Field research was conducted in 1988 and 1989 to compare effects of clethodim, fenoxaprop, haloxyfop, and sethoxydim each applied singly and sequentially at full (1X) and reduced (0.5X) rates on barnyardgrass, bearded sprangletop, and rice. A tank-mixture of propanil plus thiobencarb (2.2 + 2.2 kg ha–1) applied sequentially was included as a standard treatment. Control of barnyardgrass and bearded sprangletop was equal to that of the standard treatment both years with 1X rates of clethodim and fenoxaprop, and with 0.5X rates of clethodim, fenoxaprop, and sethoxydim each applied after propanil; rice so treated produced high grain yields. In 1988, severe rice injury occurred after the second application of clethodim at the 0.5X rate, but rice recovered. Grass control costs were reduced 57% with a single application of fenoxaprop at the 1X rate compared with the standard treatment, but net returns were not different.

The relative sensitivity of various crops and weeds to celery root residue incorporated into soil was determined in greenhouse experiments. A range of concentrations was used to determine the percentage of celery residue needed to cause a 50% reduction in plant growth (I50). The most sensitive weed was spiny amaranth and the least sensitive was common purslane. The most sensitive crop was radish and the least sensitive was celery. Selectivity was calculated as crop I50/weed I50 and varied from a maximum of 13 for celery and spiny amaranth to a low of 0.4 for radish and common purslane. Selective weed suppression might be obtained when celery residue is present.

Herbicide treatments of tank mixtures or sequential applications were applied at different growth stages and compared with standard treatments for control of barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCM], bearded sprangletop [Leptochloa fascicularis (Lam.) Gray ♯ LEFFA], and aquatic weeds in rice (Oryza sativa L. ‘Starbonnet’). Some herbicides injured rice more than the propanil (3’,4’-dichloropropionanilide) or molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) standards, but injury for all treatments was inconsequential. Postemergence tank mixture treatments that controlled barnyardgrass (two- to four-leaf stages), bearded sprangletop (two-leaf to tillering stages), and aquatic weeds better than standard treatments were propanil plus butachlor [N-(butoxymethyl)-2-chloro-2’,6,-diethylacetanilide], oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] thiobencarb {S-[(4-chlorophenyl)methyl]diethylcarbamothioate}, or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine].

Experiments were conducted in 1991 and 1992 to evaluate annual grass and broadleaf weed control with bromoxynil applied alone and with graminicides. Bromoxynil controlled velvetleaf better than entireleaf morningglory and controlled both species better than sicklepod. Mixing bromoxynil with fluazifop-P, quizalofop-P, and sethoxydim reduced control of barnyardgrass, green foxtail, large crabgrass, and shattercane. Control of broadleaf signalgrass with quizalofop-P was reduced by bromoxynil. Annual grass control with clethodim was not affected by bromoxynil.

Barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] spikelets were collected from greenhouse-grown plants at various developmental stages. Caryopses contained in a single spikelet were dormant at maturity, but dormancy was overcome when the spikelets were dry afterripened at 23 C or were treated with high temperatures, acid scarification, or punctured with a scalpel. The season at which anthesis occurred affected the length of time for afterripening. Enhanced germination due to puncturing and scarification was not related to removal of a restriction to water entry. The effectiveness of puncturing in overcoming dormancy depended on moisture content of the spikelets at the time of puncturing. Above 18% moisture content germination percentage was low regardless of the dormancy-releasing treatment.

Information on the effects of multiple weed management tactics in corn is needed to develop integrated weed management systems. The effectiveness and compatibility of an in-row cultivator as compared to a standard interrow cultivator used with reduced rates of a soil-applied herbicide, rotary hoeing, and/or a bioeconomic model for POST herbicide selection was examined. Weed control with a single rotary hoeing at corn emergence controlled annual weeds similarly to two rotary hoeings. One-third recommended use rate of alachlor controlled weeds similarly to a two-thirds rate. Reduced rates of alachlor controlled more weeds than rotary hoeing over 2 yr. The in-row cultivator required early-season weed control (rotary hoeing or reduced alachlor rate) for optimum efficacy. The in-row cultivator provided better weed control than the standard cultivator while the cost of operating the two cultivators was similar. Thus, the in-row cultivator was more efficient than the standard cultivator. Furthermore, less intensive early-season weed control was required with the in-row cultivator for maximum weed control as compared to the standard cultivator. Rotary hoeing plus the in-row cultivator provided similar weed control to other weed management tactics that required both soil-applied and POST herbicides. Gross margin was influenced more by corn yield than cost of weed management tactics.

