Less than 3 years ago,
researchers in South America discovered a new alternative to controlling
powdery mildew. Wagner Bettiol 1,
a scientist from Brazil, found that weekly sprays of milk controlled powdery
mildew in zucchini just as effectively as synthetic fungicides such as fenarimol
or benomyl. Not only was milk found to be effective at controlling the disease,
it also acted as a foliar fertilizer, boosting the plant's immune system.
Powdery mildew in the cucurbit family is caused by the organism Sphaerotheca fuliginea. It is a
serious disease that occurs worldwide. For decades, organic gardeners had to
rely on making a spray from baking soda to control the disease. Now, instead
of measuring out the baking soda and combining it with a surfactant (a
"sticking" substance) of either oil or soap, gardeners need only head for
their refrigerators.
In his experiments with zucchini plants, Bettiol
found that a weekly spray of milk at a concentration of at least 10% (1 part
milk to 9 parts water) significantly reduced the severity of powdery mildew
infection on the plants by 90%. While some gardeners may be tempted to
increase the concentration of milk for more control, Bettiol found that once
concentrations rose above 30%, an innoccuous fungus began to grow on the
plants.
How does milk control powdery mildew?
Scientist aren't 100% sure how milk works to control this disease. It seems that milk is a
natural germicide. In addition, it contains several naturally occurring salts
and amino acids that are taken up by the plant. From previous experiments
using sodium bicarbonate, potassium phosphate, and other salts, researchers
have found that the disease is sensitive to these salts. It is possible then,
that milk boosts the plant's immune system to prevent the
disease.
Milk used around the world
The benefits of using milk to control powdery mildew haven't been isolated to Brazil. Melon growers in New
Zealand are saving thousands of dollars every year by spraying their crops
with milk instead of synthetic fungicides. The melon growers in New Zealand
have been so successful that the wine industry is taking notice and beginning
experiments using milk to control powdery mildew in grapes.
What kind of milk should be used?
In Bettiol's original experiment, fresh milk was
used, straight from the cow. However, this is obviously not feasible to most
home gardeners. The research work in New Zealand actually found that using
skim milk was just as effective. Not only was it cheaper, but the fact that
the milk had no fat content meant that there was less chance of any odours.
1 Wagner Bettiol's original article was published in the journal Crop Science
(Vol. 18, 1999, pp. 489-92). It can be found on-line at:
http://147.46.94.112/journal/sej/full/c12_199908_180801.pdf
Arzeena Hamir is an agronomist and garden writer based in Vancouver, BC. She has a Master's Degree in
Agriculture and specializes in organic vegetable gardening. She frequently writes articles for websites: Suite101,
GardenGuides and ICanGarden. When not tending her own veggie
patch, she runs Terra Viva Organics.
go to Terra Viva Organics now !
