. 2000. Alternative seeding dates (fall and April) affect Brassica napus canola yield and quality. Can. J. Plant Sci. 80: [713][714][715][716][717][718][719]. Brassica napus L. canola production on the Canadian prairies often is limited by hot, dry growing conditions in early July and a short growing season. Brassica napus canola seeded in the fall just prior to freeze-up or in the early spring as soon as fields are passable may allow canola to avoid these adverse conditions. Our objective was to determine if late October (fall), or mid-to late April (April) seeding dates improve canola yield and quality relative to a mid-May (15 to 20 May) seeding date. Plant density and height, phenological development, seed yield, seed weight and seed oil content were assessed in plots sown to herbicide-tolerant B. napus canola at three seeding dates on five fallow sites and three stubble sites at Scott, SK, from 1994 to 1998. A thinner plant stand occurred for the fall compared with spring seeding dates; however, this difference rarely corresponded with less canola yield. Fifty percent flowering occurred 20 d earlier (June rather than July), reproductive growth (50% flowering to maturity) was 10 d longer, plants were 23 (fall) or 8 (April) cm shorter, and maturity occurred 13 d earlier when canola was seeded in the fall and April compared with mid-May seeding. Canola seed yield was 38% greater when seeded on the alternative dates rather than the more traditional mid-May seeding date. The yield advantage for alternative seeding dates was greater and more consistent on stubble than on fallow likely because of lack of soil crusting and temperature and wind protection from stubble. The response of seed weight to seeding date was similar to that for seed yield, indicating that a portion of the positive yield response to alternative seeding dates was associated with larger seed size. Oil content also was greater for the fall and April compared with mid-May seeding dates, but the improvement was smaller (6%) than that for seed yield. Fall-and April-seeded canola tolerated spring frosts and avoided adversely hot, dry weather during the flowering period, thus improving canola seed yield and quality. Alternative seeding dates provide canola producers in semi-arid regions with a sustainable option to diversify their cropping systems.Key words: Seeding date, dormant, stubble, fallow, herbicide tolerant, alternative cropping practice.Kirkland, K. J. et Johnson, E. N. 2000. Effets de la date de semis, automne ou avril, sur le rendement et la qualité de Brassica napus (type canola). Can. J. Plant Sci. 80: 713-719. La production du colza (Brassica napus L.) de type canola dans les prairies canadiennes est souvent plafonnée par le temps chaud et sec qui sévit en début de juillet et par la longueur insuffisante de la saison de végétation. Le semis réalisé en automne, juste avant l'installation du gel ou en début de printemps dès que les champs sont praticables permettrait éventuellement d'éviter ces mauvaises conditions. Dans cette optique, n...