Field research was conducted during the summers of 1981 and 1982 in order to determine relative infection and population increase of lesion nematodes (Pratylenchus spp.) on seven weed species that commonly occur in field-bean (Phaseolus vulgaris L.) fields in western Nebraska. Weeds were grown at three densities with and without fieldbeans. A representative sample of the root systems from plants in each plot was removed in August and the nematodes were extracted and counted. No difference in nematode infection rate was found among weed population levels. Nematodes per gram of dry root were not different in weeds grown with or without fieldbeans. Weeds grown with fieldbeans had smaller root systems, and consequently total nematodes per root system were less than in weeds grown in the absence of fieldbeans. There was a significant difference among most weed species when nematodes per gram of dry root were estimated. Hairy nightshade (Solanum sarachoides Sendt. ♯3 SOLSA) and barnyardgrass [Echinochloa crus-galli (L.) ♯ ECHCG] supported the highest numbers of nematodes per g oven-dry roots, redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE) had least numbers of nematodes/g oven-dry roots, and infestation levels on other weed species were variable but generally intermediate.

Field studies were conducted for four consecutive years to determine if repeated applications of trifluralin (preplant incorporated), metolachlor (preemergence), and fluazifop (postemergence) herbicides alone or combined could be utilized in soybean to effectively control grass weed populations and maintain optimum yield in an irrigated environment where metribuzin plus dinoseb (preemergence) and 2,4-DB plus linuron (postemergence) were used as a standard weed control system. After repeated applications each year, all treatments maintained similar yields that were no different from yields obtained from the standard system. Grass weed infestation did not increase significantly in the treatment that received only the standard weed control herbicides over the duration of the study.

Alfalfa (Medicago sativa L. ‘Vernal′) was seeded broadcast or in drill rows spaced 18 cm apart in the same operation that EPTC (S-ethyl dipropylcarbamothioate) was applied. For broadcast seeding, EPTC was applied as herbicide-treated crop seed, as granules mixed with crop seed, or as granules applied with the crop seed, but with the seed and granules carried in separate boxes on the seeder. For drill-row seeding, EPTC was applied between the rows in subsurface lines as a liquid or granular formulation; and within the rows as herbicide-treated seed, as granules mixed with the seed, or as granules carried in a box separate from the seed. Weed control and crop tolerance with the more effective simultaneous applications of EPTC were similar to those with conventional preplant-incorporated applications. To seed alfalfa (either broadcast or in drill rows) and apply EPTC in one operation, the methods wherein untreated seed and a granular formulation of EPTC were applied together but from separate boxes on the seeder were the most practical, because the mechanical components, the seed, and the formulated herbicide are all commercially available.

Various surgical cuts were used to induce germination of dormant barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] caryopses. Greater percentages of germination were obtained when the cuts were made closer to the embryo. However, removal of only the caryopsis coat covering the coleoptile or midembryo axis induced up to 10% germination compared to 70% germination for caryopses with the coat covering the radicle removed. Dormancy of barnyardgrass was not caused by the inability of the embryo to imbibe, imposed mechanical resistance of the caryopsis coat, or presence of an inhibitor. A wounding response, other than ethylene production, by the cut caryopses was possibly responsible for stimulating germination. Similar responses to cutting observed in afterripened caryopses were consistent with the suggested hypothesis.

Spring-applied herbicides were evaluated in the field in 1982 through 1984 in western Nebraska for selective weed control in irrigated seedling alfalfa (Medicago sativa L. ‘Appollo’). Weed densities were least in plots treated preplant with benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] in combination with postemergence applications of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. Combinations of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and fluazifop-butyl {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} with bromoxynil provided less grass control than sethoxydim or fluazifop-butyl applied alone. Annual weeds did not reduce alfalfa stand density.

