Areolate Mildew of Cotton
Published: 08/18/2023
Areolate mildew, also known as false mildew, grey mildew, and Ramularia leaf spot, has been reported to be caused by the fungal pathogen Ramulariopsis gossypii. Recently, evidence from Brazil suggests R. pseudoglycines may also cause the disease. Historically, it was of little importance to U.S. cotton production, but it is now a regular occurrence in the southeastern U.S.
Areolate mildew thrives during extended humid and hot summer weather, typically late July to late August. The symptoms include angular to irregular, yellow to light green, vein-limited lesions on the upper leaf surface in the lower canopy, which can then spread to the leaves in the upper canopy. Infected leaves develop tufts of white conidiophores and conidia, generally on the underside of the leaf, which eventually stop sporulating, leading to necrotic lesions and leaf shedding.
Signs of areolate mildew on cotton leaf.
Tom Allen
Symptoms and signs of areolate mildew on cotton leaf.
Tom Allen
Effective management involves using the least susceptible cultivars, scouting to identify symptom onset and appropriately timing fungicide applications, and implementing cultural practices such as crop rotation from continuous cotton.
Written and reviewed by Travis Faske, University of Arkansas; Tom Allen, Mississippi State University; Trey Price, Louisiana State University; and Terry Spurlock, University of Arkansas.
Signs of areolate mildew on cotton leaf. Image by Tom Allen.
Symptoms and signs of areolate mildew on cotton leaf. Image by Tom Allen.
Signs of areolate mildew on cotton leaf. Image by Tom Allen.
Areolate mildew of cotton. Images courtesy Tom Allen.
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