1. Using The Plant Disorder Diagnostic Key
By Paul A. Thomas, and Bodie V. Pennisi Department of Horticulture, College Of Agricultural and Environmental Sciences

2. Using The Plant Diagnostic Key
A diagnostic key is a tool used to differentiate
between many possible, yet similar looking symptoms.
Diagnostic keys are simple to use, and can significantly
speed up the diagnosis process.
However, no key can replace actual diagnostic testing.
Always test to verify assumptions before implementing
any treatments.

3. Using The Diagnostic Key
The diagnostician must
first decide how to describe the problem.
Several descriptive words should be written down prior to reviewing the many choices
provided in the key.

4. Using The Diagnostic Key
Cleared Tissue
Blackening
Dessicated
Wilted
Shiny

5. There are several categories or approaches to choose from,
depending on the extent of the
problem, or the plant parts
that are expressing symptoms
of a disorder.
Problems Involving ENTIRE Crop With or Without Pattern
Problems Involving WHOLE PLANT With Normal Shape Leaves And Stems.
Problems That Appear To Primarily Involving LEAVES, Secondarily Flowers
Problems Involving FLOWERS
Problems Involving ROOT SYSTEMS

6. Under each category, there are several choices to choose from.
Problems That Appear to Primarily Involve LEAVES and to a Lesser Extent, Flowers.
A. LEAF SHAPE ABNORMAL, twisted, or physically damaged stems, internodes normal.
AA . LEAF SHAPE NORMAL, internode length normal, but leaves off-color, cleared or have spots.
AAA LEAF SHAPE NORMAL, however, stem internodes are very long or very short.
AAAA Leaf shape normal, stem internodes normal. Stems severed / broken at soil line.
AAAAA. Leaf puckered or with expanded cells, galls, thickening of epidermis.
The three sub-choices are marked A, AA , and AAA as they are all related
to the category, however, they denote different possibilities from which we
may decide on the best fit to our described symptoms. Underneath “AA” are the next
level of choices.

7. These additional choices, marked B, and BB, allow us to further refine
our choices, and focus in on the problem.
AA . LEAF SHAPE NORMAL, internode length normal, but leaves off-color, cleared or
have spots.
B Leaf color in a small portion of the leaf is abnormal.
BB. Leaf color over a majority of the leaf surface is abnormal.

8. Next, we note the best fit sub-category.
AA . Leaves appear normal shape, discrete parts of plant are off-color, cleared or wilted. BB. Leaf color over a majority of the leaf surface is abnormal. C Entire plant pale green, poor growth with some marginal Fungicides, Herbicides yellow at the margins, few blooms, small flowers. Nutritional Deficiencies (Check roots for damage.) CC Entire plant or most leaves yellow, with central portions of the leaf strongly affected. Tissue dies within 3 to 10 days. Herbicides / Sunscald CCC. Entire plant or most leaves turn dark black-green, semi Surfactant / Soaps transparent to light, wilt, then die within 48 hours. Chlorine, Petroleum fuels)

9. best fit possibilities That we should look into.
Next, we note the
best fit possibilities
That we should look into.
AA . Leaves appear normal shape, discrete parts of plant are off-color, cleared or wilted BB. Leaf color over a majority of the leaf surface is abnormal. C Entire plant pale green, poor growth with some marginal Fungicides, Herbicides yellow at the margins, few blooms, small flowers. Nutritional Deficiencies (Check roots for damage.) CC Entire plant or most leaves yellow, with central portions of the leaf strongly affected. Tissue dies within 3 to 10 days. Herbicides / Sunscald CCC. Entire plant or most leaves turn dark black-green, semi Surfactant / Soaps transparent to light, wilt, then die within 48 hours. Chlorine, Petroleum fuels)

10. Occasionally, the diagnostician is directed to check additional
areas as many plant problems
have more than one cause.
BB. Leaf color over a majority of the leaf surface is abnormal. C Entire plant pale green, poor growth with some marginal Fungicides, Herbicides yellow at the margins, few blooms, small flowers. Nutritional Deficiencies (Also: Check roots for damage.) CC Entire plant or most leaves yellow, with central portions of the leaf affected. often dies within 3 to 10 days. Herbicides / Sunscald CCC. Entire plant or many leaves turn dark black-green, semi Surfactant / Soaps, transparent to light, then die within 48 hours. Oils, Chlorine, Petroleum