As professionals who are installing or maintaining landscapes, you understand the cost and value of the work you do. Yet, often within a few years, new landscapes become overgrown, plants die—seemingly without reason—and the client begins to question your ability. This is even more complicated when extremes in weather begin to impact the large structural trees on a property.

It is often said that Plant Health Care (PHC) is the most rewarding and profitable aspect of arboriculture and horticulture. Working as a physician rather than a mortician, you develop a lasting relationship with your client. You create a business that rewards you for years to come.

Yet, it seems that the fear and uncertainty of how to make a good diagnosis, and how best to treat a plant, keeps many an aspiring contractor from ever venturing into PHC. Trees appear unmovable, their perpetual presence presents even greater mysteries when they fare poorly, so diagnosing the problem can seem overwhelming.

Problems can include insects, diseases, site conditions, soil quality, moisture and errors in planting, all of which interact and result in plant decline. Approaching your diagnosis systematically will narrow the possible causes of plant deterioration. It will also help you to uncover the real cause of decline. The challenge is to learn how to diagnose, which will narrow the scope of possible causes, and deliver solutions that will save your client’s trees and shrubs without the benefit of many years of field experience.

Unless your company maintains properties, your initial visit to the grounds will be a 911 call because a tree doesn’t look well (or is dead). The natural inclination will be for you to examine that plant, and to make a rapid diagnosis of the problem. I urge you to avoid this common trap, as any suspected insect or disease-pest damage can be exacerbated by the conditions under which that plant lives. So I recommend reviewing the common ‘big factors’ impacting plants, before digging deeper into possible causes for plant decline.

The Macro Picture:

Plant Species: One of the most basic and often overlooked first steps is to know the identity of the plants that are having the problem. Knowing the species will narrow down your choice of causative agents by eliminating both site factors and pests or diseases which don’t generally impact that species.

Extent of Problem: Is the problem confined to a single tree/shrub on the property, multiple plants or several species? Is similar decline visible on adjacent properties, or on other properties you’ve visited nearby? Determining this can separate unique site conditions from problems facing the entire community. Site issues may include excessive or too little water, change in grade, planting depth, herbicide injury, shade or sun extremes, temperature extremes and more.

Patterns: Nature doesn’t exhibit problems in clear and concise geometric patterns. Is a cluster of dissimilar trees affected, suggesting construction damage or herbicide injury? Is it an entire planting bed, or just a single species? How are plants in the front yard versus the backyard? Was there a recent change in the property (consult with the client) and is it still visible to you?

Look for patterns that don’t fit the random process of nature, and begin to narrow down key possibilities for that property. Check other trees, shrubs and turf in affected areas, as many conditions will touch these plants before the trees exhibit decline.

Speed of Decline: How long has the tree been declining? Trees reveal useful information if you look for the evidence. This can include damage to the bark, crushing of roots, lightning strikes or slowing intermodal growth.

Each year, following the flush of spring growth, most trees set what is called an end bud, covered with a series of scales. When the tree breaks dormancy, in the spring, these scales fall off but leave ‘bud scars’ (a set of lines perpendicular to the direction of growth).

History: Where possible, it helps to know the history of the property and the area. Were there significant floods in the last several years (like in the Carolinas or Texas), or extreme droughts, hurricanes or tornadoes? These macro issues can affect trees by killing roots through salt contamination, anaerobic conditions, wind damage, moisture stress, etc. Asking your client may help fill in the gaps in your knowledge.

The Micro Picture:

Once you’ve initiated the steps outlined briefly above, summarize what you know thus far. What types of trees have been affected (similar or different tree species)? Does the problem seem to exist only on this property, or have you seen it on others in this neighborhood or in your market area? This may be enough information to point you towards a specific planting-site problem, or a plant pest issue, along with a proposed remedy (if any exists).

So what are the key micro issues that can affect trees on a given property? These can be summarized as:

Excessive moisture or drought: Lack of or excessive water will reduce tree vigor, leaving trees more susceptible to insect and disease attack. Water issues can kill feeder roots, reducing success in extracting water or nutrients from the soil.

Lack of soil oxygen is a leading cause of plant death, especially in heavier clay soils. A good soil probe is a necessary tool to check for anaerobic (sulfurous smell) conditions in the soil, indicative of root death as the cause of plant decline.

