Above-ground symptoms often mimic nutrient deficiencies, such as yellowing (chlorosis) and stunted growth, causing gardeners to over-fertilize, which only increases stress on the plant. The most distinct sign is a dramatic, firm, blackening of the roots—specifically caused by the buildup of dark chlamydospores. How the Fungus Spreads Black Root Rot - UC IPM
Black root rot thrives in cool, wet, and often alkaline (higher pH) soil conditions. It is a versatile pathogen, affecting a wide range of plants, including: black root rot fungus
Hollies (especially Ilex crenata ), Boxwood, and Citrus. Crops: Tobacco, Cotton, Carrots, and Lettuce. Above-ground symptoms often mimic nutrient deficiencies