Research was designed to reduce herbicide use by replacing POST herbicides with readily available ocean water to control weeds in turfgrasses. Sensitivity to salt stress was evaluated for large crabgrass, goosegrass, mimosa-vine, alyceclover, and yellow nutsedge, as well as the turfgrasses such as seashore paspalum, bermudagrass, St. Augustinegrass, and centipedegrass. Three different salinity levels, (55, 37, and 19 dS/m) and two salt-stress durations (3 and 6 d) were tested. Mimosa-vine was fully controlled at 55 and 37 dS/m. Alyceclover showed maximum injury at 95% when treated at 55 dS/m for 6 d and 90% when treated for 3 d. Large crabgrass was controlled at 55 dS/m. Goosegrass injury was up to 90% at 55 dS/m, but injured plants recovered to 48% at 30 d. Yellow nutsedge showed a maximum of 38% injury but showed 0% injury at 30 d. Among tested turfgrasses, seashore paspalum showed tolerance to pure ocean water at 55 dS/m, with maximum injury at 18%. At the same level of stress, maximum injury for bermudagrass was 30%, for St. Augustinegrass 60%, and for centipedegrass 100%. Lower levels of salt stress resulted in less injury but were still excessive for St. Augustinegrass and centipedegrass. Ocean water was shown to be an effective method to control mimosa-vine, and large crabgrass in seashore paspalum and bermudagrass turfs.

MON 37500 is a sulfonylurea herbicide that selectively controls Bromus spp. in winter wheat. Field studies were conducted near Sidney, NE, and Archer, WY, to determine the sensitivity of corn, foxtail millet, grain sorghum, proso millet, and sunflower to soil residues of MON 37500. MON 37500 was applied to winter wheat at 0, 35, 69, and 139 g/ha in the autumn of 1997. Rotational crops were no-till seeded into the standing residues of the previous year's crop from 1999 through 2001. Grain yields for corn, foxtail millet, and proso millet planted 18 to 20 mo after herbicide application were not affected by soil residues of MON 37500. In contrast, average grain yields of grain sorghum were reduced from 1,760 to 30 kg/ha at Archer and from 4,480 to 390 kg/ha at Sidney as MON 37500 rates increased from 0 to 139 g/ha. Thirty to 32 mo after herbicide application, average grain yields of grain sorghum were reduced from 2,360 to 620 kg/ha at Sidney and average aboveground biomass was reduced from 4,000 to 1,800 kg/ha at Archer as MON 37500 rates increased from 0 to 139 g/ha. Nineteen to 20 mo after herbicide application, average sunflower seed yields were reduced from 1,450 to 20 kg/ha at Archer and from 1,830 to 540 kg/ha at Sidney as MON 37500 rates increased from 0 to 139 g/ha. Visual injury was observed 31 to 32 mo after herbicide application, but drought in 2000 prevented collection of seed yield data. In the High Plains, foxtail millet, proso millet, and corn may be successfully grown 18 to 20 mo after the application of MON 37500 to winter wheat. Successful production of grain sorghum and sunflower may require a minimum recrop interval between treatment and planting of >36 mo.

Calcium ion in the spray water can reduce glyphosate efficacy. Ammonium sulfate (AMS) is commonly added to the spray tank to overcome the reduced efficacy. However, it is sometimes claimed that ethoxylated tallow amine surfactant (EA) is also efficacious, provided that calcium concentration is moderate (= 5 mM, 200 ppm). On response curves of ‘Plaisant’ barley treated with glyphosate, the presence of calcium ion increased the glyphosate dose needed to obtain 50% (ED50) barley growth reduction. The addition of AMS to the spray tank overcame the antagonistic effect of the calcium ion and restored glyphosate efficacy. EA was less effective than AMS at 5 or 10 mM calcium ion concentration as measured by ED50. However, at 90% growth reduction (ED90), EA was more effective than AMS at the 5 mM calcium ion concentration but less effective at the 10 mM concentration. Hence, at a moderate (= 5 mM) calcium concentration, EA would be an effective adjuvant. Calcium ion decreased the foliar uptake of glyphosate but did not affect the rate of uptake. AMS but not EA restored foliar uptake to values observed without calcium ion. EA increased spray retention, and this probably accounted for the increased glyphosate efficacy at low calcium concentration.

