Plant growth regulators were evaluated on common and African ‘Tifway’ bermudagrass. Flurprimidol plus mefluidide applied at 1.1 plus 0.14 kg ha-1 and followed by 0.56 plus 0.14 kg ha-1 at 2- to 3-week interval suppressed vegetative growth of mowed common bermudagrass for 5 wk (17 to 23%) and unmowed turf for 6 wk (40%), but severely injured the turf. The injury ranged from 25 to 32% from 2 to 6 wk after treatment. The plant growth regulators that injured common bermudagrass less than flurprimidol plus mefluidide did not suppress the mowed turf for as long a period. Vegetative growth of common bermudagrass not mowed was suppressed for 6 wk when treated once with flurprimidol plus mefluidide and twice with flurprimidol, mefluidide, imazethapyr, paclobutrazol (1.1 plus 1.1 kg ha-1), and paclobutrazol plus mefluidide. Of the plant growth regulators evaluated, only imazethapyr suppressed common bermudagrass seedheads. The suppression was 70% for 4 wk, but reduced to <70% by 5 wk. Paclobutrazol applied initially at 1.1 kg ha-1 and followed at 0.56 kg ha-1 suppressed vegetative growth of mowed Tifway bermudagrass for 5 wk and unmowed turf for 8 wk without causing severe injury. The suppression of mowed Tifway bermudagrass with two applications of paclobutrazol was as good or better than with any other plant growth regulator. All plant growth regulators suppressed vegetative growth of unmowed Tifway bermudagrass for 8 wk.

Field experiments were conducted to compare non-phenoxy herbicides with 2,4-D for broadleaf plantain, dandelion, and white clover control in cool-season turf. Herbicides tested were BAS 514, chlorflurenol, clopyralid, dicamba, triclopyr, and 2,4-D, alone and in combinations. Broadleaf plantain was controlled by 2,4-D and by clopyralid plus triclopyr at 0.21 plus 0.63 kg ae ha-1. Dandelion was controlled by 2,4-D, BAS 514 at 0.84 kg ha-1, and by the combination of clopyralid plus triclopyr at 0.16 plus 0.47 kg ha-1. Chlorflurenol, clopyralid, dicamba, or triclopyr did not control dandelion. White clover was controlled by all herbicides except 2,4-D. The combination of clopyralid plus triclopyr was the only non-phenoxy treatment which controlled broadleaf plantain, dandelion, and white clover.

Seedling timothy tolerated fenoxaprop at 0.09 kg ai ha-1 whereas seedling orchardgrass tolerated applications as high as 0.13 kg ai ha-1. Several fenoxaprop treatments increased perennial grass yields the year following establishment. Fenoxaprop appears to solve annual foxtail problems in new plantings of orchardgrass or timothy seeded alone. Over a 2-yr period, alfalfa yields in on alfalfa-grass mixture were maintained or increased from fenoxaprop applied the seedling year. In the mixtures, timothy yield declined in relation to fenoxaprop applied, but orchardgrass did not. Use of fenoxaprop on seedling alfalfa-timothy or alfalfa-orchardgrass mixtures is questionable.

Data from three field experiments were used to determine the effects of grazing cheat-infested winter wheat during tillering on cheat and wheat growth, mature biomass, and wheat grain yield components. When terminated, grazing had reduced wheat leaf area 52% and cheat leaf area by 28%. Pooled over experiments, grazing decreased mature wheat height 7 cm and wheat yield 17%. Grazing increased dockage due primarily to cheat 9%. Grazing effects on wheat yield components, biomass, and cheat panicle density varied. Grazing did not affect cheat tillering or wheat harvest index.

Field experiments were conducted to evaluate the tolerance of 79 winter wheat cultivars to cyanazine, BAY SMY 1500, and metribuzin. When known, the pedigree of the more cyanazineand BAY SMY 1500-tolerant hard red winter cultivars included ‘Hope’ and/or ‘Cheyenne’ parentage. However, the cultivars more sensitive to BAY SMY 1500, notably those with ‘Vona’ parentage, were not consistently sensitive to cyanazine. Visible injury on the hard red and soft red winter cultivars did not consistently indicate yield reductions. The soft red winter cultivars, compared to the hard red winter cultivars, were generally more sensitive to cyanazine than BAY SMY 1500.

