Travelling to the Netherlands is an eye-opening experience. The Dutch grow nearly all of their vegetables in zero-runoff hydroponic systems in sophisticated computer-controlled greenhouses, and they are famous for high yields of gourmet-quality produce. Impressive! They are also very strict about the use of pesticides and fungicides. In the year 2000, the Dutch government made the use of all synthetic fungicides illegal on food crops. Overnight many of the strawberry growers were losing 40% of their crops to powdery mildew, grey mold and the like. The hydroponic growers had to do something; so they began experimenting with organic biostimulants in tiny dosages. Amazingly, they worked! In 2001, I was invited to the Netherlands to interview the strawberry growers who were doing the first biostimulant trials for the Dutch government. They reduced their losses from 40% down to zero, they enjoyed a 10-20% increase in yield over any past year, and they were first in the line for sugar content in the fruit… all with a completely organic, ECO-1 product with no harmful chemicals.
Unfortunately, the scientists I interviewed in Holland told me that their formula was “proprietary” and they wouldn’t tell me how it worked. But that only made me more determined to solve the mystery. After all, at that time strawberry growers in the United States were fumigating the soil with methyl bromide, a chemical that not only kills life in the soil, but destroys the ozone in the atmosphere at the same time! I was inspired, motivated, and I knew there had to be a better way. After all, I had seen it with my own eyes.
After years of research and experimentation in plant physiology, microbiology and plant nutrition, the pieces finally came together! Amino acids were the key. My well water is loaded with calcium and magnesium carbonate, and lime scale used to turn my reservoirs into rock gardens! But when I started experimenting with an amino acid blend I received from a vitamin manufacturer out East, there was no more lime scale. So where did all of that extra calcium go? Into the plants! I learned that certain amino acids stimulate root cells to open up calcium ion channels, allowing the plants to take up calcium thousands of times faster than simple osmosis!
Calcium is taken up through the roots and transported with the water throughout the plant. Some of the calcium reacts with pectic acid to form “pectin”, the glue that binds the cell walls together. So instead of water between the cells, the plants had extra pectin between the cells. The plants became exceptionally strong and healthy, with thicker cell walls, and I never had to spray a single fungicide or insecticide the entire season.
Here’s how it works. When a mold spore lands on a plant leaf it wants to send down a feeding tube to get to the water between the cells to germinate and spread. But when the cell walls are thicker and there is increased calcium-pectate between the cells, the mold spores just sit there. By the time the germination tube penetrates the cells, it dries up and dies! The pectin doesn’t kill the powdery mildew; it just prevents powdery mildew from becoming systemic in the plant and spreading.
The increased calcium uptake also provides a reserve of natural protection against powdery mildew. Any extra calcium that a plant doesn’t use to strengthen the cell walls is pumped into a storage vacuole inside the cell. If a mold spore does happen to germinate, sensors on the surface of the leaf detect the chitin in the cell wall of the fungus. Plants don’t contain chitin; they contain cellulose. So when chitin is detected, the plant sends a signal molecule from the leaf surface down to the vacuole, opening up calcium ion channels inside the cell. The calcium ions released start a chain reaction that causes an oxidative burst, the plants first line of defense against powdery mildew! So the judicious use of biostimulants containing amino acids will help improve the plant’s natural resistance to pests and disease, with no harmful side effects to human beings or to the environment.
In addition to supplementing amino acids with a full plant nutrition program, here are a few more ways to prevent or eradicate powdery mildew from your garden.
Don’t over-fertilize with nitrates. Too much nitrate nitrogen encourages soft growth. The plants will develop large cells with thin cell walls, making them more susceptible to powdery mildew.
Avoid high humidity. High humidity sets up the perfect environment for molds and mildews, and it also interferes with calcium uptake.
Avoid large swings in relative humidity. It’s best to maintain relative humidity between 40-60%, with 50% being a good target. If powdery mildew starts to get established, drastically lowering humidity actually stimulates the fungus to make more spores and spread!
Provide good air movement. Provide plenty of space for your plants and use oscillating fans to produce a gentle breeze in your garden. Stagnant air allows moisture to build up on the undersides of the leaves, creating a vapor barrier. If transpiration is disrupted, calcium uptake will be disrupted as well. Adding filters on all intake vents is also a good idea.
Remove infected leaves. At the first sign of powdery mildew, carefully remove infected leaves and discard them from the grow room. Be careful not to spread the spores in the process.
Rinse spores from leaves. Leaf washes can be very effective at killing and removing powdery mildew spores. Powdery mildew spores don’t germinate from surface water on the leaves, so spores can be washed off all the way to the day of harvest. Allow adequate time for the leaves to dry so that other fungi aren’t encouraged.
Spray yucca extracts. Yucca is a natural surfactant that can be safely added to any foliar spray. Instead of the water beading up on the waxy surface of the leaves, the spray will spread out in a thin film for better coverage. Yucca is also known to have natural fungicidal properties.
Add silica. When a plant is under attack from powdery mildew and other fungi, the plant mobilizes silica to the point of infection to form callus around the surrounding cells. The silica will help prevent the disease from spreading.
Spray with potassium bicarbonate. Potassium bicarbonate additives can help kill powdery mildew spores on contact, while increasing the pH on the surface of the leaves. pH above 8.3 on the surface of leaves discourages fungi.
Use botanical oils. Some horticultural oils and essential oils improve the effectiveness of fungicidal sprays. But don’t combine oils with sulfur treatments!
Treat with biologicals. Some microorganisms produce natural plant protection agents against pathogenic fungi. Inoculate your soil with a good “maintenance” blend of plant growth promoting rhizobacteria, and occasionally spray your plants with products containing streptomyces lidicus or other beneficial microbes.
Apply systemic fungicides. Most organic controls for powdery mildew only help slow down or contain the fungi, but systemic fungicides kill powdery mildew at the source. Just make sure that the chemical fungicide is rated for consumable crops, and carefully follow all application instructions. Stay away from any fungicide that is only rated for ornamentals!
Alternate treatments. If you must use fungicides, it’s always best to follow up with treatments that have different modes of action. If you use the same active ingredient too many times, the treatment may start to lose its effectiveness over time.
Once your crop is infected with powdery mildew, it is always a battle to knock it down and keep it under control. So the best defense is growing strong, healthy, disease-resistant crops. It’s also a good idea to choose seeds and clones from well-respected breeders. The best breeders choose stock plants that are naturally resistant to powdery mildew and other pathogens, and they grow in a disease-free environment. Know your source! After that, it’s up to you. If you provide your plants with a healthy environment and feed them a balanced blend of nutrients and organic biostimulants, you can help your plants reach their true genetic potential. It’s also a lot more fun!
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