Wild-proso millet control in furrow-irrigated corn was evaluated in Colorado and Nebraska in 1986 and 1987. No single herbicide alone controlled wild-proso millet all season. In Colorado, EPTC applied preplant incorporated followed by cyanazine plus pendimethalin applied early postemergence controlled 94% of wild-proso millet. Acetochlor applied preemergence followed by cyanazine plus pendimethalin applied early postemergence controlled wild-proso millet better all season (93%) than alachlor (81%) or metolachlor (71%) followed by the same early postemergence strategy. Successful Colorado wild-proso millet management treatments (>85% season-long control) increased corn yields an average of 3260 kg ha-1 compared to the untreated control. To obtain wild-proso millet control of 90% or more in Nebraska in 1986, alachlor, cycloate, EPTC, and metolachlor applied had to be combined with cyanazine plus pendimethalin applied early postemergence. Average corn yields in herbicide-treated areas in Nebraska were 2980 kg ha-1 higher than those recorded in the untreated control.

Field studies were conducted from 1986 through 1989 to determine the feasibility of using clomazone in a winter wheat-corn-fallow rotation. Clomazone at 1.1 kg ai/ha did not control emerged downy brome in autumn nor did it control redroot pigweed and tumble pigweed that emerged after a spring application of paraquat at 0.6 kg ai/ha. However, clomazone plus atrazine at 0.6 plus 2.2 kg ai/ha provided weed control in winter wheat stubble from October to corn harvest 12 mo later. Corn yields from this treatment were equal to or greater than the conventional practice of applying atrazine plus glyphosate at 2.2 plus 0.4 kg ae/ha in the fall followed by a spring application of metolachlor plus dicamba at 2.8 ai plus 0.3 kg ae/ha. When kochia densities were high, clomazone plus atrazine controlled triazine-resistant kochia better than metolachlor plus dicamba. Atrazine at 2.2 kg/ha applied in autumn followed by clomazone at 0.8 kg/ha in April generally caused more corn injury than when the same rate of clomazone was applied in autumn with the atrazine. The percent of bleached corn plants varied with planter, year, time of application, and rate of clomazone applied. The optimum time to apply clomazone at 0.6 kg/ha was in autumn with atrazine. This treatment caused some corn bleaching but produced the highest corn yield over 3 yr. In a dry autumn and spring, less clomazone injury occurred with a planter equipped with row cleaners than those without. The injury pattern associated with planters was inconsistent when precipitation was average and no injury occurred in a wet autumn and spring.

In 1985, when weed densities were low (169 plants/m2 in untreated control), imazaquin applied at 0.07 kg ai/ha early preplant controlled over 90% of all weeds before no-till planting of soybeans. In 1986 and 1987 when weed densities were higher (589 plants/m2 in untreated control), addition of 1.1 kg ai/ha or more of metolachlor to imazaquin (0.07 kg/ha) before soybean planting controlled 95% or more of the grass weeds and 83% or more of the broadleaf weeds. Imazaquin plus metolachlor applied less than 1 day after soybean planting controlled less than 70% of the emerged weeds in 1986 and 1987; common lambsquarters was most tolerant. Early preplant treatments controlled more weeds throughout the growing season than treatments applied after planting. Splitting herbicide treatments among application times generally did not increase weed control compared to single applications. Early preplant applications resulted in higher soybean densities and taller soybeans 30 days after planting in 1986 and 1987 than treatments applied after planting. Soybean yields increased as weed control increased. Weed control and soybean yields were greater with early preplant treatments than paraquat plus alachlor plus metribuzin applied preemergence in 1986 and 1987. No carryover of imazaquin residue was detected through corn bioassay in the field.

