Pod from a radish seed plant showing the dark lesions characteristic of black spot.
Photo by Cynthia M. Ocamb, 2011.
Cause Passalora dubia, a fungus that can survive in plant debris. Spores produced on affected leaves are disseminated by wind. Common lambsquarters can also be infected.
Symptoms Oval, brown to grey-black lesions with darker brown, reddish margins develop on leaves.
Cultural control
Cause Peronosporavariabilis (formerly Peronospora farinosa f. sp. chenopodii), a fungus-like microorganism that is seedborne. Spores produced on affected leaves are disseminated by splashing water. Cool, wet weather favors disease development.
Cause The fungus Podosphaera alpina f. alpina has been reported from Washington and British Columbia and found several times by the OSU Plant Clinic. It has not been reported to be a serious pathogen.
Cause Fusarium spp. that are common saprophytes on umbelliferous crops as well as some weeds and other cultivated plants. These soilborne fungi can overwinter as chlamydospores and hyphae in soil or plant debris and on living plant roots. Conidia produced on hyphae are spread by wind and move with soil.
