23 Aug What information can you give me on using compost teas to control brown rot on stone fruits?
S.H.PennsylvaniaAnswer: Thank you for contacting ATTRA for information on using compost teas to control brown rot. I cannot answer your question directly because both scientific and anecdotal evidence indicate that you cannot gain a commercial level (or, in the East, practically any level) of brown rot control with compost tea. Monilinia fructicola, the causal agent of brown rot on stone fruits, is very difficult to control, especially in the humid eastern half of the United States. If you haven’t already done so, I urge you to go to our publication on organic and low-spray peach production, http://attra.ncat.org/attra-pub/peach.html. In that publication it explains why brown rot is so very hard to control in the East. And if you look at California organic peach grower Carl Rosato’s data (http://ofrf.org/funded/reports/rosato_92-26.pdf (PDF/2.9MB)), you’ll see that even in the arid West, he did NOT get acceptable commercial-level control of brown rot with compost teas.There is even data to suggest that compost tea sprays could make the brown rot worse! Dr. Linda Chalker-Scott at Washington State University (an organic gardener in her personal life) found that compost tea sprays increased the brown rot when sprayed on cherries. See: Dr. Linda Chalker-Scott, The Myth of Compost Tea Revisited. (PDF/31KB)To unravel the myth and the truth of compost teas as disease suppressants, you might want to go to the web site at Evergreen College (in the state of Washington and very supportive of organic farming) for an excellent powerpoint slide show on the use of compost teas as fungicides/bactericides.Also, you might find this website article (PDF/198.5KB) illuminating. This is a great review article from a Canadian organic research group which summarizes 27 studies using compost tea as a disease suppressant. The conclusions were very mixed. Sometimes it worked and sometimes it didn’t. The variability depended on the nature of the target organism, whether the tea was aerobic or anaerobic, the components of the original compost, etc. In the case of brown rot on stone fruit, only one study suggested any significant control; most suggested no control or even the opposite. In short, especially if you’re trying to grow peaches organically as a commercial enterprise, I would strongly suggest that you rely on sulfur or sulfur/Surround WP (kaolin clay) mix as described in our peach publication. Perhaps in the future, a specific compost tea recipe will be formulated which gives consistent commercial-level control of brown rot on peaches; until then, proceed with caution.