Crop diversification and crop sequencing can influence plant disease risk in cropping systems. The objective of this research was to determine the effect of 10 previous crops on leaf spot diseases of barley ( Hordeum vulgare L.) and hard red spring wheat ( Triticum aestivum L.). Barley and spring wheat were direct-seeded (no till) in the crop residue of 10 crops {barley, canola ( Brassica napus L.), crambe ( Crambe abyssinica Hochst. ex R.E. Fr.), dry bean ( Phaseolus vulgaris L.), dry pea ( Pisum sativum L.), flax ( Linum usitatissimum L.), safflower ( Carthamus tinctorius L.), soybean [ Glycine max (L.) Merr.], sunflower ( Helianthus annuus L.), and spring wheat}. Barley was evaluated for leaf spot diseases 15 times over 2 yr. Results indicate that risk for leaf spot disease on barley would be lower following wheat, crambe, canola and dry pea compared with the barley-after-barley treatment. Although barley yields were similar across all treatments one year, differences were detected in another year with the barley-after-barley treatment having the lowest yield. Spring wheat was evaluated for leaf spot diseases 22 times over 2 yr. Differences among treatments were more detectable in earlier evaluations, indicating a greater influence of crop residue and carryover of inoculum early in the season compared with later. The risk for leaf spot disease was lower when wheat was grown after canola, barley, crambe, and flax than when grown after the other crops. Although wheat yields were similar across all treatments one year, differences were detected in another year with the wheat-after-wheat treatment having the lowest yield.
