Gummy Stem Blight
Stagonosporopsis cucurbitacearum (Didymella bryoniae)
Overview
Gummy stem blight, caused by Stagonosporopsis (syn. Didymella) species, is a serious disease of watermelons, melons, cucumbers, and other cucurbits. It produces leaf spots, stem cankers that ooze amber gum, and black fruit rot. Seed, debris, and wet foliage keep the cycle going in humid plantings. Diversified rotations, drip irrigation, clean seed, and canopy management align well with organic cucurbit production and reduce reliance on repeated protectants.
Symptoms
Tan to brown circular leaf spots expand and may blight large leaf areas. Stems and vines develop water-soaked, cracked lesions that exude sticky amber gum. Crown tissue at the soil line can rot, collapsing vines. Fruit shows dark, sunken black-rot lesions that may harbor tiny black fruiting bodies. Severely affected plantings wilt runner by runner even when roots look intact.
Environmental Conditions
Humid
Prevention
Plant certified disease-free seed; hot-water treatments are sometimes used on cucurbit seed lots. Rotate cucurbits out of a bed for two to three years. Prefer drip irrigation over overhead. Choose resistant cultivars when available for your crop. Keep foliage dry in the morning sun by avoiding evening watering. Sanitize greenhouse benches and transplant trays.
Management
Remove blighted vines as soon as gumming cankers appear. Improve spacing and trellis sprawling types for air movement. Copper or other organic-approved protectants help when applied ahead of wet weather, especially on fruiting plantings. Avoid wounding stems with tools or rough harvest handling. After the crop, destroy residue rather than leaving it as a bridge to next season. Do not save seed from diseased fruit.