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United States Department of Agriculture

Agricultural Research Service

Title: Fungicides for organic cantaloupe production in Oklahoma: An initial assessment

item Shrefler, James
item Taylor, Merritt
item Roberts, Warren
item Bruton, Benny

Submitted to: Cucurbitaceae Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/12/2010
Publication Date: 11/14/2010
Citation: Shrefler, J.W., Taylor, M., Roberts, W., Bruton, B.D. 2010. Fungicides for organic cantaloupe production in Oklahoma: An initial assessment. In: Cucurbitaceae 2010 Proceedings, November 14-18, 2010, Charleston, South Carolina. p. 252-254.

Interpretive Summary: Foliar disease management is a challenge for watermelon producers in the south central portion of the United States. Because foliar disease management programs must address a complex of fungal and bacterial diseases, the development of disease prevention programs for organic cucurbit production requires the identification of fungicidal and bactericidal agents (or combinations of such agents) that are effective for managing all important diseases. Our objective was to assess the efficacy of organic approved fungicidal / bactericidal agents (or candidates for approval) on selected foliar diseases of cucurbits in field trials in Oklahoma. Results of this study demonstrate the challenges melon growers encounter in managing foliar diseases. In this case, the crop was attacked by two diseases caused by different types of organisms (bacterial and fungal). Bravo, a commonly used fungicide for cucurbit crops in this region, provided the greatest degree of control of one of these diseases, powdery mildew. Several of the alternative fungicides (such as Copper and Milstop) provided some control of powdery mildew, but these were not as effective as Bravo. Phytotoxic effects were observed on melon plants treated with some of the organic products. Foliar injury was observed following the two initial applications of Milstop and Mycostop and yields of large melons were reduced in plots treated with Milstop, Neem and Serenade. The phytotoxic effects of Milstop and Mycostop warrant further study, especially considering the fact that they provided detectable control of powdery mildew at the early evaluation dates in this trial. In contrast, the copper product gave similar control of powdery mildew to that of Milstop, Neem, and Serenade, but also produced some of the greatest yields of large fruit. While it could be argued that the copper may have been providing some control of the bacterial disease (control that was not detected in the visual evaluations), the yield values for Milstop, Neem and Serenade were also numerically lower than those of the untreated melons, although the differences were not statistically significant. This study showed that alternative pesticides can provide a certain degree of protection from cucurbit foliar diseases. In this situation, where the crop was attacked by powdery mildew and bacterial leaf spot, the copper product was the most useful of the alternative fungicides for disease management. Although the other products evaluated provided disease control similar to copper in some cases (e.g. control of powdery mildew), they were not effective for managing this disease complex. Because of the diversity of foliar diseases that may occur in cucurbit crops from one year to the next in Oklahoma, these products should be evaluated repeatedly in order to ascertain their value over a broad spectrum of disease organisms and field conditions.

Technical Abstract: Fungicides that are potentially useful in organic production were evaluated for foliar disease control in cantaloupe (Cucumis melo L. var. reticulates ’Israeli’) during 2009 at Lane, Oklahoma. Milstop (85% potassium bicarbonate), Neem oil, Bonide liquid copper (10% copper octanoate), Serenade (QST 713 strain of Bacillus subtilis 1.34%), Mycostop (dried spores and mycelium of Streptomyces griseoviridis strain K61), and Regalia SC (extract of Reynoutria sachalinensis) were applied in aqueous mixture as foliar sprays to cantaloupe. For reference, there was an untreated check and a treatment of Bravo (chlorothalonil) which is a broad spectrum synthetic fungicide. Both bacterial leaf spot, caused by Xanthomonas campestris pv. cucurbitae, and powdery mildew, caused by Podosphaera xanthii, occurred causing foliar lesions and defoliation that was severe by the end of the crop cycle. Defoliation was significantly less for plants in the Bravo treated plots compared to those in the other treatments. None of the treatments appeared to control bacterial leaf spot. Powdery mildew incidence on foliage was significantly reduced by several treatments with Bravo being the most effective. Copper was the most effective of the non-synthetic products for managing disease in the study.

Last Modified: 08/16/2017
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