Wild oat reduced light penetration and growth of dwarf hard red spring wheat in field experiments performed under nonlimiting nitrogen and moisture conditions. Wild oat grew taller than wheat and had a greater portion of its canopy above 60 cm at maturity. Light penetration in a mixed canopy was similar to that in a monoculture wheat canopy when wild oat was clipped to the height of the wheat. A mathematical model was developed which accurately predicted the reduction in the growth rate of wheat from wild oat interference. The model also predicted that interference from wild oat was due to reduced leaf area of wheat at early growth stages and low wild oat densities, and reduced light penetration to wheat leaves at later growth stages and higher densities of wild oat.

Two furrow irrigated field experiments were conducted for two years at the Research and Extension Center, Powell, WY to determine the influence of various mixed densities and durations of wild oat and wild mustard interference in sugarbeet. Sugarbeet root yields were reduced by competition from all examined densities of wild oat and wild mustard, alone and in combination. Root yield reduction was less than additive with mixed densities of wild oat and wild mustard. Root yields decreased as the duration of interference after sugarbeet emergence from a mixed density of wild oat and wild mustard increased. Sucrose content of sugarbeet was not altered by competition. Based on regression analysis, the minimum time that a mixed density of 0.8 wild mustard and 1 wild oat/m of row can interfere with sugarbeet before causing an economic root yield loss was approximately 1.6 weeks after sugarbeet emergence.

Field experiments were conducted to measure the grain yield of wheat (Triticum aestivum L. ‘ANZA’) at various wild oat (Avena fatua L. ♯ AVEFA) and wheat plant densities. Wheat yield declined as wild oat plant density increased. Wheat yield increased in wild oat-infested plots as wheat plant density increased. Regression models were developed to describe the combined effect of wheat and wild oat plant densities on wheat grain yield. Wheat yields were best described by a nonlinear regression model using the relative density of wild oat in the weed-crop stand as the dependent variable. Inclusion of crop stand as a competitive factor significantly improved the fit of all regression models tested. Wild oat were more competitive against wheat in these experiments than in experiments reported by others. Possible reasons for differences in observed competitiveness are discussed.

Tribenuron antagonized diclofop control of wild oat in greenhouse studies. Wild oat shoot fresh weight was reduced 79% when plants were treated with diclofop at 1.12 kg ha−1, but only 46% when treated with diclofop at 1.12 kg ha−1plus tribenuron at 18 g ha−1. Increasing diclofop rate increased control of wild oat but did not overcome the antagonism. Separating the applications of diclofop and tribenuron by as little as 12 s reduced the antagonism by 40%, indicating the importance of close proximity of the two herbicides on the leaf surface for the antagonistic response. The inhibitory effect of diclofop at its target site (acetylCoA carboxylase) was not reduced by tribenuron. Metabolism of 14C-diclofop by wild oat leaves was not altered quantitatively or qualitatively by tribenuron. Tribenuron had no effect on spray retention or absorption of 14C-diclofop by wild oat leaves, and only slightly decreased the total amount of radiolabel translocated out of the treated zone on the leaf. However, tribenuron decreased basipetal translocation of diclofop from the treated zone by approximately 20%. The ability of tribenuron to reduce basipetal translocation of diclofop to meristematic regions of wild oat may be a factor in antagonism.

Field experiments were conducted to determine the effect of CGA184927 rate, weed growth stage, and tank mixes with various broadleaf herbicides on the control of green foxtail and wild oat in spring wheat. CGA 184927 controlled green foxtail and wild oat equally well when applied at the 2- to 3- or 4- to 5-leaf stages. Green foxtail and wild oat were controlled at similar rates of CGA 184927 but the application rate giving > 90% control ranged from 22 to 90 g/ha over locations and years, indicating that CGA 184927 efficacy is sensitive to environmental conditions. CGA 184927 in tank mixtures was compatible with bromoxynil, clopyralid, and 2,4-D ester. However, tank mixing with metsulfuron or dicamba reduced activity on green foxtail and wild oat. Broadleaf herbicide activity on kochia and redroot pigweed was not reduced when such herbicides were tank-mixed with CGA 184927. Spring wheat tolerated 120 g/ha of CGA 184927. CGA 184927 provides growers with another herbicide option to control green foxtail and wild oat in wheat.

