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Negative Interplot Interference in Field Experiments with Leaf Rust of Wheat. Kira L. Bowen, Research assistant, Department of Plant Pathology, University of Minnesota, St. Paul 55108; P. S. Teng(2), and A. P. Roelfs(3). (2)Associate professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108; (3)Research plant pathologist, Cereal Rust Laboratory, University of Minnesota, St. Paul 55108. Phytopathology 74:1157-1161. Accepted for publication 30 April 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-1157.

Negative interplot interference occurred between plots of wheat infected with Puccinia recondita f. sp. tritici and led to the overestimation of cultivar resistance. Our study showed that negative interference was greater between two large plots (16 m²) than between two smaller plots (4 m²). Disease in the large plots was also greater. Individual factor effects, guard area widths (2 m and 4 m) and guard crops (wheat and corn) had no significant effect on the amount of interference that occurred; plots separated by 4 m had greater disease severities than those separated by 2 m. The amount of negative interference was least when plots, regardless of size, were separated by a 4-m wheat guard.