In 1987 and 1988, effects of full-season interference of individual weeds on cotton yield were measured with area of influence procedures. In 1987, one spurred anoda, common cocklebur, large crabgrass, jimsonweed, common lambsquarters, redroot pigweed, common ragweed, or prickly sida plant per 3 m of row reduced cotton yield between 1% and 7%. Sicklepod did not cause a detectable yield loss. Redroot pigweed, common cocklebur and common ragweed caused 7%, 6% and 5% yield loss, respectively, in 1987. In row weed influence varied from 17 cm (large crabgrass interference) to 86 cm (common cocklebur interference). In 1988, yield losses by individual weeds ranged from 3% to 27%. Common cocklebur, jimsonweed, and common ragweed reduced cotton yields 28%, 15% and 12%, respectively. Spurred anoda and common cocklebur influenced 160 cm and 136 cm of cotton row, respectively. Sicklepod influenced only 47 cm of cotton row.

Jointed goatgrass is a winter annual grass weed which is believed to have been introduced into North America as a contaminant in winter wheat seed. Although jointed goatgrass was first discovered in some states early in the 20th century, changing wheat production practices during the past 25 yr have encouraged its spread and increase. Winter wheat producers in the western United States are concerned about the lack of adequate selective control measures for this weed. Jointed goatgrass and wheat share the D chromosome in common and have similar growth habits. Jointed goatgrass lowers winter wheat yield by competing for growth requirements, reducing harvesting efficiency, and lowering crop quality by contaminating harvested grain. Jointed goatgrass is well adapted to stubble-mulch or reduced tillage crop production, particularly in regions where climate limits cropping options to the winter wheat-fallow rotation or continuous wheat. This review summarizes jointed goatgrass seed germination, dormancy, physiology, yield loss estimates in winter wheat, and both herbicidal and non-chemical methods of managing jointed goatgrass.

Landsat-5 Thematic Mapper spectral data and field survey information were combined to identify specific land cover types associated with 1741 dyers woad infestation points on the Cache National Forest in northern Utah. Ten of 60 possible cover types were strongly associated with current dyers woad infestations, and therefore considered highly suited to establishment and survival of the weed. Non-infested land of the same “highly suited” cover types comprised an additional 24 714 ha within the 149 021-ha study area, suggesting the potential for an eventual 124-fold increase in dyers woad incidence on the forest.

Field trials were conducted to compare on-site visual evaluations with color-infrared photography (CIR), and near-infrared (NIR) videography (video) and hand-held radiometry (HHR) for detecting and mapping dicamba injury in cotton. CIR, video, and HHR detected 48%, 42% and 36%, respectively, of the injured crop area as defined by visual evaluation (injury ratings >0 on a scale of 0 to 9). The remote techniques were unable to differentiate crop injury that did not involve the entire plant canopy. Reflectance measurements in the visible red (R) (630–690 nm) and NIR (760–900 nm) wavelengths were taken and used in herbicide dosage prediction equations. Predicted herbicide dosages were significantly, positively correlated (P≤0.01) with physical measures of herbicide present. These studies suggest that remote detection and mapping of moderate and severe herbicide injury is possible. Further, NIR videography, with near-real-time capability and low cost may be the system of choice for this type of application.

Field experiments were conducted in Oklahoma to determine the effects of winter wheat seeding date and cheat infestation level on cultural cheat control obtained by increasing winter wheat seeding rates and decreasing row spacing. Seeding rate and row spacing interactions influenced cheat density, biomass, or seed in harvested wheat (dockage) at two of three locations. Suppressive effects on cheat of increasing wheat seeding rates and reduced row spacings were greater in wheat seeded in September than later. At two other locations, increasing seeding rate from 67 to 101 kg ha–1 or reducing row spacings from 22.5 to 15 cm increased winter wheat yield over a range of cheat infestation levels.

Ammonium sulfate enhanced the initial control of johnsongrass by glyphosate and SC-0224 applied in the fall or summer. Glyphosate at 0.42 kg ha-1 in combination with ammonium sulfate at 3.33 kg ha-1 provided levels of fall johnsongrass control and spring regrowth control comparable to glyphosate at 0.84 kg ha-1. Spring applications to mixed populations of seedling and rhizome johnsongrass showed that ammonium sulfate added to glyphosate or SC-0224 afforded little enhancement of herbicide efficacy. Glyphosate or SC-0024 at 0.42 kg ha-1 applied in combination with logarithmically decreasing rates of ammonium sulfate demonstrated reduced weed control with ammonium sulfate rates above 9.7 kg ha-1.

