Natural Suppression of Rhizoctonia Bare Patch in a Long-Term No-Till Cropping Systems Experiment.

The soil-borne fungus Rhizoctonia solani AG-8 is a major concern for farmers who practice no-till in the inland Pacific Northwest, USA.  Bare patches caused by Rhizoctonia first appeared in 1999 during year 3 of a 15-year no-till cropping systems experiment near Ritzville, WA (269 mm annual precipitation).  The extent and pattern of patches were mapped each year from 1999-2012 at the 8-ha study site with a backpack-mounted global positioning system (GPS) equipped with mapping software.  Bare patches appeared in winter and spring wheat (Triticum aestivum L.), spring barley (Hordeum vulgare L.), yellow mustard (Brassica hirta), and safflower (Carthamus tinctorius L.).  At its peak in years 5 to 7, bare patches occupied as much as 18% of total plot area.  The area of bare patches began to decline in year 8 and reached near zero levels by year 11.  No measurable patches were present in years 12 to 15.  Patch area was significantly greater in continuous annual monoculture spring wheat (SW) compared to SW grown in a 2-year rotation with spring barley (SB).  Additionally, the 15-year average grain yield for SW in rotation with SB was significantly greater than for continuous SW.  Russian thistle (Salsola tragus L.), a troublesome broadleaf weed with aggressive and fast-growing tap root, was the only plant that grew within patches.  This paper reports the first direct evidence of natural suppression of Rhizoctonia bare patch with long-term no-till in North America, and the first in the world literature to document natural suppression for crops other than monoculture wheat.