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How to Prevent Fungus on Squash Plants

butternut squash image by Joy Fera from

Fungus on squash plants may be due to the presence of bacteria or certain environmental conditions that promote fungal growth. Types of fungus include white powdery mildew, downy mildew, leaf spot, scab and black rot. A fungus can destroy your garden crop of squash. Prevent fungus on your squash plants with certain organic gardening practices. Once infected, though, you may need to resort to organic sprays or dispose of the infected plant.

Amend your garden soil before planting to create a healthy mix of nutrients, good bacteria and composting materials. Plants in healthy soil have a stronger immune system and may be better able to resist fungal attacks.

Select organic, healthy squash seedlings from your garden center. The leaves of the seedlings should be consistent in coloring and the stems pliable but strong. Check under the leaves to ensure no fungus has already infected the plants.

Allow each squash plant plenty of space for air circulation during growth. Overcrowding can result in some of the plant leaves being cut off from sunlight, and therefore more susceptible to fungal growth. Apply organic mulch around the base of each plant.

Install a drip system in your garden and direct water to the soil around the squash plants. Watering directly onto the plants themselves creates a moist, humid environment on the underside of leaves. This environment invites fungal growth.

Train your squash plants to grow upwards. Use a trellis or staking device to promote vertical growth. This keeps the leaves, stems and flowers from sprawling along the ground. The vertical growth allows for better air circulation, less humidity on the undersides of leaves and keeps fruits from sitting on damp ground.

Trellises and stakes must be able to support the weight of the plant and the fruits. Fix the trellises and stakes securely in the ground.

Harvest squash frequently. Squash fruit that remains on the vine after maturity may rot. Rotting fruits invite disease and mildew to your garden.

Rotate your squash crops seasonally. By positioning your squash plants in different areas season to season, you reduce the chance of bacterial build-up in the soil due nutrient depletion. Different plants require different nutrients. If you plant acorn squash in the same area each season, that soil, in spite of amendments, may become susceptible to fungus due to the same nutrients being taken up each season.

Remove any plants that show signs of being infected with fungus that you are unable to remove using anti-fungal sprays.


Always clean your clippers as you move from plant to plant. This reduces the risk of spreading disease and fungus.

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