Fungi Algae And Disease

Excessive moisture in the air (humidity), on the leaf, and within growing media are the leading causes of fungi and mold outbreaks. Fungi are spread by spores that are carried aloft in the air. Spores are present all around us, and can be avoided only by using the strictest air quality standards. Unfortunately, maintaining this level of air quality standards is practical only in the laboratory with the use of expansive filters and air scrubbers. For gardeners, your first line of defense against fungi such as gray mold, powdery mildew, and damping off is to pay close attention to the following conditions that will readily allow spores to colonize.

  1. Maintain low humidity - 60-80%
  2. Insure proper ventilation - keep air in the garden moving!
  3. Remove all dead and dying organic matter (leaf and stem)
  4. Never over-water when growing with media!

Additional preventative measures can be taken to avoid fungi outbreaks. These measures include the use of powdered sulfur and copper; however, their use requires extreme caution because they can rapidly damage new growth if used excessively. If fungi become a persistent problem in your garden, even with preventative maintenance, you essentially have no choice but to employ a fungistat or fungicide.

Botrytis, or gray mold, is the most common fungi that plagues garden plants. It's a problem I know all too well. In July 2002, during a solid two weeks of rain, I lost an entire crop of cucumbers to this fungi. Although the humidistat in my greenhouse made sure the exhaust fans were running day and night, the moist cool air they were drawing in did little to keep moisture off the plants. Since it was the middle of July, I had my Dutch bucket system's watering cycles set for sunny skies and hot, dry air. With the sun blocked by clouds, and the air at nearly 100% humidity, transpiration slowed to a crawl and this unfortunate combination of events resulted in over-watering. Since Botrytis is present in the air at all times, the combination of these two conditions caused an explosive outbreak. It was a painful lesson to learn. So if you encounter similar conditions, keep this in mind.

Grey Mildew Stems Plants
Grey mold more commonly know as Botrytis is shown here on this fallen cucumber stem. Its cause was a combination of over-watering and excessive humidity in the greenhouse.
Grey Mold Cucumber

Powdery Mildew flourishes in cool areas with high humidity, particularly after long periods of rain which make maintaining optimal humidity difficult. Sulfur pots are used in commercial greenhouses to fight this problem since the burning sulfur changes the pH on the leaf surface making it uninhabitable for molds and mildew

Powdery Mildew flourishes in cool areas with high humidity, particularly after long periods of rain which make maintaining optimal humidity difficult. Sulfur pots are used in commercial greenhouses to fight this problem since the burning sulfur changes the pH on the leaf surface making it uninhabitable for molds and mildew

Rockwool Cubes
Excessive moisture in this rockwool cube led to the demise of several pepper seedlings as shown here suffering from damp-off.
Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook


Post a comment