The effect of soil moisture, temperature, and light intensity on the spray deposition of fenoxaprop and imazamethabenz applied to wild oat plants was examined by using fluorescent tracer dye. Based on either biomass or total leaf area, the apparent deposition of the two herbicides diminished in the following order: shading > low temperature ≥ drought ≥ “optimum” > high temperature. The enhanced phytotoxicity of both herbicides under shading could be associated with increased spray deposition; and reduced fenoxaprop phytotoxicity under high temperature stress could be related to reduced deposition. Changes in spray deposition were attributed mainly to differences in herbicide interception due to altered plant morphology. Reduced retention for both herbicides was exhibited only in the plants grown at high temperature. Under “optimum” conditions, fenoxaprop phytotoxicity was directly associated with leaf orientation and thus with the proportion of projected leaf area at the time of herbicide spraying. Given similar application conditions, spray deposition of fenoxaprop and imazamethabenz on wild oat could be estimated by determining the ratio of the projected leaf area, as measured by an image analyzer, to the total leaf area.

Twenty-nine wild oat (Avena fatua L. ♯3 AVEFA) and Avena sterilis L. ♯ AVEST accessions having various areas of origin and/or growth characteristics were grown to maturity in controlled environmental chambers. The four environments consisted of a 16-h photoperiod until 3 weeks after emergence, when the photoperiod was decreased (DP) 1 h per week for 8 weeks at a constant 14, 20, or 26 C (DP 14, DP 20, or DP 26); and an 8-h photoperiod until 3 weeks after emergence, when the photoperiod was increased (IP) 1 h per week for 8 weeks at a constant 20 C (IP 20). The relative growth rate of the accessions was similar in each environment. The length of the second leaf was up to 15 cm greater under 8- than 16-h day length at 20 C for some accessions, but was similar under both day lengths for other accessions. The width of the second leaf was greater under 14 than 20 C and was narrower with a 16-h than an 8-h photoperiod. Tiller initiation was slower in the DP 14 and IP 20 than in the DP 20 and DP 26 environments. Days to panicle emergence for individual accessions ranged from 10 to 57 days higher in the DP 14 than in the DP 20 environment. Seed produced on plants grown at 14 C had lower germination in water and 1500 ppm gibberellic acid than seed from plants grown at 20 C. Wild oat accessions varied in morphological characteristics, days to panicle emergence, and dormancy, and responded differently to changes in photoperiod and temperature. Wild oat morphological characteristics, days to panicle emergence, and dormancy did not consistently relate to species or area of origin.

Studies were conducted to evaluate the effect of wild oat (Avena fatua L. # AVEFA) interference in lentils (Lens culinaris Medik). An infestation of 32 and 65 wild oats/m2 maintained up to 5 weeks in the field did not reduce lentil grain yield. However, 32 wild oats/m2 reduced yields 32% when allowed to remain for 7 weeks and 49% if they remained until harvest time (11 weeks). Sixty-five wild oats/m2 reduced grain yield 42 and 61% for the same time periods, respectively. In the growth chamber, 69 wild oats/m2 reduced lentil plant dry weight 29% if allowed to remain for 3 weeks, 61% for 5 weeks, and 72% for 7 weeks (harvest time). The field data suggest that wild oat control measures may be delayed for several weeks after lentil emergence without reducing crop yield.

Experiments were conducted with isolated protoplasts of wild oat (Avena fatua L. # AVEFA) and isolated chloroplasts of wild oat and wheat (Triticum aestivum L.), to determine if the methyl sulfate salt of difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) might influence photoreactions in these species. Difenzoquat did not affect CO2 fixation, uncoupled electron transport, or proton uptake. At concentrations of 0.5 mM and 1 mM, difenzoquat caused a slight, but statistically significant, inhibition of photophosphorylation. Experiments assaying coupled electron transport indicated that inhibition of photophosphorylation occurred not through uncoupling, but by an energy-transfer inhibition. This same effect was observed in isolated mitocondria of both species, with about 50% inhibition of state 3 respiration rates occurring with 10 μM difenzoquat. However, no important differentials were observed in the relative susceptibilities of wheat and wild oat mitochondria. Difenzoquat also functioned as a weak autooxidizing electron acceptor in photosynthetic electron transport. Therefore, difenzoquat-induced leaf chlorosis and necrosis may result from a bipyridilium-type electron acceptor activity if sufficient herbicide is absorbed.

Research was conducted to determine environmental and cultural factors influencing triallate phytotoxicity to hard red spring wheat. Triallate injured ‘Alex’ wheat more than ‘Coteau’ but injury was not influenced by triallate application date. Wild oat control was greater when triallate was applied immediately before seeding compared to 12 d before seeding. Triallate tolerance in wheat did not relate to solid stem characteristic. Injury was highest when wheat was seeded in a 4-cm incorporated triallate layer and least when wheat was seeded below the treated layer. However, triallate injury to wheat was similar at both seeding depths within the 8-cm incorporated triallate layer. Triallate at 1.1 kg ai ha-1 reduced wheat fresh weight approximately 33% with a soil at 8 C but over 84% with a soil at 24 C.