The potential reduction in surface runoff loss of band-applied herbicides was studied in a rainfall simulation. Concentration and loss of atrazine, metribuzin, and metolachlor applied in a band 25, 50, or 75 cm wide on 1-m2 plots graded to < 0.5% slope were compared with that from a broadcast preemergence application. Herbicide concentration in runoff decreased with time after initiation of runoff and as application band width decreased. Band width reduced herbicide concentration in runoff to a greater extent than time after initiation of runoff. The 50-cm band treatment reduced atrazine and metribuzin loss 69 and 71%, respectively, from the broadcast treatment. Forty-nine percent less metolachlor was lost from the 50-cm band than from the broadcast treatment. Herbicide concentration or loss in surface runoff did not differ between the 50- and 25-cm band width treatments. Herbicide lost in runoff ranged from 4 to 7% of application with the smaller loss associated with narrower band widths. The greater reduction in atrazine and metribuzin loss in surface runoff than that associated with the reduction in input alone may be attributed to leaching or adsorption of herbicide by soil in the nonsprayed strip as runoff flowed from the treated to the nontreated areas. Band application of herbicides may provide an effective, consistent means to reduce herbicide loss in surface runoff.

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.

The degradation of 14C-labeled metolachlor, acetochlor, and pretilachlor in control and soils with 10-yr metolachlor- history or 3-yr butylate history was studied by monitoring the evolution of 14CO2 in soil biometer flasks. The degradation rate of 14C-phenyl-labeled metolachlor was similar in soils with 0- and 10-yr metolachlor history over 52 d. 14C was released from carbonyl-labeled metolachlor about 40% faster than from phenyl-labeled metolachlor in both soils. Soil sterilization by autoclaving reduced significantly the metolachlor degradation rate in both soils. Degradation of 14C-labeled EPTC in soils with 3-yr butylate history was much faster than in soils with no history. Soil sterilization reduced the EPTC degradation rate, confirming microbial degradation. The degradation rates of acetochlor, metolachlor, and pretilachlor were similar in soils with and without butylate history. Most of the 14C that remained in history and nonhistory soils was extractable with ethyl acetate or sodium hydroxide. Three major metabolites of metolachlor and EPTC were detected by thin-layer chromatography (TLC) of extracts from both soils. In contrast to the situation with carbamothioate herbicides, soils exposed repeatedly to metolachlor or other acetanilides are not prone to become adapted to these herbicides. Soils with carbamothioate history did not exhibit any apparent cross-adaptation toward acetanilide herbicides.

Herbicidal control of triazine-resistant (TR) kochia was evaluated in no-till grain sorghum. Herbicides were applied early preplant (EPP) or POST. In EPP experiments, herbicides plus nonionic surfactant at 0.25% v/v were applied 7, 2, or 0 wk before planting (WBP). Fluorochloridone at 0.8 kg ai/ha applied 7 or 2 WBP, pyridate at 1.0 kg ai/ha applied 2 WBP, and paraquat at 0.4 kg ai/ha applied 0 WBP controlled 94 to 99% of TR kochia; a prepackaged mixture of glyphosate plus 2,4-D at 0.3 plus 0.6 kg ae/ha and paraquat at 0.4 kg/ha applied 7 or 2 WBP controlled 71 to 82% of TR kochia; and 2,4-D ester at 0.6 kg ae/ha applied 2 WBP controlled 75% of TR kochia. Linuron at 0.8 kg ai/ha and atrazine at 2.2 kg ai/ha were ineffective. In the POST herbicide experiments, where paraquat plus metolachlor at 0.6 plus 1.7 kg ai/ha were applied 17 d before planting, various combinations and rates of bentazon plus atrazine, bromoxynil, and dicamba with adjuvants provided good control of TR kochia that was less than 8 cm tall.

Weed management programs in ‘Superior’ potato with PRE and POST rimsulfuron treatments were investigated during 1992, 1993, and 1994 in Virginia on a State sandy loam soil. Common ragweed control by PRE combinations of metolachlor with linuron or metribuzin was higher when treatments included PRE or POST rimsulfuron. Common lambsquarters control was 93 to 96% by treatments that included POST rimsulfuron. In the absence of PRE herbicides, POST applications of 35 g ai/ha rimsulfuron plus 280 g ai/ha metribuzin controlled weeds comparable to sequential applications of this combination. Potato recovered from occasional terminal leaf chlorosis caused by rimsulfuron, rimsulfuron plus metribuzin, and organophosphate insecticides combined POST with rimsulfuron plus metribuzin. These studies demonstrate that rimsulfuron can be a useful component of weed management programs that include metolachlor, linuron, and metribuzin.