A greenhouse study was designed to evaluate a series of silicone adjuvants for increasing efficacy and rainfastness of Na-acifluorfen, isopropylamine-glyphosate, and Na-bentazon on velvetleaf and common lambsquarters. Silicone adjuvants were identified that increased both herbicide efficacy and rainfastness at 0.9 to 1.2 L ha-1. Specificity of adjuvants for specific target weed species and herbicides was evident. Effective silicone adjuvants were identified that did not increase soybean injury by Na-acifluorfen or Na-bentazon beyond that observed with crop oil concentrate. The efficacy of the best silicone adjuvant did not appear to be solely a function of reduced surface tension of the spray solution.

Experiments were conducted in North Carolina and South Carolina, 1989, to evaluate methods of infesting research plots with witchweed. At both locations sowing witchweed (mixed with very fine sand) in or beneath the maize planting hole resulted in more rapid attachment of witchweed than other methods. Sowing witchweed only in the maize planting hole increased significantly witchweed attachment compared to the control late in the season at Evergreen, NC. At Dillon, SC, in fumigated soil, sowing witchweed seeds to the side of the maize row in a band or in planting holes or broadcasting and incorporating with a hoe increased witchweed attack. Broadcasting and raking was ineffective.

Ten herbicides were evaluated for poison-hemlock control in established alfalfa in Utah. Hexazinone, metribuzin, and terbacil controlled poison-hemlock 90% or more but diuron and pronamide did not. Either glyphosate or 2,4-D applied in May at 1.1 kg ae ha-1 controlled poison-hemlock 97 to 98% compared to 60 to 75% with 2,4-DB at that rate. Dicamba and bromoxynil did not control poison-hemlock.

2,4-D diethanolamine control of kochia was influenced by the source of water used as the spray carrier. Sodium bicarbonate in one water source related to the reduced kochia control. Sodium bicarbonate in a water spray carrier antagonized 2,4-D control of all plant species evaluated. Antagonism increased with the tolerance of a species to 2,4-D, concentration of sodium bicarbonate, and spray volume. Sodium bicarbonate antagonism of 2,4-D phytotoxicity was greatest with low temperature and relative humidity.

Field studies were conducted over 2 yr and two locations per year in soft red winter wheat to determine the efficacy of thifensulfuron and thifensulfuron plus DPX-L5300 (2:1 ratio) on all wild garlic reproductive bulbs. The herbicide formulations controlled wild garlic equally. Aerial bulblet control was excellent (>90%) with either herbicide regardless of application timing (March 21, April 8, and April 29) and significantly better than the standard treatment of the butoxyethanol ester of 2,4-D. Control of developing underground offset bulbs was less complete compared to aerial bulblets, and was found to depend on application time. Offset bulbs were controlled better when herbicides were applied in late March or early April compared to the April 29 treatment date. The rate response (9 to 70 g ha-1) was positive for the control offset bulb production at the two earlier dates but not at April 29. These herbicides also adversely affected the germination and viability of the bulbs that were produced.

The effects of 14 herbicide treatments, tested in the establishment phase, were investigated on timothy productivity in two field experiments conducted at Melfort, Saskatchewan. Satisfactory weed control achieved with chlorsulfuron, metsulfuron, thifensulfuron, bentazon, diclofop plus bromoxynil, and MCPA/mecoprop/dicamba during the establishment year ensured good forage establishment which in turn caused a ‘residual effect’ for 1 to 3 yr increasing individual cut as well as cumulative forage dry matter yields significantly. In the stand established in 1985, when field pennycress (97 m-2) was the dominant weed in the seedling stage, these treatments increased yields 29 to 52% over a 3-yr period. In the stand established in 1986, when common lambsquarters (27 m-2) was the dominant weed, these treatments increased cumulative yields 24 to 44%. Sethoxydim and fenoxaprop, tested alone, caused significant crop injury in both experiments.