Chemical Injury: Herbicides can impact trees far from their intended target, as their roots travel great distances. Use of non-selective root-uptake herbicides, which are applied to control weeds, can kill plants growing nearby, but the symptoms can take a year or more to become evident.

Excessive fertilizer may burn roots by extracting water from them (osmosis), while leaves may be injured by sprays applied in hot and humid conditions. Some herbicides cause obvious twisting or curling of leaves, while others may cause leaf yellowing, browning, or leaf drop.

Mechanical Injuries: Crushed roots from construction, trunk damage by mowers, heavy equipment, and pruning that is not done to acceptable standards can all be causes for tree decline.

Winter Injury: Ice, excessive cold without snow cover, high, desiccating winds, and snow load can cause damage that takes years to repair, and may predispose trees to additional pest or disease pressure. Evidence of this damage should be noted in the early spring, as continued decline can extend beyond leafing out.

Mulch Volcanos: The propensity to cover trunks with up to a foot of mulch has reduced mower and string trimmer injury; however, it has created numerous other serious tree issues, including rooting in the mulch and bark diseases. This is usually a major culprit of plant decline. No more than three inches of mulch should be added to a tree, and only after the existing mulch decomposes.

Plant Location: Many flowering or ornamental trees are naturally understory trees, preferring to grow in shadier locations; they are planted in full sun so clients can enjoy them! The result is poor performance, slow growth and extreme susceptibility to pests.

A few examples include: White birch, dogwoods and redbuds. We also seem to ignore moisture requirements and place moisture-loving plants in dry spots, while plants needing good drainage are planted in poor drainage locations. The adage, “Right tree, right location,” has never been more true.

Finally, we come to diseases, insects and nutritional deficiencies.

These are the issues most PHC workers tend to focus on. While they represent only thirty to forty percent of the causes of plant problems, they generate the majority of the income.

Nutritional deficiencies: These are difficult to detect in less severely alkaline sites, but may result in poor growth, off-color plants (versus the norm) and lower resistance to pest pressure.

Planted trees are frequently ill-suited for alkaline soil areas, and their associated mycorrhizae can’t function properly. We often see maples, oaks, camphor and birch with chlorotic yellow and browning leaves, stunted growth and poor site performance as the result.

Insect & Disease Pests: The thing that most frightens less experienced PHC workers is the myriad of pests that can attack trees. Recall that knowing a tree species will narrow your possibilities, because few pests actually kill trees, and many pests are specific to the few trees they attack.

Examine the crown (soil interface) of the tree, and examine for trunk flair. Check the bark, saw dust, sap or holes caused by entering or existing insects. Look for obvious fungal growths such as conks, or large fruiting bodies. Next, evaluate the lower branches for galls, chewing or damage. Finally, examine leaves to see if they are chewed or laced, or if there is honeydew.

Are there any specific discolorations or sooty mold on the leaves? Are they off-color, missing entirely, larger, smaller, or about the same size as healthy trees of the same species? This examination process allows you to then match tree species to their typical pests, and to then offer effective solutions.

Signs of the Pest: Sometimes you’ll get lucky and find the adult or larval stage of the pest or even their pupal cases, or eggs. This makes your identification easier, even if you can’t identify this pest by its life stage initially. Smartphones are all equipped to take great pictures, and pests can be confirmed at sites like and others. Invasive pests that the USDA is most concerned about, such as the Emerald Ash Borer, can be found at

Summary: If you view a landscape in its entirety, rather than as a number of discrete plants, patterns and challenges become more obvious. I have found that a more deliberate, strategic, and encompassing review of the property is helpful in narrowing the issues. This assures that you don’t single out a nuisance pest, assuming that it’s responsible for the plant’s decline, when the problem is endemic to the site.

In addition to identifying solutions to control a pest, disease or solve a nutrient deficiency, it is incumbent upon us as stewards of the environment to choose the most environmentally-sound, effective solutions for plant health care issues. This means using the smallest treatment doses possible, to have the least environmental impact.

While giving and receiving training is often a difficult task in a busy horticultural or full-service landscape business, the steps outlined above can help you to unravel the puzzle that you may be presented with when you step onto a property, and even to catch a problem before plants die.

EDITOR’S NOTE: Rob Gorden is the director of urban forestry and business development at Arborjet. He specializes in the development of trunk injection technology and solutions for many serious invasive pest problems nationwide, as well as the creation of organic solutions for tree, shrub and horticultural market sectors. He may be contacted at or