Field and laboratory studies were conducted to evaluate the efficacy of several herbicides applied after small-grain harvest on Russian thistle (Salsola iberica Sennen and Pau # SASKR) control and subsequent seed germination. Best postharvest control of Russian thistle was with chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} treatments, paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), and bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) plus metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], where control ranged from 73 to 96%. During the summer-fallow year, chlorsulfuron and paraquat decreased Russian thistle population and biomass compared to the untreated control. Germination of large seeds from plants treated with paraquat and both rates of chlorsulfuron was reduced at least 64% compared to seeds of similar size from untreated plants.

The effect of Jerusalem artichoke (Helianthus tuberosus L. # HELTU) density and duration of interference in soybeans [Glycine max (L.) Merr. ‘Hodgson 78’] was investigated in two studies. Jerusalem artichoke densities of 1, 2, and 4 tubers/m of row reduced soybean seed yield by 31, 59, and 71%, respectively. Soybean height, branches/plant, pods/plant, and seed weight were usually reduced by all three weed densities. Soybean leaf area and relative growth rates were reduced by densities of 2 and 4 tubers/m of crop row, and net assimilation rate (NAR) was reduced by 4 tubers/m of crop row. Jerusalem artichoke interference at 4 tubers/m of row for 4, 6, 8, and 20 weeks (full season) reduced soybean yields 9, 10, 38, and 82%, respectively. Branches/plant, pods/plant, and seeds/plant were reduced after 8 weeks of interference. These results suggest that Jerusalem artichoke is highly competitive with soybean and should be controlled within 6 weeks after planting.

The effect of quackgrass [Agropyron repens (L.) Beauv.] density and duration of interference on soybeans [Glycine max (L.) Merr.] was investigated in two studies. In the density study, the average reduction in soybean yield by quackgrass densities of 520 and 910 shoots/m2 was 19 and 55%, respectively. Quackgrass densities of 95 and 160 shoots/m2 did not significantly reduce soybean yields. The number of branches that produced pods, the number of pods and seeds per plant, and soybean height were reduced by the two highest densities. In 1980, quackgrass densities of 265 and 595 shoots/m2 reduced soybean leaf area and plant dry weight. Leaf area partitioning (LAP), leaf weight partitioning (LWP), and net assimilation rate (NAR) of soybeans were reduced by a quackgrass density of 595 shoots/m2. In the duration study, interference by a natural stand of quackgrass for 6 weeks, 8 weeks, and full-season decreased soybean yield an average of 11, 23, and 33%, respectively. Results from the duration study suggest that a selective postemergence herbicide for the control of quackgrass in soybeans would be beneficial if available.

Greenhouse and field studies were conducted to compare root development of jointed goatgrass to winter wheat. Time of seminal root development in jointed goatgrass was similar to that of winter wheat and to root development predicted by a model. The only exception was the epiblast node roots (−1A and −1B), which developed approximately 1 phyllochron later in jointed goatgrass than in winter wheat. At crown nodes, A and B roots developed later in jointed goatgrass than in winter wheat, but development of X and Y roots at these nodes was similar for both species. First-order branching at a given root axis in jointed goatgrass roots began approximately 1 phyllochron after development of that axis, compared to 2.5 phyllochrons for winter wheat and the model. Second- and third-order branching of jointed goatgrass roots began 1 and 0.5 phyllochrons earlier than the respective branching of winter wheat roots. Leaf and tiller development followed the same pattern with time for both species. Maximum distance between crown roots was 1.5 to 3 times greater in winter wheat than in jointed goatgrass. Root length density at the 0- to 10-cm depth was less for jointed goatgrass than for winter wheat, but there were no differences at greater depths. The frequency of branching of first-order laterals was greater for jointed goatgrass than for winter wheat. In the field, the relationship of jointed goatgrass shoot development to accumulated growing degree-days was linear (R2 = 0.97), with a slope and y-intercept similar to winter wheat (R2 = 0.95). These data, showing slight differences in root growth and development between jointed goatgrass and winter wheat, may be used in predictive modeling to better understand the biology and ecology of each species, and may be used in conjunction with other models to establish weed threshold levels and improve selective placement of fertilizers and herbicides to benefit crop development.

