Got Mildew? Get Milk!
by Arzeena Hamir

Less than 3 years ago, researchers in South America discovered a new
alternative to controlling powdery mildew. Wagner Bettiol, 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.

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 writer for Organic Living Newsletter. You
can subscribe to this free e-newsletter at www.tvorganics.com