2017 ASHS Annual Conference

Bacterial spot, caused by Xanthomonas cucurbitae, is an emerging disease of pumpkin and winter squash in the Midwestern states and some of the cucurbit growing areas of the world. X. cucurbitae infect leaves and fruits. Affected fruits are usually colonized by opportunistic fungi and bacteria, which results in fruit rot. During 2011-2013, field surveys were conducted in Illinois, Indiana, Iowa, Kansas, Michigan, Missouri, Nebraska, Ohio, and Wisconsin to assess incidence and severity of the bacterial spot in pumpkin and squash. During four weeks of the harvest, 111, 132, and 126 fields in 2011, 2012, and 2013, respectively, were visited. Symptomatic fruit were observed in 95 (86%), 117 (89%), and 113 (90%) of the fields visited, with overall 34, 23, and 19% fruit infected, in 2011, 2012 and 2013, respectively. In some of the fields, more than 90% of fruits were affected. In a field trial, we found that X. cucurbitae survived for more than 24 months in infected pumpkin leaves and fruits buried at 5 and 15 cm deep. There is not known cucurbit cultivar resistant to X. cucurbitae. We have evaluated 27 chemical compounds and biocontrol agents for their efficacy for management of X. cucurbitae in pumpkin and found that mancozeb (Dithane M45), cupper hydroxide (Kocide 3000), copper octanoate (Cueva SC), and an extract from Reynoutria sachalinensis (Regalia) were the most effective compounds in reducing incidence and severity of bacterial spot in leaves and fruits of pumpkin. X. cucurbitae is a seedborne pathogen. Our studies showed that hot-water treatment at 55°C for 15 min and HCl treatment at 0.5% concentration for 40 min eradicated the pathogen in both naturally-infected and artificially-inoculated pumpkin seeds without any significant adverse effect on either seed germination or seedling vigor. Effects of crop rotations for management of the disease is being investigated. X. cucurbitae is identifies based on the colony characteristics on yeast dextrose agar, PCR test using RST 2 and RST 3 primers, and pathogenicity test