Leaching of dl-strigol at six rates between 0.3 and 4.5 kg/ha through columns of sandy loam soil was estimated using a witchweed [Striga asiatica (L.) Kuntze # STRLU] germination bioassay. After 21 days of leaching daily with 1.27 cm of simulated rainfall, about 86% of the applied chemical remained in the top 2.5 cm of the soil, about 6% in the zone between 2.5 and 7.5 cm, and less than 1% in the soil at depths between 7.5 and 30 cm. However, even with the lowest rate of the chemical application, sufficient dl-strigol was leached to a soil depth between 22.5 and 30 cm to cause most, if not all, of the witchweed seeds to germinate. These results suggest that dl-strigol has a potential for use as an effective tool for a witchweed control or eradication program. No significant degradation of the chemical occurred in moist soil during the 21-day period.

Retention, absorption, translocation, and metabolism of 2,4-D [(2,4-dichlorophenoxy)acetic acid] by common waterplantain (Alisma triviale Pursh. # ALSPA) at three growth stages were investigated to determine the basis for differential susceptibility of common waterplantain at different growth stages. Plants in the five-leaf and scape elongation stages retained more 2,4-D than plants in the early flowering stage. Absorption of 14C-2,4-D by the flower stalk was less than absorption by the treated leaves regardless of growth stage. The majority of the absorbed 14C translocated out of the treated plant part was recovered in the aerial portion of the plant younger than the treated leaves or in the corm, with greater movement of 14C into the corm at the older growth stages. Metabolism of 14C-2,4-D did not differ among the growth stages. The results suggest that the greater sensitivity of common waterplantain at the scape elongation stage to 2,4-D is due to greater translocation to the corm when compared to the five-leaf stage, and greater retention when compared to the early flowering stage.

Combination treatments of 2,4-D [(2,4-dichlorophenoxy)acetic acid] + mecoprop {2-[(4-chloro-o-tolyl) oxy] propionic acid} + dicamba (3,6-dichloro-o-anisic acid) injured actively growing bermudagrass [Cynodon dactylon (L.) Pers. # CYNDA] immediately after treatment. Treatments made at the normal (1.1 + 0.6 + 0.1 kg ai/ha) rate in August, September, or October, did not affect winter survival. A triple rate (3.3 + 1.8 + 0.3 kg/ha) delayed growth of ‘Tifgreen’ and ‘Tifdwarf’ more the following April than ‘Tifway’ and ‘Ormond’. Due to a reduction in turf stand from herbicide treatments, the cover of common chickweed [Stellaria media (L.) Cyrillo # STEME] was higher in plots to which herbicides were applied in August or September than in untreated plots. The cover of weeds was lower in Tifway and Ormond plots than in Tifgreen and Tifdwarf plots.

Soil uptake, translocation, and metabolism of simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) by tolerant poplar clone Populus × euramericana I-45/51, a section Aigeiros hybrid, and intolerant clone P. maximowiczii × P. trichocarpa Kingston, a section Tacamahaca hybrid were compared. Concentrations of simazine in the two clones were not different 48 h and 1 week after application. However, the presence of 2-chloro-4-amino-6-ethylamino-s-triazine (G-28279), a less toxic simazine metabolite, was detected in tolerant clone I-45/51 after 12 h and it increased steadily through 1 week after simazine application. In contrast, no trace of G-28279 was found in susceptible clone, Kingston.

Atomizer type, spray volume, and herbicide rate influenced the effectiveness of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in controlling vegetation. In general, paraquat controlled vegetation more completely when applied from atomizers that discharged sprays with the angle between the edges of the pattern less than 80°. Increasing spray volume increased control for marginal herbicide rates. Increasing herbicide rate increased control and tended to overcome less effective atomizer performance or reduced spray volume. Vegetation was effectively controlled with cone- or fan-pattern-type nozzles at spray volumes as low as 50 L/ha. Cone- and fan-pattern atomizers were equal to or more effective than either rotary or flooding-type atomizers in all tests.