Clomazone is used in the Central Great Plains for weed control during fallow in a winter wheat-fallow rotation. Improved precipitation storage during non-crop periods has stimulated new crop rotations such as winter wheat-corn or proso millet-fallow. The objective of this study was to determine if clomazone applied in the fall after winter wheat harvest would injure succeeding spring-planted crops. Greenhouse studies indicated crop tolerance to clomazone was in the order of safflower > corn > proso millet > barley > winter wheat. Clomazone did not affect grain yields of safflower, corn, or proso millet grown at two field sites with different soil textures (silt loam and sandy loam), nor germination of seed from treated plants of these crops. A no-till production system with clomazone increased grain yields for all crops compared to the conventional system where tillage replaced clomazone for fallow weed control.

Field experiments were conducted in 1983, 1984, and 1985 at Stoneville, MS, to evaluate the differential growth of 17 biotypes of bermudagrass in two cotton planting patterns. Growth comparisons (parallel = along the row, perpendicular = across the row, and height) were made among biotypes and between solid and skip-row cotton planting patterns, 1- and 2-m row widths, respectively. Biotype growth parameters differed significantly regardless of cotton planting patterns. Bermudagrass growth, perpendicular and parallel to rows, was greater in skip-row than in solid planted cotton by ≥5 and ≥7 wk after planting, respectively. Bermudagrass was taller in skip-row vs. solid planted cotton at ≥18 wk after planting. When averaged over biotypes, growth of bermudagrass was 3 to 4 times greater in skip-row than in solid cotton planting patterns by 18 wk after planting.

Five field experiments were conducted at two locations in Virginia during 1988–89 to evaluate DPX-V9360 and CGA-136872 for postemergence control of johnsongrass in field corn grown under no-till and conventional conditions. DPX-V9360 at rates of 35 (except in no-till plots), 52, and 69 g ai ha-1 applied to 8-leaf johnsongrass was 88 to 98% effective in 1988. CGA-136872 at 25, 49, and 99 g ha-1 was 80% effective at the highest rate. Applications of these herbicides to 6-leaf johnsongrass resulted in 69% or less control. DPX-V9360 at 35, 52, and 69 g ha-1 and CGA-136872 at 20 and 40 g ha-1 applied to johnsongrass up to 48 cm in height provided 77 to 97% control at 7 WAT3 in an excellent stand of conventionally planted corn during 1989. Crop yields were more than doubled with herbicide treatments relative to yields in control plots. At a second location where crop damage caused by other factors resulted in a weak stand, DPX-V9360 provided 61 to 96% control compared to 29 to 56% control with CGA-136872.

The effect of urea ammonium nitrate (UAN) on the antagonism of sethoxydim, haloxyfop, or the methyl ester of haloxyfop activity by bentazon was evaluated in greenhouse and field trials on yellow and giant foxtail. Including UAN in the spray solution in the absence of bentazon did not enhance the activity of any of the three grass herbicides. However, adding UAN to sethoxydim or haloxyfop in the presence of bentazon decreased the bentazon antagonism of grass activity. Conversely, UAN increased bentazon antagonism of the activity of haloxyfop methyl ester. The differential effect of UAN was not linked to effects on spray solution pH.