SAN 582 at 1.1, 1.2, 1.3, 1.5, and 1.6 kg ai/ha; alachlor at 1.7, 2.2, and 2.8 kg/ha; and metolachlor at 1.7, 2.2, and 2.8 kg/ha were applied preemergence without and with atrazine at 1.7 kg/ha in no-till corn at two locations near Blacksburg, VA, in 1993 and 1994. SAN 582, alachlor, and metolachlor controlled TR-smooth pigweed when applied without or with atrazine, and with only a few exceptions, control was greater than 60%. The highest rate of individual herbicides was more effective than the lowest rate in most cases. Early control of TR-smooth pigweed was similar from all three herbicides, especially at higher rates, but control later in the season tended to be best with alachlor. As expected, atrazine applied alone did not control TR-smooth pigweed, and crop yields were increased with herbicide treatments compared to no treatment.

The successful introduction of a new crop depends upon the availability of economical, safe, and effective herbicides for that crop. Greenhouse trials identified PRE herbicide applications of 4.5 kg ai ha−1 of metolachlor and of alachlor, 2.2 kg ai ha−1 of linuron and of pendimethalin, and 1.1 kg ai ha−1 of desmediphan as noninjurious to sweet white lupin. POST applications of 0.28 kg ai ha−1 of sethoxydim and of fluazifop and 0.22 kg ai ha−1 of haloxyfop also did not injure the sweet white lupin. Field trials indicated that safe and effective weed control could be obtained with combinations of linuron with metolachlor, alachlor, or pendimethalin depending on weed species present.

CGA-154281 and temperature effects on metolachlor absorption and metabolism were studied in corn seedlings grown in untreated soil or soil treated with metolachlor, CGA-154281, or both. Seedlings were grown under a cool (21/13 C, 16-h day) or warm (30/21 C, 16-h day) temperature regime and exposed to 14C-metolachlor for 10 min at either 21 or 30 C. Corn grown under the cool temperature regime absorbed slightly more 14C-metolachlor than corn grown under the warm temperature regime. Corn held at 21 C during a 10-min 14C-metolachlor exposure period metabolized metolachlor more slowly than corn held at 30 C. Decreased corn tolerance to metolachlor observed at lower temperatures may be due in part to slower metolachlor metabolism. Corn grown in the presence of metolachlor plus CGA-154281 metabolized 14C-metolachlor to the glutathione conjugate twice as fast as corn grown in the presence of metolachlor alone. The increase in metabolism rate was due to a fivefold increase in glutathione-S-transferase (GST, EC 2.5.1.18) activity and not to an increase in glutathione (GSH) content. Results are consistent with the hypothesis that CGA-154281 protects corn from metolachlor injury by enhancing GST activity, which accelerates metolachlor detoxification via GSH conjugation.

The response of ‘C-20’ navy bean and ‘Frankenmuth’ soft white winter wheat grown in rotation to clomazone, imazethapyr, bentazon, and acifluorfen was examined. Clomazone at 560 and 430 g ai ha−1 plus 800 g ai ha−1 pendimethalin and 2000 g ai ha−1 chloramben visibly injured navy bean in 1 of 2 yr. However, navy bean seed moisture at harvest and yield was not reduced compared to the weed-free control. PPI and PRE treatments of 70 g ai ha−1 imazethapyr did not injure navy bean or reduce yield. Imazethapyr applied POST at 70 g ha−1 plus nonionic surfactant visibly injured navy bean. The addition of urea ammonium nitrate to imazethapyr enhanced visible injury and seed moisture compared to nonionic surfactant alone in 1 of 2 yr. However, seed yield was not reduced. Seed moisture at harvest was greater following treatment with 430 g ai ha−1 acifluorfen plus nonionic surfactant or urea ammonium nitrate and 140 and 280 g ha−1 acifluorfen plus 840 g ai ha−1 bentazon in 1 of 2 yr compared to the weed-free control, but yield was not reduced. Wheat yield was reduced in 2 of 2 and 1 of 2 yr by 560 g ha−1 and 430 g ha−1 clomazone, respectively, plus pendimethalin plus chloramben compared to the weed-free control. Wheat yield was not reduced by imazethapyr, bentazon, or acifluorfen.

