Field experiments were conducted over a 3-yr period to evaluate the efficacy and crop yield response of selected herbicides to control loose silky bentgrass in fall rye. Loose silky bentgrass was controlled 18 to 100% with trifluralin preemergence incorporated at 0.4 to 0.6 kg ai ha-1, chlorsulfuron preemergence at 0.024 kg ha-1 and metsulfuron early postemergence at 0.006 to 0.024 kg ha-1. Rye yield was unaffected by these herbicides 2 of 3 yr. In a farm demonstration trial trifluralin preemergence incorporated at 0.4 kg/ha controlled loose silky bentgrass.

Weed Science is facing two critical challenges. They are funding and interdisciplinary research, which to some extent are intertwined, but I will attempt to discuss them separately. Although some of my remarks may be critical of weed scientists let me say at the outset that the main reason we have these two challenges is because we have been highly successful, thanks to our visionary and dedicated scientists over the years. We have stayed ahead of the curve and have done too good a job. I would like to point out here that contrary to the beliefs of many outside our profession, we do more than spray and pray. We are ahead of the curve because we have conducted extensive and intensive research on application technology, formulations, environmental impacts, metabolism, mode of action, tillage practices, and many other areas.

Limited information exists on sweet corn tolerance to postemergence (POST) applications of clopyralid under Ontario growing conditions. Eight sweet corn hybrids were evaluated for tolerance to clopyralid in three field experiments conducted in 2001 and 2002 in Ontario. Clopyralid was applied POST at 200 and 400 g ai/ha, the proposed and twice the proposed registered rate for use in sweet corn in Ontario. Sweet corn response to clopyralid did not vary among the hybrids tested. In 2001, visual injury among hybrids 7 d after treatment (DAT) with clopyralid at 400 g/ha was less than 3%. Subsequent visual injury evaluations at 14 and 28 DAT showed no differences among sweet corn hybrids at either rate of clopyralid evaluated. The application of clopyralid at 200 and 400 g/ ha had no detrimental effect on plant height or marketable yield of any of the eight sweet corn hybrids. On the basis of visual injury, height, and marketable yield response ‘Calico Belle’, ‘CNS 710’, ‘DelMonte 2038’, ‘GG 222’, ‘GG 246’, ‘GH 2684’, ‘Reveille’, and ‘Rival’ are all tolerant to the POST application of clopyralid.

Thiazopyr at 0.14, 0.28, and 0.42 kg ai/ha and pendimethalin at 1.1 kg ai/ha applied preemergence (PRE) were compared as components in weed management systems for no-till cotton. Mid- and late-season control of mixtures of large crabgrass, goosegrass, and fall panicum by thiazopyr at 0.28 kg/ha was 89 to 97% and 11 to 50%, respectively, compared with 11 to 38% midseason and 0 to 5% late-season control by pendimethalin. Thiazopyr at 0.42 kg/ha and pendimethalin controlled broadleaf signalgrass 44 and 0%, respectively, late in the season. Adding fluometuron PRE at 1.7 kg ai/ha had little to no effect on large crabgrass, goosegrass, and fall panicum control but increased broadleaf signalgrass control 47 to 79 percentage points compared with thiazopyr or pendimethalin alone. Late-season control of annual grasses by thiazopyr or pendimethalin plus fluometuron PRE followed by methazole plus MSMA early postemergence (POST)-directed and cyanazine plus MSMA late POST-directed was at least 95% at two locations and 80% at the third location. Common lambsquarters was controlled 54 and 95% in systems without and with fluometuron PRE, respectively. Acceptable control of ivyleaf, pitted, and tall morningglories at all locations and smooth pigweed at two of three locations was achieved only in systems with POST-directed herbicides. Adding POST-directed herbicides to systems with thiazopyr or pendimethalin plus fluometuron PRE increased cotton yield at two of three locations. Treatments had no effect on fiber quality.

Picloram was applied to leafy spurge using flexible and rigid ropewick applicators for 3 yr at each of two upland pasture sites. The ropewick applicators were a cost-effective way to apply picloram to control leafy spurge compared to broadcast application, but minimal advantage was demonstrated for the segmented, flexible unit compared to the rigid applicator. Picloram applied as an 80 g ae/L solution through ropewick applicators controlled leafy spurge equal to broadcast picloram at 1.1 kg/ha while using 36% as much picloram.