Field and laboratory experiments were conducted to evaluate the effect of glyphosate concentration, surfactant concentration, and ammonium sulfate on the control of giant burreed when applied through a ropewick applicator. Under non-flooded conditions, a 30% (v/v) solution of glyphosate applied with a ropewick applicator gave the highest giant burreed injury in 1987 and 1988, and reduced corm and rhizome viability compared to the nontreated control in 1987. Warm, dry conditions may have been responsible for poor long-term control in 1988 by reducing translocation of glyphosate to rhizomes. Addition of ammonium sulfate or surfactant did not influence glyphosate toxicity to giant burreed when applied with a ropewick applicator. In the laboratory, leaf necrosis at the point of application was observed with surfactant at 0.6% or 1.2% regardless of glyphosate concentration. Absorption of 14C-glyphosate increased two-fold with the addition of surfactant, and translocation to roots and rhizomes decreased almost two-fold as surfactant concentration was increased from 0 to 1.2%. Electrolyte leakage increased with 30% glyphosate when surfactant concentration was increased from 0 to 1.2%. Localized leaf necrosis and disruption of tissues inside the leaf may be responsible for reduced giant burreed control with glyphosate and surfactant applied in high concentrations.

Field studies were conducted in 1987, 1988, and 1989 at Lethbridge, Alberta to determine suitable herbicides for the control of Russian thistle and kochia in field corn grown in a dryland cropping system. Soil-applied atrazine or cyanazine provided inconsistent control of these weeds under dryland conditions. Combining inter-row tillage or 2,4-D applied postemergence with soil-applied atrazine improved the consistency of weed control over years. Postemergence atrazine and dicamba plus 2,4-D controlled Russian thistle and kochia in all years. Corn yields reflected the level of weed control attained with each treatment. The suitability of the various treatments for weed control in corn grown under dryland crop production systems is discussed.

Four herbicide treatments applied in the spring or fall were evaluated for leafy spurge control and forage production in eastern and western North Dakota during a 5-yr experiment. All treatments gradually reduced the leafy spurge infestation at both locations except 2,4-D at 2.2 kg ae ha-1 applied annually in the spring or fall and picloram plus 2,4-D at 0.28 plus 1.1 kg ae ha-1 applied annually in the fall. The most cost effective treatment was picloram plus 2,4-D applied annually in the spring which provided a net return of $284 and $108/ha in eastern and western North Dakota, respectively, and averaged 80% leafy spurge control. Picloram at 2.2 kg ha-1 was reapplied only when leafy spurge control declined to less than 70% and provided a net return of $96/ha in eastern North Dakota, but a net loss of $235/ha in western North Dakota. Dicamba at 9 kg ae ha-1 was applied up to four times to maintain 70% control with an average net loss of $458/ha. Total potential production and value of forage will determine if a specific treatment is cost effective in any one location.

Research was conducted in 1987 and 1988 to identify effective horseweed control strategies in no-tillage soybean production. Paraquat at 560 g ai ha-1 plus metolachlor at 2200 g ai ha-1, linuron at 840 g ai ha-1, and nonionic surfactant at 0.25% (v/v) applied preemergence provided less than 61% horseweed control. Glyphosate at 840 g ai ha-1, 2,4-D ester at 560 g ai ha-1, HOE-39866 at 840 g ai ha-1, or BAS-514 at 70 g ai ha-1 applied early preplant controlled more than 96% when followed by the above preemergence herbicide combination. Substituting either glyphosate at 840 g ha-1 or HOE-39866 at 840 g ha-1 for paraquat in the preemergence application program significantly increased control. Adding BAS-514 at 70 g ha-1 to preemergence treatments containing paraquat significantly improved control. The substitution of metribuzin, metribuzin plus chlorimuron (10:1 ratio), or linuron plus chlorimuron (16:1 ratio) for linuron resulted in greater control and soybean yield. Sequential applications controlled horseweed equal to or better than a single preemergence application at the same total rate.

Clomazone was evaluated preplant incorporated (PPI) or post-transplant (PT) for weed control in sweet potatoes. No crop injury by clomazone was detected. Clomazone controlled (≥90%). broadleaf signalgrass, large crabgrass, barnyardgrass, and prickly sida at all rates and methods of application (MOA). Common cocklebur was controlled (≥93%) by clomazone at 1.1 kg ai ha-1 applied PT or at 3.4 kg ai ha-1 PPI in 1988 and at all rates and MOA in 1989. Clomazone did not control carpetweed.