A 4-yr field study was conducted during 1998 through 2001 at Stoneville, MS, to determine the effects of narrow-row transgenic cotton and soybean rotation on purple nutsedge populations and crop yield. Crop rotations over 4 yr included cotton and soybean sown in the following patterns: CCSS, CSCS, SCSC, SSCC, and continuous cotton (CCCC) and soybean (SSSS), where cotton is denoted as (C) and soybean as (S), all with herbicide programs that were glyphosate based, non–glyphosate based, or no purple-nutsedge control (NPNC). Purple nutsedge populations and shoot dry biomass were reduced in cotton and soybean rotation and continuous soybean by 72 and 92%, respectively, whereas in continuous cotton, purple nutsedge populations increased by 67% and shoot dry biomass was reduced by 32% after 4 yr. Reductions in purple nutsedge populations also occurred in soybean when cotton was rotated with soybean (CSCS and SCSC), compared with continuous cotton. Among herbicide programs, the glyphosate-based program was more effective in reducing purple nutsedge populations, compared with the non–glyphosate-based program. Seed cotton yield was greater with cotton following soybean (SCSC) than with cotton following cotton (CCCC, CCSS) in 1999. However, seed cotton yields were similar regardless of crop rotation systems in 2000 and 2001. Seed cotton yields were equivalent in the glyphosate-based and non–glyphosate-based programs in 1999 and 2001. During 1999 to 2001, seed cotton yields were reduced by 62 to 85% in NPNC compared with yields in glyphosate- and non–glyphosate-based programs. Soybean yields were unaffected by crop rotation systems in all the 4 yr. Among herbicide programs, non–glyphosate-based program in all 4 yr and glyphosate-based program in 1999 and 2000 gave higher soybean yield compared with NPNC. After 4 yr of rotation, purple nutsedge tubers and plant density were highest in continuous cotton and lowest in continuous soybean. Both herbicide programs reduced tubers per core and plant density compared with NPNC, and the glyphosate-based program was more effective than the non–glyphosate-based program. These results show that in cotton production, severe infestations of purple nutsedge can be managed by rotating cotton with soybean or by using glyphosate-based herbicide program in glyphosate-resistant cotton.

Mapping weed infestations in an annual crop has implications not only for site-specific herbicide applications but also for planning future management strategies and understanding weed ecology. A controlled laboratory experiment, involving detached leaves, was conducted to investigate the potential to discriminate two crop and five weed species using hyperspectral and multispectral remote sensing. Stepwise discriminant function analyses showed that reflectance in the visible and “red-edge” regions of the spectrum were consistently required for species discrimination. The seven species were correctly identified 90 and 89% of the time using the hyperspectral and multispectral data, respectively, and the classification rules derived from discriminant function analyses. Errant species prediction with the hyperspectral data resulted in a grass being predicted as a grass and a broadleaf as a broadleaf. However, for multispectral data, incorrect classifications were more serious because errant predictions sometimes resulted in a grass being classified as a broadleaf and vice-versa. Further studies using plants at a variety of growth stages, from a variety of environments, and at the canopy level are warranted.

