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

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.

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.

Using The Diagnostic Key Cleared Tissue Blackening Dessicated Wilted Shiny

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

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.

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.

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)

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)

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