Acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied 7 days after cowpea [Vigna unguiculata (L.) Walp.] emergence (unifoliolate leaf stage) gave better control than later applications. Cowpea control was obtained with one acifluorfen application at 7 days after cowpea emergence in 1981, but in 1980 and 1982, applications at 7 and 14 days were necessary for acceptable control (> 80%). Acifluorfen reduced cowpea plant dry weights relative to the weedy control. A single application 7 days after emergence reduced cowpea plant growth more than one at 21 days after emergence. Of all times of application, the greatest soybean [Glycine max (L.) Merr.] injury occurred when acifluorfen was applied at 7, 14, and 21 days after emergence, but seed yields were not reduced relative to the untreated weed-free control. There was no difference in response among three weedy cowpea cultivars to acifluorfen.

Three annual applications of glyphosate [N-(phosphonomethyl)glycine] with three ropewick applicators were compared to hoeing and cultivation for the control of johnsongrass [Sorghum halepense (L.) Pers. ♯3 SORHA] in cotton (Gossypium hirsutum L. ‘Acala SJ-2′) in 1980 and 1981. The three applicators provided about equal control of johnsongrass. Averaged over treatments, years, and dates of application, plots treated with glyphosate contained 83% fewer live johnsongrass shoots (14/m2) than cultivated control plots (84/m2) 2 to 3 weeks after each application. Glyphosate-treated plots yielded an average of 81% more seed cotton (2010 kg/ha) than cultivated control plots (1110 kg/ha). However, yields of treated plots averaged 33% less than plots maintained weed-free by hoeing. Although applications of glyphosate reduced johnsongrass populations 83%, the competitive effect of johnsongrass on cotton prior to the initiation of treatments, plus the competition from escape plants between treatments, prevented cotton from yielding normally.

The effects of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} rate, order, and timing of sequential herbicide applications, and the addition of oil concentrate on sethoxydimbentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H-one 2,2-dioxide] antagonism were studied on broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. ♯3 BRAPP], fall panicum (Panicum dichotomiflorum Michx. ♯ PANDI), and large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA] in field experiments during 1980 and 1981. Tank-mixing bentazon with sethoxydim reduced control of these species compared to applications of sethoxydim alone. Sequential applications of the herbicides prevented the antagonism. Variations in time between and order of sequential applications had no consistent effect on efficacy. Increases in sethoxydim rate reduced the severity of the antagonism in some cases, while the addition of oil concentrate had no effect.

The response of 22 potato (Solanum tuberosum L.) cultivars to soil-incorporated and foliar applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one] at rates of 0.5 and 1.0 kg ai/ha, was evaluated in field experiments from 1979 to 1982. Metribuzin significantly reduced the yield of marketable tubers in several potato cultivars. Foliar applications generally resulted in more injury than soil applications. Yields were reduced primarily through stand reduction and a decreased number of tubers per plant. Neither tuber size nor specific gravity of tubers was significantly reduced in the cultivars studied. The most susceptible cultivar was ‘Alaska Red’, followed by ‘Rhine Red’, F72117, ‘Caribe’, and ‘Shepody’. Other cultivars evaluated were highly tolerant to metribuzin, irrespective of rate or method of application. There was an increase in hollow heart in cultivars ‘Atlantic’ and ‘Lemhi Russet’ following treatment with metribuzin.

The tolerance of broad bean (Vicia faba L. Moruna and Alameda) to glyphosate [N-(phosphonomethyl)glycine] was studied under field conditions. Chlorosis, rolling of apical leaves, and reduced growth were the typical symptoms caused by glyphosate on broad bean plants. Visual phytotoxicity from glyphosate at 60 and 120 g ae/ha was very slight. Moderate or severe crop injury was caused by glyphosate at 360 and 600 g ae/ha, when applied before blooming. Seed yields were 2, 4, 9, 23, and 47% lower than the control after glyphosate applications at 60, 120, 240, 360, and 600 g ae/ha, respectively, when averaged over stages of growth and locations. Broad bean was more susceptible to glyphosate at the vegetative stage, when the plants had five to seven nodes, and less susceptible at the late-flowering and pod-bearing stage. Double applications of glyphosate at 120 g ae/ha reduced seed yield more than 10% compared with similar treatments at 60 g ae/ha, regardless of growth stage. Glyphosate decreased seed yields mainly by reducing the number of pods per plant, but germination, fiber content, and gross energy of the seeds were not altered.

