Economic thresholds for wild radish, wild oat, hemp-nettle and corn spurry in spring barley

Abstract

The yield response of spring barley (Hordeum vulgare L. 'Morrison') to a range of densities of wild radish (Raphanus raphanistrum L.), wild oat (Avena fatua L.), hemp-nettle (Galeopsis tetrahit L.), and corn spurry (Spergula arvensis L.) was investigated in field experiments on Prince Edward Island from 1991 through 1994. Barley yield was modelled as a function of both barley and weed density. In the absence of weed competition, barley seed yield, number of main shoots, number of heads, and thousand-kernel weight varied significantly during the 4 yr of the study. Increasing densities of wild radish and wild oat reduced the number of barley heads primarily by interfering with tillering, but wild oat also reduced barley thousand-kernel weight. Hemp-nettle and corn-spurry at densities up to 200 plants m −2 had little effect on barley yield, except in a year of low barley yield potential. Estimated economic thresholds for wild radish, wild oat, hemp-nettle and corn spurry at a barley population of 250 plants m −2 were 37, 45, 122 and 297 plants m −2 , respectively, assuming a weed-free yield of 4 t ha −1 , a crop price of $100 t −1 , and weed control costs of $30 ha −1 . Key words: Avena fatua, Galeopsis tetrahit, Hordeum vulgare, Raphanus raphanistrum, Spergula arvensis, yield loss, weed interference, economic threshold