Diagnostic Tools: From the Simple to the Sophisticated

One of the most important jobs we perform as arborists is diagnosing tree problems. Knowing what is wrong with a plant or tree is obviously key to its proper health management. If you would like to do more than remove trees for a living, consider expanding your education of proper tree care. Inspection and diagnosis, as well as treatment of tree problems can keep your clients pleased and their trees providing you income for many years to come.

When diagnosing plant problems, accurate observations are critical. A thorough understanding of plant biology is your most important asset. Since plant scientists agree that 90% of plant problems begin with the soil or are soil-related, a complete knowledge of soil characteristics and properties is also very valuable. Several different tools are helpful in performing your diagnosis. Some of them you already have, while others could be added to fill out your diagnostic tool kit. Let's see how well equipped you are.

Basic Tools

Every arborist probably has a pocket knife. A sturdy knife with a locking blade is best. I learned this by sacrificing some blood to a yellow poplar several years ago while excavating some root collar borer galleries. A sharp knife can be useful to slice a twig to check its color, look for symptoms of Verticillium wilt or Dutch elm disease, or remove loose bark to find a brood of earwigs going about their business. I carry a Leatherman Wave pocket tool that is very versatile.

The next most important tool is probably a spade or small shovel. This can be used to expose the trunk base and root flare (often buried too deep) and to examine roots and basic soil properties, such as moisture, compaction, and texture. To get a better picture of the soil your tree is growing in you can use a soil probe. Provided you can get it in the ground, this tool extracts a core of soil and shows you the soil layers or horizons. You can also use it to take small root samples, soil samples for later analysis, and discover soil mottling or anaerobic soil conditions. A lot of the soil samples I take leave me wondering how the tree survived as long as it did.

To inspect the tree above ground some basic pruning gear is needed. Good pruning shears (bypass style) let you collect samples. It is not cool to break a branch or twig off in front of a client! A fine-toothed pruning saw is used to take larger samples. A pole pruner may be needed to collect samples too high to reach or to remove the occasional fall webworm web or suspicious looking foliage.

A good pair of tools for looking under bark for insects or disease is a hammer and chisel. You can also use either one to sound for decayed or dead wood. The chisel is good for minor excavations when your shovel is too far away.

A hand lens (ten to sixteen power) is a necessity for detecting and identifying mites and scale crawlers. Other visual aids that are occasionally helpful are binoculars and a bioscope or dissecting microscope.

If you're like me, your samples can accumulate before you get them to your office or a diagnostic lab. Hopefully they don't dry out and crumble to nothing in the back of your truck. Plastic bags, a few vials, a marking pen and labels help to keep your samples fresh and accurately identified. I would hate to call up a client and tell them their pin oak has bacterial leaf scorch when their prize tree is a sugar maple.

These are the very basic tools for diagnosis. I have found the following group of more technical tools just as essential to me. Even if you are not a consulting arborist, consider investing in these aids to your diagnostic technique. They may pay for themselves many times over.

Technical Improvements

A soil penetrometer is a useful tool to locate soil hardpans and construction layers. A pressure gauge gives you a rough measure of the amount of soil compaction. It is a very good tool to show the difference between soils on a construction site and in an undisturbed site. It may solve the mystery of why one tree in a yard is thriving while another fails. They range from fairly simple units with only a pressure gauge to more complex units with built-in GPS units and computer database programs.

Soil pH meters measure the acidity or alkalinity of the soil. Trees differ in their optimal pH range, so measuring pH is an integral part of tree health care. There is a wide variety of pH meters available. Some are much easier to use than others, although you tend to trade accuracy for ease of use.

An increment borer can be used to determine a tree's growth rate by examining the annual rings for the last several years. This method is rather invasive and works best with ring-porous trees. There are newer methods that are less harmful (see resistograph) but this tool gives you more information than measuring twig elongation.

A diameter measuring tape can allow you to determine both the circumference and diameter of a tree, plus you can measure the twig elongation from each previous year to give you a good picture of tree health.

While the favorite tool for decay detection was once an ice pick, current devices can provide the arborist with more information. For instance, a battery-powered drill with a twelve inch by 1/8 inch diameter bit will help you discover how much sound wood you have before you hit decay. Another popular tool is the IML resistograph, which measures the resistance of the wood to its drill bit and graphs it on a sheet of pressure sensitive paper. Some models can also download the results to your computer. The resistograph can show you the annual growth rings as well as the thickness of sound wood and the presence of decay.

A very valuable tool that is becoming more popular with arborists is the Supersonic Air Knife. Its primary diagnostic use is the quick removal of soil from around the base of the tree without disturbing its roots. While a shovel can be more economical to use on one tree, supersonic air lets you uncover many root systems in a short amount of time with much less effort. Since safety standards recommend that every tree you diagnose should have a root collar examination, one of these tools will pay for itself quickly. Besides exposing the root collar and locating girdling roots, they can also be used for vertical mulching and radial trenching. These two time-proven methods of soil remediaton benefit tree root growth and the air tool performs them twice as fast with minimal root damage. My favorite of these tools is the Air Knife due to its light weight, ease of use and lower price.

Finally, as I give presentations on tree care across the country I have found my camera to be a valuable communication tool. My new digital camera has been great for displaying pictures for my consulting reports and hopefully soon my website.

Of course, the information tools provide is only the first part of making a diagnosis and treating a problem. If you would like to improve your diagnostic and treatment skills consider attending a regional or national conference of the International Society of Arboriculture. ISA focuses on research and education. I have attended every annual conference since my first one in 1979 and have always come away with valuable information that improves my job performance.