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Title: Fungicide rotation schemes for managing Phytophthora fruit rot of watermelon across southeastern United States

item Kousik, Chandrasekar - Shaker
item PINGSHENG, JI - University Of Georgia
item DAN, EGEL - Purdue University
item LINA, QUESADA-OCAMPO - North Carolina State University

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2017
Publication Date: 5/1/2017
Citation: Kousik, C.S., Pingsheng, J., Dan, E., Lina, Q. 2017. Fungicide rotation schemes for managing Phytophthora fruit rot of watermelon across southeastern United States. Plant Health Progress. 18:28-34. doi:10.1094/PHP-RS-16-0059.

Interpretive Summary: For the past several years, fruit rot of watermelon caused by a fungus has resulted in severe loss to watermelon growers in southeastern states and hence it is considered an important problem and a top-research priority by the National Watermelon Association (NWA). The fruit rot causing fungus has also developed resistance to several commercially available fungicides (chemicals that can kill or slow down fungus). Therefore, an ARS scientist in Charleston, SC, in cooperation with scientists at Purdue, NCSU, and the University of Georgia developed fungicide rotation schemes to manage Phytophthora fruit rot of watermelon across the southeastern United States. It is important to rotate fungicides in different groups to prevent the development of a resistant fungal pathogen. The results were based on tests conducted in NC, SC, and GA. These fungicides and rotation schemes developed for the southeast can be used by growers to manage fruit rot of watermelon. These results will inform growers that fungicides should be part of an overall disease management strategy that also includes the use of well drained fields, water management and crop rotation. The information from this research is proving useful to growers, extension agents and University researchers across the United States.

Technical Abstract: Southeastern states produce about 50% of the watermelons in the United States (U.S.) where conditions are optimal for development of Phytophthora fruit rot prevail. Phytophthora fruit rot significantly limits watermelon production by causing serious yield losses to growers before and after harvest. The effect of fungicide rotations and Melcast scheduled sprays on development of Phytophthora fruit rot were conducted in Phytophthora capsici infested fields at three locations in southeastern U.S. (North Carolina, South Carolina, and Georgia). The mini seedless cultivar Wonder and seeded cultivar Mickey Lee (Pollenizer) were used. Five weekly applications of fungicides were made at all locations. Significant fruit rot (Range 53-91%, Mean 68%) was observed in the non-treated control plots in all three years (2013-2015) and across locations. All fungicide rotation schemes significantly reduced Phytophthora fruit rot compared to non-treated controls. Overall, the rotation of dimethomorph+ametoctradin (Zampro) with oxathiapiprolin (Orondis) was very effective across three locations. Rotations of actigard/cyazofamid+mefenoxam/ fluopicolide /ethaboxam / oxathiapiprolin or mandipropamid alternated with fluopicolide were similarly effective. Use of Melcast may occasionally help reduce one spray application. Application of Actigard, K-Phite or Forum during early stages of fruit development may also be useful. Though many fungicides are available for use in rotations, under very heavy rainy conditions and pathogen pressure the fungicides may not offer adequate protection and hence an integrated approach should be used.