disease, other tree pests, and environmental stressors
• Stunted growth and thinning canopy: While occasional feeding is sometimes manageable, repeated or attacks stress trees. Over time, that slows growth, thins the canopy, and impacts the tree’s appearance.
• Vulnerability to secondary problems: Weak trees face increased risk, not just from the pests that caused the damage, but other pests like wood-boring beetles, tree diseases, dieback, and overall decline. This is especially true in urban environments where compacted soils and heat islands can compound stress.
• Limited recovery for young trees: Young trees do not have the energy reserves that mature and established trees do. With thinned canopies, they may struggle to recover and thrive after feeding damage.

Trees Most at Risk from Leaf-Feeding Pests

While some leaf-feeding pests may feed on any healthy tree (food is food), some trees are more vulnerable to pests and, in some cases, to the damage they cause.

• Young or newly planted trees
• Trees stressed by environmental conditions like drought, soil competitions, heat islands
• Trees already weakened by other tree diseases or pests
• Some specific hosts: Douglas and true firs, elm trees, cottonwoods and poplars, pine trees, aspen and birch
• Monocultures and low-diversity urban canopies (they allow pests to spread more easily)

Canopy diversity, as well as proper tree care, can help make your trees more resilient against tree pests, and leaf-feeding pests, over time.

How to Prevent Leaf-Feeding Tree Pest Problems

In addition to ensuring canopy diversity, protecting your urban forest or managed landscape from leaf-feeding pests starts with ensuring trees are thriving in low stress environments and they’re being monitored.

Additional strategies include:

• Ensure proper moisture and water trees deeply during droughts or dry periods
• Mulch to protect roots and regulate soil temperature
• Prune wisely as over-pruning can create unnecessary stress
• Monitor trees and foliate for any signs of tree pests or disease
• Remove infested branches when appropriate and dispose of them away from other trees
• Work with certified arborists or tree service companies when infestations are a clear and present danger to your trees
  

The key strategy is always to identify early and act quickly.

What to Do If You Have Leaf-Feeding Tree Pests

If you’re monitoring your trees, you may discover leaf-feeding pests. If and when you do, the first step is to correctly identify the pest. Not all leaf-feeders require an aggressive response and many healthy, mature trees can tolerate some minor feeding without long-lasting impact.

That said, if you notice leaf-feeding pests, take the following steps:

1. Identify the pest and the affected trees. Contact an arborist if you need help doing this.

2. Monitor the damage. If it’s widespread or severe, contact an arborist.

3. Water and mulch the tree to provide support and ensure it is otherwise healthy.

4. Remove local infestations when possible. For example, if there are tents on one branch, you can remove that branch.

5. Contact an arborist or tree service if the defoliation is severe or if the pests continue to return year after year as this can create long-term problems for tree health.

As always, be mindful of stressors like overpruning, or drought as these can impact overall tree health and make the problem worse.

If you suspect you have tree pests and need help with identification, mitigation, or even overall support, please reach out to our tree services team.

As always, tree health starts with strong stock. Young and newly planted trees can be especially vulnerable to regional pests and that’s just one reason we work hard to provide native and regionally adapted cultivars with healthy root balls. This reduces stress at transplant and ensures environmental resiliency.

Whether you're looking for retail or wholesale nursery stock or tree support, we’re here to help. Reach out to our team today and let’s build healthy forests and landscapes together.