White rust of garden cress
Dan Egel, Vegetable Pathologist, SWPAC, Purdue University
Usually when it is my turn to contribute to the picture of the week, I use a vegetable disease that I have observed recently. So, earlier this week when I saw white rust on garden cress (Lepidium sativum) I thought of the picture of the week. However, I didn’t observe white rust in Indiana. Rather, I found white rust in Mazar-i-Sharif, Afghanistan.
Nevertheless, white rust (caused by the fungus Albugo) is a disease that can affect Indiana farmers. Figure one shows the concentric white pustules of the fungus growing on garden cress. Other symptoms include irregular white chlorotic (yellow areas) on the upper surface of leaves and systemic infections which can cause leaves to twist and curl (not shown). Other hosts include sugar beet, cabbage, cauliflower, lettuce and spinach.
I was surprised to see white rust in Afghanistan since it gets quite warm during the day. However, nights are cooler. I suspect this infection started some time ago when the days were cooler. White rust also requires moisture. The garden cress I observed was well irrigated and growing close to the ground to take advantage of any dew.
For control of white rust, clean till the field after production and practice crop rotation. For more information about possible fungicides and other measures, consult the Midwest Vegetable Production Guide for Commercial Growers 2013.
Click image to enlarge
Figure 1: White rust can cause white raised pustules on the leaf, such as the garden cress leaf shown here.