The age-old question of, “Why is that tree looking so sickly?” is one that is at the crux of integrated pest management, plant health care, diagnosis, monitoring and scouting. Another way to describe this time-honored query is more along the lines of what most customers think, which is, “What’s wrong and how do we fix it?” In a landscape with healthy soil, abundant light and appropriate rainfall, problems tend to be few and far between. Sure, living organisms can cause injury; we see it every day. But arborists would be doing their clients a huge disservice if insects and diseases were the only influencers that were considered as causes. Nonliving, or abiotic factors, must be considered as well.
Typical chlorosis symptoms.
Eyes wide open
Experienced tree service providers know that the list of possible causes of a particular perceived illness is usually long and sometimes uncertain. It helps to add clarity by working through a step-by-step process that contains several components:
Identification of the tree species — the starting point for all problem causes.
Gathering of relevant historical information about the site and surroundings, both in recent times and over the past five to seven years. This could include utility line trenching, soil moved for construction, cold winters, hot summers, neighbor’s pool parties, lawn service applications, etc.
Consideration of the three basic categories of causal agents: (generally) diseases, insects and nonliving influences.
Review of previous maladies of/on the tree: what the tree has been treated for by your company or other companies.
Matching the general appearance of the tree with the general symptoms of previous tree problems: spots on leaves, holes in trunk, thin crown.
Investigating known influences of the tree in question by species, such as spruce and spruce spider mites or poplar and cytospora canker; comparing the appearance of the leaves, bark or branches to the photos of documented resource guides.
Gaining outside information and assistance from university extension personnel and fellow arborists.
When the above series of steps is utilized, the list of possibilities usually shrinks from many to few. A sometimes known, sometimes unknown “X-factor,” or little-known secret, is that well over half of the primary causes of tree decline or symptom expression are due to nonliving or abiotic influences.
Diagnosing tree problems can be difficult, especially in one-off situations, such as when a new customer calls out of the blue and asks for the diagnosis of a sick-looking tree, and the only information provided is that, “it just started looking that way last week.” Such a scenario usually brings the internal response from veteran arborists, “Oh, yeah, and if that’s true, pigs should be flying right about now.”
Instead of looking at a tree for the first time, it’s much easier to find success with causal determination if a scouting and monitoring protocol has been in place. Scouting, sometimes referred to as inspection, is usually a one-time endeavor. It’s used for both investigation of a poor-looking tree or proactively in an effort to investigate the entire property, much like an air conditioner inspection at the beginning of summer or an annual doctor visit to detect early signs of heart disease.
Utility line trenching and repair is always a concern.
While these types of inspection are helpful, it’s wise to go one step further, to scout on a regular basis through the season – to monitor. Weekly, biweekly, monthly or seasonal scouting pays big dividends through being able to spot a disease, insect or abiotic causal agent. Spending time in a landscape gives the inspector an important feel for the issues at hand and the changes that are occurring over time. As well, it’s a great bottom line profit center for tree service companies, as monitoring is a legitimate arboricultural service that utilizes the technicians’ training, experience and education for the good of the customer.
After each scouting, a quick but pithy report on the trees in the landscape should be generated, noting current age, condition and location of concerns for each species. This type of tree care that involves frequent inspections puts the inspector way ahead of the game, allowing for the gathering of large amounts of information about the site, the neighboring sites, the planting process and other contributing factors.
Common abiotic problems
When a tree fails to express the symptoms of disease, insect, nematode or animal injury, other influencing factors are responsible. Some of the more common ones are:
Moisture:Each tree species has an ideal moisture level for its root system. Others tolerate a wide variety of soil moisture conditions. When trees experience too little for a long period, it is generally referred to as drought. At the other end of the spectrum, when too much water is received, the spaces between soil particles fill up with excessive water, replacing the oxygen. If this occurs for a long period of time, roots tend to rot, soften and fail to function well. Determining if moisture is a causal agent can be difficult, as the excess or lack is present under the soil surface, out of sight of the tree scout. Using a soil probe, such as a piece of rebar or long screwdriver, can be helpful in taking a snapshot of current moisture conditions. Checking the soil moisture level should be a routine part of each scouting inspection.
Nutrients: Like moisture levels, it’s possible for the soil to provide too much or too little. Nutrient deficiencies often show up on high or low pH and heavy clay or sandy soils, due to the lack of availability and capacity to retain various elements. A condition known as chlorosis can refer to the l