Gummy Stem Blight Control – Treating Black Rot Fungus In Cucurbits

Bonnie L. Grant

Gummy stem blight is a fungal disease of melons, cucumbers and other cucurbits. It is a contagious disease which can spread across a field of fruits. The fungus damages the tissues of the stem at all stages of development. Stem blight treatment must start before you even plant the seeds to be entirely effective. Find out what is gummy stem blight so you can prevent this problem in your vegetable garden.

What is Gummy Stem Blight Disease?

Gummy stem blight fungus is most active during periods of warm, wet weather. The spores of the fungus can spread in soil or by air. The fungus will overwinter in milder climates in soil and plant debris.

The leaves will get necrotic areas of dead tissue that turn brown and have a darker halo. The stems and fruit will show black, soft spots or large brown lesions that are bordered by black. The dark coloring of these lesions also lends the disease the name of black rot fungus.

Black Rot Fungus Characteristics

Stem blight forms when seeds or sites are previously infected with the fungal spores. When conditions are 85% humid or wet and warm, with temperatures averaging in the 60’s, the fungal spores bloom.

You should start treating black rot fungus at the first signs of the disease. Unfortunately, the first signs vary dependent upon plant species. Many get water spotting on the foliage or stems could ooze black or brown gummy beads of fluid. It is difficult to identify these early signs of gummy stem blight, which is why preparation of the seedbed, purchasing resistant seeds and rotating crops are important prequels to stem blight treatment.

Ultimately, plants affected by this disease will bear rotten fruits, which are unmistakable and inedible.

Prevention of Gummy Stem Blight

The first stages of a disease free cucurbit crop are preparation and rotation. Never plant cucumbers, melons or other susceptible plants in the same area as the previous season’s crop. The plant debris, and even seeds, left over in the soil will harbor the spores of black rot fungus.

Careful preparation of soil prior to planting removes all old organic matter. Use seeds from a reputable seed company that has a history of fungus-free seeds. Since the disease can manifest even on seedlings, inspect any that you have purchased from a nursery prior to purchase and planting. Gummy stem blight signs on seedlings are brown lesions and dry leaf edges. Do not plant suspect specimens.

Treating Black Rot Fungus

In most cases, removal of old plant debris, rotation and resistant species will prevent the appearance of gummy stem blight. In climates with warm, moist bloom conditions, the fungal spores are carried on the wind and you may have to combat the disease even if you took preventative steps.

The most common method is the use of fungicides as a stem blight treatment. Dusts or sprays of fungicides useful for preventing and combating powdery or downy mildew have been shown to be effective against gummy stem blight disease.

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