The cool, damp climate conditions throughout winter provide the perfect backdrop for cups of tea and home-baked goods. Unfortunately, these conditions also provide the perfect breeding ground for gray mold to form on crops as well as harvested produce. Visible as brown spots and then as a fuzzy gray coating on fruit, gray or Botrytis mold can be extremely destructive to your harvest if left untreated, but can easily be prevented and reversed. Read on to learn more about this winter fungus and simple, bee-friendly solutions for your harvest.

How Botrytis Mold Forms and Spreads

Beginning in the form of Botrytis cinerea spores, gray mold develops in rotting leaves, stems, and fruits and spreads from there to healthy plants. While direct contact is the most common way for the mold to be transmitted, it can also travel with water and the wind and easily enters into wounds or blemishes on the surface of the fruit. Because these are the main methods of transmission, there are several practical steps that you can take to prevent these spores from forming and spreading to other parts of your crop. 

  1. Keep the Leaves Dry

    Wet leaves provide a breeding ground for mold and can also transfer mold from one part of a plant to another. Keep leaves as dry as possible using a soaker-hose system rather than a sprinkler system and ensuring adequate sunlight to dry out the leaves during the day. Any wilted or fallen plant debris will trap moisture and promote mold growth, so remove all old, rotten, and decaying plant debris regularly to prevent gray mold from forming. A hint for avoiding future problems with Botrytis mold: Never put diseased plant matter into a cold compost as this will cause the disease to spread. Instead, use a hot composting system to kill mold spores, bacteria, weeds, and diseased plant material in general.

  2. Promote Good Airflow

    Airflow goes hand-in-hand with keeping your plants dry and free from gray mold. For row crops, this means spacing the plants and rows far enough apart and using wire cages and/or trellises for tomatoes. For fruit trees, ensure good airflow and light exposure by pruning your trees as needed — especially the higher branches that could block the sunlight from reaching the lower branches and pathways.

  3. Compost and Mulch

    Growers know that the health of your plants begins with the soil. A regular application of healthy compost, manure, worm castings, and other organic matter improves the soil structure — and hence filtration — while providing the available, slow-release nutrients that your plants need to stay healthy and strong. 

    In addition to organic matter that improves your topsoil, a mulch layer on top can also help by keeping the moisture where you need it (avoiding moist leaves and reducing the need for additional watering) and help to prevent gray mold-containing droplets from splashings back up onto the plant

  4. Adequate Postharvest Handling

    After the harvest, Botrytis mold can form and spread through your fruit if the fruit is left in moist conditions. To prevent post-harvest mold and rot, harvest the fruit when dry, dip the fruit into a bleach solution of 1 tablespoon sodium hypochlorite 5.25% per 1 gallon of potable water. After dipping the fruit, rinse in clean potable water and air-dry immediately. 

Remedying the Beginnings of Gray Mold

Sometimes, despite our best efforts, Botrytis mold could begin to appear on your stems and fruits, and you need to apply fungicides quickly in order to save your crop. If the season is predicted to be especially wet, you might also opt for a preventative fungicide treatment at the beginning of flowering and continuing regularly throughout the fruiting period.

Bee-Friendly Fungicides

Whether you’re an organic or conventional grower, any fungicides you choose to use should take your pollinators into account. All of the following fungicides are bee-friendly options for protecting your crops from seasonal gray mold:

  1. Neem oil: The clarified hydrophobic extract of neem (Azadirachta indica) provides moderate fungicide activity against gray mold and is organic-approved as well as being non-toxic to plants and bees. If you don’t see sufficient improvement to the beginnings of gray mold, follow up with one of the stronger products mentioned above.
  2. Potassium bicarbonate preparations: These mineral preparations are capable of killing several plant diseases immediately and provide residual protection for approximately two weeks after application. Follow the instructions provided for mixing the preparation with water and apply every one or two weeks until the weather is no longer cool and damp. 
  3. Copper-soap preparations: These fungicide preparations help to protect against disease spores and are effective on grapes, berries, and tree-fruits. Begin application at the start of flowering and continue weekly or every 10 days until harvest.
  4. Bacillus subtilis: This patented probiotic strain is permitted for organic use and provides broad-spectrum protection against various kinds of molds.
  5. Other chemicals: While not necessarily bee-friendly, the chemicals chlorothalonil, pyrimethanil, cyprodinil, and fludioxonil are also labeled for use with Botrytis mold.

Niche Solutions for Specialty Growers

A vineyard in Sonoma, California.

Formed by and for growers over 100 years ago, Fruit Growers Supply Company is dedicated to providing the tools you need to succeed. Beginning with corrugated packaging, we have now expanded to custom irrigation systems, sustainable pallets, and fruit-growing fertilizers, fungicides, and more. Find the best products for treating Botrytis mold at our retail stores in Orange Cove, Woodlake, Riverside, Porterville, or Santa Paula, and contact us about improving your set-up to prevent gray mold from affecting your crops.

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