About Spinach White Rust Disease
White rust is a fungal disease caused by the pathogen Albugo occidentalis. There are many strains of Albugo that can affect a wide variety of plants. However, the Albugo occidentalis strain is host specific to spinach and strawberries. Initial symptoms of spinach white rust disease may look very much like the initial symptoms of downy mildew. As the disease progresses, the two become distinguishable by their specific symptoms. However, an infection of white rust can weaken spinach plants and cause them to be more susceptible to secondary disease infections, so it is not impossible to find a spinach plant that is infected with both white rust and downy mildew. The first noticeable sign of spinach white rust is chlorotic spots on the upper sides of spinach leaves. This is also an initial symptom of downy mildew. When leaves are flipped over to inspect the undersides, there will be corresponding white blisters or bumps. In downy mildew, the undersides of infected leaves will have a purple to gray colored downy or fuzzy substance, not white raised bumps. As white rust progresses, the chlorotic spots on the top of the leaves may turn white, and when releasing their spores, the white blisters may turn a reddish brown. Another telltale sign of white rust on spinach is severe wilting or collapse of the spinach plant. Once these symptoms are present, the plant will be un-harvestable and should be dug up and destroyed to prevent further spread.
Controlling White Rust on Spinach Plants
Spinach white rust is a cool season fungal condition. Ideal conditions for its growth and spread are cool, damp, dewy nights and mild daytime temperatures of spring and fall. Optimal temperatures for the disease are between 54 and 72 degrees F. (12-22 C.). White rust on spinach usually goes dormant during the hot, dry months of summer but can return in autumn. Spores of the disease are spread from plant to plant by wind, rain, watering splash back, insects, or un-sanitized garden equipment. These spores stick to dew or wet plant tissues and infect the plant with two or three hours. The most effective spinach white rust treatment is prevention. Systemic fungicides can be applied at the time of planting new seedlings of spinach plants. Be sure to read product labels to ensure that the fungicide is safe for use on edibles and intended for spinach white rust. Fungicides which contain Bacillus subtilis have shown the most effectiveness against this disease. Garden debris and tools should be properly sanitized regularly. It is also recommended that a three year crop rotation be done when growing spinach.
