Issue 5, May 23, 2011

To Be Organic, or not to Be Organic, with Your Veggies and Manage Disease, That Is the Question?

We have had several "organic" vegetable samples submitted to the U of I Plant Clinic, due to the wet and favorable conditions for disease. All veggies (organic and conventional) can be susceptible to a plant pathogen (if it is present), and with just the right environmental conditions one can unfortunately get diseased plants! Once a plant that is considered to be organic is infected with a disease there may not be a lot of options for disease control. This is why it is very important for those who wish to grow organic veggies, and not use chemicals, to focus on disease prevention or cultural management of diseases. The following disease prevention tips are good for all vegetable gardeners (conventional or organic) in order to protect against disease!

  1. Try to grow either resistant or tolerant plant varieties. The U of I Extension website, "Illinois Vegetable Guide", has a list of "recommended varieties" that can be grown in Illinois at:

    In addition, the U of I Extension website, "Watch Your Garden Grow", has recommended varieties, as well as other information that may help you gain success with your garden at:
  2. Plant clean seed or "certified seed," because some plant pathogens can be seed-borne! Be careful if you save your seed, because it could be harboring disease for the next year's crop! Be sure to buy transplants that don't look sickly or have symptoms of disease. You may be bringing unwanted plant pathogens to your garden!
  3. Wash off garden equipment and disinfect pots or trays with steam or bleach.

    For more information go to the U of I Extension website, "Illinois Vegetable Guide" web site at:
  4. Be careful if using irrigation ponds or recycling water, because water can also be a home to plant pathogens such as bacteria.
  5. Remove or "rogue" diseased plants from your garden to prevent further disease spread. Prevent the "build-up" of disease inoculum in your garden by turning over old plants and crop residue immediately after harvest.
  6. Choose a well-drained site for your garden in order to reduce the risk of infection from soil pathogens. For additional helpful tips on picking a garden site, go to the U of I web site, "Illinois Vegetable Guide" at:
  7. Wide row spacing encourages air movement, which helps to discourage the development of foliar disease.
  8. Do not overwater! In order to prevent most foliar diseases, drip irrigation is the preferred watering method, because you are not promoting disease development by wetting the foliage. You will need to allow for adequate time for foliage to dry if using overhead irrigation. For additional information on proper watering, you can go to the U of I web site, "Illinois Vegetable Guide" at:
  9. One of the most important cultural methods to control disease is crop rotation! This can get complicated, but basically, try to move crop families around to different locations in your garden each year.
  10. Scout for any signs of disease and remove this disease material or if possible, consider using an "organic" fungicide as a last resort. If you are unsure of a problem, the U of I Extension web site called "Hort Answers," may be able to help! Here is the link:

    In addition, there is a U of I Extension web site called, "Common Problems for Vegetable Crops" that may prove to be helpful at:
  11. Lastly, there are some fungicides that are considered to be organic including copper- and sulfur-based fungicides. Copper fungicides have some activity against a broad range of fungi and bacteria, but their effectiveness may be limited if disease pressure is high. Sulfur compounds can give some control of many plant diseases, but are mainly used to control powdery mildew. Be aware that both copper and sulfur can burn some crops under certain conditions. There are also organically approved bicarbonate fungicides and peroxide-type fungicides available, but remember that these products will only suppress the pathogen on the plant surface. Basically, these products "sterilize" the foliage. Some other organic options are products that contain microbes or their by-products, such as species of Trichoderma, Bacillus, and other beneficial organisms; however, timing and correct application is required. In addition, these beneficial organic products should be applied prior to infection and some may need time to populate the soil to be effective.
  12. Most importantly, you need to correctly identify the pest in your garden! This is key for disease management! You are always welcome to submit a plant sample to the U of I Plant Clinic for an accurate diagnosis!

Some other great U of I Extension web sites for information about gardening is "A Taste of Gardening," found at and "My First Garden" at

If you are really serious about organic gardening, check out the following web site, "The New Agriculture Network." (Stephanie Porter)

Stephanie Porter

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