In the greenhouse, glyphosate [N-(phosphonomethyl)glycine] at 0.6 kg ae/ha applied directly to seeds alone or seeds on the soil surface reduced germination and shoot dry weight of common rye (Secale cereale L. ♯3 SECCE). Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) applied similarly at 0.6 kg ai/ha reduced germination and shoot dry weight of downy brome (Bromus tectorum L. ♯ BROTE) and wheat (Triticum aestivum L. ‘Daws' ♯ TRZAX). Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] at 0.6 kg ai/ha applied to seeds, soil, or seeds and soil had very little effect on germination, but significantly reduced shoot dry weight of common rye, downy brome, wheat, and jointed goatgrass (Aegilops cylindrica Host. ♯ AEGCY). Pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] at 0.6 kg ai/ha, and propham (isopropyl carbanilate) at 3.4 kg ai/ha plus extender (p-chlorophenyl-N-methylcarbamate) at 0.4 kg ai/ha substantially reduced shoot height and dry weight of all species, regardless of application method, with pronamide completely inhibiting shoot elongation and dry-weight production in three of the four species.

A 9-yr large-scale integrated pest management (IPM) study was initiated in 1985 to develop and refine profitable conservation cropping systems in the Palouse wheat-growing region of the Pacific Northwest. Weed scientists from the USDA-ARS and the land-grant universities of ID and WA led a team of researchers and extension personnel from eight disciplines to investigate the interactions of crop systems, tillage systems, and weed management levels (WML) on crop production. Ineffective weed control has been a major deterrent to the adoption of conservation tillage by wheat growers. With this in mind, the primary focus of the scientists on the IPM project was integrated weed management (IWM) in conservation crop production systems for highly erodible land. For the first time in the Pacific Northwest, systems research developed a conservation production system using a 3-yr crop rotation that controlled weeds effectively, reduced erosion, was less risky than traditional farming systems, and was profitable. Broadleaf weeds were more prevalent in the 3-yr rotation of winter wheat-spring barley-spring pea compared to continuous wheat in both conservation and conventional tillage systems. In conservation tillage, troublesome grass weeds included wild oat and downy brome. Wild oat was controlled effectively at the moderate and maximum weed management levels under conservation tillage in the 3-yr rotation. Two years out of winter wheat (such as in the 3-yr rotation) reduced downy brome populations. In contrast, growing a spring crop 1 yr, followed by 2 yr of winter wheat was not effective for controlling downy brome. Effective weed control was instrumental in developing successful conservation IPM cropping systems, and education and technology transfer were important in helping action agencies assist growers in adopting these systems.

Mayweed (Anthemis cotula L. # ANTCO) achenes and seed were germinated in the laboratory at constant temperatures ranging from 5 to 30 C. Maximum percent germination occurred at 20 C for both achenes and seed. Under all conditions tested, achene germination was less than seed germination. Both acid scarification for 15 min and soaking in 14 mM gibberellic acid (GA3) more than doubled achene germination. Pericarp leachate inhibited achene and seed germination only at high concentrations, indicating that inhibitors in the pericarp are not a primary cause of low germination in achenes. Optimum germination of achenes and seed occurred at pH 4.5 and over a range from pH 3 to pH 6. Achene germination was inhibited to a greater degree by moisture stress than was seed germination. It appears that structural integrity of the pericarp is the predominant factor affecting mayweed germination.

