Gummy Stem Blight

Stagonosporopsis species

Fungalalso: Gummy stem blight, Black rot of cucurbits

A fungal disease of cucurbits that blights leaves and stems and then rots the fruit, oozing gummy amber droplets from cankers on the vines. Known as gummy stem blight on the foliage and black rot on the fruit, it hits melons, cucumbers, squash, and pumpkins, especially in warm, wet weather, and rides in on seed.

🔎 How to spot it

Look for browning that starts at the leaf edges and spreads inward, and for dark, water-soaked cankers on the main stems and crowns that ooze a red to amber gummy liquid. On the fruit, watch for water-soaked spots that turn completely black as they rot, the black-rot stage. Tiny black fungal dots often pepper the older lesions.

🥀 Damage it causes

Stem cankers can girdle and kill vines, and leaf blight defoliates the plant, while the black-rot stage rots fruit in the field and in storage. A bad case in warm, wet weather can collapse a planting and spoil much of the harvest, with the fruit rot continuing after picking.

🔬 What causes it

Gummy stem blight is caused by Stagonosporopsis fungi, long grouped under the name Didymella bryoniae, which overwinter on crop debris and ride in on infected seed. Spores spread by wind, splashing rain, and overhead watering and enter through wounds and pores. Warm, wet, humid weather and prolonged leaf wetness strongly favor it.

🛡️ Prevent it

Start with clean or treated seed and rotate cucurbits so two or more years pass before they return to a spot. Use drip rather than overhead irrigation, space and trellis for airflow, and avoid handling wet vines. Clean up and destroy crop debris at season end, and grow resistant varieties of watermelon, melon, and squash where available.

🧯 If it is already here

There is no cure for badly infected plants, so remove and destroy affected vines and fruit and keep the foliage dry. On a valued crop, protectant fungicides applied early and repeated in wet weather can slow it; follow the label and rotate products. Clean seed, rotation, and debris cleanup prevent far more than spraying after the fact.

💡 Good to know

The amber gum oozing from dark stem cankers is the signature that names the disease, and the same fungus causes the black rot that ruins the fruit. Because it is seed-borne and survives on debris, clean seed, rotation, and end-of-season cleanup are the foundation of control, with fungicides only a supplement in wet years.

🌱 Plants it affects

49 plants in the library can be affected by this problem

Acorn Squash

Armenian Cucumber

Atlantic Giant Pumpkin

Bitter Melon

Black Beauty Zucchini 🍉Black Diamond Watermelon 🥒Boston Pickling Cucumber

Charleston Gray Watermelon

Cheddar Cauliflower

Cinderella Pumpkin

Concord Grape

Costata Romanesco Zucchini

Crenshaw Melon

Crimson Sweet Watermelon

Delicata Squash 🥒Diva Cucumber 🥒English Cucumber

Galia Melon

Honeydew Melon

Hubbard Squash

Jack-O-Lantern Pumpkin 🍉Jubilee Watermelon

Kabocha Squash

Kirby Cucumber

Lemon Cucumber

Marketmore Cucumber 🍉Mini Love Watermelon 🍉Moon and Stars Watermelon

Muscadine Grape

Niagara Grape 🍉Orangeglo Watermelon

Sugar Baby Watermelon 🎃Sugar Pie Pumpkin

Suyo Long Cucumber

Thompson Seedless Grape

Tromboncino Squash

Winter Melon

Yellow Crookneck Squash 🍉Yellow Doll Watermelon

Yellow Summer Squash

For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.