Margaret Tuttle McGrath
Recent findings of new hosts has increased the challenge of managing Phytophthora blight. This disease is a major problem in pepper and all cucurbit crops. It also occurs in eggplant and tomato. Pod rot in lima bean due to Phytophthora capsici , the pathogen causing blight in cucurbits, has been occurring in the mid-Atlantic region since first seen in 2000 (Figure 1).
Growers in the mid-west had been reporting worst Phytophthora blight in cucurbits
planted after green beans and soybean. In Michigan in 2003, dying green bean
plants were observed with blight symptoms in the crown and upper stems. These
symptoms were confirmed to be caused by Phytophthora capsici (Figures
2 and 3). New York growers need to be on the look out for dying green bean
plants. Report possible occurrences of Phytophthora blight on snap bean to local
extension specialists so that presence in NY of strains of Phytophthora capsici
pathogenic on bean can be verified.
Weeds may provide a means for Phytophthora capsici to survive between susceptible crops. This could explain why long rotations have not been effective in some fields. Research conducted in FL has revealed that Phytophthora capsici can survive on roots of some weeds. Proportion of weeds with the pathogen were low, but purslane was one of the more common ones.
|Figure 1. Pod rot in lima bean due to Phytophthora capsici (courtesy of Robert Mulrooney, University of Delaware).|
|Figure 2. Snap bean plants in a low section of a field dying due to Phytophthora blight (courtesy of Amanda Gevens and Mary Hausbeck, Michigan State University).||Figure 3. Symptoms of Phytophthora blight on snap bean (courtesy of Amanda Gevens and Mary Hausbeck, Michigan State University).|
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