Fighting Blight and Fungal Problems in an Organic Garden


Blight is one of the most serious fungal problems you could encounter in an organic garden. So how should you handle this and other fungal issues? As a garden designer and consultant, I am often asked how to deal with this problem. The answer, as with so many things, is that prevention is better than cure.

What is the burn?

Blight is the name given to a range of fungal infections that can attack different plants. The type of blight most commonly referred to, however, is a blight that attacks potatoes, tomatoes, and other members of the same plant family, also called “downy mildew.”

Throughout history, many catastrophic crop losses have occurred due to this fungal infection, caused by a microorganism called Phytophthora infestans. He was implicated in famines in Europe in the 1840s, including the notorious potato famines in Ireland and Scotland.

Home growers in many regions face this problem, and although we are not generally dependent today on a small number of crops, and therefore generally do not have as large an impact as in the past, it can still cause yields to drop dramatically. .

When blight occurs, fungal spores spread through plant tissues, creating brown areas on foliage that spread into a wet rot. It can spread from leaves to stems, flowers and fruits or tubers if left unchecked. The spores persist in the soil for years, creating a difficult problem to eradicate from a growing area once it takes hold.

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Prevent burn

Although it may be very difficult, if not impossible, to completely eliminate the risk of blight, you greatly reduce the risk of serious infestation of this problem or other serious fungal problems by doing the following:

  • Place plants in optimal locations with ideal growing conditions. The healthier the plants, the less likely they are to succumb to disease.
  • Grow blight resistant varieties which, although not usually fully immune, are less likely to have a serious problem.
  • Harvesting early, before late blight is likely to become a problem, for example, growing early potatoes to harvest before July.
  • Get the correct spacing with your potatoes, tomatoes and other crops so that there is good air circulation between the plants.
  • Water the soil at the base of the plant rather than from above; try to avoid wetting the leaves as much as possible; and water early in the day so the plant dries out more before nightfall.
  • Prune lower leaves and use mulch to minimize splashing of spores on plants.
  • Make sure you don’t grow potatoes, tomatoes, or other related plants in the same spot year after year. Practice crop rotation to reduce the chances of fungal buildup in the soil.

What to do for burns

If you spot the blight on your plants, it’s important to act as soon as possible to reduce its spread. The sooner you remove affected material, the greater the chance of containing the outbreak.

Take any affected material and discard it. Keep it away from your garden and composting areas. Practice good hygiene, wash your hands and gardening tools so you don’t spread the disease to other plants in your garden.

If the problem has not spread too much, you may consider spreading an antifungal treatment to other currently unaffected but susceptible plants nearby. For example, you can use a spray of baking soda in water (10 grams per 1 liter of water), applied carefully above and below all leaves early in the morning. There are also fungicides that contain a bacteria called Streptomyces lycidus that you could use.

This spray and others of its type will not eliminate all risks and are not entirely effective. But they could somewhat reduce the chances of the problem spreading.

If the problem has spread too far, unfortunately, such measures will do little to help. That’s why it’s so important to stay alert and act quickly.

With potatoes in particular, there is another drastic measure you might be able to take to save at least some of your crop. If more than a quarter of the leaves of the potato plants show burns, cut off all stems at ground level, remove all material and discard immediately. After a few weeks, you can then dig up your potatoes; these may not be affected and you can eat or store them as normal.

If you have severe blight or other severe fungal problems on tomatoes or other crops, you may lose all yield this year. But by taking the prevention measures mentioned above, you should reduce the chances of the same thing happening next year.


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