By Mitch Lippencott
ISA Certified Arborist® OH-6715A
September 11, 2025
We're not so different, humans and trees. We're both born with tools to keep ourselves upright and thriving. We are impacted by many of the same stressors and overcome them in similar ways. But because the majority of you reading this are people, not plants, human responses to stress may seem obvious, while tree responses are a mystery.
Let's close this gap in understanding by focusing on common tree stressors, what they look like, and how to manage them in human terms. To maintain a light degree of stress, I'll even include a quiz at the end (not a joke - read closely!).
2 diagrams will be critical to keep in mind as you read - the disease triangle and the integrated pest management pyramid.
The disease triangle shows disease is only possible when a pathogen, a susceptible host, and a favorable environment are all present. If any of those is lacking, disease cannot happen.
The integrated pest management control pyramid shows the most responsible and long-term solution to pest prevention is proper culture. This means native trees planted in appropriate locations, soils rich in microorganisms, and gardens promoting pollinators and predators. In this model, chemicals are the least-used option.
Our team member Scott making a tree pruning cut!
Pruning
Luckily, the days of bloodletting as medicine are long gone. Today, we would never cut our calf to cure influenza or apply leaches to arthritic joints. Yet, that's still how we treat our trees. Aside from a few specific fungal situations and removing co-dominant leads from young trees, pruning stressed trees makes the situation worse. As with the human body, wounds should be kept as minimal and as small as possible.
Nutrient Deficiency/Toxicity
When we're hungry, we eat. Trees do, too -- an unobstructed root system and full canopy can provide a tree all it needs to succeed.
We know what starvation looks like in humans and understand the problems caused by lack of specific nutrients (decreased immune system from lack of vitamin C, fatigue and pale skin from iron deficiency, etc.), but we don't think of tree nutrition in the same way.
An example of chlorosis in a tree, likely due to an iron or manganese deficiency
In trees, nutrient deficiencies can be indicated by small, misshapen, and/or discolored leaves. A hungry tree may look wilted, or droop. It may begin to produce branches on the trunk because it no longer has the energy to pump water to existing leaves. Like us, trees can be otherwise healthy, but suffer because of a single lacking nutrient (yellow leaves due to manganese deficiency, for example).
While organic fertilizers like the ones we apply at Russell Tree Experts are nearly impossible to over-apply, excess petroleum-based fertilizers can be as deadly to trees as excess donuts to humans. Over-fertilized trees may develop bark cracks or poor structure from rapid expansion. More critically, they may outpace the natural microorganisms in the air and soil around them, leaving them reliant on humans to provide necessary food.
The point of all this is trees and humans both require a diverse diet, and are typically able to achieve it with natural feeding. Supplementation to fulfill those dietary needs is only needed if there's a specific deficiency. Fertilizing a tree stressed from drought is no more helpful than giving a sandwich to a man who's been burned.
An example of how a leaf can curl and droop due to drought stress
Heat/Drought Stress
We all know the misery of standing in the sun on a hot day. Unlike us, though, trees can't sweat or jump in a pool. Instead, they close their stomata (the pores on their leaves) to help preserve water, and shed leaves to decrease the surface area the sun can dry out.
Heat and drought stressed trees often look wilted, with dry, brown, curled leaves falling in summer. The takeaway? If you're in heat, a dose a cough syrup won't make you less hot, but drinking plenty of water will allow you to sweat and cool naturally. Similarly, it's common for trees to look unhealthy in summer, but the only solutions are cooler temperatures and more water - pruning or fertilizer only make things worse.
Pathogens
Like most illnesses in humans, most tree infections are short-lived and controlled by the tree itself. We rely on beneficial fungi, bacteria, and viruses in our guts. But trees create symbiotic (helpful for both) relationships with microorganisms in the air, water, and soil. If a disease gets past a tree's microorganism army, the tree can block its own vascular system to isolate the pathogen in place.
A Colorado blue spruce tree (Picea pungens) affected by rhizosphaera needle cast.
Also like us, healthy living prevents tree disease and shortens recovery. This means mulching the root zone, watering during drought, and yes, even applying fertilizer and pruning out diseased branches.
The signs and symptoms of tree pathogens vary broadly. Cherry black knot and cedar-hawthorn rust develop fruiting bodies on branch tips and fruits. Crabapple scab causes premature leaf drop, while rhizosphaera needlecast causes permanent needle loss in spruces. All are host-specific - they cannot pass from one type of tree to another.
In both humans and plants, some pathogens require additional action. As with drugs in humans, fungicides should only be used on plants in specifics dosages and intervals, and should only be used as needed to prevent resistance.
QUIZ TIME!
We’ve made it to the end of this article, which means quiz time! Time to put your newfound knowledge to the test! Tip: It is an open-note quiz. If you take and submit the quiz with a passing grade (3 or more correct answers), you’ll be entered in to win a free RTE gift bag. Shipping and handling free for those in the 48 contiguous United States. Winner will be drawn on Thursday, September 18th. You may retake the quiz if you only scored 1 or 2 correct answers in your first attempt! As always, thank you for taking the time to read our articles. For a free tree work quote by 1 of our 25+ ISA Certified Arborists®, call us at (614) 895-7000 or visit RussellTreeExperts.com/Quote!
Take the quiz HERE.
ADDITIONAL ARBOR ED™ ARTICLES!
Mitch Lippencott I Regional Manager, Russell Tree Experts
Mitchell Lippencott joined Russell Tree Experts in 2020 and has been in the green industry for over 20+ years with a diverse background ranging from working for a landscape design company, a retail garden center, and two municipalities! Mitch is an alum from The Ohio State University, a licensed pesticide applicator, a qualified tree risk assessor, and an ISA Certified Arborist®. Outside of work, he enjoys traveling, cooking, and gardening!