Spraying milk on cucumbers kills mildew

October 13, 1999

THE doorstep pint has the makings of an ideal fungicide for protecting organically grown cucumbers and other vegetables, according to researchers in Brazil. It attacks a mould known as powdery mildew, which is a major problem for organic farmers scrambling to meet the growing demand for chemical-free vegetables.

The mould, Sphaerotheca fuliginea, appears as a powdery white growth on the leaves of cucumbers and courgettes (zucchini). It damages the plants by causing the leaves to shrivel up. At present, only chemical fungicides are available.

Milk's fungicidal powers were discovered by Wagner Bettiol of the environmental laboratory of Embrapa, the Brazilian Agricultural Research Corporation, in Jaguariuna, north of São Paulo. Bettiol, who was looking for cheap ways to control plant pests, observed that byproducts from milk-processing factories killed powdery mildew on courgettes. So he decided to simply spray fresh milk on the plants to see if it had the same effect. To his surprise, he found that it did. In fact, spraying heavily infected plants twice a week with a mixture of one part cow's milk to nine parts water was at least as good at stopping mildew as the chemical fungicides fenarimol and benomyl, Bettiol discovered.

In many cases, milk was both faster and more effective. After two to three weeks of spraying with milk, the area of leaves infected was in some cases only a sixth or less of the area affected on plants treated with chemical fungicide (Crop Protection, vol 18, p 489). Bettiol says several organic growers in his region have successfully controlled less severe mildew infections on courgettes and cucumber by spraying once a week with 5 per cent milk solutions.

Bettiol is not yet sure why milk works so well, but he speculates that it helps the plants in two ways. Milk is known to kill some microorganisms. It also contains potassium phosphate, which boosts the plant's immune system and so may help it inhibit the mildew's growth.

"If this works, it could be very useful," says Rob Haward of the Soil Association, which sets standards for organic farming in Britain.
-end-
Author: Debora MacKenzie

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New Scientist

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