Imidazolinone-resistant and -tolerant corn hybrids give growers a new weed control option. Field experiments were conducted in 1993 and 1994 to evaluate imazethapyr for controlling weeds in no-till corn planted into winter wheat stubble in a winter wheat–ecofallow corn rotation. Imidazolinone-tolerant (IT) and imidazolinone-resistant (IR) corn were protected genetically from injury by imazethapyr that was applied preplant, preemergence, or postemergence to ‘Pioneer Brand 3417,’ ‘Pioneer Brand 3417 IR,’ ‘ICI Seeds 8532,’ and ‘ICI Seeds 8532 IT’ hybrids. No difference in corn injury occurred between IR and IT corn. Imazethapyr applied to resistant or tolerant corn hybrids could be used to control weeds in ecofallow corn. Imazethapyr at 35 or 70 g ai/ha controlled triazine-resistant kochia better than the standard herbicide treatment of metolachlor plus cyanazine.

Field studies were conducted for 3 yr to evaluate the persistence of metolachlor and alachlor applied to ‘Centennial’ soybean and to determine their residual effect on ‘Mars' rice. At labeled use rates of metolachlor at 2.8 kg ai/ha and alachlor at 3.9 kg ai/ha, soil residue levels in the fall 5 months after application on Crowley and Midland silt loam soils averaged 0.04 and 0.05 ppmw, respectively. Metolachlor fall soil residues averaged 3.5 times higher when applied at 5.6 and 11.2 kg/ha compared to 2.8 kg/ha, but residues for labeled and double rates of alachlor were similar. In the spring 9 months after herbicide application, soil residues averaged over years did not exceed 0.06 ppmw. The 3-yr rice yields were not affected by residual metolachlor or alachlor.

A cropping system of soybeans and rice grown in alternate years for 4 yr controlled red rice when combined with effective herbicide treatments applied to the soybean crop. Effective herbicide treatments in soybeans were preplant incorporated applications of alachlor, metolachlor, or alachlor plus trifluralin each followed by postemergence over-the-top applications of bentazon plus mefluidide, postemergence directed applications of paraquat, or sequential applications of postemergence over-the-top bentazon plus mefluidide and postemergence directed paraquat. Control of red rice in soybeans reduced red rice infestations in the subsequent rice crop. Red rice infestations were lower in rice grown the fourth year than in rice grown the second year. Postemergence over-the-top or directed herbicide treatments used alone or combined with preplant incorporated applications of trifluralin did not control red rice in soybeans with subsequent red rice infestations in the rice crop.

Three seed lots each of two varieties of field corn were compared in greenhouse and field studies. Cold test germination percentages of the seed lots were as follows: 79, 85, and 93% for ‘DK656’; 77, 84, and 91% for ‘T1100’. Tank mixes of metolachlor or metolachlor with safener CGA-154281 plus atrazine or formulated metolachlor/atrazine with and without the safener were applied preemergence. Crop stand of either variety or among seed lots within a variety was not affected by herbicide treatments. In the greenhouse, fewer corn plants were injured and growth of plants was greater with herbicides with safener than herbicides without safener. Plant heights and weights at harvest from the most vigorous seed lot of DK656 were higher than those of the other two seed lots. Herbicide treatments with the safener did not cause significant injury to corn in the field. Yields of both varieties increased with herbicide treatments in one conventional planting. No significant differences in injury or yields occurred among seed lots within varieties.

