More basil downy mildew images.
Basil downy mildew – a new fungal disease that plagued commercial and home-garden crops in 2008 and 2009 – is again sending unlucky basil plants to an early grave in the Northeast this summer. By late June, the disease had already been detected in New York, New Jersey, and Ohio, says Margaret McGrath, plant pathologist at Cornell University’s Long Island Horticultural Research and Extension Center, Riverhead, N.Y.
The first symptom that gardeners or growers are likely to spot is a slight yellowing on the upper surface of the leaves. Turning affected leaves over will reveal the grayish-purple (sometimes almost black) dusty growth of the pathogen’s spores. Removing individual affected leaves won’t stop the disease, since the spores are easily moved on air currents.
McGrath suggests dropping everything when you first discover the disease on your plants, harvesting healthy-looking leaves, and preserving them as you usually would (by drying, freezing, making pesto, etc.) so you will have basil to enjoy later.
More information:
Downy Mildew Wars – Article by McGrath in American Vegetable Grower.
NPR interviews with McGrath:
Report basil downy mildew (and see reports of others):