An area of influence method with biweekly destructive harvests 5 through 19 wk after planting (WAP) was used to monitor the reciprocal interference of common cocklebur and cotton in 1987 and 1988. Plant heights, leaf area, and leaf, stem, boll, fiber, and total plant biomass dry weights were measured in 15-cm increments away from common cocklebur or from a randomly selected cotton plant out to 105 cm. Data indicated that cotton less than 60 cm from common cocklebur was shorter, had less leaf area and lower leaf, stem, boll, and biomass dry weights than cotton beyond 60 cm from common cocklebur or cotton grown without common cocklebur interference. Differences in leaf area and biomass between cotton grown with and without common cocklebur interference were greater at and beyond 13 WAP sample dates than before 13 WAP. By 15 WAP, cotton leaf area and biomass were reduced an estimated 11% and 15%, respectively, averaged over the entire 105 cm of row. Cotton yield, harvested 27 WAP, was reduced an estimated 31% on plants grown with one common cocklebur plant per 2.1 m. Cotton yield was reduced on plants out to 99 cm from common cocklebur. Common cocklebur and cotton plants grown alone were taller, had greater leaf area, and greater leaf, stem, and biomass dry weight than those respective plants grown adjacent to cotton. Common cocklebur grown alone produced 67% more biomass than did cotton grown alone. Cotton plants grown adjacent to other cotton plants produced 89% and 96% less boll and fiber weight, respectively, than plants grown alone.

Intact soil columns were evaluated as a screening technique to determine the effect of tillage on herbicide movement through soil. Alachlor was applied at 3.3 kg ai ha-1 to intact surface 0- to 10-cm and subsurface 10- to 20-cm soil columns (15-cm diam) taken from long-term no-till and conventional tillage plots and leached with 11.6 pore volumes (7 L; 39 cm) of water at a rate that did not create ponding. Leachate was collected in 0.07 pore volume fractions. Twice as much alachlor leached from surface no-till than from surface conventional tillage columns. The differences in leaching patterns from the surface soil can be attributed to the effect of tillage on soil physical and chemical properties. Using intact soil columns in the laboratory can be a useful rapid screening technique to evaluate tillage impacts on herbicide movement.

The objective of this research was to modify the senior author's previously developed method for predicting yield losses in maize crops attributable to johnsongrass. The new method is based on the following assumptions: a) relative leaf frequency determines relative biomass; b) total biomass is constant despite the crop/weed ratio; and c) biomass, and therefore leaf frequency, are related to grain yield. Experiments in Argentina from 1986 to 1989 supported the above hypotheses, and the new method was more accurate than the old for predicting relative species biomass in johnsongrass/maize mixtures. Maize grain yield reductions associated with weed interference were also more accurately predicted.

A 4-yr study (1985, 1987, 1988, 1989) was conducted on the same field plots at Shafter, CA to evaluate the efficacy of prometryn in controlling black nightshade on planting beds of cotton. Two rates (1.7 and 2.2 kg ai ha–1) were applied at two times (mid March before the preplant irrigation and early April at cotton planting) each year. Incorporation of prometryn into moist planting beds with a powered rotary tiller operated at 10 cm deeper resulted in excellent control of black nightshade under low to moderate weed pressure in 1985 and 1987. Control of nightshade with early and late applications of 1.7 kg ha–1 of prometryn under high weed pressure in 1988 was only 70% at harvest, and yield losses of cotton averaged 25%. Yields of cotton treated with 2.2 kg ha–1 of prometryn in 1988 were not significantly different from weed-free plots. Only the late application of 2.2 kg ha–1 of prometryn prevented significant cotton losses under extreme weed pressure in 1989. Cotton yield losses with the other prometryn treatments ranged from 78 to 100%. Losses of cotton in weedy-check plots that received only cultivation ranged from 22% in the absence of rain or irrigation at cotton planting in 1987 to as much as 100% when rain fell in 1988 or plots were irrigated at planting in 1989. Plots hoed one time 4 wk after cotton planting yielded an average of 84% as much seed cotton as weed-free plots. In an attempt to determine why the efficacy of prometryn declined between 1985 and 1989, several experiments were conducted in 1988 to 1990 to discover reasons for this poor control of nightshade. Because efforts failed to provide evidence for the movement of the herbicide with water, the development of weed resistance to prometryn, or accelerated degradation of this herbicide in soil, increasing weed seed populations in soil were believed to have contributed greatly to the declining nightshade control from prometryn. The fact that prometryn applied and incorporated into flat soil provided excellent control of nightshade in 1990 under sprinkler irrigation indicated that both soil moisture and incorporation techniques limited activity of prometryn in planting beds in 1988 and 1989. Incomplete control of nightshade plus good soil moisture at planting contributed to the high weed populations in 1988 and 1989.

