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TECHNICAL SESSION: Integrated Management of Plant Diseases

Updates on management of bacterial spot of cucurbits incited by Xanthomonas cucurbitae
Mohammad Babadoost - University of Illinois - Crop Sciences Dept. Xiaoyue Zhang- University of Illinois, Sita Thapa- Univ of Illinois, Salisu Sulley- University of Illinois - Crop Sciences Dept

Bacterial spot of cucurbits, caused by Xanthomonas cucurbitae, is a serious emerging disease in many cucurbit-growing areas of the world. X. cucurbitae infects leaves and fruits. Surveys in the North Central Region showed that more than 85% of pumpkin and winter-squash fields had fruits infected with X. cucurbitae. In some of the fields, more than 90% of fruits were affected. Screening of more than 500 pumpkin and squash cultivars and accessions did not identify in any lines with reliable resistance to X. cucurbitae. In our field trials, X. cucurbitae survived for more than 24 months in infected pumpkin leaves and fruits buried at 5 and 15 cm deep. X. cucurbitae survived in naturally-infected and artificially inoculated seeds at 4 and 22°C for more than 18 months. Our studies showed that hot-water treatment at 55°C for 15 min or HCl treatment at 0.5% concentration for 40 min eradicated X. cucurbitae in pumpkin seeds. We evaluated 27 chemical compounds and biocontrol agents for their efficacy for management of X. cucurbitae in pumpkin fields, and found that mancozeb (Manzate PRO Stick), copper hydroxide (Kocide 3000), copper octanoate (Cueva SC), and an extract from Reynoutria sachalinensis (Regalia) were the most effective compounds in reducing the severity of bacterial spot in pumpkin leaves and fruits. Effects of crop rotations for management of the disease are being investigated. In addition, we have collected some bacterial isolates from pumpkin plants, which showed antagonism to X. cucurbitae in in vitro assays.