Frederick A. Holm

Appropriate Crop Seeding Rate When Herbicide Rate is Reduced1

Abstract: 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. Nomenclature: Barley, Hordeum vulgare L.; hard red spring wheat, Triticum aestivum L.; lentil, Lens culinaris Medic. Additional index words: Integrated weed management, weed interference, economic return.

Defining Optimum Herbicide Rates and Timing for Wild Oat (Avena fatua) Control in Spring Wheat (Triticum aestivum) 1

Abstract: 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. Nomenclature: CGA 184927 (proposed common name, clodinafop propargyl), 2-propynyl-(R)-2-[4-(5-chloro-3-fluoro-2-pyridyloxy)-phenoxy]-propionate; fenoxaprop-p-ethyl, (±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid; flamprop-methyl, N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine; imazamethabenz, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-4(and 5)-methylbenzoic acid (3:2); ICIA 0604 (proposed common name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enone; wild oat, Avena fatua L. #3 AVEFA; hard red spring wheat, Triticum aestivum L. ‘CDC Makwa’ and ‘CDC Teal.’ Additional index words: Graminicides, leaf stage, application parameters, weed interference, economic return.

Herbicide resistant transgenic flax field test : Agronomic performance in normal and sulfonylurea-containing soils

SummaryTwo linseed flax (Linum usitatissimum) lines transformed with a mutant Arabidopsis ALS gene conferring resistance to sulfonylurea herbicides were tested in a replicated, randomized field test against its nontransformed commercial cultivar parent (cv. NorLin) in normal soil and in soil containing the commonly used sulfonylurea herbicides chlorsulfuron (Glean®) or metsulfuron methyl (Ally®). There were no significant differences between the transgenic lines and the parent for any agronomic trait measured in untreated soil, indicating that there is no detrimental effect of T-DNA or foreign gene expression. Similarly, there were no significant differences for performance of the transgenic lines between the untreated and the herbicide treated soils, indicating that the transferred gene does confer a field level of tolerance to the flax. The control NorLin was devastated by the presence of the herbicides in the soil.

Glyphosate-resistant wheat persistence in western Canadian cropping systems

Abstract 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. Nomenclature: Barley, Hordeum vulgare L.; canola, Brassica napus L.; field pea, Pisum sativum L.; spring wheat, Triticum aestivum L.

Development of a Laboratory Bioassay and Effect of Soil Properties on Sulfentrazone Phytotoxicity in Soil

Abstract 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 (I50 values) 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. Nomenclature: Sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl]methanesulfonamide; sugar beet, Beta vulgaris L. ‘Beta 1385’.

Environmental Effects on the Relative Competitive Ability of Canola and Small-Grain Cereals in a Direct-Seeded System

Abstract Growing crops that exhibit a high level of competition with weeds increases opportunities to practice integrated weed management and reduce herbicide inputs. The recent development and market dominance of hybrid canola cultivars provides an opportunity to reassess the relative competitive ability of canola cultivars with small-grain cereals. Direct-seeded (no-till) experiments were conducted at five western Canada locations from 2006 to 2008 to compare the competitive ability of canola cultivars vs. small-grain cereals. The relative competitive ability of the species and cultivars was determined by assessing monocot and dicot weed biomass at different times throughout the growing season as well as oat (simulated weed) seed production. Under most conditions, but especially under warm and relatively dry environments, barley cultivars had the greatest relative competitive ability. Rye and triticale were also highly competitive species under most environmental conditions. Canada Prairie Spring Red wheat and Canada Western Red Spring wheat cultivars usually were the least competitive cereal crops, but there were exceptions in some environments. Canola hybrids were more competitive than open-pollinated canola cultivars. More importantly, under cool, low growing degree day conditions, canola hybrids were as competitive as barley, especially with dicot weeds. Under most conditions, hybrid canola growers on the Canadian Prairies are well advised to avoid the additional selection pressure inherent with a second in-crop herbicide application. Combining competitive cultivars of any species with optimal agronomic practices that facilitate crop health will enhance cropping system sustainability and allow growers to extend the life of their valuable herbicide tools. Nomenclature: Barley, Hordeum vulgare L.; canola, Brassica napus L. or Brassica rapa L.; oat, Avena sativa L.; rye, Secale cereale L.; triticale, × Triticosecale W.; wheat, Triticum aestivum L.

Transgenic flax with environmentally and agronomically sustainable attributes

Among the major concerns raised about the commercialization of transgenic herbicide-resistant crop cultivars are the fear that such lines will increase chemical usage and non-sustainable agronomic practices, that the transgenes will not be efficacious under field conditions, or that there will be an agronomic penalty, such as reduced seed yield, in exchange for the new trait. To address these concerns, transgenic sulfonylurea-resistant flax (Linum usitatissimum L.) lines were tested in replicated, randomized field trials over three years. The results show that at least one transgenic line is fully resistant to the field doses of the herbicides, shows no agronomic penalties regardless of the presence or absence of the herbicides, and will lead to less chemical usage and more sustainable agronomic practices in commercial production.