Bulbous oatgrass, a weed in parts of the United States and Europe, is an unusual grass, which forms corms at the stem base. Growth and development of this creeping perennial grass was investigated in the field and in pots outdoors. Under the mild climate of the Willamette Valley, Oregon, shoots emerged in early autumn. Plants grew vegetatively and formed corms during the winter and spring. Aboveground portions of the plant stopped growing and senesced in the summer. The absolute growth rate of the plants was highest in early May, shortly before the onset of flowering. In early May, the growth rate of corms was higher than that of the shoot.

Experiments were conducted in 1987 and 1988 at two locations each year to determine how two weed management strategies and three planting dates affected the cost and amount of herbicide needed to control weeds in peanuts. Weed management strategies used for each planting date included preventive, which duplicated a standard grower program, or an integrated weed management system. The least expensive strategy depended upon weed species composition, weed populations and planting date. In all cases, the integrated weed management strategy required less herbicide (acid equivalent or active ingredient) than the preventive strategy.

Three field experiments were conducted in 1987 through 1989 to evaluate hogpotato control and rotational crop response resulting from applications of five herbicides. At the end of the first year, triclopyr and imazapyr controlled hogpotato late-season as high as 87 and 94%, respectively. Following a sequential application in 1988, triclopyr and imazapyr controlled 94 and 100% of hogpotato, respectively, during the 1989 growing season. Hogpotato biomass, collected at the termination of the experiments, was reduced by all treatments at all locations except at Altus where dicamba was applied in 1987 followed by a spot application of glyphosate in 1988. Soils from these experiments were bioassayed for residual herbicide activity using three potential rotational crop species. Tebuthiuron and imazapyr caused the greatest biomass reductions with cotton and wheat being the most sensitive species to these herbicides.

Field experiments were conducted in Missouri in 2004 through 2006 to compare the efficacy of fall and spring herbicide treatments for control of winter and summer annual weeds in no-tillage corn. Applications in the fall and 45 d before planting (45 PP) of 2,4-D and simazine; rimsulfuron, thifensulfuron, and 2,4-D; or glyphosate and 2,4-D controlled at least 90% of all winter annual weeds through 1 wk after corn planting (WAP), with a few exceptions. Applications made 30 d before planting (30 PP) of 2,4-D and glyphosate or rimsulfuron, thifensulfuron, and 2,4-D provided greater than 90% control of most winter annual weeds 1 WAP. Winter annual weed control was reduced with herbicide treatments applied 7 d before planting (7 PP), compared with earlier application timings. Summer annual weed control 5 WAP increased as the time between application and planting decreased. Fall applications resulted in greater weed biomass 5 WAP, compared with spring applications.

The effect of CGA 152005 residues in the soil on six crops grown in rotation with field corn was investigated over a 2-yr period. CGA 152005 at 10, 15, 20, and 30 g ai/ha was applied postemergence (POST) to corn in 1994. CGA 152005 at 15 and 30 g ai/ha, atrazine at 1,000 g ai/ha, CGA 152005 at 15 g plus atrazine at 500 g ai/ha, and CGA 152005 at 30 g plus atrazine at 1,000 g ai/ha were applied POST to corn in 1995. Soybean, pea, cabbage, tomato, pepper, and potato were planted each spring, 1 yr after herbicide application. Cabbage exhibited injury and yield reductions that increased with increasing application rate, and pepper exhibited slight injury at the highest rate and yield reduction in 1995. Cabbage yields were reduced by CGA 152005 plus atrazine, and tomato yields were reduced by CGA 152005 and CGA 152005 plus atrazine in 1996. Yields of other crops were not affected in either year.

