PPDL Picture of the Week
November 14, 2016
Alternaria leaf blight of carrot
Dan Egel, Extension Plant Pathologist, Southwest Purdue Agricultural Center
Although most of us have put away our gardening tools, some
vegetables grow well in the fall.
Carrots are favored by warm days and cool nights. Unfortunately, similar temperatures also
favor the disease Alternaria leaf blight of carrot. This disease is caused by a fungus, Alternaria dauci, that may survive on
crop residue in the soil.
Figure one shows a stand of carrots with several leaves that
appear chlorotic (yellow). A closer examination
reveals small lesions on the leaves.
Loss of leaves may lead to fewer or smaller carrots (Figure 2).
Since leaf wetness is necessary for disease initiation and
spread, avoid overhead irrigation. The
disease may be spread on seeds, therefor care should be taken when purchasing
or saving seed. Crop rotations of at
least two years will help to lessen disease severity. When carrot production is done, old crop
residue should be plowed under.
Finally, several fungicides may help to manage this disease. For the home gardener, products with the
active ingredient chlorothalonil may be labeled for this disease. Organic gardeners may find copper hydroxide
or copper sulfate formulations that are approved for use. Commercial growers should consult the Midwest
Vegetable Production Guide <mwveguide.org>.