DISTRIBUTION OF SETARIA VIRIDIS IN WESTERN CANADA

Abstract

Setaria viridis (L.) Beauv. (green foxtail) was present in 84, 32, and 28% of the 406 fields surveyed in Manitoba, Saskatchewan, and Alberta, respectively. In Alberta and Saskatchewan, S. viridis occurred more frequently on moderately coarse- to coarse-textured soils than on finer soils. Densities and the extent of infestation in each field was greater on coarse-textured soils than on fine-textured soils in these two provinces. However, in Manitoba, the presence of this species was not related to soil texture, since the frequency of occurrence in fields, the extent to which each field was infested, and the maximum densities recorded in each infestation were uniformly high for all soil textural groups. In Manitoba, 43% of the infestations included densities of 1000 or more plants per m2 and the highest density recorded was 10,000/m2. This weed is more widespread than was reported in previous surveys and infests nearly 28% of the cultivated acreage in Western Canada. In laboratory tests, emergence was similar in clay, loam, or sandy loam soils kept at field capacity or at higher moisture levels within a temperature range of 10–24 C. Emergence was reduced by planting at depths below 5 or 7.6 cm, depending upon soil moisture. Germination increased with temperature, and it is suggested that coarse-textured soils are invaded most readily because they warm up faster than fine-textured soils. Cropping practices may also affect distribution since the buildup of S. viridis is believed to be checked by summer-fallowing. The frequency of summer-fallowing in Manitoba is lower than in Saskatchewan. This may account for the high populations of S. viridis in Manitoba.