Inheritance of resistance to diclofop was studied in three wild oat biotypes (designated B, C., and H) from the Willamette Valley of Oregon. Cultivated oat (cultivar ‘Monida’) was crossed, including reciprocals, to three wild oat biotypes. Leaves of each F1 plant were spotted with diclofop as a nondestructive test for resistance or susceptibility. All F1 hybrids were resistant, indicating that resistance is dominant and is under nuclear control. The F2 plants where Monida was the maternal parent were screened with diclofop, and F2 plants of the Monida/C cross were screened with fenoxaprop because the parent C biotype was resistant to fenoxaprop. At lower doses, a 3:1 (R:S) segregation ratio in F2 was observed and at higher doses a 1:3 (R:S) segregation ratio was often observed. The F2:3 families segregated in a 1:2:1 (all resistant : segregating resistant and susceptible all susceptible) ratio when treated with a 1.1-kg ae ha−1 dose of diclofop. This confirms that resistance to diclofop in the B, C, and H biotypes is primarily under monogenic control, with resistance being dominant to susceptibility at lower herbicide doses. At increased doses, susceptibility becomes dominant. Knowledge of the inheritance of resistance may help in the development of containment measures to prevent the spread of herbicide-resistance genes.

Greenhouse and field experiments were conducted at the Lacombe Research Station to evaluate mixtures of sethoxydim and fluazifop on green foxtail, wild oat, wheat, and barley in canola. In both environments the two herbicides interacted on the grass species in a synergistic manner. Many of the observed responses to mixtures of sethoxydim and fluazifop were 100% greater than those expected assuming an additive interaction between the herbicides. Mixtures with at least 80 g ha-1 of sethoxydim and 80 g ha-1 of fluazifop controlled more than 90% of green foxtail, wild oat, wheat, and barley under field conditions. These experiments indicate that the sethoxydim/fluazifop mixture is both complementary and synergistic. The mixture may allow reduced herbicide application rates and therefore reduced herbicide costs and less potential for negative environmental impact.

The germination of caryopses on water or GA3 solutions was used to characterize the degree of primary dormancy present in the seed progeny of 10 genetically pure lines of wild oats (Avena fatua L. # AVEFA). These 10 lines represented a range of types from lines exhibiting no dormancy to those with a high degree of dormancy. Repeated propagation of these pure lines under constant environmental conditions identified several genetically inherited characters that were associated with the inherited differences in degree of primary dormancy. Correlation of the seed development period, number of primary caryopses produced, and caryopsis moisture content to the degree of primary dormancy shows: a) Lines characterized by low degrees of primary dormancy were, in general, those that had a short seed development time and produced few heavy seed low in percent water; and b) lines characterized by high degrees of primary dormancy were, in general, those that had a long seed development time and produced many light seed high in percent water. The adaptive advantage of the coupling of physiological and morphological characters with degree of dormancy is discussed and the possibility that some characters are determined by others is indicated.

Greenhouse and field studies were conducted to examine the interaction of sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon for selective weed control in safflower. Under greenhouse conditions, the addition of chlorsulfuron to sethoxydim or fluazifop-P slightly improved the control of green foxtail above that achieved with either herbicide alone. Control of wild oat and wild mustard was similar with the tank mixes and each herbicide alone. In the field, control of wild oat with sethoxydim or fluazifop-P was not altered by adding chlorsulfuron or thiameturon in tank mixes. Similarly, control of common lambsquarters and wild mustard with chlorsulfuron or thiameturon was not affected by adding either sethoxydim or fluazifop-P in tank mixes. Plant height, date of flowering, seed yield, and quality data indicated that safflower tolerated these herbicides applied alone or in combination. Sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon provide a postemergent alternative for selective control of grass and broadleaf weeds in safflower.

Germinated seeds of wild oat populations that were susceptible (S) or resistant (R) to triallate at the recommended soil-applied rate (1.7 kg/ha) were treated with six triallate concentrations on filter paper in petri dishes. Measurement of shoot length 8 d after treatment provided an accurate indication of differences among populations, and was more reliable than determining shoot fresh weight. ED50 values (herbicide concentrations that reduced shoot length by 50% relative to untreated controls), derived from nonlinear regression analysis, indicated four and five levels of response to triallate among eight S and seven R populations, respectively. The ED50 values varied from 0.11 to 11 ppm a.i. triallate for the most susceptible to the most resistant populations, respectively. Routine testing of wild oat samples suspected of resistance, at triallate concentrations of 0.5 or 1 ppm in the petri dish bioassay, effectively identified populations that had become resistant to the recommended soil-applied rate.

