A study was conducted to determine the dose–response of purple nutsedge tuber sprouting and plant growth to glyphosate. Tuber sprouting on day 6 satisfactorily fitted the probit model, with a predicted effective dosage causing 50% inhibition of response (ED50) of 30 mM, which is similar to that with 25 mM of ED50 on day 3. In addition, together with the dose–response analysis of bud growth on day 6, it was shown that bud growth of purple nutsedge was more sensitive to root- or tuber-absorbed glyphosate or both than was tuber sprouting; the former had 1.25 mM of ED50. During the V1–2 stage, purple nutsedge injury, including shoot dehydration, wilting, and yellowing, appeared sequentially when glyphosate was absorbed. When compared with the dose–response of shoot greenness of purple nutsedge at the V5–7 stage under the root-absorbed glyphosate treatment, purple nutsedge at the V1–2 stage was less sensitive to root-applied glyphosate. Further studies for determining the efficacy of glyphosate applied on root and foliage of purple nutsedge at the V5–7 stage showed that injury from glyphosate occurred within 7 d after foliar treatment, and the ED50 values of glyphosate for shoot survival and leaf chlorophyll were 13.1 and 14.5 mM, respectively. However, the response of plants was less sensitive to root-absorbed glyphosate, which had an ED50 of 101 mM. This finding might be the result of direct injury of roots caused by glyphosate, resulting in the delayed and diluted effect of this herbicide from root to shoot.

Field experiments evaluated halosulfuron and glyphosate for yellow nutsedge control in glyphosate-resistant field corn in 1997 and 1998. Treatments included single and sequential glyphosate applications with or without halosulfuron. Single glyphosate applications provided less than 75% yellow nutsedge control. Sequential applications with at least 1.68 kg ae/ha of glyphosate provided 85% or greater yellow nutsedge control 82 or 115 d after treatment (DAT). Halosulfuron was required to consistently obtain 80% or greater yellow nutsedge control. Nearly all treatments resulted in 90% or greater velvetleaf control 82 or 115 DAT. At the same rating times, giant foxtail control was 95% or greater for sequential glyphosate treatments and treatments containing acetochlor. Corn treated with sequential glyphosate applications containing at least 1.26 kg/ha of glyphosate or containing halosulfuron resulted in greater corn yields than with single glyphosate applications. Halosulfuron was required for consistent yellow nutsedge control, but halosulfuron did not control grasses.

Studies were conducted in 1998 and 1999 in Ohio to determine the effect of postemergence (POST) application timing of glyphosate on weed control and grain yield in glyphosate-tolerant corn, and how this was influenced by corn planting date and the use of soil-applied herbicides. Glyphosate was applied based on giant foxtail height. Two applications of glyphosate provided better weed control than a single application, especially when applied to weeds 10 cm or less in early-planted corn. Yield was reduced occasionally with a single application on 5- or 10-cm weeds, because of weed re-infestation. Failure to control weeds before they reached a height of 15 to 30 cm also resulted in occasional yield loss. Application of atrazine or acetochlor plus atrazine prior to glyphosate did not consistently increase weed control or yield. Results suggested that glyphosate should be applied before weeds reach 15 cm in height to avoid corn grain yield loss.

