Gummy stem blight, caused by Didymella bryoniae, is a fungal disease affecting cucurbits such as cucumber, watermelon, muskmelon, squash, and pumpkin. It manifests through leaf spots, stem cankers, vine wilt, and black rot of fruit. This disease thrives in wet and humid conditions and can cause severe crop losses if left unmanaged.

---

Key Points on Gummy Stem Blight of Cucumber

1. Hosts

• Affects cucurbits including cucumber, watermelon, muskmelon, squash, pumpkin, and gourd.

2. Symptoms

• Leaf and Stem:
  • Pale brown or gray spots on leaves and petioles, often leading to yellowing and defoliation.
  • Elongated streaks on stems with gummy amber exudates, starting at joints.
  • Severe infections cause plant wilting and death.
• Fruit:
  • Initial fading of color, progressing to gray or brown irregular spots with hardened gummy droplets.
  • Spots turn black, forming lesions that allow secondary infections, leading to wet rot (watery mass).
• Diagnostic Sign:
  • Presence of dark brown to black fruiting bodies in clusters, visible without magnification.

3. Spread and Survival

• Transmission:
  • Conidia spread via air, water splashes, and mechanical means.
  • Striped cucumber beetles (Diabrotica undecimpunctata howardii and Acalymma vittatum) and melon aphids transmit the pathogen non-persistently.
  • Beetle-induced injuries are key infection sites.
• Pathogen Survival:
  • Overwinters in dead plant material, infecting subsequent crops.

4. Favorable Conditions

• High humidity (>90%) and temperatures between 20–24°C during rainy/wet seasons.

5. Impact

• Severe defoliation, cracking of stems, and death of plants.
• Fruit lesions lead to secondary infections and complete fruit loss.

6. Management

• Cultural Practices:
  • Remove infected plant debris to reduce inoculum.
  • Use crop rotation with non-host plants.
  • Ensure proper spacing for air circulation to lower humidity.
• Resistant Varieties: Cultivate resistant cucurbit cultivars.
• Pest Control:
  • Manage striped cucumber beetles and aphids to reduce injury sites.
• Fungicide Application: Preventive fungicides can control early infections during conducive conditions.

---

Gummy stem blight is a complex disease affecting multiple parts of cucurbits and requires integrated management strategies to prevent significant yield losses. Timely identification of symptoms, reducing pest vectors, and maintaining field sanitation are essential for sustainable control of this destructive disease.

Image Credits: Plantvillage