Organic Disease Control for a Wet Spring

If you didn’t know, many parts of Central Appalachia are in a temperate rain forest, which means we’re trying to grow plants in a very humid environment with lots of rainfall.  Our warm, wet summers encourage the growth of all kinds of plant diseases, especially fungi.  In organic gardening, we have very few options for dealing with diseases once they appear and are limited to preventative measures.  Before you start spraying a fungicide on your plants, take note of the many preventative measures you can implement:

  • Plant Resistant Varieties: Breeders are constantly striving to stay ahead of disease issues by breeding resistance or disease tolerance into new varieties.  If you know you have a bad issue with early blight or powdery mildew, for instance, you can look for varieties that are resistant to these diseases.
  • Good Airflow: Fungi and bacteria thrive in wet conditions, and you can help keep leaves dry by providing adequate spacing for plants, using trellises to get vining plants off the ground, and keeping weeds down so they don’t crowd your plants.
  • Watering: Growing plants under plastic with drip irrigation is the best way to protect plants, but this is expensive and not practical for most home gardeners.  Water your plants thoroughly once or twice a week and avoid watering every day.  If you must use overhead irrigation, watering in the morning lets the leaves dry off by nightfall.  Also, don’t situate your garden in areas with poor drainage.
  • Healthy Soil: actively working to build up healthy soils will go a long way toward preventing disease.  Healthy soils grow healthy plants and also contain billions of good microbes that will keep the bad microbes in balance.  Add lots of organic matter to your soil, use mulches, avoid tilling as much as possible, and use cover crops in the winter to build up soil health.
  • Remove Diseased Material: It’s good to cut off diseased parts of plants or remove the whole plant entirely.  Do not leave the diseased material in the garden or put it in your compost.  It is best to trash or burn this stuff.  Remove all dead plant material in the fall so it’s not left to host diseases through the winter.
  • Hand and Tool Hygiene: If you touch diseased plants, make sure you wash or sanitize your hands and tools before touching your healthy plants.  When using clippers to cut off diseased leaves, I recommend carrying a cup of rubbing alcohol to sterilize your tool EACH time you make a cut.
  • Crop Rotation: diseases can build up in the soil and if you plant a crop in the same spot year after year, you are basically feeding pathogens their favorite food each time and they will multiple quickly.  By rotating crop families, you starve the pathogens and help keep their numbers low.  A three year rotation is the minimum recommendation.

With the tremendous amounts of rainfall we’ve received so far this spring, these preventative measures may not be enough to prevent disease outbreaks this season.  Preventative spraying of fungicides may be your best option for keeping disease under control, especially on sensitive crops like tomatoes and cucurbits.  Organic sprays can be effective preventative measures, but will not cure a problem once it’s been established.  When implementing a fungal disease control strategy, the best practice is to use two or more different fungicides, to prevent diseases from developing resistance.  For organic gardening, here are your options:

  • Copper and lime-sulfur are broad spectrum anti-fungals that can be used to prevent a long list of fungal diseases.  They must be used preventatively, either at the first signs of disease or better yet, before you even see it.  Check the label for application rates for different plants and diseases. The overuse of copper can cause it to build up in your garden soil and may cause toxicity issues over time.
  • Potassium Bicarbonate is very effective for Powdery Mildew, a common fungal problem that is especially bad on cucurbit family plants.  It is being studied for other fungal problems and may be used in rotation with Copper and Serenade.
  • Bio-fungicides employ a patented strain of bacteria to fight a broad range of fungal pathogens.  Basically, these sprays are designed to colonize leaf surface and root zone with good bacteria to prevent and fight off bad fungi. They can be used as a foliar spray, soil drench and an inoculant for seeds.  Brand name products include Serenade, Actinovate, and Mycostop.  You can harness the power of beneficial microbes by building a Compost Tea Brewer and spraying your crops with the tea.  I’ve not yet tried this, but I’ve heard good things about it.

Fungi are living organisms and are constantly mutating and evolving new strains.  The overuse of one chemical may breed resistant strains, so best practices include the use of two or three different fungicides in rotation (i.e. alternate what you use each week).  This prevents the build up of resistant genes in the fungi and can help in the case of copper to prevent too much of this mineral from building up in the soil.

With the wet spring we’ve been having, it’s important to stay out in front of fungal problems before they take over your garden!  Best of luck this year!

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