Field studies were conducted over a 7-yr period at Lacombe, Alberta, to study the relationship between the duration of Tartary buckwheat interference [Fagopyrum tatarium (L.) Gaertn. # FAGTA] and yield of barley (Hordeum vulgare L.), oats (Avena sativa L.), wheat (Triticum aestivum L.), flax (Linum usitatissimum L.), and rapeseed (Brassica campestris L.). The data were pooled over years and analyzed by multiple regression. The equations were as follows: ŷ = 15.46 + 0.39X1 + 0.00x2 −0.11x3 (barley), ŷ = −15.44 + 0.49x1 + 0.02x2 + 0.08x3 (oats), ŷ = −2.04 + 0.39X1 + 0.05x2-0.03x3 (wheat), ŷ = −4.38 + 1.14x1 −0.04x2 + 0.01x3 (flax), and ŷ = −13.85 + 0.40x1 – 0.01x2 + 0.04x3 (rapeseed); where ŷ was the estimated percent yield loss of the crop, x1 was the duration (days) of the Tartary buckwheat in the crop, x2 was the number of Tartary buckwheat plants/m2, and x3 was the number of crop plants/m2. The time that Tartary buckwheat remains in the crop contributed most to the yield loss observed in all crops. Yield loss between 0.4 and 1.1% per day was attributed to this variable alone. For a given x1, x2, and x3 value the order of percent yield loss was flax>oats>wheat> barley>rapeseed.

Honey mesquite (Prosopis glandulosa Torr. # PRCJG) was treated with four herbicides at 1.1 kg ae/ha at 14 dates from April 30 through September 23 over a 2-yr period. Overall, clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was the most effective herbicide, killing 80% or more of the honey mesquite at most dates. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] were less effective than clopyralid. Honey mesquite control was correlated with Julian day of year sprayed, 15 plant, 11 environmental, and 8 herbicide concentration variables. Most effective control was negatively correlated with Julian day of year sprayed and new xylem ring thickness. Control was positively correlated with total daily apparent photosynthesis, upward methylene blue dye movement in the xylem, and herbicide concentration in the xylem 3 days after spraying. The only environmental variable of 11 measured that was significantly correlated with honey mesquite control was soil water and that was only with picloram. The concentration of herbicide in the stem was highest for clopyralid, followed by picloram, and then by 2,4,5-T and triclopyr, which were about equal. Variables most useful in regression equations for predicting control with herbicides were total daily apparent photosynthesis and rate of upward movement of methylene blue dye. Variables most incorporated into regression equations relating honey mesquite control with herbicide content were herbicide concentrations in the xylem 3 or 30 days after treatment.

The influence of surfactant type and concentration on the efficacy of asulam {methyl [(4-aminophenyl) sulfonyl] carbamate} for controlling rhizomatous johnsongrass [Sorghum halepense (L.) Pers. # SORHA] was evaluated in field and greenhouse studies. Under field conditions, nonoxynol (9 to 10 POE) [α-lp-nonylphenyl)-w-hydroxypoly (oxyethylene)] applied at concentrations of 6% (v/v) with asulam at 2.8 kg ai/ha reduced rhizomatous johnsongrass biomass by 35%, with no consistently significant difference in asulam's performance between surfactant concentrations of 0 and 3% (v/v) being observed. Asulam applied with nonoxynol at concentrations of 3 and 6% (v/v) reduced sugarcane (Saccharum interspecific hybrids) yields and significantly offset any advantages from increased johnsongrass control. In greenhouse studies, where johnsongrass foliage was washed either 0, 1, 6, 24, or 48 h after treatment (HAT), the degree of johnsongrass control with asulam was generally not affected by the type of surfactant (paraffin-base petroleum oil-surfactant blend or alcohol-surfactant-water mixture) used. At least 48 h was needed to insure adequate basipetal translocation, hence maximum inhibition of rhizome regrowth with asulam applied alone. Increasing the surfactant concentration shortened this interval to 48 h (0.25%) to 24 h (0.5 to 1%) to 6 h (3%) to 1 h (6%).