Greenhouse and laboratory experiments showed that the biological activity of EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide) was lost more rapidly in soils if they had been previously treated with this herbicide. Treatments which reduced or eliminated the microbial activity in the soil restored the herbicide activity in ‘problem’ soils. A combination of 2 kg/ha of the insecticide fensulfothion (diethyl-4-methylsulphinyl phenyl phosphorothionate) with EPTC + R-25788 also restored the biological activity of the herbicide. Field trials confirmed the decreased biological activity with repeated use of EPTC + R-25788; other herbicides recommended for grass weed control in corn (Zea mays L.) performed satisfactorily in these ‘problem’ soils. The performance of EPTC + R-25788 was improved by a rotation away from it for one season (using another herbicide) but the level of activity was still below that obtained in a soil treated with EPTC + R-25788 for the first time. A new formulation of EPTC + R-25788 containing a herbicide extender R-33865 (O,O-diethyl-O-phenyl phosphorothioate) was not affected by the enhanced microbiological breakdown and provided effective season-long weed control in the ‘problem’ soils.

CGA-43089 [α-(cyanomethoximino)-benzacetonitrile], CGA-92194 {α-[(1,3-dioxolan-2-yl-methyl)imino] benzeneacetonitrile}, and MON-4606 [5-thiazolecarboxylic acid, benzyl ester, 2-chloro-4-(trifluoromethyl)], applied as seed treatments at 1.25 g/kg seed, prevented yield losses in grain sorghum [Sorghum bicolor (L.) Moench.] in the field due to metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl)acetanilide] or acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide] applied at 1.7, 2.2 and 1.7 kg/ha, respectively. CGA-92194, applied at 0.8 g/kg seed, prevented yield reduction from metolachlor applied at 4.5 kg/ha. MON-4606 was more effective in protecting grain sorghum when applied as a seed treatment than when applied in the furrow with a clay or sand granule as carrier.

The performance of BAS 9052 {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexen-1-one} was evaluated when applied postemergence to rhizome and seedling johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in soybeans [Glycine max (L.) Merr. ‘Bragg’ and ‘Centennial’] when the soybeans had four or five trifoliate leaves (V3 to V4 stages) or when they had six to eight trifoliate leaves (V5 to V7 growth stages). The degree of weed control was more strongly associated with rainfall conditions than with the size of the johnsongrass. An exponential equation was used to describe the relationship of soybean seed yield to BAS 9052 rate. BAS 9052 applications of 0.28 kg ai/ha provided an estimated 98% of the potential soybean yield increase when rainfall was adequate but, 0.41 kg ai/ha was required when the plants were grown under moisture stress. Soybean yields were increased by 260 kg/ha when BAS 9052 was applied at the V3 to V4 compared to the V5 to V7 growth stage.

In the pea straight growth bioassay, both benazolin and indole-3-acetic acid (auxin) solutions promoted the elongation of etiolated pea (Pisum sativum L. ‘Alaska’) epicotyls. Maximal elongation occurred at auxin concentrations ranging from 10-6 to 10-4 M; comparable elongation occurred at a benazolin concentration of 10-4 M. Results of this bioassay indicate that benazolin functions as an auxin, but is much less active than naturally occurring indole-3-acetic acid.

Yellow nutsedge (Cyperus esculentus L. # CYPES) was hoed in two cotton (Gossypium hirsutum L. ‘Acala SJ-2′) fields each year (1979 to 1981) for 2 to 12 weeks after crop emergence to evaluate the influence of several nutsedge-free periods on the growth and reproduction of nutsedge and yields of seed cotton. Compared to the control (plots cultivated but not hoed), a 2-week nutsedge-free period reduced the average number of nutsedge shoots at harvest by 52% (61 vs 29 shoots/m2). Additional hoeings for 4 to 12 weeks further reduced populations by 67 to 87%. Compared to tubers counted in the spring, populations of tubers in control plots increased 3- to 12-fold by harvest. However, compared to control plots, two weekly hoeings reduced tuber populations at harvest by 70 to 90% (treatment average of 884 vs 221 tubers/m2), and additional hoeings tended to reduce, or reduced, tuber populations further (75 to 98% reduction). When cotton yields were reduced in control plots in 1979 and 1980, a 2- to 6-week nutsedge-free period substantially decreased yield losses. Averaged over six locations, yields in plots with a 4- to 12-week nutsedge-free period were greater than yields of control plots.

