Composted waste from urban yards may have reduced brown rot disease in a San Joaquin Valley peach research plot. The plot treated with composted lawn clippings, tree prunings and leaves, showed no incidence of brown rot disease 2 harvests in a row in 1994.

Brown rot affected 20 to 24% of fruit in adjacent research plots treated with traditional composts and fertilizers at typical levels. Also in 1994, unamended (control) peach trees had three times more disease than the trees amended with composted urban waste, according to plant pathologist Themis Michailides.

Peaches grown with composted yard clippings had no brown rot disease.

In a postharvest evaluation of the 1994 first harvest, peaches from compost-amended trees had 0% brown rot and the unamended control had 2.5%. However, 24% of the fruit in the neighboring conventional plot had brown rot. In the second harvest, the compost-amended fruit had 0% brown rot, the unamended had 5%, and the fruit from the conventional plot had 20% brown rot. Michailides, who is based at Kearney Ag Center in Parlier, doesn't know why “green waste” appears to reduce brown rot, but he has a theory.

“We found millions of yeast spores on the fruit surfaces in plots treated with urban compost,” Michailides says. “The more yeast we had on the fruit, the less brown rot developed.”

The green waste compost may carry the harmless yeast into the orchard or may alter the fruit surface to encourage the yeast to grow, he says. Its presence also may block development of brown rot.