Featured Diagnosis: Bacterial Leaf Spot of Cucurbits

Bacterial leaf spot on pumpkin leaf. Note the yellow halo
surrounding the dark lesion.  (Photo: NMSU - PDC)

Bacterial Leaf Spot of Cucurbits – Bacterial leaf spot of cucurbits is caused by the bacterium, Xanthomonas campestris pv. cucurbitae. This disease causes sporadic losses in cucurbit crops grown in temperate climates. In New Mexico, the disease is not common, but can occur when warm, humid conditions are persistent. The disease attacks a number of different hosts including pumpkin, cucumber, gourds, and summer and winter squash.

Symptoms may appear on both the foliage and the fruit. On the foliage, the disease causes small somewhat round water-soaked lesions on the underside of the leaf. A yellow spot appears on the upper leaf surface. In a few days, the spots turn brown with a distinct yellow halo. The appearance on fruit is variable and depends on rind maturity and how much moisture is present. Initial lesions are typically small, slightly sunken, mostly round spots with a tan to beige center. As the spots enlarge (reaching up to 15 mm in diameter), they become noticeably sunken and the rind may cracks. 

Sunken bacterial leaf spot lesion on pumpkin
(Photo: J. French, NMSU-PDC).

Bacterial leaf spot lesion extends into the seed cavity
 (Photo: N. Goldberg, NMSU-PDC)

Bacterial leaf spot on a white pumpkin
(Photo: J. French, NMSU-PDC)