Field studies were conducted at 35 sites throughout the north-central United States in 1998 and 1999 to determine the effect of postemergence glyphosate application timing on weed control and grain yield in glyphosate-resistant corn. Glyphosate was applied at various timings based on the height of the most dominant weed species. Weed control and corn grain yields were considerably more variable when glyphosate was applied only once. The most effective and consistent season-long annual grass and broadleaf weed control occurred when a single glyphosate application was delayed until weeds were 15 cm or taller. Two glyphosate applications provided more consistent weed control when weeds were 10 cm tall or less and higher corn grain yields when weeds were 5 cm tall or less, compared with a single application. Weed control averaged at least 94 and 97% across all sites in 1998 and 1999, respectively, with two glyphosate applications but was occasionally less than 70% because of late emergence of annual grass and Amaranthus spp. or reduced control of Ipomoea spp. With a single application of glyphosate, corn grain yield was most often reduced when the application was delayed until weeds were 23 cm or taller. Averaged across all sites in 1998 and 1999, corn grain yields from a single glyphosate application at the 5-, 10-, 15-, 23-, and 30-cm timings were 93, 94, 93, 91, and 79% of the weed-free control, respectively. There was a significant effect of herbicide treatment on corn grain yield in 23 of the 35 sites when weed reinfestation was prevented with a second glyphosate application. When weed reinfestation was prevented, corn grain yield at the 5-, 10-, and 15-cm application timings was 101, 97, and 93% of the weed-free control, respectively, averaged across all sites. Results of this study suggested that the optimum timing for initial glyphosate application to avoid corn grain yield loss was when weeds were less than 10 cm in height, no more than 23 d after corn planting, and when corn growth was not more advanced than the V4 stage.

Determination of the active growth state of weeds may lead to more reliable predictions of herbicide efficacy. Experiments were conducted at Lacombe and Lethbridge, Alberta, Canada, from 1996 to 1998 to determine if wild oat leaf extension (growth) rate could be used to predict the efficacy of imazamethabenz and ICIA 0604. As expected, wild oat control increased and wild oat biomass decreased with increasing imazamethabenz and ICIA 0604 rates. Mean wild oat growth rates ranged from 6 to 44 mm over a 24-h time interval. Wild oat control at 25% of the recommended doses of ICIA 0604 or imazamethabenz increased as wild oat growth rate increased. However, wild oat growth rate did not influence herbicide efficacy at higher herbicide rates. Regression analysis confirmed that wild oat control at the lowest application rates increased 6 or 14% for every 10 mm of wild oat growth during the 24 h preceding herbicide application of ICIA 0604 or imazamethabenz, respectively. Covariance analysis confirmed the influence of wild oat growth rate on wild oat control by imazamethabenz but not by ICIA 0604. Monocot leaf extension rates may be useful for predicting herbicide efficacy in integrated weed management or decision support systems.

Imazethapyr-based weed control treatments were evaluated in water-seeded imidazolinone-resistant (IR) rice in Louisiana in 2000 and 2001. Treatments included imazethapyr applied to soil before seedling flood (surface [SURF] applied) or no soil application (no SURF), followed by imazethapyr applied postemergence (POST). Averaged over SURF application treatments (SURF, no SURF), all imazethapyr mixtures increased control of barnyardgrass at 14 and 42 d after POST treatment (DAT) compared with imazethapyr alone. Treatments containing imazethapyr-applied SURF followed by POST treatments controlled red rice 90 to 96% at 21 DAT. Alligatorweed and hemp sesbania control increased with POST mixtures compared with imazethapyr-only treatments at 35 DAT. Rice yield increased with imazethapyr applied SURF compared with no SURF application, averaged over POST applications. Other herbicides will be required to control troublesome weeds such as hemp sesbania and alligatorweed in an IR rice production system.

Experiments were conducted in Virginia in 2000 and 2001 to investigate responses of winter wheat and diclofop-sensitive and -resistant Italian ryegrass to the experimental herbicide mixture AE F130060 03 and crop safener AE F107892 applied postemergence. AE F130060 03 at 15 or 18 g ai/ha with or without methylated seed oil controlled both diclofop-sensitive and -resistant Italian ryegrass 82 to 99% and reduced inflorescence emergence 59 to 98%. Although AE F130060 03 controlled existing Italian ryegrass 4 wk after any application, timing of application influenced late-season Italian ryegrass control and inflorescence emergence. Applications to two- to three-leaf Italian ryegrass resulted in greater emergence of Italian ryegrass after application than applications made to two- to three-tiller or four- to five-tiller Italian ryegrass. Wheat injury by AE F130060 03 was greater than injury from diclofop, but wheat appeared to fully recover; and yields from AE F130060 03–treated wheat were similar to yields of diclofop-treated wheat and at least 21% greater than yields from nontreated wheat. In greenhouse experiments, differential growth responses between diclofop-sensitive and -resistant Italian ryegrass occurred after AE F130060 03 application at normal (15 g ai/ha) and below-normal application rates. When rates were increased beyond normal application rates, growth responses were similar between diclofop-sensitive and -resistant Italian ryegrass.

