Rhizoctonia root rot and take-all of wheat in diverse direct-seed spring cropping systems

Abstract

The percent area of patches of wheat plants stunted by Rhizoctonia solani AG8 in years 3 and 4 of a direct seed (no-till) cropping systems study conducted under dryland conditions of Washington state was the same for continuous spring wheat (Triticum aestivum) (no crop rotation), spring wheat after spring barley (Hordeum vulgare), or first- or second-year spring wheat after consecutive crops of safflower (Carthamus tinctorius) and yellow mustard (Brassica hirta). Similar percent area of patches occurred in plots sown to spring barley after spring wheat and in the safflower and yellow mustard. Greenhouse studies confirmed that safflower and yellow mustard as well as several other broadleaf crops are susceptible to R. solani AG8. Between years 3 and 4, some patches increased in size, some new patches formed, and a few patches present in year 3 were not present in year 4. Seventy to 80% of the wheat plants sampled in year 4 of the study had at least 10% roots with take-all caused by Gaeumannomyces graminis var. tritici, including wheat after back-to-back safflower and yellow mustard (not susceptible to this pathogen). A one-time application of zinc at 1.1 kg/ha at planting provided no visual response of the stunted plants where the application passed through one side of a patch. The effect of crop rotation on grain yield of spring wheat related to water supply, with lower yield after the broadleaf crops because they extract more water (leaving less water for the next crop) than either wheat or barley.