Optimizing Wild Oat (Avena fatua) Control with ICIA 06041

Abstract: Wild oat (Avena fatua) control often is an integral management practice in cropping systems that include cereal crops. Experiments were conducted at two locations in Saskatchewan (Saskatoon and Scott), Canada, from 1994 to 1997 to determine the influence of ICIA 0604 rate (50, 100, 150, and 200 g ai/ha), water volume (30, 50, and 100 L/ha), spray mixture pH (unbuffered, close to pH 7.0; reduced, pH 4.0), late morning and evening application times, and sodium bicarbonate concentration of water source (Saskatoon water, negligible; Scott water, 695 mg/L) on wild oat fresh weight and wheat (Triticum aestivum) grain yield. Reducing ICIA 0604 rate below the recommended label rate (200 g/ha) increased wild oat fresh weight by 22% and decreased wheat grain yield by 7% when applied with 50 or 100 L/ha of water. Applications with 30 L/ha of water resulted in more wild oat growth (19%) and less wheat yield (6%), regardless of the ICIA 0604 rates. Spray mixture pH or time of application did not modify the effects of ICIA 0604 rate and water volume on wild oat fresh weight and wheat yield at Saskatoon. At Scott, the negative effects of ICIA 0604 rates lower than 200 g/ha applied with 50 or 100 L/ha of water were most apparent when applications were made in the morning, especially with an unbuffered spray mixture. ICIA 0604 applications made in the evening with 50 or 100 L/ha of water resulted in the lowest wild oat fresh weights and greatest wheat yields, regardless of the ICIA 0604 rate or spray mixture pH. Antagonism between sodium bicarbonate in the unbuffered water from Scott, as indicated by the spray mixture pH effect, and the time of application effect were important factors controlling treatment responses at Scott. Lower than recommended ICIA 0604 rates often maintained net returns, even though wheat yield responded negatively to reduced ICIA 0604 rates. Understanding the effects of water quality on wild oat control will allow producers to make prudent decisions regarding the optimal application parameters for ICIA 0604. Nomenclature: ICIA 0604 (proposed common name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enone; wild oat, Avena fatua L. #3 AVEFA; hard red spring wheat, Triticum aestivum L. Additional index words: Water volume, spray mixture pH, time of application, weed interference, AVEFA.

Interactions of ALS-Inhibiting Herbicide Residues in Three Prairie Soils

Abstract The objective of this study was to determine if the presence of two acetolactate synthase (ALS)-inhibiting herbicide residues in different Saskatchewan soils would result in additive, synergistic, or antagonistic interactions. This was determined through field trials where herbicides were applied sequentially over the course of 2 yr. The herbicides examined in these experiments were imazamethabenz, flucarbazone, sulfosulfuron, and florasulam, each in combination with imazamox and imazethapyr. The phytotoxicity and persistence of the herbicides in soil was assessed using an oriental mustard root inhibition bioassay. The determination of herbicide interaction was made through the comparison of the experimentally observed values to theoretically expected values derived from a mathematical equation. On the basis of the bioassay analysis, it was found that the herbicide residue combinations resulting from sequentially applied ALS-inhibiting herbicides in the three soils produced additive injury effects rather than synergistic or antagonistic interactions. Nomenclature: Florasulam; flucarbazone; imazamethabenz; imazamox; imazethapyr; sulfosulfuron; oriental mustard, Brassica juncea L. ‘Cutlass’.

Effects of Soil Factors on Phytotoxicity and Dissipation of Sulfentrazone in Canadian Prairie Soils

Studies were conducted to examine the effects of soil properties on sulfentrazone phytotoxicity and dissipation under laboratory conditions. The pH values of five soils from Saskatchewan were altered through acidification with hydrochloric acid (HCl) and alkalization with calcium carbonate (CaCO3). The phytotoxicity of sulfentrazone to sugar beet (Beta vulgaris L. Beta 1385), determined using a shoot length bioassay, was reduced when soil pH was lowered and was greater when soil pH increased. Concentrations corresponding to 50% inhibition (I50 values) obtained from the dose–response curves were correlated with soil pH, demonstrating the relationship between soil pH and sulfentrazone phytotoxicity. Dissipation of sulfentrazone was examined in soils incubated at 25 °C and moisture content of 85% field capacity. Sulfentrazone dissipation followed a two-compartment model, and sulfentrazone half-lives estimated from the dissipation curves ranged from 21 to 111 days. Half-lives were correlated with soil pH (R = –0.857, p = 0.014) and soil organic carbon content (R = 0.790, p = 0.034) but not with clay content (R = 0.287, p = 0.533). Soil characteristics, particularly soil pH and organic carbon content, affect the bioactivity of sulfentrazone and influence both sulfentrazone efficacy in weed control and its potential for carry-over injury to subsequent crops.