Field studies were conducted for 3 yr to determine weed and potato response to preemergence (PRE) and postemergence (POST) applications of rimsulfuron, metribuzin, and rimsulfuron plus metribuzin. Preemergence applications of rimsulfuron at 27 g ai/ha and POST applications at 18 g/ha controlled barnyardgrass, redroot pigweed, and wild buckwheat. Common lambsquarters was controlled by PRE or POST applications of metribuzin or a tank mixture of 18 g/ha rimsulfuron plus 140 g ai/ha of metribuzin. ‘Russet Burbank’ potato was relatively tolerant to all rimsulfuron, metribuzin, and rimsulfuron plus metribuzin applications, and potato yield was not reduced compared to the hand-weeded control.

Field experiments evaluated barnyardgrass, broadleaf signalgrass, and rhizomatous johnsongrass control with sethoxydim, clethodim, fluazifop-P, quizalofop-P, and fenoxaprop applied alone and with bentazon or chlorimuron when crop oil concentrate or BCH 815 was used. Bentazon strongly antagonized sethoxydim and clethodim. BCH 815 partially reduced the antagonism with sethoxydim and clethodim compared with crop oil concentrate. Chlorimuron was most antagonistic towards fluazifop-P, fenoxaprop, and quizalofop-P, and BCH 815 did not reduce antagonism. Additional experiments evaluated Italian ryegrass control with diclofop applied alone and with bromoxynil, metribuzin, 2,4-D amine, or tribenuron plus thifensulfuron with these adjuvants. The amine formulation of 2,4-D and tribenuron plus thifensulfuron reduced Italian ryegrass control with diclofop, irrespective of the adjuvant.

In order to find the most effective and economical method of incorporation, six preplant herbicides for cotton (Gossypium hirsutum L.) were incorporated with a tandem disk or field cultivator, or sprayed on unbedded soil prior to bedding with a disk bedder. These treatments were compared to incorporating sprayed beds with a rolling cultivator and no incorporation. A mixed population of pigweed (Amaranthus hybridus L. # AMACH and Amaranthus retroflexus L. # AMARE) was present each year. There was no significant difference in pigweed control among incorporation with a disk, field cultivator, or rolling cultivator. Puncturevine (Tribulus terrestris # TRBTE) and barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] were controlled best following rolling cultivator incorporation. Cotton lint yields were not affected by incorporation methods or herbicides. Economic analysis and weed control indicate that the field cultivator was the best way of incorporation.

DPX-79406 was evaluated for POST annual grass weed control in both controlled environment and field experiments. In controlled environment experiments, green foxtail was most susceptible to DPX-79406; whereas yellow foxtail was least susceptible of the species evaluated. DPX-79406 at 12 g/ha completely controlled six leaf black-seeded proso millet, yellow foxtail, green foxtail, and barnyardgrass. In the field, DPX-79406 at 3.0 to 25.0 g/ha effectively controlled annual grass weeds without injury to three- to six-leaf corn. There was more variation in the effectiveness of DPX-79406 applied in the field. Early POST applications provided less weed control than the late application, especially for barnyardgrass, because of weeds emerging after application. As a result, higher doses were sometimes needed for effective control. In weed-free field trials at two sites in 1990 and 1991, corn tolerated doses up to 75 g/ha of DPX-79406 applied at the three- to six-leaf growth stage. However, doses as low as 18.8 g/ha applied at the six- to nine-leaf growth stage reduced grain yield. In 1991, corn tillering increases and height and yield reductions were related linearly to the dose of DPX-79406 applied during later growth stages. DPX-79406 should be applied early POST in order to avoid crop injury while providing effective weed control.