Glyphosate plus 2,4-D at 0.3 + 0.5 or 0.4 + 0.7 kg ae ha-1 applied 31 to 1 d before seeding did not affect wheat yields or grain test weights, in field experiments in conventionally tilled and no-till winter wheat. In the conventionally-tilled system in each of two years and in the no-till system in a year with 48 mm rain within 7 d before wheat was seeded, picloram applied at 0.14 kg ai ha-1 from 31 to 1 d before seeding reduced crop yields by 7 to 8%. In the conventionally-tilled system in a year with only 2 mm rain within 7 d before wheat was seeded, 2,4-D at 3.4 kg ae ha-1 and dicamba at 0.14 kg ae ha-1 applied 30 to 1 d before seeding, reduced wheat yields by 7 and 4%, respectively. Grain test weights in both tillage systems were increased slightly by picloram at 0.14 kg ha-1, but were decreased slightly by dicamba at 0.14 kg ha-1, in the year with little rain before sowing. Test weights did not differ among herbicides or tillage systems in the year with significant rain a few days before seeding.

Jointed goatgrass (Aegilops cylindrica) is a serious problem for winter wheat producers throughout the western U.S. Interference from this weed can severely reduce grain yield and contaminate harvested grain, resulting in dockage losses. There are currently no selective herbicides registered for controlling jointed goatgrass in wheat. Imazamox, an imidazolinone herbicide, was applied to an imidazolinone herbicide-resistant (IMI) wheat mutant of the winter wheat cultivar ‘Fidel.’ Jointed goatgrass control from spring postemergence application of imazamox ranged from 61 to 97% when applied at 36 g/ha. Negligible crop injury from imazamox treatment was observed at 36 g/ha at several locations under dryland environments in the U.S. Pacific Northwest. Wheat yield was increased 19 to 41% by imazamox treatment in three of four experiments. Percent dockage resulting from jointed goatgrass spikelet contamination of harvested wheat grain was eliminated by imazamox treatment. Introduction of the IMI trait into commercial wheat cultivars could provide an effective method for selective control of jointed goatgrass in winter wheat.

In three replacement series experiments, winter wheat (Triticum aestivum L.), jointed goatgrass (Aegilops cylindrica Host. #3 AEGCY), and downy brome (Bromus tectorum L. # BROTE) were paired in all possible combinations to determine competitive relationships during vegetative growth. Under growth chamber conditions of ample fertility and soil moisture and day/night temperatures of 18/10 C, relative yield totals for the three species were similar, indicating that they compete for the same resources. Both winter wheat and jointed goatgrass had greater plant growth and higher relative crowding coefficients than downy brome, which indicated a hierarchy of relative competitiveness of winter wheat > jointed goatgrass >> downy brome. In other growth chamber studies, winter wheat was slightly more competitive than jointed goatgrass regardless of fertility levels. Winter wheat was the superior competitor at 18/10 C and −33 kPa (soil moisture), whereas jointed goatgrass was superior at 27/10 C and −300 kPa, conditions that are frequently encountered in the Pacific Northwest.

A seed remover using a modified water-spray system was constructed to separate weed seeds rapidly and effectively from a silt loam soil A 1-kg soil sample can be washed through the seed remover in 6 min. Using a 500-μ mesh sieve, only 70% of small shepherdspurse seeds were recovered, while 100% of larger seeds of henbit, curly dock, wild oats, and downy brome were recovered. The modified seed remover system reduced the required man-hours by more than 50% compared to previous systems.

In a kiln experiment, temperatures of 200 to 400 C for 120 sec reduced germination of jointed goatgrass seeds 50 to 100%. Postharvest field burning of wheat and jointed goatgrass stubble destroyed 43 to 64% of the jointed goatgrass spikelets located on the soil surface. Seeds contained in spikelets that were minimally burned (slightly browned) germinated 32 to 65%, while seeds contained in spikelets moderately (less than 50% charred) and severely burned (greater than 50% charred) germinated 5 and 0%, respectively. Field burning destroyed 90% or more of jointed goatgrass seeds in spikelets located on the soil surface. Burning may be a feasible method for controlling small infestations of this weed.