Field studies were conducted to evaluate weed control, tuber yield, gross return, economic return on investment (EROI), and net return in glyphosate-resistant ‘Ranger Russet’ potato in 2000 and 2001 at the University of Idaho Aberdeen Research and Extension Center near Aberdeen, ID. Three types of weed control programs were evaluated: a total glyphosate program of single or sequential applications (TGLY), tank mixtures of glyphosate and residual herbicides applied early postemergence (GLY + RES EPOST), and residual preemergence herbicides followed by (fb) a late postemergence glyphosate application (RES PRE fb LPOST GLY). A standard rimsulfuron + metribuzin + nonionic surfactant EPOST treatment was included for comparison. The standard EPOST treatment and all glyphosate-containing treatments controlled hairy nightshade 88 to 99%. RES PRE fb LPOST GLY treatments improved hairy nightshade control compared with the RES PRE components applied alone. All herbicide treatments controlled kochia 87 to 99% and green foxtail 87 to 100%. Redroot pigweed and common lambsquarters were controlled ≥85 and ≥89%, respectively, by all herbicide treatments except a single EPOST application of glyphosate at 420 g ae/ha. Depending on the year, sequential applications of glyphosate, GLY + RES EPOST, or RES PRE fb GLY LPOST treatments controlled weeds better than single EPOST glyphosate applications. Single LPOST glyphosate applications generally controlled kochia, redroot pigweed, common lambsquarters, and green foxtail better than single EPOST applications. However, single EPOST glyphosate applications controlled hairy nightshade better than a single LPOST application of glyphosate at 420 g/ha. RES PRE fb GLY LPOST treatments improved redroot pigweed, common lambsquarters, and green foxtail control, compared with the RES PRE components applied alone, depending on the RES PRE component and the year. Sequential applications of glyphosate at 840 g ae/ha and the standard nonglyphosate EPOST, GLY + RES EPOST, and RES PRE fb GLY LPOST treatments generally provided similar weed control. No crop injury was observed as a result of any herbicide treatment. Sequential applications of glyphosate at 840 g/ha had better tuber yields and economic returns than a single EPOST or LPOST application of glyphosate at 420 g/ha or a single LPOST application of glyphosate at 840 g/ha. A single EPOST application of glyphosate at 420 g/ha had lower tuber yields and economic returns than a single EPOST application of glyphosate at 840 g/ha. The RES PRE alone treatments, except metribuzin + pendimethalin, had similar tuber yields, EROI, and net returns as sequential applications of glyphosate at 840 g/ha. Glyphosate + rimsulfuron resulted in lower tuber yields than sequential applications of glyphosate at 840 g/ha, whereas EROI and net returns were similar. All other combinations of glyphosate and residual herbicides except glyphosate + pendimethalin EPOST, had similar tuber yields, EROI, and net returns as sequential applications of glyphosate at 840 g/ha.

Experiments were conducted in 2000 and 2001 to evaluate efficacy of AE F130060 03 plus AE F107892 applied postemergence for the control of Italian ryegrass in barley. AE F130060 03 plus AE F107892 controlled Italian ryegrass when applied at two application rates and at three timings. Barley successfully recovered from initial injury caused by early-postemergence (EP) and middle-postemergence (MP) application timings. The late-postemergence (LP) timing resulted in lower yield than the EP or MP application timings. AE F130060 03 plus AE F107892 applied EP controlled Italian ryegrass similar to flufenacet plus metribuzin applied delayed preemergence (DPRE) when rainfall was received. Barley yields were also similar. However, with insufficient rainfall, AE F130060 03 plus AE F107892 provided superior Italian ryegrass control. EP treatments of AE F130060 03 plus AE F107892 after a DPRE application of flufenacet plus metribuzin or chlorsulfuron plus metsulfuron completely controlled Italian ryegrass and resulted in excellent yields.