Triazine-resistant (TR) biotypes of weeds normally susceptible (S) to triazine herbicides first were documented in Ontario in 1974. By 1988, at least nine weed species had TR biotypes, and at least 50% of the corn-producing areas were infested. Corn has been grown the longest in the southwestern Ontario, but TR weeds are only a minor problem there. Predominant agronomic practices in the southwest include crop rotation, atrazine use on 60% of corn land, use of other postemergence herbicides, interrow cultivation, little silage corn, and little manure returned to the land. Corn, particularly grain corn, is new as a large hectareage crop in eastern Ontario. However, more than 75% of corn land in that area is infested with two or more TR weed species. Predominant agronomic practices in the east include continuous corn, nearly all fields are atrazine treated, use of postemergence herbicides is not common, cultivation is rare, 25% of the corn is for silage, and manure from corn silage is returned to all cultivated land. Adequate herbicide programs exist to control TR weeds in corn and other crops. However, the spread from field to field and from farm to farm is often rapid, particularly in eastern Ontario.

The efficacies of microencapsulated (ME) and emulsifiable concentrate (EC) formulations of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were compared in petri dish and soil bioassays. At equimolar concentrations, EC-alachlor inhibited shoot growth of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], and fall panicum (Panicum dichotomiflorum Michx. # PANDI) more than ME-alachlor. ME- and EC-metolachlor caused similar effects on the three grass weeds tested. ME- and EC-alachlor in combination caused effects on barnyardgrass shoot growth intermediate to results with either formulation alone. Air-drying and remoistening of alachlor-treated filter paper or soil before sowing barnyardgrass or fall panicum caused greater shoot length and fresh weight reduction than ME-alachlor that was not dried.

Field experiments were conducted in 1993 and 1994 to evaluate barnyardgrass control with fenoxaprop-ethyl applied alone or in a mixture with bentazon or bensulfuron. Bensulfuron at 52 g ai/ha did not reduce barnyardgrass control with fenoxaprop-ethyl applied at rates of 56, 75, or 94 g ai/ha. In contrast, mixing bentazon at 1.1 kg ae/ha with fenoxaprop-ethyl reduced barnyardgrass control and rice yield compared with fenoxaprop-ethyl applied alone or mixed with bensulfuron.

A 3-yr study was conducted to compare the performance of several herbicides applied alone and in mixtures under three flooding conditions in dry-seeded rice (Oryza sativa L. ‘Labelle’). When the soil remained moist during the 2-week unflooded periods (1979 and 1981), weed emergence was slowed and no advantage with respect to enhanced weed control and increased rice yields could be demonstrated over that of the standard sequential propanil (3′,4′-dichloropropionanilide) application. However, in 1980 when drought stress may have reduced initial postemergence activity and weeds emerged during the 14-day unflooded periods, differences in weed control between herbicides were obtained. Results of this study also indicate that yield losses from weed competition resulted primarily from early season competition, and that the principal advantage of the residual herbicides in dry-seeded rice may be to eliminate the need for retreatment with propanil when flooding is delayed or fields are drained.

Field experiments evaluated barnyardgrass, broadleaf signalgrass, and rhizomatous johnsongrass control with clethodim applied with Agri-Dex® crop oil concentrate at 1.0% v/v, the adjuvant Dash® at 1.0% v/v, the methylated seed oil Sun-It II® at 1.0% v/v, a blend of silicone surfactant plus methylated seed oil (Dyne-Amic® at 0.5% v/v) or nonionic surfactant (Kinetic® HV at 0.125% v/v), two silicone surfactants (Sylgard® 309 and Silwet L-77® surfactant) at 0.125% v/v, two other conventional nonionic surfactants (Latron AG-98™ and Induce®) at 0.25% v/v, and the acidified soya phospholipid LI-700®. When compared with the conventional nonionic or silicone-based surfactants and LI-700, clethodim at 70 g ai/ha controlled barnyardgrass more effectively when applied with Dash or Sun-It II. Broadleaf signalgrass and rhizomatous johnsongrass were controlled more effectively when clethodim was applied with Agri-Dex, Dash, Sun-It II, or Dyne-Amic. Clethodim at 70 g/ha applied with Dash or Sun-It II controlled grasses equally or greater than clethodim at 140 g/ha.