Leaves of greenhouse-grown honey mesquite [Prosopis juliflora (Swartz) DC var. glandulosa (Torr.) Cockerell # PRCJG] initially absorbed more triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} from application of the ester than the amine salt. After 24 h, however, honey mesquite had absorbed 66% of the applied ester formulation and 72% of the amine formulation. Triclopyr was rapidly transported from the treated leaf to other plant parts. Triclopyr concentrations recovered 4 h after treatment in the upper canopy, lower canopy, and roots averaged 0.12, 0.19, and 0.09 μg, respectively. Concentrations of triclopyr recovered after 24 h were not significantly different than after 4 h in the canopy. No ester from ester application was recovered in the canopy, other than that in the treated leaf. Triclopyr recovered from stems of honey mesquite in the field ranged from 0.16 to 0.72 μg/g in phloem and from 0.04 to 0.20 μg/g in xylem from a broadcast spray application of the butoxyethanol ester at 1.12 kg/ha. Concentrations of triclopyr were usually not significantly different in either the upper or lower stems whether sampled 3 or 30 days after treatment.

Experiments were conducted from 1979 to 1982 to determine whether selected herbicide treatments applied before or after harvest would provide adequate weed control without the use of tillage between crops in continuous winter wheat (Triticum aestivum L.) production systems. of the herbicide treatments evaluated, only oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) at 2.2 kg ai/ha applied prior to wheat maturity adequately controlled summer annual weeds each year. Populations of yellow nutsedge (Cyperus esculentus L. # CYPES) and/or clammy groundcherry (Physalis heterophylla Nees) increased from continued preharvest use of oryzalin in no-till treatments and were greater than those resulting from conventional tillage or various postharvest no-till treatments containing glyphosate [N-(phosphonomethyl)glycine]. After 4 yr, populations of winter annual Cruciferae spp. at one location were lower in treatments that had poorer control of summer annual weeds or volunteer wheat. At a second location, winter annual broadleaf species were more numerous in conventionally tilled than in no-till treatments. Wheat yields obtained with no-till treatments were lower than yields obtained with conventional tillage in seasons favorable for high yields.

Solar heating (SH) of the soil by mulching it with transparent polyethylene (PE) during the hot season elevated the soil temperature by 10 to 18 C above that of the non-mulched soil. SH for 4 to 5 weeks resulted in effective control of most summer and winter annual weeds, the effect lasting for more than 5 months after PE removal. Melilotus sulcatus Desf., Astragalus boeticus L. and bull mallow (Malva nicaeensis All. # MALNI) were not controlled by SH. Perennial weeds which propagate from vegetative parts were only partially controlled with short SH, but mulching for 8 to 10 weeks improved control. Mulching the soil with perforated or shaded transparent PE or black PE resulted in a smaller increase of soil temperature and thus less efficient weed control. A combination of SH with soil-incorporated EPTC (S-ethyl dipropylthiocarbamate) or vernolate (S-propyl dipropylthiocarbamate) did not improve the weed control over SH alone, but significantly enhanced the disappearance of the herbicides from the soil. SH inhibited the disappearance of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl]-4(1H)-pyridinone} but did not change the residual phytotoxicity of bromacil (5-bromo-3-sec-butyl-6-methyluracil). SH treatment improved plant growth and increased the yield of wheat (Triticum aestivum L. ‘895′) and turnip (Brassica rapa L. ‘Purple top’), but not of parsley (Petroselinum sativum Hoffm.).

