Commercial producers and homeowners who grow cucurbits, such as cantaloupe, watermelon and cucumber, could suffer heavy losses from gummy stem blight. This disease is caused by the fungus Didymella bryoniae, which can infect leaves, stems, and vines at all plant developmental stages. The same pathogen may infect fruit on the vine and in storage, and is commonly known as black rot.
Gummy Stem Blight Symptoms
Emerging seedlings may exhibit darkened water-soaked spots on leaves and stems, which later develop into dry, tan/brown lesions. Stems may become girdled resulting in plant death. Circular tan-to-brown lesions may begin to develop near the leaf edges, progressing primarily along the veins in older plants (Figure 1).
Lesions on veins, stems, and vines can initially appear water-soaked and orange-brown in color. Lesions will eventually progress to be dry, cracked and tan. If the pathogen infects the fruit, causing black rot, water-soaked spots will appear. These spots will expand to become sunken, discolored, and irregularly-shaped (Figure 3). Leaf and stem lesions may exude a gummy substance, which is amber to red-brown in color (Figure 2).
Figure 1: Cantaloupe with circular tan-to-brown lesions near the leaf edge (Photo: Kenny Seebold, UK)
Figure 2: Cantaloupe stem exuding amber to red-brown gummy substance (Photo: Kenny Seebold, UK)
Figure 3: Watermelon fruit exhibiting black rot symptoms (Photo: Kenny Seebold, UK)
Introduction into Planting and Disease Development
Gummy stem blight can be introduced by seeds or transplants. In addition, the pathogen can survive from season to season on crop debris and weeds. Moisture plays a key role in infection and spread of the pathogen, and temperatures between 61°F and 75°F are ideal for disease development. Wounds caused by picking, pruning, or insects allow sites for the pathogen to enter the plant.
Management
- Plant only certified, disease free seeds and transplants
- Rotate to crops other than cucurbits for 2 to 4 years. Ensure that volunteer cucurbits are removed during these periods.
- Plow under plant debris after completion of the season to allow it to completely decompose and reduce the amount of the pathogen that overwinters.
- Control insects and powdery mildew as they can predispose plants to gummy stem blight.
- Limit wounds and damage to plants during the growing season to reduce points of entry for the pathogen.
- Apply fungicides. FRAC group 3 fungicides are very effective, while options in FRAC groups 7, 9, 11, and 12 can also be used in rotation. Rotate fungicides to maintain their efficacy; resistance can be developed where a single mode of action is relied on.
Additional Information
- Gummy Stem Blight and Black Rot of Cucurbits (PPFS-VG-08)
- Vegetable Production Guide for Commercial Growers (ID-36)
- Home Vegetable Gardening in Kentucky (ID-128)
By Kimberly Leonberger, Extension Associate, and Emily Pfeufer, Extension Plant Pathologist
Kentucky Pest News 