Summary. In five long‐term field experiments begun in 1963, each of four herbicides was applied to plots either planted with the same crop each year or uncropped. The following treatments were applied annually: MCPA at 24 oz/ac to barley at the 5‐leaf stage, triallate at 24 oz/ac to barley pre‐emergence, simazine at 24 oz/ac to maize pre‐emergence, linuron at 12–24 oz/ac to carrots preand post‐emergence. The main assessments reported in this paper are crop yield and persistence of herbicide residues. In the fifth experiment, these herbicides were applied twice each year at about double the above these to plots kept as far as possible free from all vegetation. MCPA did not affect the yield of barley and disappeared from the soil within 2–3 weeks of each application. In the uncropped plots, the time for the applied dose (3 lb/ac) to reach the limit of detection was reduced from 3 weeks in 1964 (after three previous applications) to 4 days in 1968 (after ten previous applications). Tri‐allate did not affect the yield of barley. Soil residues could be detected for 5–6 months following each dose of 24 oz/ac. When applied at 48 oz/ac twice yearly, a residue persisted but with no progressive build‐up during the 6‐year period. Agreement between bioassay and CLC methods of determining residues varied from good to a factor of 4, with CLC usually, but not always, providing a higher figure. No residues of pre‐allate could be detected in the barley straw or grain. Simazine did not influence the yield of maize during 1963–67. In 1968 there was a significant reduction in yield of foliage and stems but not in grain yield. Simazine applied to maize disappeared from the soil rapidly during the first 6 weeks; after this period 20–25% of the applied dose could be recovered. The remaining residues declined slowly and 1–2 oz/ac could be detected 23–50 weeks after application. No residues were found below the 0–2 in. soil level. When 48 oz/ac was applied twice annually a residue persisted varying from 8 to 27 oz/ac/6 in. There was no accumulation from year to year and no evidence that repeated treatment influenced breakdown rate. Most of the simazine remained in the 0–2 in. soil level. In three out of four determinations there was good agreement between CLC and bioassay results. Linuron reduced the yield and % dry matter content of carrot roots in 1965 and 1966 probably because of exceptional short‐term phytotoxicity, otherwise there was no effect. Half the applied dose of 8–16 oz/ac disappeared from the soil within 8 weeks and residues were undetectable after 6 months. The residues in the uncropped plots did not fall below 11 oz/ac. Most remained in the 0–2 in. layer of soil but some herbicide was found in the 2–4 and possibly 4–6 in. layers. Progressive build‐up of residues did not occur and repeated treatment did not influence breakdown rate. No linuron could be detected in carrot roots in 1965; in 1966, following an abnormally late application, 05 ppm was found. Chemical analyses of soil samples taken at regular intervals during 1...

Field experiments were conducted in 1990 and 1991 at Scott, Saskatchewan to determine the effect of row spacing (11 22,33,46 cm) and seeding density (50,90,150,220 kg ha-') on thd. ability of spring barley to compete with weeds. Barley yield was greatest with narrow row spacings and increased seeding densities, however there was no spacing x density interaction. Biomass production of wild oats (Avena fatua L.), wild mustard (Brassica kaber (D.C.) L.C. Wheeler) and volunteer canola (Brassica campesrris L.)were significantly reduced by both narrower row spacings and increased seeding densities, but there was no row spacing by seeding density interaction. Adjusting barley rows from 46 to 11 cm produced yield increases over all densities of 77 and 67 percent in 1990 and 1991, respectively. Similarly, increasing the seeding density from 50 to 220 kg ha-' resulted in yield increases of 80 and 93 percent over aU spacings in 1990 and 1991, respectively. mon throughout the prairie cereal growing area and was reported to K. J. Kirkland is the Superintendent at

Knowledge of optimal combinations of graminicide rate and stage of application could improve the effectiveness and net benefit of commonly used graminicides. A study was conducted at two locations in Saskatchewan, Canada, from 1994 to 1997. Factorial combinations of five graminicides (CGA 184927, fenoxaprop-p-ethyl, ICIA 0604, imazamethabenz, and flamprop-methyl), three graminicide rates (full, two-thirds, and one-third recommended label rate), and three leaf stages of wild oat (Avena fatua; two-, four-, and six-leaf) were compared to determine their effect on wild oat fresh weight, wheat (Triticum aestivum) seed yield, and net return. Wild oat fresh weight increased and wheat seed yield decreased to a greater extent at Saskatoon (median wild oat fresh weight of 56 g/m2) than at Scott (median wild oat fresh weight of 85 g/m2) when graminicide rate was reduced from the recommended label rate. Net return consistently decreased at both locations and among all graminicides when application rate was reduced from two-thirds to one-third of the recommended label rate. Imazamethabenz applied at progressively later growth stages caused greater wild oat fresh weight at both locations and reduced wheat yield and net return. Applying other graminicides at the earliest (two-leaf) stage of wild oat generally resulted in more or similar levels of wild oat fresh weight compared with delayed applications, especially at Saskatoon. With the exception of imazamethabenz, crop yield and net return were unaffected by leaf stage at both locations. The optimal graminicide rate is mostly dependent on the level of wild oat infestation, and the best time to control wild oat is dependent mostly on the particular graminicide.