A soil bioassay experiment was conducted in Blacksburg, VA, to determine the effect of isoxaben application timings and rates on duration of weed control. Flats containing soil were imbedded into the field. Isoxaben was applied in the spring, fall, and spring followed by fall (double application) at 0.56, 0.84, and 1.12 kg ai/ha. Flats were moved to a greenhouse at 0, 1, 3, 6, and 9 months after treatment (MAT) and seeded with yellow rocket, buckhorn plantain, and spotted spurge for the bioassays. Weed counts from treated flats were compared to those in untreated flats to determine percent control. Fall and spring followed by fall applications provided approximately 20% greater control of yellow rocket 3 MAT and 30% greater control 6 MAT, compared to a single spring application of isoxaben. Isoxaben at all rates controlled yellow rocket > 70% at 6 mo after fall application. At 3 MAT, fall and spring plus fall-applied isoxaben provided about 15 and 20% greater buckhorn plantain control, respectively, compared to spring application. The two highest rates of isoxaben controlled buckhorn plantain > 70% at 3 mo after fall application, but provided poor control at 6 MAT. Control of spotted spurge was similar among the three application timings for isoxaben and was unacceptable at most evaluation dates. Overall, isoxaben applied at 1.12 kg/ha provided better control of all three weed species for a longer time than the reference herbicide, oxadiazon, applied at 3.36 kg/ha.

Weed Science is knowledge about unwanted plants and about methods to control such plants. The concept “weeds” probably was born when man first learned that desirable plants would grow better if surrounding plants were killed. Knowledge of elementary weed control began when man learned that unwanted plants died if they were separated from the soil. Thus rudimentary Weed Science is as old as man's efforts to grow crop plants.

Field experiments were conducted to compare performance of glyphosate with three different boom arrangements in a winter wheat-fallow rotation near North Platte, NE, in 1994 and 1995. One boom was optically controlled, and the other boom was for broadcast herbicide applications. Spraying with both booms at the same time was called “dual boom.” The sprayers were tested during May, June, and July on two weed density levels established by applying glyphosate at 0.42 kg ae/ha with and without atrazine at 0.84 kg ai/ha in October following wheat harvest. The dual-boom and the broadcast herbicide applications were more efficient in controlling weeds than the optically controlled system. The dual boom reduced weed density 4.5-fold compared with the optically controlled sprayer used alone. Horseweed < 8 cm tall was more difficult to control with the optically controlled sprayer than redroot pigweed and kochia because of its cylindrical-shaped growth patterns. Barnyardgrass and green foxtail seedlings with an erect growth pattern were also difficult for the sensors to detect. Poorer control with the optically controlled sprayer was associated with failure to identify small weeds, chlorotic plants, inconsistency among sensors, and too wide a field of view (FOV), as sensors were spaced farther apart than presently recommended. The number of sensors on a boom needs to be increased to improve the performance of the optically controlled sprayer.

‘Karla’, ‘Klages', ‘Morex’, and ‘Steptoe’ cultivars of spring barley (Hordeum vulgare L.) differed in susceptibility to postemergence recommended application rates of diclofop {(±)-2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid}, difenzoquat [1,2-dimethyl-3,5-diphenyl-1H-pyrazolium], chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide}, and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] in 1981 and 1982. Metribuzin injured Morex, and difenzoquat injured all cultivars within 2 weeks after herbicide application. Metribuzin reduced height and crop biomass compared to the hand-weeded control. Herbicide treatments did not affect grain yield at Moscow, ID, in either year. However, metribuzin reduced yield of Karla and Morex, and diclofop reduced yield of Karla compared to the hand-weeded control at Pullman, WA, in 1982. Barley injury and grain yield loss depended on herbicide treatment and cultivar. Early season herbicide injury to barley did not indicate grain yield response at harvest.

A mail survey was undertaken in 1991 to obtain information on beginning weed science courses being taught in the United States and Canada. Out of 74 questionnaires sent to 44 states and 7 provinces, there were 54 responses of which 49 institutions had a beginning weed science course. The responses showed that these courses are taught primarily once a year (88%) in the fall term (77%). Most schools are under the semester system (82%) with the credits arranged so that there are about 30 hours of lecture per term with a one-credit laboratory. The students in beginning weed science courses are mostly seniors (47%) and juniors (34%) and are primarily from Agronomy, Plant Science, or Crop Science departments (46%) and Horticulture (23%). The average time spent on different topics agreed well with the priorities and are listed in the text. The survey also gathered data on weed identification requirements, special requirements of individual courses, evaluation of students, additional comments by instructors, and special teaching guides or techniques that instructors are willing to share with others.