Experiments were conducted over 4 yr to investigate the effects of four postemergence herbicides on soybean [Glycine max (L.) Merr. ‘Williams 79’] yield under weed-free conditions. Bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, and naptalam/dinoseb {2-[(1-naphthalenylamino)carbonyl] benzoic acid}/[2-(1-methylpropyl)-4,6-dinitrophenol] alone and in combination with 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid] applied to soybeans at the V3 and V5 soybean growth stages caused early crop injury, but soybeans outgrew most of the injury by 21 days and there was no effect on yield. Bentazon plus 2,4-DB with or without adjuvant did not affect the yield of five soybean cultivars tested.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was applied to peanuts (Arachis hypogaea L. ‘Florunner’) for Texas panicum (Panicum texanum Buckl. # PANTE) control at 0.07, 0.14, and 0.28 kg ai/ha under five application schedules; a single application at 0, 1, 3, or 5 weeks after ground cracking, or multiple applications at 1 + 5 weeks or 1 + 3 + 5 weeks after ground cracking. Peanuts were planted at two different times (normal and late). A herbicide application at the third week (normal planting), or the third or fifth week after ground cracking (late planting) provided acceptable Texas panicum control. Control generally increased with rate. However, increasing paraquat rates with single applications on late-planted peanuts or multiple applications to normal- and late-planted peanuts tended to reduce yield and grade. A single application of 0.07 or 0.14 kg/ha applied the third week after ground cracking consistently provided the best balance between Texas panicum control and crop safety.

Five varieties of 3-month-old citrus rootstocks were grown for 1 month in nutrient solution containing 0, 10-3, 10-4, or 10-5 M of norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3 (2H)-pyridazinone] to assess the effect of this herbicide on growth and chlorophyll levels. The uptake, translocation, and metabolism of root-applied 14C-norflurazon was also examined in these rootstocks. Norflurazon treatment reduced chlorophyll level and lowered overall growth in sour orange (Citrus aurantium), Swingle (Poncirus trifoliata × C. paradisi), Milam (C. jambhiri), and Cleopatra mandarin (C. reshni) rootstocks. Herbicide treatments had little or no effect on chlorophyll levels or growth in Carrizo (C. sinensis × P. trifoliata). In Cleopatra, unlike in other rootstocks, leaf chlorosis was evident only along the midrib and major veins. Herbicide treatment reduced leaf flush (leaf production) in Swingle but not in other rootstocks. By the end of a 4-week treatment period, total absorption of 14C-norflurazon was greater in Swingle than in the other rootstocks. 14C-norflurazon detected in the roots (excluding taproot) of Swingle was greater than in the other rootstocks. The amount of 14C-norflurazon translocation to the foliage was limited in all rootstocks. Stem and taproot also contained only a small amount of 14C-norflurazon. Leaf extracts of all five rootstocks contained no parent compound, but up to 90% of recovered 14C was identified as 14C-norflurazon in root extracts. Differences in the uptake, translocation, and metabolism of norflurazon among citrus rootstocks were small and did not appear to explain their differential sensitivity to this herbicide.

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%.

Benzyl isothiocyanate (BITC) was formulated in dry granules with tung oil and calcareous loess to facilitate safe handling of the water-sensitive lachrymator. Crop and weed seeds were exposed to granular BITC at 40 mg ai/kg (w/w) substrate on moist sand for 2 days. When the pretreated seeds were washed with water and placed on BITC-free sand in a germination chamber for 15 days, germination in comparison to untreated seeds was 0 to 8% for pitted morningglory (Ipomoea lacunosa L. # IPOLA), sicklepod (Cassia obtusifolia L. # CASOB), milo [Sorghum bicolor (L.) Moench. ‘Funks G-522DR’], and red rice (Oryza sativa L. # ORYSA) seeds; 15 or 16% for velvetleaf (Abutilon theophrasti Medic. # ABUTH) and johnsongrass [Sorghum halepense (L.) Pers. # SORHA]; and 39% for barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG]. Subjecting milo seeds to moist sand medium that contained BITC granules at 10, 20, and 40 mg ai/kg substrate reduced germination of milo by 78, 97, and 100%, respectively. However, BITC granules applied to the growth medium 2 to 4 days prior to sowing seeds had little effect on germination and growth of milo or sicklepod. Thus, BITC-treated soil soon became safe for newly sown seeds, but seeds present in soil when the toxin granules were applied failed to recover from exposure to BITC and deteriorated within 15 days.

The influence of soil pH on the uptake, degradation, and movement of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in soil was examined. Phytotoxicity decreased as pH increased in a silty clay loam with an adjusted pH range of 5.9 to 7.5. Fresh weights of sorghum [Sorghum bicolor (L.) Moench. ‘Funks G-499 GBR’] shoots grown in soil at pH 7.5 and containing 0.8 or 1.6 ppbw chlorsulfuron were not different from the controls while large differences occurred at pH 5.9. Uptake of 14C-chlorsulfuron by wheat (Triticum aestivum L. ‘Centurk’) in a silty clay loam with a pH of 5.9 was 67 to 100% greater than at pH 7.5. Soil pH strongly influenced the degradation rate of chlorsulfuron in a laboratory incubation study. Chlorsulfuron half-life in a silty clay loam was 1.9 weeks at pH 5.6 and 10 weeks at pH 7.5. Soil thin-layer chromatography indicated a high leaching potential for chlorsulfuron, and mobility increased as soil pH was increased.