Spinach downy mildew – if you see it, please report it

Meg McGrath, Cornell University Plant Pathologist based in Long Island, recently (October 2020) received reports of spinach downy mildew in New England and New York states.

The pathogen that causes downy mildew (DM) is an oomycete that does very well in cool, humid conditions – like our fall/winter high tunnels. The symptoms are unique: initially, leaves appear yellow from above, and then they form purplish-gray fuzzy growth on the undersides of leaves (see below).

There are many different races of the spinach DM pathogen, and most spinach varieties are resistant to one or more races of DM. However, the challenge is that we don’t know what races are prevalent here in the Northeast.

If, at any point during the season, you suspect that you have spinach DM, please contact your local extension specialist and send an e-mail directly to Meg at mtm3@cornell.edu. We’d like to try to identify the races of the pathogen that are present. You can also read more about the management of the pathogen here.

Typical purplish-gray fuzzy growth (sporulation) on the bottom of spinach leaves infected with downy mildew.