Annual applications of three nitrogen (N) rates, two broadleaf herbicides, and six annual-grass herbicides in Kentucky bluegrass (Poa pratensis L.) turf were made from 1974 to 1981. With each increment increase in N (2, 4, and 6 kg N/200 m2), the percentage cover of crabgrass (Digitaria spp.) and number of common dandelion (Taraxacum officinale Weber # TAROF) plants were reduced when compared with the next lower rate. There was an interaction between crabgrass control by the annual-grass herbicides and fertilizer rates. When highly effective herbicides were used, there were no differences in crabgrass control related to N rate. When less effective herbicides or no annual-grass herbicides were used, there were great changes directly related to N rate. Each increment of increased N rate increased the turf quality rating. The broadleaf herbicides resulted in differential quality ratings, although differences were relatively small. Highest quality ratings were for plots treated with the three most effective annual-grass herbicides. Residues in the ppb range of some herbicides were detected in soils sampled about a year after the eighth annual herbicide treatments, but residues were below the phytotoxic level and therefore would have had no effect on control of weeds.

Dicamba (3,6-dichloro-o-anisic acid), 2,4-D [(2,4-dichlorophenoxy)acetic acid], and picloram (4-amino-3,5,6-trichloropicolinic acid) were applied as simulated spray drift to sugarbeets at several growth stages. When applied at early growth stages 2,4-D tended to decrease root yield but decreased purity and extractable sucrose content by as much as 54% when applied at later growth stages. Dicamba at 0.14 kg ae/ha and 2,4-D at 0.28 kg ae/ha decreased extractable sucrose/ha and tended to decrease root yield at harvest while picloram at 0.028 kg ae/ha did not significantly reduce root yield or sucrose content at harvest compared to the control. All rates of 2,4-D from 0.035 to 0.28 kg ae/ha increased sucrose losses during post-harvest storage at 5 C and 95% relative humidity. Dicamba and picloram at 0.14 and 0.028 kg ae/ha, respectively, caused similar storage losses. Sugarbeets that are inadvertently exposed to 2,4-D, dicamba, or picloram spray drift during the growing season should be processed immediately after harvest.

In 1979 and 1980, ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. # IPOHE] seed were planted in field plots at monthly intervals beginning with March and continuing through October. During the first 9 weeks, seedlings from the July plantings grew more rapidly than those from the other monthly plantings and produced the heaviest fresh weights. Vegetative growth slowed after the 9-week harvest and seedlings from June plantings had heavier fresh weights at the 12-week harvest. Plants from the July planting produced the greatest number of seed at both the 9- and 12-week harvests. After scarifying, seed produced by plants from April through August (12-week harvest) germinated best with the 27/32 C night/day air temperature regime, but also germinated at 15/21, 21/27, and 27/32 C regimes. Ivyleaf morningglory seed did not germinate at an air temperature regime of 10/15 C. With an air temperature regime of 32/38 C the germination of some lots began to decrease.

Metribuzin [4-ammo-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.4 kg ai/ha controlled rape (Brassica hitra Moench. # SINAL) when applied 2.5 to 10 cm deep in a horizontal layer or in lines 1 to 4 cm apart. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.8 kg ai/ha did not control ‘Rox Orange’ forage sorghum [Sorghum bicolor (L.) Moench. # SORVU] satisfactorily when applied in a subsurface layer, in lines, or in vertical bands 1, 2, and 3 cm apart up to 10 cm deep. Applications of trifluralin at 1.1 kg ai/ha in vertical bands followed by 0.6 kg ai/ha mixed in the surface 2.5 cm controlled forage sorghum as well as or better than surface application followed by incorporation. The combined subsurface and surface trifluralin placement systems were effective for application depths up to 7.5 cm and band spacings up to 2 cm wide. The development of effective subsurface herbicide injection systems would make the use of herbicides requiring incorporation feasible in reduced tillage crop production systems.

