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
- Control common lambsquarters in the vicinity of plantings since this weed can be host to the pathogen.
- Avoid overhead irrigation or apply such that plants are not wet for extended periods of time.
Reference Testen, A.L., McKemy, J.M., and Backman, P.A. 2013. First report of passalora leaf spot of quinoa caused by Passalora dubia in the United States. Plant Disease 97:139.