Mechanical wounding broke dormancy and promoted germination of primary dormant pure-line wild oat (Avena fatua L. # AVEFA) caryopses that were in the first physiological stage of dormancy. Caryopses incubated in petri dishes responded to wounding by germinating more rapidly than wounded caryopses incubated in soil. There was no difference in germination between wounded and lanolin-covered wounded caryopses when incubated in soil. The less dormant AN265 caryopses responded to the wounding treatment more rapidly than the more dormant caryopses of M73 in both petri dish and soil incubation systems. Chlorocholine chloride (CCC), an inhibitor of gibberellic acid (GA) biosynthesis, reduced the germination rate of wounded AN265 and M73 caryopses above and at 1 mM, respectively. Application of 25 mM CCC to wounded dormant AN265 caryopses decreased the level of hexose in the embryo to 47% of the control level. There was no significant effect of CCC on the endosperm hexose, embryo and endosperm imbibed fresh weight, and sucrose and starch content. The results suggest GA or GA biosynthesis is the limiting factor to germination.

The efficacy of current wild oat herbicides and their high cost have resulted in use rates that are less than those recommended. While acceptable weed control may be attained at less cost, this practice does not consider the potential for increased wild oat seed production. The objective of this experiment was to determine the interaction of wild oat density and reduced imazamethabenz rates on wild oat seed production in spring barley. As wild oat densities increased from 8 to 1,100 plants m−2, wild oat seed production increased from 180 to 9,950 seed m−2 without herbicide, and from 0 to 2,810 seed m−2 using 0.53 kg ai ha−1 imazamethabenz. This general pattern was modeled using a cumulative logistic function. Estimates from this model indicated that < 1 wild oat seed m−2 was produced at population densities of ≤ 20 plants at any imazamethabenz rate. Imazamethabenz rates of 0.26 kg ha−1 or greater at wild oat densities of less than approximately 190 plants m−2 did not result in wild oat seed production above the initial population density. As wild oat density increased, however, imazamethabenz rates below 0.40 kg ha−1 resulted in substantially greater wild oat seed production compared to the recommended rate.

The ability of Medicago sativa to suppress weed growth may provide a viable alternative to chemical weed control and allow crop producers to reduce herbicide inputs. Quantitative information regarding the suppressive effect of M. sativa on weed populations in current cropping systems is lacking. A survey was conducted in Manitoba, Canada, in 1993 and 1994 to investigate weed populations in commercial cereal fields that had been preceded by either M. sativa hay or cereal grain crops. A total of 117 fields were surveyed; approximately half from each field type. Principle component analysis indicated that the inclusion of M. sativa in crop rotations resulted in weed communities different from those of continuous cereal fields. Naturally occurring populations of Avena fatua, Cirsium arvense, Brassica kaber, and Galium aparine were lower in cereal fields that had previously contained M. sativa than in cereal fields that had been preceded by a cereal crop. Lower field uniformity values for C. arvense and Avena fatua indicated that these weeds were also more patchy in the M. sativa rotations. Population differences between field types were nonsignificant for Amaranthus retroflexus, Chenopodium album, and Polygonum convolvulus, and although populations of Taraxacum officinale and Thlaspi arvense were greater in M. sativa/cereal fields than in continuous cereal crops. No consistent effect of field type on Setaria viridis populations was observed. These results show that M. sativa effectively suppressed some, but not all, of the weeds found in the study area. Including M. sativa hay crops in crop rotations can be part of an integrated weed management strategy for weeds such as A. fatua, B. kaber, and C. arvense.

A seedling bioassay was used to determine the response of triallate-resistant (R) and -susceptible (S) wild oat populations to difenzoquat and EPTC. The bioassay, based on seedling shoot length at 10 d after treatment, provided a reliable and rapid means of determining if wild oat populations were resistant to difenzoquat. Using a bioassay concentration of 15 ppm difenzoquat, it was possible to identify populations that were resistant to the recommended foliar-applied rate (0.85 kg ai/ha). Expected herbicide dosages that reduced shoot length by 50% (ED50) derived from nonlinear regression analysis indicated three and two levels of response to difenzoquat among eight S and seven R populations, respectively, indicating within population variability in their response to difenzoquat. Of the populations tested, none was resistant to EPTC. On the contrary, some R populations had lower ED50 values than did S populations, suggesting an increased sensitivity to EPTC.

A study under glasshouse conditions determined the effect of germination stimulants, potassium nitrate and ethephon, on emergence of several pure lines of wild oat from soil. Effect of the two chemicals on stimulating emergence was variable and no synergism noted when used together. Examination of exhumed seed showed that these treatments reduced seed viability. By counting the number of dead and adding to those that emerged, total seed removed from the soil was obtained. All treatments removed seed from the soil seedbank, especially when seed was old, near the soil surface, was primary seed, or from low or intermediate dormancy lines. However, because of the insensitivity of a large proportion of the seed and the high rates required it is unlikely that either potassium nitrate or ethephon has practical use for field application.