Greenhouse and field experiments were conducted to evaluate the efficacy of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} on Russian thistle (Salsola iberica Sennen and Pau # SASKR) in a spring wheat (Triticum aestivum L.) summer-fallow rotation. In the greenhouse, when chlorsulfuron was applied to Russian thistle at three stages of growth, shoot dry weight was reduced similarly with either 4.4 g ai/ha plus surfactant or 140 g ai/ha plus surfactant. In the field, postharvest control (1981) of Russian thistle with 17.5 to 140 g/ha of chlorsulfuron ranged from 35 to 60% without surfactant and from 76 to 93% with surfactant. During the summer-fallow year (1982), Russian thistle treated in the preflowering stage of growth was not effectively controlled with 17.5 or 35 g/ha. In contrast, residual control from postharvest treatments 1 yr after application ranged from 90 to 100%. Chlorsulfuron applied in the crop (1983) controlled Russian thistle throughout the growing season. All treatments of chlorsulfuron applied in 1981, 1982, and 1983 increased wheat yield at least 75%.

The effect of Russian thistle density and duration of interference on spring wheat was investigated in two 3-yr field studies. In the density study, the best fit regression equation predicted a loss in spring wheat yield of 0.5, 0.5, and 0.6% in 1983, 1984, and 1985, respectively, for each percent of the total biomass contributed by Russian thistle. In 1985, when rainfall was 46% below normal, the highest weed density produced greater than 70% of the total plant biomass and reduced yields more than 50%. In contrast, in 1984 when rainfall was 65% above normal, the highest weed density produced less than 20% of the total plant biomass and reduced yields 11%. In the duration study, the predicted yield loss was 2.3 and 0.7% for 1983 and 1984, respectively, for each week of interference. In 1985, yield was not significantly reduced until after 6 weeks of interference. In both studies, spikes/m of row had the highest correlation with yield and were affected the most by weed interference.

Field studies were conducted to evaluate the effect of quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE] density and soil moisture on corn (Zea mays L.) growth and yield. Quackgrass densities ranging from 65 to 390 shoots/m2 reduced corn yield 12 to 16%. A quackgrass density of 745 shoots/m2 reduced corn yields an average of 37% and significantly reduced corn height, ear length, ear-fill length, kernels/row, rows/ear, and seed weight. In the soil moisture study, quackgrass was shorter than corn throughout the growing season, and analyses of corn leaf tissue indicated that quackgrass did not interfere with the nutrient status of the corn. In 1979, soil moisture was not limiting and corn yields were similar in all treatments regardless of irrigation or the presence of quackgrass. In 1980, soil moisture was limited and irrigation increased the yield of quackgrass-free corn. Irrigation also increased the yield of quackgrass-infested corn to a level similar to irrigated corn. When light and nutrients are not limiting factors, an adequate supply of soil moisture can eliminate the effects of quackgrass interference on the growth, development, and yield of corn.

A 1984–1985 and 1988–1989 field study near Pullman, WA, evaluated the effect of two winter wheat planting geometries on the growth of wheat and competition against jointed goatgrass. Treatments included paired and constant row planting geometries of wheat and locations of jointed goatgrass within each geometry. No planting geometry by weed location interactions occurred at any harvest date for plant height, shoot number, leaf area, plant dry weight, or N uptake for either wheat or jointed goatgrass. During the 1984–1985 growing season, N uptake data indicated that by heading, jointed goatgrass had taken up N that had been deep-banded between wheat rows located 25 cm from the weed. Winter wheat yields were not different in the paired-row and the constant row spacing geometry in a weed-free environment. Within years, for both planting geometries, winter wheat yield reduction from weed competition was similar for the jointed goatgrass locations. In contrast, based on jointed goatgrass spikelets produced, wheat grown in paired-rows was more competitive against jointed goatgrass compared to constant row spacing.

