Photo: Many times decay in trees is not as obvious as this large cavity in a European Linden (Tilia x europea) and special tools are required for assessment.
The most important equipment for diagnosing plant problems is
perhaps the simplest – a gallon size plastic bag and some hand pruners. With the hand pruners I can cut off an
afflicted branch and store it in the plastic bag until I get back to our lab. Plastic bags are better than paper bags
because they keep in moisture and prevent samples from drying out too
quickly. Whenever I take a sample of a
diseased or infested branch, I always make sure to obtain the symptomatic area,
the healthy area, and the area in-between.
This “transition zone” from unhealthy to healthy tissue is often the
most helpful for making accurate plant diagnoses. If I can’t get my sample to the lab asap, I’ll
store it in the fridge to prevent saprophytic decay fungi from decomposing it. To date, I haven’t put a plant sample in my
salad bowl, but I have to be extra careful when I’m hungry and tired!
Other tools that are important for taking samples are a pole
pruner for cutting limbs that are out of reach, and a hand saw for removing
afflicted branches that are too large for hand pruners. I never go without my camera and always take
lots of pictures to remind me of things later and to include in the diagnostic report. A notepad and pen are essential. I also like to bring some diameter tape for measuring
the girth of trees. I do carry around
glass insect vials, but rarely get the chance to actually capture any offending
insects. A hand lens is useful for magnifying
things in the field, but a microscope back at the lab is essential. I remember once scrutinizing a California
Privet (Ligustrum ovalifolium) shoot
that was displaying symptoms of privet rust mite. I squinted through my contact lenses at the
curled, misshapen leaves, and after not seeing anything, I assumed that the
mites had done their damage and left. Just for kicks, I threw the shoot under the
microscope, and lo and behold! there was an entire microscopic world scrambling
all over the leaves, privet rust mites included! I then promptly wondered what invisible
little buggers were scrambling all over me!Photo: California privet displaying symptoms of infestation by privet rust mite - curled, distorted, stunted, and yellowed new growth.
Other important tools for the tree doctor are a hammer and
chisel for extracting wood from cankers and a pocket knife for looking beneath
thin bark of branches. As for trying to
figure out how decayed a tree is, some highly specialized (and expensive) equipment
has been developed. One technique is to
use a Resistograph®. This microdrill
takes advantage of the fact that decayed wood has lost strength and has a lower
resistance to drill penetration than sound wood. A graph that looks like an EKG is produced,
and is great for impressing tech-oriented people and plant geeks alike. Sounding with a mallet and using an increment
borer or battery –operated drill are some less expensive methods of detecting
decay in living trees. A long rod is a
cheap and easy way of probing into tree cavities to see how large they
are.
In addition to inspecting the leaves, branches, and trunk, it
is absolutely critical to assess the belowground portion of a plant. Frequently, the root cause of a plant problem
is just that – the roots. My most
important tool here is a small, three-pronged hoe that I use to pull away soil
and mulch from where the trunk meets the ground and examine this area known as
the root collar. I check for circling
roots that can girdle the tree or shrub and to see if it is planted too
deeply. An air excavation tool can also be used to remove soil without injuring roots. Another common belowground
problem is soil compaction which means that sufficient water and air are not
getting to the root system. I use a
penetrometer, a long pointed rod with a gauge at one end of it, to give me a
qualitative assessment of soil compaction.
At new houses or recently re-modeled houses, my penetrometer always displays
a red reading, indicating that the soil is too compacted for roots to
grow. A more quantitative assessment of
soil compaction would be to take a bulk density test. I also always bring a soil probe or hand
shovel and bags for taking soil samples to measure nutrient levels and soil pH.
Photo: Soil compaction of this recently completed parking lot is the root cause of poor soil drainage and thinning of these Inkberry Hollies (Ilex glabra).
My other essential tools are the resources I can turn to
when I need further information to make an accurate diagnosis. There are a lot of books out there, but the
ones that I find the most helpful are listed below. Talking with colleagues and getting a second
or third opinion also helps proper diagnosis.
Our local Cooperative Extension office has staff to help both
professional horticulturists and homeowners diagnose plant problems. Call CCE-Suffolk at 631-727-4126 and
CCE-Nassau at 516-292-7990. With the
right tools and a lot of practice and patience, you’ll be a pro at diagnosing
plant problems!
Books to Aid Plant Diagnosis:
• Costello, L.R., E.J. Perry, N.P. Matheny, J.M. Henry, P.M.
Geisel. 2003. Abiotic Disorders of Landscape Plants: A Diagnostic Guide. Oakland, CA, University of California,
Publication 3420.
• Dirr, M.A. 2009. Manual of Woody Landscape Plants: Their
Identification, Ornamental Characteristics, Culture, Propagation and Use, 6th
Edition. Champaign, IL, Stipes Publishing.
• Johnson, W.T. and H.H. Lyon. 1991. Insects That Feed on
Trees and Shrubs, 2nd Edition. Ithaca, NY, Cornell University Press.
• Sinclair, W.A. and H.H. Lyon. 2005. Diseases of Trees and
Shrubs, 2nd Edition. Ithaca, NY, Cornell
University Press.
• Vittum, P.J., M.G. Villani, and H. Tashiro. 1999.
Turfgrass Insects of the United States and Canada. Cornell University, Ithaca,
NY.