Field studies were conducted in 2001 and 2002 to determine the effect of clethodim, sethoxydim, and halosulfuron on centipedegrass seedhead suppression, seed yield, and seed germination. Clethodim (0.28 kg/ha), sethoxydim (0.31 kg/ha), and halosulfuron (0.06 kg/ha) applications were made at −2, 0, 2, 4, and 6 wk after mowing stopped (WAMS) in each year. Seedhead suppression varied in severity between 2001 and 2002, with increased suppression in 2001. Clethodim reduced seedhead emergence 50 and 33% when applied at 2 and 4 WAMS, respectively, in 2001. Sethoxydim reduced seedhead emergence by 21 and 18% when applied at 2 and 4 WAMS, respectively, in 2001. Halosulfuron had no effect on seedhead emergence in either year and did not reduce seed yield at any application timing. Clethodim reduced seed yield between 22 and 44% at all application timings. The pattern of yield reduction from sethoxydim was similar to that caused by clethodim; however, yield reduction with sethoxydim ranged between 7 and 48% for all application timings. The greatest reduction in seed yield occurred when clethodim and sethoxydim were applied 4 WAMS. Seed germination was not affected by halosulfuron or sethoxydim at any application timing. Clethodim, when applied at 4 and 6 WAMS, decreased seed germination by 17 and 20%, respectively.

Effect of weed interference duration and weed-free period on glufosinate-resistant rice was evaluated in 1998 and 1999. Weed interference for more than 2 wk reduced plant height 12 wk after emergence compared with the season-long weed-free treatment. Grain yield loss of 1,090 to 4,880 kg/ha was observed when weeds were allowed to interfere with rice from 2 wk to season-long. The weed-free period study indicated that early control of weeds could sustain rice growth and yield potential. This research suggests that effective weed control from 1 to 6 wk after rice emergence is important in fields with high weed densities for maximizing yield potential of glufosinate-resistant rice.

Soft red winter wheat tolerance and Italian ryegrass control with AE F130060 00 plus AE F115008 00 at 12.5 plus 2.5 g ai/ha applied alone and mixed with dicamba, 2,4-D, or thifensulfuron plus tribenuron were examined in separate field experiments. AE F130060 00 plus AE F115008 00 applied alone in December injured wheat 12% or less, whereas mixtures with thifensulfuron plus tribenuron injured wheat 15% or less. AE F130060 00 plus AE F115008 00 applied alone in February or mixed with dicamba, 2,4-D, or thifensulfuron plus tribenuron injured wheat 3% or less. No treatment affected yield of weed-free wheat. AE F130060 00 plus AE F115008 00 applied in December controlled Italian ryegrass 86 to 99% in May and increased wheat yield 142 to 254%. At two of four locations, Italian ryegrass control was greater with the December application of AE F130060 00 plus AE F115008 as compared with the February application. Dicamba or 2,4-D mixed with AE F130060 00 plus AE F115008 00 reduced Italian ryegrass control in May approximately 10% in half the trials but did not affect wheat yield compared with AE F130060 00 plus AE F115008 00 applied alone. Thifensulfuron plus tribenuron mixed with AE F130060 00 plus AE F115008 00 did not affect Italian ryegrass control or wheat yield. Under greenhouse conditions, the rate of AE F130060 00 plus AE F115008 00 needed for 80% Italian ryegrass visible control and 80% shoot fresh weight reduction was increased 60 to 68% in mixtures with 2,4-D. Dicamba increased the rate needed for 80% visible control and shoot fresh weight reduction 132 to 139%.

Wild garlic (Allium vineale L.), also called crow garlic in many English-speaking countries, is a perennial weed with a particularly noxious reputation. Although a native of Eurasia, it has found an especially suitable home in the eastern United States, among other places. Wild garlic has little redeeming value despite its similarity to cultivated garlic (Allium sativum L.). The property of wild garlic of passing its excessively strong flavor to food is infamous among dairymen and wheat (Triticum aestivum L.) growers, for whom contamination by the weed causes a serious reduction in product quality (Anonymous 1975; Holm et al. 1991; Iltis 1949).