Research was conducted at Rosemount, Minnesota in 1979 and 1980 to evaluate the effect of soil moisture on quackgrass [Agropyron repens (L.) Beauv. # AGRRE] interference in soybeans [Glycine max (L.) Merr.]. Four treatments were studied: 1) nonirrigated soybeans, 2) irrigated soybeans, 3) nonirrigated soybeans, quackgrass-infested, and 4) irrigated soybeans, quackgrass-infested. Percent N, P, and K of soybeans was not affected by quackgrass interference. Irrigation did not increase the yield of quackgrass-free soybeans. The yield of quackgrass-infested soybeans was increased by irrigation when soil moisture was limited, but yields were always less than quackgrass-free soybeans. Quackgrass was nearly the same height or taller than the soybeans at all stages of soybean development and offered substantial competition for light throughout the growing season. This research indicates that an adequate supply of soil moisture can reduce quackgrass interference in soybeans, but cannot eliminate it, since quackgrass apparently continues to compete with soybeans for light.

Increased crop densities and postplant tillage were evaluated as nonchemical methods to supplement metribuzin for improved broadleaf weed control in dry pea and lentil. The effects of 50, 100, and 150% of recommended 220 kg/ha pea and 67 kg/ha lentil seeding rates and two dates of rotary hoeing and harrowing on pea, lentil, and broadleaf weeds were studied with and without metribuzin for two years. Under favorable growing conditions, crop competition gave 72 and 99% weed control in pea and 33 and 70% weed control in lentil with the 50 and 150% seeding rates. Under less favorable conditions, control was 21 to 39% with the low and high pea and lentil seeding rates. At recommended seeding rates, metribuzin gave greater than 90% control in either crop or year. Postplant tillage 12 to 27 d after planting slightly reduced crop densities in three tillage treatments in one year, but not the second. Postplant tillage did not affect crop yield or improve weed control. In all studies, pea was similar to or more competitive than lentil in suppressing broadleaf weeds. Because neither non-chemical practice significantly improves weed control, changes are not recommended for weed management in pea and lentil.

Imazamox-resistant hybrids resulted from a cross between jointed goatgrass and an imazamox-resistant wheat (cv. FS-4 IR wheat). Two imazamox-resistant hybrids were discovered in a research plot where FS-4 IR wheat seed had been replanted from the harvest of an imazamox efficacy study conducted the year before at a different location. These hybrid plants survived imazamox applied at 0.053 and 0.069 kg ai ha−1 in the field and produced seven viable seeds (BC1). This seed germinated, and chromosomes were counted from the roots (2N number ranged from 39 to 54). In the greenhouse, six of the seven plants survived an application of 0.072 kg ai ha−1imazamox, which confirmed that the resistance trait had been passed to these progeny. A large amount of phenotypic variation was observed in the mature BC1 plants. A genetic description of the movement of the resistant gene is proposed based on the case of the gene being located on the D and the A or B genomes. Management strategies to reduce the occurrence of herbicide-resistant hybrids are presented.

PALWEED:WHEAT is a bioeconomic decision model for determining profit-maximizing postemergence herbicide treatments for winter wheat in the Washington–Idaho Palouse region. PALWEED:WHEAT performed relatively well economically in 2 yr of on-farm field tests. However, the model was less sensitive than desired in prescribing postemergence broadleaved herbicides in the presence of high densities of broadleaved weed seedlings. Therefore, PALWEED:WHEAT was revised in response to the field testing. This paper compares the revised model's agronomic and economic performance to the original model in computer simulations. The revised model, PALWEED:WHEAT II, differs from the original model in several respects: (1) exponential functions replace linear functions in predicting weed survival, (2) preplant application of a nonselective herbicide is entered as an exogenous binary variable, (3) separate indices of broadleaved and grass competition are substituted for an aggregate weed competition index in the wheat yield function, (4) hyperbolic replaces logistic functional representation of weed damage to wheat yield, and (5) separate models are estimated for winter wheat after spring dry pea and for winter wheat in all examined crop rotation positions. In simulations including a variety of agronomic and economic conditions, PALWEED:WHEAT II recommended postemergence herbicide types and rates that consistently complied with agronomic and economic theory. Furthermore, the revised model, especially when estimated from the relevant wheat after pea data set, was markedly more balanced in recommending both broadleaved and grass herbicides in response to observed densities of both weed groups. The substantial change in herbicide recommendations in response to changes in model functional specifications following field testing confirms the importance of field testing and revision of bioeconomic decision models.