As a part of an overall tree health care plan, the application of fungicides can play an important role. The key to utilizing them effectively is in the details: the how, when and frequency. How they are used begins with establishing a need. Trees that are struggling due to fungal infections should be evaluated for how well they would fit into an application regime.

Every disease has a window of vulnerability, so application timing is crucial. Treatments made outside of this time frame may be ineffective. Application frequency is often dictated not only by the specifics of the disease, but also the severity. Within the window, a heavily infected tree might benefit from several fungicide applications, whereas a tree that’s affected to a lesser degree may only need one to control the disease.

Regular inspection is of value in the overall multiyear scheme of treatment.


Start with evaluation

All projects have a starting point, either by default or by plan. With fungicide programs, it’s wise to start with evaluation, which is a multifaceted endeavor. A thorough consideration of each factor will determine the best approach.

Condition – Consider the overall health of the tree(s) in question. Identify defects such as heartwood decay, cracks in bark and sapwood, codominant leaders, previous topping actions, stem girdling roots, leaning, deep planting and root plate degradation. If several of these are present in the tree, treatment may not be worthwhile. On the other hand, specimens with just one defect can be assets to the landscape and thus are good candidates for inclusion in a fungicide program.

The condition of a specimen should be noted in evaluation and prioritization.


Growing area characteristics – Locations on a property that are not conducive to healthy root growth and/or room for shoot growth are a limiting factor. Compacted soils, constricted space, impervious covers and proximity to utilities are just some of the factors that can affect a tree’s growing area.

Target – A target is defined as an item of importance that could be damaged by the falling of a tree or limbs. People and property (houses, cars, decks, fences) are the most common targets. In terms of fungicide programs, trees that are in good condition but have valuable targets within range are usually worthy of inclusion.

Trees with Diplodia tip blight infections may not need to be treated year in and year out. Regular inspection is the key.


Value to the property owner – Certain trees are more important than others, at least in relation to function and emotional attachment. Well-placed trees that provide shade, wind protection and landscape structure are generally of high value. Some trees have emotional value, such as those planted to mark a significant event in the property owner’s life.

Species – Some arborists may put a greater value on ginkgo, walnut, native pines, persimmon, tulip tree and yellow buckeye over species such as silver or bigleaf maple, tree of heaven and mulberry. And some tree species are overplanted. If a property contains a dozen of one species, losing a couple due to other factors and beginning a planting program to increase the diversity of the landscape makes good sense.

History – A tree’s treatment history should be taken into consideration. If a tree has been injected for a particular disease 10 times, the damage done by the treatment process has likely weakened the tree and compromised the vascular system to the point where it has a shorter life expectancy than previously untreated trees.

Taking into consideration potential targets — what a tree or its limbs could fall on — is an important part of the evaluation and prioritization process.

Prioritize trees

If funds for a fungicide program are limited, prioritize. Using the evaluation criteria, lay out several treatment plans for your clients. It’s important to discuss the evaluation of each specimen with your clients, especially for trees they have an emotional attachment to, and to help you discover the tree’s history.

The condition of a specimen should be noted in evaluation and prioritization.

Regular inspection

The most important part of a fungicide program is regular inspection. You can give away the inspection plan if you want, but remember, people tend to value what they pay for. If you’re a certified arborist, you’ve invested in training and also have attained experience and diagnostic skills, so charging a reasonable fee for a routine inspection is appropriate. Inspections are good for the trees and the rest of the environment, good for the customer and good for your business.

Not all trees on a given property provide the same value, so prioritization is a must when devising a fungicide program.

Indicate an end point

Some diseases are ongoing, ever-present and never go away. Others have a definite beginning and end, especially when a dry year or two comes after a series of wet years. Diplodia tip blight is a good case in point. After inspection, the presence of the disease is noted and a high-priority tree is treated for several years with good results. If the spring is drier than normal, backing off on applications for a couple of years fits well with an integrated pest management approach.

In these situations, passing this information on to the client underscores the inherent value of your skill set, and helps to dispel the notion that tree service companies are out to make all the cash they can from an unknowing public. When a tree disease is under control, the true value of an inspection-based fungicide program is made clear.

Communicate clearly

Be sure to communicate clearly with the property owner about every inspection and fungicide application. As a university faculty member, I hear from your clients who wonder if they need to continue treatments. In response, I question them about the communication with their tree service provider, usually starting with: “What has been used and for what purpose?”

Trees in need of treatment for other maladies may not be good candidates for fungicide programs.

Some clients respond with a clear sense of what has been done and why, they’re usually just wondering if they need to continue with applications or if there’s a new and better product that could be utilized. On the other end of the spectrum, some clients claim that there has been no communication or that a door hanger was left with an unintelligible message scribbled on it. An important part of a quality fungicide program communicates the status of each tree on the property and whether there’s a need for any treatments.