Redstem filaree is becoming widespread and abundant on the Canadian prairies. A field study was conducted to determine the growth, development, and seed yield response of redstem filaree when grown under noncropped conditions and planted at various dates throughout the growing season in Alberta. Redstem filaree emerged within 7 to 13 d of planting with an accumulated 57 to 134 growing degree days (GDD). Flowering occurred within 46 to 65 d (327 to 779 GDD) of planting. Plants that emerged in August or later did not flower in that season and survived as winter annuals. Spring-emerging redstem filaree plants matured within 79 to 100 d (729 to 1,193 GDD). Plants that emerged in May and June attained more biomass and produced threefold more seeds than plants that emerged in July or later. Redstem filaree seed production ranged from 2,400 to 9,900 seeds/plant depending on emergence date and environmental conditions. Information from this study will assist in developing integrated management strategies for this increasingly important weed.

Few postemergence (POST) herbicides provide adequate control of broadleaf weeds in potato. Field experiments were conducted at Lethbridge and Vauxhall, Alberta in 1991 and 1992 to determine the suitability of rimsulfuron and HOE-075032 for selective POST control of weeds in potato. Rimsulfuron applied at 15 to 30 g ai/ha controlled flixweed, kochia, and redroot pigweed and suppressed the growth of redstem filaree. HOE-075032 at 50 to 60 g ai/ha provided comparable control. The potato cultivars, ‘Shepody,’ ‘Norchip,’ ‘Russet Burbank,’ ‘Niska,’ and ‘Ranger Russet,’ tolerated up to 80 g/ha rimsulfuron, but rimsulfuron at 120 g/ha caused fissures in some tubers and reduced marketable and total tuber yields. Tuber quality factors such as specific gravity and chipping ability were not affected by rimsulfuron. HOE-075032 at 15 to 30 g/ha caused fissures in tubers and reduced marketable and total tuber yield of all potato cultivars. Rimsulfuron, but not HOE-075032, provided excellent selective POST broadleaf weed control in potato.

Interference between redstem filaree and round-leaved mallow was studied under controlled environmental conditions. Each species was grown in monoculture at densities of 2, 4, 8, and 12 plants per 20-cm-diam pot and in mixtures at all possible combinations of these densities. Leaf area per plant was similar for both species but round-leaved mallow grew taller and produced more shoot biomass than redstem filaree when each was grown in monoculture. Mixed culture responses varied with the proportion density of each species. A reciprocal yield model was tested and modified to account for this significant density interaction. When grown in mixture, round-leaved mallow usually gained in leaf area and shoot biomass at the expense of redstem filaree indicating that it was the superior competitor. Calculated competition ratios indicate that round-leaved mallow was about twice as competitive as redstem filaree under the growing conditions of this study.

Few postemergence (POST) herbicides are available for broad-spectrum weed control in pea. Field experiments were conducted to determine the suitability of imazamox to provide selective control of grass and broadleaf weeds in pea. Imazamox controlled several grass and broadleaf species, but the rate required to attain 90% control ranged from 7 to 36 g ai/ha depending on the weed species. Imazamox efficacy differed with the adjuvant included in the spray mixture. Merge adjuvant often increased imazamox activity on weeds more than Sun-It II methylated seed oil or a combination of Agral 90 adjuvant plus 28–0–0 liquid fertilizer. Pea exhibited excellent tolerance to imazamox up to the highest rate applied, 40 g/ha. Pea yield comparable to that of the hand-weeded control was attained with 20 to 30 g/ha of imazamox. Imazamox offers growers a POST option for broad-spectrum weed control in pea.

A field study was conducted to determine the effect of increasing seed rates of spring wheat (Triticum aestivum) on redstem filaree (Erodium cicutarium) biomass and seed production and on wheat yield in a zero-tillage cropping system. Wheat was sown at 50, 100, 150, 200, and 300 kg/ha in an experiment four consecutive years to determine annual and accumulated effects over time. Redstem filaree was most competitive with wheat when it emerged before or with wheat and when rainfall was plentiful during May and June. Redstem filaree biomass and seed production were markedly inhibited by drought conditions. An increase in wheat seed rate from 50 to 300 kg/ha reduced redstem filaree biomass and seed production by 53 to 95% over the years. There was little yield benefit to increasing the seed rate of weed-free wheat above 50 kg/ha. However, in the presence of redstem filaree, an increase in wheat seed rate from 50 to 300 kg/ha resulted in wheat yield being increased by 56 to 498%. Over four consecutive years, an increase in wheat seed rate from 50 to 300 kg/ha reduced redstem filaree in the soil seedbank by 79%. Higher seed rates of wheat can be an effective component of an improved program for redstem filaree management in conservation tillage cropping systems.