Tebuthiuron, picloram, hexazinone, and bromacil were evaluated at 0.5, 1.0, and 2.0 g ai or ae per plant for sacahuista control on gravelly loam soils in western Texas. Tebuthiuron applied at 2.0 g per plant killed 87% of the sacahuista, which was significantly greater mortality than that achieved with the same rate of bromacil (62%) and hexazinone (44%). The 2.0 g plant-1 rate of tebuthiuron, bromacil, and hexazinone reduced live canopies of sacahuista 88 to 98%. Picloram did not control sacahuista. Sacahuista mortality increased curvilinearly with increasing rates of tebuthiuron and bromacil, whereas the response to hexazinone was linear.

Although water is crucial to the performance of preemergence herbicides, pesticide performance has rarely been related to irrigation management. This 2-yr study investigated the effect that amount of irrigation water applied had on activity of simazine. Three rates of simazine at 0, 1.12, and 2.24 kg/ha were applied to a 3-yr-old nectarine orchard that was irrigated with microsprinklers. The performance of simazine was compared between irrigation treatments initially targeted to provide water at 110 (efficient) and 175% (overwatered) of crop water requirements. Simazine effectiveness was based on the survival of oat and cucumber plants that were seeded at 0, 14, 28, 56, and 84 d after herbicide application. A longer time interval to 50% survival indicated prolonged herbicidal activity. Results were consistent between years in that simazine's performance was consistently greater in efficient irrigation treatments. The greatest increases were measured at the higher simazine application rate (2.24 kg/ha); overall averages for the length of time to reach 50% survival for cucumber were 50 and 23 d and for oats were 55 and 15 d for efficient and overwatered irrigation treatments, respectively. Use of an efficient irrigation management technique could have enhanced simazine's performance through a decreased leaching of residues from the weed root zone or less chemical or biological degradation (or both). Adoption of efficient irrigation management has been identified as a best management practice to mitigate leaching of pesticide residues to groundwater in coarse soils in California. This study indicates that efficient irrigation improves simazine performance and that both factors, pesticide application and irrigation management, should be considered when developing a weed management system.

The effect of metribuzin at six rates of application was evaluated on four soybean (Glycine max L.) cultivars and on common hempnettle (Galeopsis tetrahit L.) over a three-yr period (1985 to 1987). The cultivars Maple Amber and Baron were susceptible to metribuzin whereas the cultivars Maple Isle and KG-20 were tolerant of metribuzin. Metribuzin caused progressively greater reductions in plant stands and loss in yield in the susceptible cultivars as rate of application increased. Metribuzin at 0.5 kg ha-1 or higher controlled over 90% of common hempnettle.

Various chemical and mechanical weed control treatments for kidney bean production were evaluated on irrigated, sandy loam sites from 1993 to 1995 near Staples, MN. Weed biomass can be controlled either mechanically or chemically, but a combination of the two gave the most effective and dependable weed control over years. Good weed control by either mechanical or chemical means reduced white mold infection of dry bean because of better aeration of dry bean plants and thus less favorable conditions for infection. Dry bean seed yields were inversely related to weed yields, and weed competition was similar from indigenous stands of either grass or broadleaf weeds. Row cultivation was more effective than rotary hoeing for controlling weeds, reducing white mold infection of dry bean, and increasing dry bean seed yields.

The development of a linuron-free weed management strategy for carrot production is essential as a result of the herbicide reevaluation programs launched by the Pest Management Regulatory Agency in Canada for herbicides registered before 1995 and the discovery of linuron-resistant pigweed species in Ontario. Field trials were conducted in one of Ontario’s main carrot-growing regions on high organic soils in 2016 and 2017. Pigweed species seedlings were effectively controlled with PRE treatments of prometryn, pendimethalin, S-metolachlor, or glufosinate. POST treatments of pyroxasulfone and metribuzin followed by predetermined biologically effective dose (≥90% control of pigweed seedlings) of acifluorfen, oxyfluorfen, fluthiacet-methyl, and fomesafen achieved excellent crop selectivity and commercially acceptable pigweed species seedling control under field conditions. Carfentrazone-ethyl or fomesafen applied PRE severely reduced seedling emergence and yield in the wet growing season of 2017. This study demonstrated clearly that an alternative linuron-free strategy can be developed for carrots. The strategy of exploring the potential to use the biologically effective dose of selected herbicides to achieve crop selectivity and control of pigweed species seedlings was verified.