Development of bacterial spot, incited by Xanthomonas cucurbitae, in pumpkin fields

This study was conducted to assess occurrence of bacterial spot, incited by Xanthomonas cucurbitae, on pumpkin leaves and fruit. Development of the disease was monitored in 9, 14, and 15 commercial pumpkin fields in 2009, 2010, and 2011, respectively, in Illinois. Bacterial spot was observed from 4-leaf growth stage until the green leaf tissue was unavailable. Three types of lesions were observed on leaves, which were described as Type I, Type II, and Type III lesions. Type I lesions were small (1 mm), angular, brown necrotic spots, and numerous on each leaf. Type II lesions were angular, beige in the center with brown halo, numerous on each leaf, and measured 1 to 4 mm. Type III lesions were angular, translucent spots with a narrow chlorotic halo, only a few spots on each leaf, and measured 4 to 8 mm. Incidence and severity of bacterial spot on leaves were the greatest when fruit began to turn to orange. Bacterial lesions were observed on fruit from 1 week after fruit set until harvest. Lesions on fruit were circular, water-soaked, sunken, with beige centers and chlorotic halo, and measured 1 to 3 mm. Occurrence of bacterial spot on fruit was assessed in 17, 50, and 65 commercial pumpkin fields in 2009, 2010, and 2011, respectively. The disease on fruit was observed in 100%, 80%, and 88% of the fields surveyed in 2009, 2010, and 2011, respectively. The incidence of fruit with bacterial spot in all fields surveyed was 46%, 35%, and 24% in 2009, 2010, and 2011, respectively.