Tree Pests: Sap feeding Pests

Everyone wants healthy trees. From homeowners and property managers to landscapers and city foresters. The best part of healthy trees is that they’re naturally more resistant to pest infestations and better able to handle the recovery if they do happen.

Some tree pest problems are easier to spot than others, and among the more challenging are the sap-feeding pests, mostly because they’re typically very small (aphids and mites). Still, as they work to extract nutrients and water from your trees, they can, over the long term, create problems for a healthy canopy.

Learning to identify them and what to do if you see them is an important part of keeping your trees healthy.

Quick Links:

• What Are Sap-Feeding Tree Pests? (Tree Pests Explained)
• Why Sap-Feeding Tree Pests Are a Growing Problem in the Intermountain West & PNW
• Common Sap-Feeding Tree Pests in the West
• Common Signs of Sap-Feeding Tree Pests
• Trees Most at Risk from Sap-Feeding Pests
• How to Protect Trees from Sap-Feeding Pests
• What to Do If You Have Sap-Feeding Tree Pests

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

Sap-feeding tree pests, including mites and aphids, feed on trees by piercing the leaves or needles, stems, or twigs and pulling out the sap. While leaf-feeding tree pests chew on the leaves and wood-boring pests tunnel through the bark, sap-feeders have a proboscis designed for piercing.

While these insects may be small, they are mighty and move in numbers that can weaken trees by removing nutrients and water, impairing new growth, and creating stress that not only reduces vigor but also makes trees more susceptible to tree diseases and other pests.

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

Sap-feeding tree pests are not new to the West, but many cities, urban forests, and managed landscapes are experiencing more pest pressure as environmental stressors increase. In western states like Colorado and Utah, in particular, warmer temperatures and drought are placing stress on expanding urban canopies. That we’re planting and expanding urban forests is great, but when combined with the environmental stressors, the conditions are favorable for sap-feeding pests.

The temperature changes, including warmer growing seasons and shorter winters, mean some pets are able to survive winters more successfully, remain active longer, and increase their populations more quickly.

Why is this particularly important in the West?

• Increased vulnerability: Drought-stressed trees are more vulnerable because they have fewer resources to build resilience, defend themselves against pests, and recover from damage. Including drought-tolerant trees from Utah and Colorado in your canopy can help.
  
  
• Urban stressors create ideal conditions- Increased heat, whether from heat islands or reflected heat, along with soil compaction and limited root zones, increases tree stress and makes them susceptible to pests.
  
  
• Rapid Reproduction- Even without extended warm periods, aphids, mites, and whiteflies reproduce quickly, building large populations in a short amount of time. This is especially true during warm, dry weather, so areas with significant drought may see more activity and larger populations.
  
  
• Milder winters increase survivability- Winter used to kill off significant numbers of pests, but with milder winters, they’re not experiencing the same level of winter mortality, and that means, come spring, they’re ready to go.
  
  
• Honeydew creates secondary concerns- Sap-feeding tree pests sometimes create a substance called honeydew, a sticky substance that can leave black mold on everything from leaves and branches to cars, sidewalks, and other structures. In managed landscapes with significant sap-feeding tree pest problems, this can create a larger community problem.

While wood-boring tree pests may kill a healthy tree, sap-feeding pests aren’t likely to do this on their own. Unfortunately, they’re still dangerous, as repeated infections can create significant problems for new growth and tree health, ultimately making trees more vulnerable to other issues.

Common Sap-Feeding Tree Pests in the West

One of the things that makes sap-feeding tree pests so challenging is their size, so they sometimes go unnoticed until their numbers are significant and damage is clear. That damage can include distorted growth (due to nutrient deficiencies), discoloration, honeydew buildup, and general signs of stress.

That said, let’s take a look at the more common sap-feeding tree pests in the west, who they are, and what they do.

Aphids and Mites

Small and soft-bodied, they can be a variety of colors (brown, black, yellow, or red) and often cluster on new growth or the underside of leaves. They do create honeydew, but they might also cause leaf curling or distorted growth.

Woolly Aphids & Elm Aphids- Woolly aphids often look like a tiny walking piece of cotton. This sometimes makes it easier to spot them as clusters are clear. Elm aphids feed predominantly on elm trees and can cause leaf curling or galls. Both of these create honeydew.

Spider Mites- Mites are tiny arachnids and are very difficult to spot due to their size. However, the damage they cause includes stippling, leaf discoloration, and leaf drop. You might also notice webbing if the infestation is severe enough.

Mealybugs & Whiteflies- Mealy bugs, like woolly aphids, may appear like cotton (you’re going to sense a theme here that suggests if you see cotton on a tree that shouldn’t have it, check for pests!). Whiteflies, on the other hand, are tiny white moths that, when disturbed, will flutter. Both of these pests produce honeydew.

Scale Insects

These are tricky as they are almost camouflaged, as they often look like bumps or growth on the tree itself, whether that’s on the bark, twigs, stems, or leaves themselves.

