The most common root disease in hydroponic systems is root rot caused by the fungal-like organism, Pythium. Other fungal diseases that are occasional problems include Fusarium root and crown rot, Phytophthora, and Rhizoctonia. Symptoms are very similar among these diseases and are usually first noticed as wilting or tip burn on leaves. The root system will be brown with sparse root hairs and sometimes soft and/or stunted. A trained diagnostician may be needed to determine which specific fungus is the culprit.
Prevent disease organisms from entering the growing system. Start out with a clean system by properly disinfecting trays, rafts, beds and troughs. Effective chemical disinfectants include 10% solutions of chlorine bleach or hydrogen peroxide based-products products intended for hydroponic systems. Follow all label instructions.
General management of root rots relies heavily on encouraging healthy plant growth. Most root pathogens are opportunists and can cause the most damage on already stressed plants.
Low oxygen levels in the nutrient solution favor disease so increase dissolved oxygen levels through proper aeration. Maintain a proper root zone temperature (68-72F is optimum). Use a balanced nutrient solution to avoid over-fertilization and regularly check total soluble salts and pH levels.