Field experiments were conducted over 3 yr at two locations in northwest Kansas to evaluate the efficacy and crop tolerance of EXP 31130A alone and with other herbicides in corn. EXP 31130A alone and in combination with acetochlor, atrazine, or metolachlor controlled kochia and redroot pigweed 93% or greater regardless of location, year, or tillage system. Green foxtail control in 1997 and 1998 was > 90% with EXP 31130A in combination with chloroacetamide herbicides but varied among experiments with EXP 31130A alone. Control of puncturevine with EXP 31130A alone or in tank mixtures was 75% or greater at five of six sites. EXP 31130A alone and in combinations caused minor, early-season, corn leaf bleaching and/or stunting under conventional tillage. However, no injury was detected in no-till systems. In 1996, no-till corn receiving EXP 31130A treatments yielded similarly or up to 29% more than hand-weeded corn. Yields did not differ among treated, untreated, and hand-weeded corn in 1996 under conventional tillage, where weed interference was not as intense as under no-till conditions. Conventional-tillage corn receiving EXP 31130A alone or in tank mixtures in 1997 yielded similarly to hand-weeded corn. Averaged over experiments, corn yield in 1998 increased by 10 to 18% with applications of EXP 31130A alone or in combinations compared to untreated corn.

Field studies at three sites in Georgia evaluated broadleaf weed and nutsedge management in peanut with PPI applications of imazethapyr and metolachlor and POST applications of paraquat in mixture with imazethapyr or bentazon. Imazethapyr at 36 g ai/ha applied PPI alone or in mixture with metolachlor at 2750 g ai/ha controlled coffee senna; entireleaf, ivyleaf, pitted, smallflower, and tall morningglories; bristly starbur; and prickly sida better than metolachlor applied PPI. Yellow nutsedge control was generally higher where metolachlor was applied PPI. Postemergence control of the aforementioned species and sicklepod was similar with paraquat plus imazethapyr and paraquat plus bentazon. Peanut yields with paraquat plus imazethapyr and paraquat plus bentazon were similar. With one exception, peanut yields from imazethapyr PPI systems were higher than metolachlor PPI systems when POST herbicides were not used. Inclusion of metolachlor with PPI application of imazethapyr increased yields only at one location.

Sweet corn was grown with a living mulch of white clover, a dead mulch of rye, and without mulch, in both till and no-till conditions. Unplanted controls were also included in the experimental design. Corn yields were highest in clover treatments early in the experiment but lowest in later years. The declining yields in the clover living mulch were related to the strip application of glyphosate which allowed establishment of perennial and biennial weeds, notably dandelion and horseweed. These overwintering weeds apparently prevented effective control of summer annuals, especially redroot pigweed, common lambsquarters and large crabgrass, by atrazine and metolachlor. Presence of a rye mulch decreased weed biomass and had no detrimental effect on corn yield. In general, corn yield was not affected by tillage, although the number of marketable ears was reduced in the no-till treatments during the drought year of 1988. The much greater weed biomass in the unplanted control treatments showed the importance of crop competition for weed control in sweet corn cropping systems.

Field studies were conducted to determine the influence of annual herbicide treatments plus cultivation on weed populations and corn yields in ridge-till corn during a 3-yr period at Mitchell, NE, and a 7-yr period at North Platte, NE. When the experiment was initiated at North Platte, no weeds were present before corn planting. It took 4 yr before triazine-resistant kochia became a problem before corn planting in plots treated with atrazine, but these were controlled by other operations prior to corn harvest. In the cultivated check, green foxtail densities before harvest increased from 0 in 1985 to 32 plants 100 m−2 in 1991. Annual applications of dicamba plus 2,4-D 10 d early preplant followed by cultivation controlled triazine-resistant kochia and velvetleaf, but common lambsquarters, nightshade species, and green foxtail increased. Volunteer corn was controlled with cultivation. After 3 yr at Mitchell, the annual weed population increased 10-fold in the cultivated check. Thus, corn yields were reduced 64% with two cultivations compared with an annual early preplant application of dicamba plus 2,4-D followed by alachlor plus cyanazine PRE and two cultivations. With two cultivations under low annual weed populations at North Platte, grain yield from the cultivated check treatment was not different from annual treatments of herbicides after 7 yr. Metolachlor plus atrazine occasionally caused a reduction in corn grain yields.