Oystershell Scale- Easy to identify, as its name suggests, there’s an oyster shell-shaped covering. Typically, they attack ash, maple, willow, lilac, and other deciduous trees. When infestations are severe, they can cause significant decline and branch dieback.

Cottony Maple Scale- Again, white cotton appearance, but this time on the eggs, which are often found in clusters on twigs and branches. They typically affect maples and other hardwood trees.

Pine Needle Scale- Found on, you guessed it, pine needles, it appears as small white scales. Severe infestations often result in thinning foliage, yellowing, and reduced tree health.

European Elm Scale- Commonly found on elm trees, European elm scale creates a lot of honeydew. So if you’ve got elms, and you’re noticing black sooty mold on trees, vehicles, and structures, this may be the culprit.

Lecanium Scale- These are brown scales, rounded, and normally found on twigs and smaller branches of a wide variety of deciduous trees.

Leafhoppers & Treehoppers

While the name might conjure up images of grasshoppers, these sap-feeding tree pests are quite a bit smaller and wedge-shaped. When this group attacks, they cause stippling and other discoloration, increased tree stress, and reduced growth.

Potato Leafhopper- While the primary host is potato plants, they’ll also go after most landscape trees and shrubs. They cause leaf curling and browning as well as a condition known as ‘hopper burn,’ where the leaves look yellow, brown, or have small “burn’ spots at the margins and tips.

Rose Leafhopper- Here, roses are the primary host, but they will also feed on other ornamentals. They cause stippling and leaf destruction, ultimately impairing the tree's ability to produce healthy leaves and resulting in weak, vulnerable ornamental trees.

Spittlebugs

They’re named for, you guessed it, spittle. During their immature stages, they produce frothy masses that help protect the young from environmental and predatory threats, allowing them to safely mature.

Meadow Spittlebug- These are fairly common across the US, not just in the Intermountain West, where they feed on a wide variety of plants. While they don’t do major damage, it is noticeable when you’ve got an infestation.

Pine Spittlebug- As the name implies, they predominantly feed on pine shoots and needles. Heavy infestations can impair growth and significantly alter the appearance of young pine trees.

Psyllids

These tiny insects are sometimes called “jumping plant lice” because they can jump. Despite their size, they can cause leaf curling, galls, and distorted growth.

Hackberry Psyllid- These typically attack hackberry trees, causing galls or growths that look like blisters on the leaves. The primary impact here is largely aesthetic, but when the infestations are severe, they are quite noticeable.

Pear Psylla- If you have pear trees, you’ll want to be aware of these sap-feeding pests. When there is an infestation, they can distort leaves and shoots, reduce fruit quality, and produce large amounts of honeydew.

Adelgids & Wooly Adelgids

These insects are closely related to aphids, with the woolly variety resembling woolly aphids. They primarily attack conifers, leading to needle loss, gall formation, branch dieback, and long-term health concerns.

Out West, the Cooley Spruce Gall Adelgid is fairly well-known, especially for the cone-like galls they form on spruce and Douglas fir trees.

Common Signs of Sap-Feeding Tree Pests

When it comes to identifying tree pests, sap feeders leave very distinctive signs, helping you distinguish them from wood-boring pests or leaf feeders. As described above, each tree pest has its own signs, but there are quite a few common indicators that might help you narrow down your infestation to sap-feeders before trees are fully stressed.

• Honeydew on leaves, branches, vehicles, sidewalks, etc.
• Black mold, often sooty in appearance, on leaves
• Stippling, speckled, or yellowing leaves
• Curling or distorted leaves
• Leaf drop and branch dieback
• White cottony masses in your trees, on branches or leaves
• Foamy masses in your trees, on branches or leaves
• Visible tree pest populations, including aphids, mites, scale, and whiteflies
• Galls, abnormal growths, or blisters on leaves or bark
• Increased ant activity near the tree (they are attracted to the honeydew)
• Yellow or brown needles on a conifer
  

For sap-feeding pests, one of the more recognizable signs is honeydew. As you do your tree health and maintenance checks, keep an eye out for black mold, sticky leaves, and ants, as they will let you know that sap-feeding pests are active and allow you to manage the problem before it becomes severe.

Trees Most at Risk from Sap-Feeding Pests

While sap-feeding pests can be found on just about any tree, certain trees and growing conditions are more likely to invite an opportunity for an attack. For example, stressed trees are more vulnerable to pests and their damage.

Trees Most Commonly At Risk

• Young or newly planted trees- They are still establishing their root systems, and that will challenge any recovery from pests.
• Drought-stressed trees- As discussed, drought is a major challenge for trees, limiting their strength, resilience, and vigor. They’re more susceptible to pest infestations and will also struggle with recovery.
• Urban trees- This is predominantly an issue for trees planted in areas with limited root zones. This might mean compacted or low-nutrient soils, but stress makes trees more vulnerable.
• Trees already weakened- Whether from tree diseases, other pests, or multiple infestations, trees that have experienced chronic stress are vulnerable.
• Specific tree species- Elm, maple, hackberry, pear, spruce, fir, Douglas fir, and pine species. All of these have specific tree pests that prefer those species as hosts.
• Monocultures or low-diversity canopies and landscapes- Monocultures are inherently risky. Any time there’s a large concentration of a single tree species, especially some of the species noted above, it’s easier for pests to establish and spread.

