As a weed, wheat has recently gained greater profile. Determining wheat persistence in cropping systems will facilitate the development of effective volunteer wheat management strategies. In October of 2000, glyphosate-resistant (GR) spring wheat seeds were scattered on plots at eight western Canada sites. From 2001 to 2003, the plots were seeded to a canola–barley–field-pea rotation or a fallow–barley–fallow rotation, with five seeding systems involving seeding dates and soil disturbance levels, and monitored for wheat plant density. Herbicides and tillage (in fallow systems) were used to ensure that no wheat plants produced seed. Seeding systems with greater levels of soil disturbance usually had greater wheat densities. Volunteer wheat densities at 2 (2002) and 3 (2003) yr after seed dispersal were close to zero but still detectable at most locations. At the end of 2003, viable wheat seeds were not detected in the soil seed bank at any location. The majority of wheat seedlings were recruited in the year following seed dispersal (2001) at the in-crop, prespray (PRES) interval. At the PRES interval in 2001, across all locations and treatments, wheat density averaged 2.6 plants m−2. At the preplanting interval (PREP), overall wheat density averaged only 0.2 plants m−2. By restricting density data to include only continuous cropping, low-disturbance direct-seeding (LDS) systems, the latter mean dropped below 0.1 plants m−2. Only at one site were preplanting GR wheat densities sufficient (4.2 plants m−2) to justify a preseeding herbicide treatment in addition to glyphosate in LDS systems. Overall volunteer wheat recruitment at all spring and summer intervals in the continuous cropping rotation in 2001 was 1.7% (3.3 plants m−2). Despite the fact that volunteer wheat has become more common in the central and northern Great Plains, there is little evidence from this study to suggest that its persistence will be a major agronomic problem.

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.

Sulfentrazone is a phenyl triazolinone herbicide used for control of certain broadleaf and grass weed species. Sulfentrazone persists in soil and has residual activity beyond the season of application. A laboratory bioassay was developed for the detection of sulfentrazone in soil using root and shoot response of several crops. Shoot length inhibition of sugar beet was found to be the most sensitive and reproducible parameter for measurement of soil-incorporated sulfentrazone. The sugar beet bioassay was then used to examine the effect of soil properties on sulfentrazone phytotoxicity using 10 different Canadian prairie soils. Concentrations corresponding to 50% inhibition (I50values) were obtained from the dose–response curves constructed for the soils. Sulfentrazone phytotoxicity was strongly correlated to the percentage organic carbon (P = 0.01) and also to percentage clay content (P = 0.05), whereas correlation with soil pH was nonsignificant (P = 0.21). Because sulfentrazone phytotoxicity was found to be soil dependent, the efficacy of sulfentrazone for weed control and sulfentrazone potential carryover injury will vary with soil type in the Canadian prairies.

. 2010. Variation in chickpea germplasm for tolerance to imazethapyr and imazamox herbicides. Can. J. Plant Sci. 90: 139Á142. Tolerance to the imidazolinone class of herbicides would be a desirable agronomic trait for chickpea (Cicer arietinum L.) grown in western Canada. Identification of germplasm tolerant to imidazolinones and incorporation of this tolerance into future varieties will allow an integrated weed management strategy in chickpea. The current study evaluated the variation of diverse chickpea germplasm and cultivars available in Canada for tolerance to the imidazolinone class of herbicides under greenhouse conditions. Large differences among the genotypes in response to a mixture of imazethapyr and imazamox were observed. Several accessions were identified with tolerance to a mixture of imazethapyr and imazamox. Conventional breeding for imazethapyr/ imazamox tolerance in chickpea is feasible. The simple screening used in the current study allows for rapid progress towards the development of herbicide-tolerant cultivars.

A study was conducted at three locations in Saskatchewan, Canada, in 1996 and 1997 to determine if increasing the seeding rate of wheat, barley, and lentil by 50% would maintain weed control and crop yield when herbicides are applied at reduced rates or not at all. Three herbicide rates (½ of full, ¾ of full, and full recommended label rate), along with an untreated check, two crop seeding rates (normally recommended and 1.5 times normally recommended rates), and three crops were tested. Increasing seeding rate did not affect weed fresh weights, crop yield, and net return responses to herbicides applied at reduced rates or not at all when averaged across crops, years, and locations. Increased seeding rate, independent of the different herbicide applications, had infrequent and inconsistent effects among the crop by year by location combinations. More broadleaf and grass weed growth, less crop yield, and lower net returns generally occurred when herbicides were not applied or applied at reduced rates. These trends were especially prominent when herbicides were not applied to cereal crops at Saskatoon (40% yield reduction) and when herbicides were applied at ½ the full label rate rather than higher herbicide rates to wheat at the other two locations (16% yield reduction). In 1996, lentil yield and net returns did not respond to herbicide application and rate because of poor grass weed control across all herbicide rates. Lentil yield and net returns decreased by 11% (full vs. ¾), 22% (¾ vs. ½), and 46% (½ vs. none) when herbicides were applied at progressively lower rates in 1997. Reduced herbicide rates did not affect net returns for cereal crops, indicating that herbicide rates lower than the full label rate may be economically viable in certain crops.