INFLUENCE OF FIELD BURNING AND SOIL TREATMENTS ON GROWTH OF WHEAT AFTER KENTUCKY BLUEGRASS, AND EFFECT OF RHIZOCTONIA CEREALIS ON BLUEGRASS EMERGENCE AND GROWTH

摘要

Studies were conducted to assess the importance of soil-borne pathogens as impediments to the production of direct-drilled wheat following Kentucky bluegrass in rotation. Bluegrass sods were collected as cores from commercial seed fields in October (after open-field burning) and in December and March (after exposure to normal freezing and thawing), treated with glyphosate after a 2- to 3-week period of green-up in the glasshouse, and then planted to wheat 21 days later. Wheat seedlings in the 3- to 4-leaf stage were stunted and spindly in either burned or nonburned sods collected in October, but grew significantly better in burned than nonburned sods collected in December and March. Fumigation (methyl bromide), simulated tillage, and application of metalaxyl as a drench, singly or as combined treatments, improved the growth of wheat in nonburned sods. Growth of wheat in nontreated burned sods collected after frost had penetrated the upper portions was equivalent to that in fumigated sods. Experimental freezing at -20 degrees C for up to 96 h, of burned and nonburned sods collected in October, followed by thawing also improved the growth of wheat subsequently sown directly into these sods. The stunted and spindly seedlings had roots girdled and severed by lesions typical of Rhizoctonia root rot. Isolates of Rhizoctonia cerealis were recovered from these roots and caused poor seedling emergence and stunted root and shoot growth of both wheat and bluegrass. The results suggest that both R. cerealis and Pythium spp. are potentially important soil-borne pathogens of wheat when following Kentucky bluegrass in rotation and that burning done routinely to improve the yield of bluegrass seed can also reduce the potential for damage caused by Rhizoctonia and Pythium root rots of wheat seeded directly into bluegrass sod.