Under greenhouse conditions, jimsonweed (Datura stramonium) L. ♯3 DATST) grown in soil treated with vernolate (S-propyl dipropylthiocarbamate) was more sensitive to postemerence application of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] than jimsonweed grown in untreated soil or soil treated with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Vernolate followed by acifluorfen was more phytotoxic than acifluorfen alone. Bentazon applied to jimsonweed after a pretreatment with vernolate at 2.2 kg ai/ha was more effective than the same rate of bentazon applied alone. Trifluralin did not enhance the activity of acifluorfen or bentazon on jimsonweed. Laboratory studies showed that more acifluorfen was absorbed by vernolate-pretreated jimsonweed than by untreated jimsonweed. No differences in bentazon absorption between vernolate-pretreated and nontreated jimsonweed were measured.

In field studies 0.1 ppmw ae or less 2,4-D [(2,4-dichlorophenoxy)acetic acid] applied by sprinklers in 5.1 cm of water over 8 h did not affect the number or dry weight of leaves or length of canes of 1-yr-old Concord grape plants (Vitis labrusca L.). A second application at 0.01 ppmw or higher to the same plants 1 yr later reduced growth of leaves, canes, and trunk. Combined effects of root pruning (required to position plants for treatment the second year) and 2,4-D probably account for this apparent anomaly. When 2,4-D was applied annually at 1.0 ppmw or less to established plants for three consecutive years, growth, yield, and fruit quality were not affected. No residues of 2,4-D were detected in the fruit at harvest (detection limit 0.05 ppmw). Grapes treated with 1.0 ppmw 2,4-D developed moderate injury symptoms.

Season-long weed control has been a goal of some producers of irrigated corn (Zea mays L.) to reduce competition, lessen weed seed production, facilitate crop harvest, improve water efficiency (particularly with furrow irrigation), and improve aesthetic properties of fields. Field experiments were conducted for 3 yr on sprinkler-irrigated corn on a loamy fine sand. Five herbicides applied at layby generally provided season-long control of grass weeds and reduced weed seed production up to 100%. Pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] was particularly effective. Yields of irrigated corn were not increased by layby herbicide application. Use of corn rows spaced 91 cm apart and use of a shorter, early-maturing, horizontal-leaf corn cultivar resulted in greater weed growth and weed seed production than did use of 76-cm rows and a taller, full-season, upright-leaf corn cultivar. After nearly complete weed control with herbicides for 2 yr, withholding herbicide use in the third year allowed weed growth which reduced corn yield. Indications were that weed control efforts need to be continuous in irrigated corn production.

Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] was applied to dry soils (2%, w/w moisture content) that were either wetted immediately or remained dry for 1 to 8 days prior to wetting. Two degradation products were isolated with thin-layer and column chromatography from soils that were kept dry for 4 days before wetting. The major product was identified as 2,3-dihydro-3,3-dimethyl-2-oxo-5-benzofuranyl methanesulfonate which accounted for more than 80% of the degradation products. The products were detected 1 day after application to dry soil (between 1 and 3% moisture content), while at moisture contents greater than 3% (w/w) very little ethofumesate was degraded. Radiolabeled ethofumesate and breakdown products were extracted with methanol from dry and wetted soils, and the soil samples were oxidized to quantify nonextractable radioactivity. The percentage of nonextracted ethofumesate was at least 5% greater in dry soil than in wet soil. Activity loss of ethofumesate applied to dry soil probably is due to both chemical degradation and strong adsorption.