Sap-feeding pests don’t usually kill healthy trees, but as with any tree disease or pest, repeated infestations take a toll. This is especially true of susceptible species or highly stressed trees.

How to Protect Trees from Sap-Feeding Pests

We know how to spot them, a bit how to identify them, but how do you stop them? This is often the most important question. The good news is that, unlike wood-boring beetles, it is possible to manage sap-feeding pests, especially if you catch them early.

For homeowners, landscape managers, property managers, or city foresters, the most important goal and prevention strategy is to maintain tree health. Consider yearly monitoring as part of your tree inventory and keeping a history of tree health so you know where to focus your efforts. Proactive monitoring will allow you to address any problems before they become severe.

Practical Steps to Protect Your Trees

1. Regular watering. Trees with adequate water are better able to withstand pest pressure and recover as needed. This means supplemental winter watering during periods of drought.
2. Remember to mulch. Mulch protects roots. It helps keep soil moist, moderate temperatures, and protects roots from extreme weather.
3. Monitor and inspect trees regularly. Don’t just do a drive-by. Check leaves, new growth, and any twigs for signs of a pest problem. A tree inventory can help you focus resources on the most vulnerable trees in a large urban forest.
4. Pay attention to high-risk species. In that tree inventory, note the species that are susceptible to tree pests and tree diseases, and proactively check them. Elm, hackberry, maple, pear, spruce, and pine are prime targets, especially if planted in clusters or low-diversity areas.
5. Encourage beneficial insects. Many of these sap-feeding pests have natural enemies in the environment. Sometimes the best defense is a good offense. Work to create environments where ladybugs, lacewings, parasitic wasps, and other beneficials can naturally control pest populations.
6. Be mindful of excessive fertilization. While you want to push canopy growth, overly lush trees with lots of tender new growth can attract aphids and other pests. Be mindful of when, where, and how you’re fertilizing trees.
7. Proactively prune at the right time. While tree pruning is part of regular tree maintenance, when there are localized infestations, pruning can be the best call.
8. Watch for stress and other problems. Many pests are opportunists, and if a tree is struggling, even with environmental stress, it may be where you find your next pest outbreak.
9. Act early. When pest populations are just growing, it’s much easier to manage. Monitoring can help you catch things early and avoid not only more expensive interventions but also more effective ones.
   

Healthy trees are the best way to keep your trees safe from disease and from pests, including sap feeders.

What to Do If You Have Sap-Feeding Tree Pests

You’ve read our blog, you’ve looked at your trees, and you suspect you might have a problem. Now what?

In Douglas Adams’ immortal advice, “Don’t Panic.” Sap-feeding pests rarely kill healthy trees. They can, however, over time, create significant stress, especially if trees are already struggling with urban or environmental stressors. Still, there are things you can do and, if you need help with any of these steps, call a certified arborist.

1. Identify the pest. How you manage the problem will depend on the pest. If you’re not sure, call an arborist!

2. Determine the severity of your infestation. A small number of insects may not require any intervention. However, if there’s a lot of honeydew, branch dieback, leaf drop, or general canopy decline, you want to take action, especially if this is a repeat infestation.

3. Work on improving tree health. Healthy trees are more resilient and better at fighting off and recovering from problems. Water, mulch, and reduce urban and environmental stress.

4. Keep an eye on your at-risk trees. Again, severity will determine the course of action: if there’s an increase in honeydew, dieback, canopy decline, or other symptoms, the infestation is worsening, and it’s time to intervene.

5. Contact an arborist if treatment is necessary. If you think the problem is worsening, contact an arborist. Timing is critical for management. When in doubt, reach out!

6. Inspect nearby trees, especially if they’re the same species. Sap-feeding pests, left to their own devices, can spread quickly, especially in monocultures or low-diversity landscapes.

The truth is this: while pests are a problem, they’re usually an indicator of a bigger problem, like drought stress, aging trees, low-diversity, low-quality stock, or trees poorly suited to your location.

At SuperTrees, we start with high-quality stock, and air pruning helps ensure you’re planting trees with strong roots that support resilient growth.

In addition to great trees, we’ve got great people. Our certified arborists can work with you to build a healthier urban forest. We work with everyone from homeowners (at our retail nursery) to landscapers, property and HOA managers, and municipalities (big and small).

We can help with everything from supplemental watering and pest management to tree inventories, canopy diversification, and long-term tree management. In short, we can help you start with the right trees in the right spot and, from there, help manage and monitor their health.

Whether you’re looking to replace older trees at the end of their lifecycles, diversify your canopy, source custom-propagated trees, or diagnose problems, we’re here to help. Reach out to our team today!