Imazethapyr at 0.07 and 0.10 kg ai ha-1 applied preplant incorporated (PPI), preemergence (PRE), and postemergence (POST) was evaluated at two locations in 1988 and 1989 for safety to dry edible beans. Bean stunting, leaf crinkling, and interveinal chlorosis were evident from imazethapyr and varied from 1 to 57%. Imazethapyr significantly reduced bean height and delayed maturity. PPI and POST applications of imazethapyr at 0.07 and 0.10 kg ha-1 did not reduce bean seed yields compared to yields of the untreated control. Bean cultivar by herbicide interactions were significant for bean injury but varied with year and location.

Tolerance of two metribuzin-tolerant and two metribuzin-sensitive early maturing soybean cultivars to two rates of acifluorfen, imazethapyr, metribuzin, and thifensulfuron was evaluated under weed-free conditions. Acifluorfen at 1120 g ai ha-1 reduced plant height by 3 cm and thifensulfuron at 18 and 35 g ai ha-1 delayed physiological maturity by 3 d. No herbicide treatment reduced soybean yield when compared with a weed-free check. Soybean yield of the two metribuzin-tolerant and the two metribuzin-sensitive cultivars did not change as metribuzin rate was increased from zero to 280 to 560 g ai ha-1.

Postemergence grass weed control in turf-type bermudagrass is currently available only with repeated applications of organic arsenicals and/or with combinations of metribuzin which decrease turf quality. Research was conducted to determine tolerance of the turf-type bermudagrass cultivars, Tifway, Ormond, and common, to diclofop rates ranging from 0.54 to 4.48 kg ai ha-1 with and without MSMA (2.2 kg ai ha-1) and metribuzin (0.2 kg ai ha-1). Bermudagrass cultivars tolerated diclofop well. When injury was evident, a rate response was noted, with higher rates (3.4 and 4.5 kg ha-1) resulting in increased phytotoxicity. However, this level of phytotoxicity was acceptable and the turf soon recovered (3 to 14 d). The addition of crop oil concentrate (1.25% v/v) did not affect turf quality. Addition of MSMA resulted in slightly lower turf quality than diclofop alone. However, these responses were acceptable and usually the turf recovered by 14 d after treatment. Metribuzin applied alone or in combination with diclofop damaged turf to unacceptable levels and up to 21 d were required for turf recovery.

Alfalfa seed yield and Canada thistle densities were measured in 10 fields in southern Alberta to assess the effect of thistles on seed yield. Thistle density and seed yield from each field were fitted to the Weibull, hyperbolic, and linear equations and a random coefficient and linear equation were used to obtain an “average yield loss curve”. Estimated average losses in alfalfa seed yield were >34% and >48% at thistle densities of 10 and 20 shoots m–2, respectively.

Cotton response to triclopyr was evaluated when it was applied over-the-top at simulated drift rates to pin-head square and early bloom cotton growth stages in 1987 and 1988. The herbicidal effects of triclopyr were most evident after a lag period of 10 to 15 d. Triclopyr at 60 g ai ha-1 applied at pin-head square reduced cotton height in 1987, but not in 1988. Triclopyr applied at pin-head square and early bloom reduced cotton flowering initially, as measured by white bloom counts, in both years. Total blooms were reduced in 1987, but not in 1988. Cotton maturity was delayed by triclopyr application during early bloom, as shown by a decrease in percent open bolls, and a decrease in first pick cotton yields. Cotton yield was lower in plots receiving triclopyr, with the greatest yield reduction caused by a 60 g ha-1 triclopyr application at early bloom.

Sicklepod control with seven chemical treatments was evaluated in 25-cm and 97-cm soybean row widths. Metribuzin applied preplant incorporated followed by metribuzin applied preemergence, and metribuzin applied preplant incorporated followed by either imazaquin or chlorimuron applied postemergence controlled sicklepod over 90% early in the season, and row spacing did not influence control at that evaluation. In late season ratings, all herbicide treatments controlled sicklepod better in 25-cm rows than in 97-cm rows. However, only imazaquin applied sequentially or metribuzin followed by chlorimuron in 25-cm rows controlled sicklepod greater than 80% late in the season. Sicklepod control in 25-cm row soybean with either imazaquin or metribuzin plus chlorimuron applied preplant incorporated was equivalent to or better than sequential preemergence and postemergence treatments of these three herbicides in 97-cm rows. All treatments resulted in lower yields than the weed-free check in the 97-cm rows, whereas all herbicide treatments except the sequential application of metribuzin gave yields equivalent to the weed free check in 25-cm rows.