Biotypes of field bindweed (Convolvulus arvensis L. ♯3 CONAR) identified in Indiana varied widely in susceptibility to glyphosate [N-(phosphonomethyl)glycine] but not to 2,4-D [(2,4-dichlorophenoxy)acetic acid] or bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] in field tests. Significant differences in injury to two of the biotypes occurred with glyphosate applied at 1.12 to 4.48 kg ai/ha in greenhouse tests. Differences of greater than 70% in injury rating, root and shoot dry weight, and shoot regrowth dry weight occurred between the two biotypes at 2.24 kg/ha glyphosate. The susceptibility of the tolerant biotype at 2.24 kg/ha glyphosate was decreased by 40% as it increased in age, while the susceptible biotype sustained complete foliar necrosis when treated at all plant ages tested. Susceptibility differences between the two biotypes could not be correlated to differences in leaf stomatal or epidermal cell number. These studies suggested that the variable control of field bindweed observed in the field may be due to the occurrence of biotypes within a given population of this weed which differ in their susceptibility to glyphosate.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), 2,4-D [2,4-dichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), and 2,4-D plus dicamba were applied as postemergence herbicide treatments in two experiments to weed-free dormant bermudagrass [Cynodon dactylon (L.) ♯3 CYNDA] turf in the Piedmont region of Georgia. Herbicides were applied as a split application to separate plots on February 2 plus February 16 and February 16 plus March 3 (± 4 days) on four bermudagrass cultivars (‘Tifway’, ‘Tifgreen’, ‘Tifdwarf’, and ‘Ormond’) in one experiment and to Tifway with vertical mowing treatments for thatch removal in a second experiment. In 2 of 3 years, paraquat applied to dormant turf in February delayed growth of bermudagrass in April. The growth of Tifway and Tifdwarf was retarded more from paraquat at 1.2 kg ai/ha in one year than Tifgreen or Ormond. Dicamba applied alone or with 2,4-D delayed turf growth in early spring more than did 2,4-D alone. In thatch-free turf, selected treatments of paraquat, dicamba, and 2,4-D plus dicamba also delayed spring growth of bermudagrass more than did 2,4-D.

Grid applications of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] pellets at 2.2 kg ai/ha or less did not effectively control honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell ♯3 PRCJG], blackbrush acacia (Acacia rigidula Benth. ♯ ACARI), lotebush condalia [Condalia obtusifolia (Hook.) Weberb. ♯ CNCOF], granjeno (Celtis pallida Torr. ♯ CETPA) or twisted acacia [Acacia tortuosa (L.) Willd.] growing as mixed stands on clay loam or clay soils. Efficacy of hexazinone apparently was affected little by variation in rainfall ranging from 35% less to 51% greater than the long-term average during the year of application. Apparent mortality of honey mesquite, granjeno, and lotebush condalia was increased by increasing the application rate from 2.2 to 4.5 kg/ha on clay loam soils. Control of honey mesquite, blackbrush acacia, and twisted acacia with 2.2 kg/ha was better when applied to sandy clay loam than to clay soils.

In the greenhouse, glyphosate [N-(phosphonomethyl)glycine] at 0.6 kg ae/ha applied directly to seeds alone or seeds on the soil surface reduced germination and shoot dry weight of common rye (Secale cereale L. ♯3 SECCE). Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) applied similarly at 0.6 kg ai/ha reduced germination and shoot dry weight of downy brome (Bromus tectorum L. ♯ BROTE) and wheat (Triticum aestivum L. ‘Daws' ♯ TRZAX). Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] at 0.6 kg ai/ha applied to seeds, soil, or seeds and soil had very little effect on germination, but significantly reduced shoot dry weight of common rye, downy brome, wheat, and jointed goatgrass (Aegilops cylindrica Host. ♯ AEGCY). Pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] at 0.6 kg ai/ha, and propham (isopropyl carbanilate) at 3.4 kg ai/ha plus extender (p-chlorophenyl-N-methylcarbamate) at 0.4 kg ai/ha substantially reduced shoot height and dry weight of all species, regardless of application method, with pronamide completely inhibiting shoot elongation and dry-weight production in three of the four species.

Witchweed (Striga asiatica Lour. ♯4 STRLU) seed remained viable for 6 yr under open-shelf laboratory conditions and for 14 yr when deep buried under field conditions. Seed kept in normal atmosphere of the laboratory for < 1 through 6 yr had the following germination percentages: 2, 95, 95, 94, 83, 38, and 7. Newly harvested seed will not germinate because of postmaturity ripening requirements. There were no viable seed after 7 yr of shelf storage in the laboratory. Seed buried in the field gave 60 to 90% germination the first season after production. Annual recovery and testing showed a gradual reduction in viability to 10% at year 14 for the deepest buried seed; shallower buried seed expired sooner. No germination occurred thereafter.

Johnsongrass [Sorghum halepense (L.) Pers., ♯3 SORHA] dry weight and johnsongrass culms/ha at harvest were more negatively correlated with soybean yield reductions than the number of johnsongrass plants/ha present at 4 to 6 weeks after planting. However, plant numbers can be determined in sufficient time to implement control measures to prevent yield reduction. Prediction equations for estimating soybean yield at various johnsongrass populations are Ŷ = 1776 + 424e-.023x2 for 0.25-m row spacing and Ŷ = 1668 + 643e-.004x2 for the 1-m row spacing, where Ŷ = estimated yield and x = the number of johnsongrass plants/10 m2. Full-season heavy johnsongrass competition reduced soybean yields from 59 to 88%. Soybeans in the 1-m row spacing were more competitive with low johnsongrass densities than in the 0.25-m row spacing. The johnsongrass-free requirement for soybeans was 4 weeks after planting and soybeans could not tolerate heavy infestations of johnsongrass for more than 5 weeks without loss in yield potential. Application of sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 3 or 4 weeks after planting was effective in controlling heavy infestations of johnsongrass and preventing yield reductions due to competition.

