Mr. Kretschmann is an organic vegetable farmer. He was interested in seeing whether foliar application of water extracts made from compost would be an effective method of controlling fungal diseases. He also wanted to know whether the age of the compost might have any bearing on its efficacy.
He made composts out of leaves and chicken manure, extracted them with water, then sprayed the extracts weekly on his tomato plants. Some extracts came from a compost pile that had been made the previous winter, and some from a pile made the winter before that. The experiment was run in triplicate, and with untreated controls, on field-grown tomatoes.
Mr. Kretschmann observed Septoria leaf spot and early blight on all plots. He also reports some small incidence of late blight. By the end of the season almost all plants were affected. Disease incidence may have been slightly lower among those plants treated with extracts made from the younger compost, but the effect would probably not be statistically significant. He did, however, make the serendipitous finding that of the two tomato varieties he was growing– Belstar and Sunbeam– the former was distinctly more susceptible to fungal disease.