Diagnosis of Plant and Turf Disorders: Abiotic and Nutritional Problems
Domain 2 tests diagnosis: separating insect damage, infectious disease, abiotic injury, and nutrient deficiency. Florida's sandy, often high-pH soils and intense summer weather create predictable problems that look like pests or disease. The exam rewards a process - pattern on the plant, pattern in the landscape, history, and a soil or plant test.
Use plant patterns
Mobile nutrients (N, P, K, Mg) are pulled from older leaves, so deficiency shows first on older growth. Immobile nutrients (Fe, Mn, Zn, B, Ca) cannot move, so deficiency shows on new growth. Infectious disease usually produces localized lesions, spots, wilt, or rot with a distinct edge; abiotic injury is often uniform on one species or exposure, with sharp lines from drift, fertilizer burn, or reflected heat. Herbicide injury causes distortion: twisted or strapped leaves from phenoxy herbicides, chlorosis, or root pruning.
Florida nutrient signatures
High pH and free lime in fill or irrigation water tie up iron, manganese, and zinc, producing interveinal chlorosis on new growth. In palms, magnesium deficiency yellows older fronds, potassium deficiency causes translucent or necrotic spots on older fronds, manganese deficiency frizzles new fronds, boron deficiency produces hook-leaf and stubby new fronds, and iron deficiency yellows new fronds. Centipedegrass is acid-loving; above pH 7 it yellows and declines.
Diagnostic sequence
Ask about irrigation, fertilizer, mowing, and chemical history; check soil pH and thatch; pull roots to look for rot, grubs, or nematode damage; compare healthy and affected areas; sample soil or send a plant to a diagnostic lab before treating.
Worked example
A centipede lawn is uniformly yellow, worst in new growth, with no spots or insects. Soil pH is 7.8. The pattern, species, and pH point to iron/manganese chlorosis from high pH, not chinch bug. The plan is a soil test, acidifying amendment if warranted, foliar iron for temporary color, and no lime.
Traps that cost marks
Do not lime a yellow lawn without a soil test because it can worsen iron chlorosis. Do not confuse cold injury in spring with disease. Do not read palm Mg, K, Mn, and Fe symptoms as interchangeable. Do not treat take-all root rot as a pest problem; high pH and stress are key drivers.