Tree Health: Fighting Fungus

The history of the site is telling; imagine inspecting this tree 10 years in the future and not knowing that the roots were cut early on in the tree’s life.
Photos by John C. Fech, UNL, unless otherwise noted.


Fighting Fungus … a daunting magazine article title and overall endeavor indeed. However, it’s a battle worth waging, regardless of the difficulty factor. Though a bit on the trite side, the phrase attributed to Theodore Roosevelt, “Nothing in the world is worth having or worth doing unless it means effort, pain, difficulty,” is often shortened and modified to “nothing worth having is easy” and certainly applies in this case.

Though it’s sometimes a difficult task, the challenge of keeping trees healthy and fungus-free is best accomplished through a multifaceted approach. Identification, monitoring, evaluation of methodologies, preventative measures and conducive growing conditions are some of the more important considerations.

Regular inspection

Whether you call it monitoring, scouting or inspection, a regular close-up look at trees on a customer’s property is a tried and true part of integrated pest management and integral to fighting fungus. If the goal is to keep fungi at bay, you need to know when and where they are attacking, or at least present. If you don’t look, there is no real way to know.

So, what is “regular?” In terms of tree inspection, regular means frequent and thorough. Since many fungi that cause problems for trees are active in the spring, regular inspection should be more frequent in the spring than in the summer or fall. As a result, symptoms are noticed sooner and there is more time left in the year to treat. When maladies are noted in the fall, the action is more a matter of notation and recommendation for follow-up applications in spring, especially if the treatment threshold has been surpassed.

The often underutilized part of inspection is profit. In short, do it, do it often and make money from it. When one considers the investment of time, training and effort that a qualified tree worker puts into their career, it needs to pay off in one way or another. If certification through the International Society of Arboriculture (ISA) or a state arborists association has been achieved, the knowledge, skill and experience must be factored into the equation. After all, the ISA doesn’t hand out certification to just anyone.

A good way to be sure that inspections are an integral part of the income stream is to explain to customers that inspections are just as important as spray applications. Depending on where your customers live, it may be wise to equate monitoring for insects with a fall furnace checkup or a spring air conditioning service. No one wants to suffer through a cold winter or hot summer without relief. If the temperature outside is the same as it is inside in summer or winter, then the equipment is broken or it’s an anomaly.

In terms of the number of site inspections, it’s dependent on the disease susceptibility of the species on the property and the localized conditions. For example, if a given customer has a ginkgo, a red oak and an Osage orange tree, they would need fewer inspections per season than one with a crabapple, an Austrian pine and a cottonwood; the former are generally considered to be disease-resistant trees, while the latter are more likely to develop fungal problems from time to time. Likewise, since many fungal pathogens require high moisture content on foliage to develop and infect a tree, properties with low air flow across leaves are more likely to be conducive to ongoing problems than ones with good air circulation. These factors should be made clear to a customer when pitching the service of regular inspections.


Determination in the endeavor of fighting fungus on landscape trees is important from two perspectives: determination in the sense of persistence, and determination in the sense of identification.

First, identification. Even after years and years of diagnosing unknown maladies, determining which exact causal agent is responsible for the symptoms that have been produced on a tree can be challenging. How can you fight something if you don’t know what it is?

Determination, or diagnosis, can start in many ways. My preference is to begin with known maladies of the tree species. For example, crabapple has a long history of susceptibility to powdery mildew, apple scab, fire blight and cedar apple rust. If the customer has a crabapple, your first step is to get to know the symptoms of these diseases and compare the current presentation of the leaves, stems and trunk to those established characteristics.

A good second step is to consider the micro and macroclimates of the property. When I was starting out in horticulture and arboriculture, a wise arborist did me the favor of teaching me how to walk the entire property, as well as the adjacent lots and neighboring areas, looking for clues as to what might be influencing the current situation. He taught me to carry a clipboard and use it to make notes on wind patterns, sunlight penetration, coverage of the root system with impervious surfaces, and competition from other species.

Knowing the history of a site is useful as well. Interviewing the owner and possibly the neighbors about recent herbicide applications to the turf, soil modifications, utility work, and the performance of other woody species can be helpful in determining what’s causing the tree’s health to decline.

Leaf scorch on dogwood underscores the need for regular inspection.

It’s not all about fungus. To eliminate possible nonliving/abiotic organisms as causal agents, items important to learn to distinguish between fungus and non-fungus. In fact, one of the little known secrets of determination is that less than half of the causes of tree problems are related to fungal or bacterial organisms. Overwatering, lack of separation of turf and trees, planting errors and mower blight are just some of the non-fungal inputs that can cause trees to suffer.

Next, persistence. Because it’s not easy, sometimes it just takes time to get it right. After a good first look, take the time to check the resources on your bookshelf. Go online and type in phrases such as “maple diseases in the Northwest” or “ash problems” into Google Images or Yahoo Image Search. You’ll be amazed at what you find. Talk to other service technicians in your company and university extension faculty about possible causes.

As you move through the process, stay in communication with the client. They’ll appreciate your thoroughness and your persistence.


Whether you’re delivering a joke at a dinner party or buying an airline ticket, timing is undeniably crucial. The same is true when fighting fungus on broadleaf and evergreen trees. Too early or too late with inspection, determination or treatment is not going to cut it. Correct timing is important for each of these factors. The timing needs to be right for inspection in order to be ahead of the curve, to read and react in relation to the clues given by the plant. The determination of the causal agent needs to be on track, and needs to be done in advance of the treatment application if one is necessary. Treatments applied before or after the vulnerable stage of the fungus or plant part are simply not effective and should be viewed as a disservice to the customer.

Each is important on its own, but the correct timing of all three needs to occur in order to conquer fungus. With time, training and experience, as well as due consideration of the key elements presented in this article – regular inspection, species vulnerability and characteristics, the history of the site, differentiation between abiotic and biotic causes, persistence and timing – the fight can be won.

John C. Fech is an ISA Certified Arborist, PNW ISA Certified Tree Risk Assessor at the University of Nebraska-Lincoln and a frequent contributor.

(Article courtesy of Tree Services Magazine: