Suspected fungus on red mustard
Thank for your question to Ask an Expert. Our fall weather certainly has been a friendly environment for fungus. We'll need a little more help from you to give you a more specific diagnosis - a close-up photo of the fungus along with a more general view of your garden. You can add up to 3 photos to your response. Also let us know more about your garden area - is it a raised bed, in the ground, how is the drainage in your garden, and are you providing any protection from the heavy rains? You might also consider bringing your photos and/or samples to the Multnomah Co Extension office. Our Master Gardeners there can take a closer look and help you identifiy solutions. They are located at:
2701 NW Vaughn St. Suite 450 Portland, OR 97210
Hours: 10AM - 2PM Monday - Friday
After conducting a little more research, it is most likely that your mustard greens are infected with either downey mildew or Sclerotinia Stem Rot. Both overwinter in plant debris or in soil. Downey mildew starts out as light green-yellow lesions on the upper leaf surface and, in high humidity, a grayish white moldy growth appears on the leaf's underside. Later the leaf may become papery and die. Sclerotinia Rot is mainly on aboveground parts, producing a cottony white mold. As leaves decay, small white bodies appear in the mold and gradually change from white to black as hardened sclerotia develop.
Unfortunately there is little you can do once these diseases are present. Controls are aimed at preventiving the diseases and involve reducing humidity and improving air circulation (a challenging task with the weather this fall!). There are no chemicals approved for home use. Rotating your plantings at least every 2 years will also help to prevent these and other diseases and pests. Hope this gives you a better idea what is going on with your mustard greens.