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Spinach is a member of the plant family Chenopodiaceae, which also contains the
crop plants beets and Swiss chard as well as weeds such as nettleleaf goosefoot
and lambsquarters. Downy mildew, caused by the oomycete pathogen Peronospora farinosa,
which exists as different races or subtypes, can develop on all of these plants.
An important question for spinach growers is this: can isolates of the pathogen
that cause downy mildew on beets, Swiss chard, or weed hosts cause downy mildew
on spinach? Monterey County, California Farm Advisor Steve Koike and colleagues
conducted research to answer this question. Isolates of the pathogen from nettleleaf
goosefoot, lambsquarters, beet and Swiss chard were each used to inoculate spinach.
The result: no disease development. In a separate experiment, the downy mildew pathogen
from spinach was used to inoculate nettleleaf goosefoot and lambsquarters. The result
again was no disease development. The bottom line is that spinach growers need not
worry about related Chenopodiaceae such as nettleleaf goosefoot, lambsquarters,
beets or Swiss chard as potential sources of inoculum for their spinach crop. Even
though the bluish-purple evidence of the pathogen on the underside of leaves is
similar in appearance on all of these plants, the particular isolates of the downy
mildew pathogen have very specific and limited host ranges.
To contact Mike Matheron go to: matheron@ag.arizona.edu.
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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
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