The effects of 16 herbicides from 14 different chemical classes on levels of soluble protein, hydroxyphenolics, anthocyanin, and chlorophyll were determined in light- and dark-grown soybean [Glycine max (L.) Merr. ‘Hill’] seedlings. Growth-reducing concentrations of the herbicides were supplied to 3-day-old dark-grown soybean seedlings in liquid culture. Soluble protein (per axis) was reduced by fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide}, and propanil (3′,4′-dichloropropionanilide) 24 or 48 h after treatment. In light-grown plants, soluble hydroxyphenolic compound levels were decreased on a per axis basis after 48 h by all chemical treatments except by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate}, DSMA (disodium methanearsonate), fluridone, MH (1,2-dihydro-3,6-pyridazinedione), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], TCA (trichloroacetic acid), and 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Total chlorophyll content in hypocotyls of these seedlings was decreased by fluridone, metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one], norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone], paraquat, and 2,4-D, but others had no significant effect. Anthocyanin accumulation in hypocotyls of 48-h light-grown seedlings was decreased by atrazine, fenuron (1,1-dimethyl-3-phenylurea), metribuzin, norflurazon, paraquat, propanil, and propham (isopropyl carbanilate). Phenylalanine ammonia-lyase (PAL) activity (previously reported work) was positively correlated with anthocyanin levels in tissues after treatment with these 16 herbicides, but not with glyphosate [N-(phosphonomethyl)glycine]. There was, however, no correlation between extractable PAL activity and chlorophyll, soluble hydroxyphenolic compounds, or soluble protein content. These results indicated that extracted PAL activities usually reflect relative in vivo activities and that PAL activity is limiting to phenylpropanoid synthesis in vivo.

Early-preplant herbicide application for uncultivated production of soybean [Glycine max (L.) Merr. ‘Williams’] slot-seeded into untilled oat (Avena sativa L. 'Stout’) stubble was studied. Foliar- and soil-active herbicides were applied to stubble of recently harvested oats to control weeds without tillage so that soil moisture could accumulate during the fallow period. The following spring, five herbicide treatments were applied 0, 2, 4, and 6 weeks prior to soybean planting as well as preemergence to control weeds selectively in uncultivated soybeans. Broadleaf weeds were more effectively controlled than grass weeds, but both were controlled adequately with several herbicide combinations and at all five application times. Selective control of weeds was sufficient to eliminate yield loss of uncultivated soybeans seeded into untilled oat stubble. This production method could provide the Great Plains soybean producer with an effective weed control system while conserving soil, soil moisture, labor, and fuel.

The potential interactive effects between the herbicides chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] benzenesulfonamide}, PP009 {butyl 2-[4-[5-(trifluoromethyl-2-pyridinyl) oxy] phenoxy] propanoate}, and BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexene-one} and the air pollutant ozone (O3) on the growth of sorghum [Sorghum bicolor (L.) Moench. ‘Funk G623rg’] and velvetleaf (Abutilon theophrasti Medic. # ABUTH) were examined. All three herbicides were applied postemergence either before or after a single 6-h fumigation of sorghum and velvetleaf seedlings with O3 at 0, 0.1, and 0.2 ppmv. Chlorsulfuron was applied at 0, 0.06, or 0.12 kg ai/ha, while PP009 and BAS 9052 OH were applied at 0, 0.6, and 1.2 kg ai/ha. Two weeks after treatment, dry weight responses of velvetleaf seedlings revealed that PP009 interacted synergistically while chlorsulfuron and BAS 9052 OH interacted antagonistically with O3. The sequence of O3 fumigation and herbicide treatment appeared to be an important factor determining the type of interactive effects of these herbicides with O3. The interactive effects of all three herbicides with O3 on sorghum seedlings were additive regardless of the sequence of O3 fumigation and herbicide treatment.