Experiments were conducted in the field and laboratory from 1978 to 1981 to determine the effect of crop residues, manure, and inorganic nitrogen on wild oat (Avena fatua L. ♯3 AVEFA) seed (seed as used here represents an intact floret) dormancy. Turkey manure usually stimulated wild oat seed germination more than crop residue, cow manure, or inorganic nitrogen. Seed germination of different wild oat accessions varied in response to turkey manure. Germination of dormant seed in water was stimulated after 8 weeks or after overwintering in the presence of turkey manure in the field and after 10 days in the presence of turkey manure in petri dishes in the laboratory. Turkey manure caused growth of wild oat shoots in petri dishes, but usually roots were absent. A nonmicrobial, water-soluble component of turkey manure was responsible for stimulating wild oat seed germination. Turkey manure treatment of dormant wild oat seed increased the percentage of seed that would not germinate in gibberellic acid. Germination of nondormant wild oat seed of Accession 77 was reduced, but Accession 64 was unaffected by turkey manure. Germination of wild oat was low when the seeds overwintered on the soil surface, regardless of seed age or length of overwintering.

The effect of repeated inoculations of the rust Puccinia cardui-pycnocephali Sydow (Uredinae) on growing rosettes of Mediterranean specimens of slenderflower thistle (Carduus tenuiflorus Curt. ♯3 CRUTE) and Italian thistle (Carduus pycnocephalus L. ♯ CRUPY), and Australian specimens of Italian thistle was investigated, using a Mediterranean strain of the rust collected mainly on Italian thistle. Growth of slenderflower thistle was not affected, but growth of both specimens of Italian thistle was decreased significantly when inoculated with the rust. This decrease was significantly higher on Australian specimens.

Velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH) grown under monoculture consistently exceeded velvetleaf intercropped with soybeans [Glycine max (L.) Merr. var. ‘Amsoy 71′] in leaf area, nodes with fully developed leaves, canopy width, branches, and number of capsules as early as 3, 3, 4, 5, and 8 weeks, respectively, after simultaneous emergence. Velvetleaf plants without soybean competition eventually developed over nine times the dry matter of velvetleaf intercropped with soybean. The only components of velvetleaf plants sampled which sometimes increased significantly when soybean was defoliated in a manner simulating damage caused by the green cloverworm (GCW) (Plathypena scabra F.) were leaf area, number of leaves, and number of main-stem nodes. Soybeans in Iowa are attacked by the GCW late enough in the growing season that velvetleaf surviving previous weed management efforts benefited only slightly.

Velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH) and Powell amaranth (Amaranthus powellii S. Wats. ♯ AMAPO) control with pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] was dependent on proper timing of application. Preemergence and early postemergence pendimethalin treatments provided effective control, but control rapidly diminished with later postemergence treatments, particularly on Powell amaranth. Time-course studies on the effects of pendimethalin on the growth of these species indicated that pendimethalin inhibited shoot growth by slowing or stopping the production of leaves and branches, as well as reducing leaf size and internode length. Pendimethalin appeared to have its greatest effect on portions of the shoot undergoing cell division.

Five presumed biotypes were identified among field bindweed (Convolvulus arvensis L. ♯3 CONAR) clones collected from a field population near Lafayette, IN. Consistent variations in leaf morphology, floral characteristics, and accumulation of shoot and root biomass were found between biotypes when grown in a controlled environment. The biotypes also differed in their flowering capacity. The earliest flowering biotype formed flowers 23 days before the latest and produced 19 times more flowers per plant, which indicated further differences in seed production potential between biotypes. Pollination studies helped to differentiate biotypes within the population and showed that the presumed biotypes were self-incompatible. Vegetative reproduction potential of the biotypes varied from 1.8 to 74.5% in the number of root buds that developed into shoots. The variability in growth and reproduction observed between these field bindweed biotypes may explain the survival and adaptability of a population of this weed as environmental conditions and control practices change.