Field experiments were conducted in 1996 and 1997 to evaluate the effects of six johnsongrass densities on picker- vs. stripper-harvest efficiency, fiber properties, loan rate, and lint yield loss of cotton. The weed densities employed were 0 (the check), 3, 4, 5, 8, and 15 plants/15 m of row. With three or fewer weeds in 1996 and four or fewer in 1997, harvest efficiencies were 4.9 to 7.6% higher for stripper- than for picker-harvested cotton. At four and higher weed densities in 1996 and at five and higher in 1997, differences in harvest efficiency between the two machines were not significant. For each weed per 15 m of row, stripper-harvest efficiency in 1996 and 1997 was reduced 0.3 and 0.6%, respectively; picker-harvest efficiency was not affected by the johnsongrass densities included herein. Fiber fineness (i.e., micronaire) was significantly reduced at densities of 8 weeds/15 m of row in 1997 and at 15 weeds in both years. A questionable increase in staple length was detected at the 3-weed density in 1996. Reductions in fiber strength were noted in 1997 at densities of 3, 8, and 15 weeds/15 m of row. No influences on fiber length uniformity were shown. In 1996 the loan rate for picker-harvested lint was 570 points/kg higher than for stripper-harvested lint at 8 weeds/15 m of row. In 1997 it was 741, 801, 1,058, 1,225, 1,074, and 1,329 points/kg higher at weed densities of 0, 3, 4, 5, 8, and 15 plants/15 m of row, respectively. In 1997 picker-harvest loan rate was reduced 49 points/kg of lint, and stripper-harvest loan rate was reduced 85 points. Over both years, picker-harvest lint yield was reduced 32 to 43 kg/ha (3.9 to 5.5%) for each weed per 15 m of row, and stripper-harvest lint yield was reduced 29 to 43 kg/ha (3.5 to 5.2%).

Field studies were conducted in 1998 and 1999 at two Illinois locations to compare flumioxazin and pendimethalin for preemergence (PRE) weed control and determine the benefit of these herbicides when followed by (fb) postemergence (POST) herbicides, glyphosate, imazethapyr, and imazamox. In early weed control ratings taken before POST applications, flumioxazin alone at 105 g ai/ha or pendimethalin alone at 1,120 g ai/ha resulted in less than 80% control of giant foxtail, but controlled common lambsquarters at least 85% in all experiments. Control of large-seeded broadleaf weeds with flumioxazin or pendimethalin varied greatly between experiments. At Urbana in 1998, where moisture was adequate before and after PRE applications, flumioxazin controlled velvetleaf, common cocklebur, and ivyleaf morningglory at least 90%. With the latter two species, control decreased in the subsequent year, probably because of the reduced precipitation after the PRE applications. Sequential applications including a PRE herbicide provided control up to 25% greater than did POST only treatments. At Dekalb in both years and Urbana in 1998, soybean yields were greater with most treatments containing a PRE fb POST application than with the treatments containing only POST applications.

Greenhouse and field research evaluated yellow nutsedge growth, vegetative control, and tuber production after application of glyphosate, various acetolactase synthase (ALS)–inhibiting herbicides, and tank mixtures thereof. Yellow nutsedge was controlled by the herbicides halosulfuron at 35 g ai/ha, chlorimuron at 12 g ai/ha, and imazethapyr–imazapyr at 62 g ai/ha (> 70% control); imazethapyr at 70 g ai/ha, glyphosate at 840 g ae/ha, cloransulam at 17.5 g ai/ha, and rimsulfuron at 17.5 g ai/ha (40 to 70% control); and imazamox at 45 g ai/ha (< 40% control). Compared with the untreated control, tuber fresh weight in the field was reduced 45 to 91%, and tuber density was reduced 33 to 90% by all herbicide treatments 42 wk after treatment (WAT) except imazamox and rimsulfuron. Tuber sprouting was reduced to 19% in plots treated with halosulfuron and pyrithiobac compared with untreated yellow nutsedge 42 WAT. Chlorimuron and imazethapyr–imazapyr controlled yellow nutsedge at least 90%, prevented panicle formation, and reduced tuber density and fresh weight by 90% or more 14 WAT in the greenhouse. The addition of glyphosate to cloransulam or imazethapyr increased yellow nutsedge control and reduced tuber density and fresh weight when compared with either ALS-inhibiting herbicide or glyphosate applied alone. Tuber density data indicated that there were 8 tubers for every gram of tubers harvested. Yellow nutsedge height was 15 to 20 cm 4 to 5 wk after tillage, using growth analysis data. Long-term yellow nutsedge management may be aided with treatments that reduce tuber production.

Weed-detecting reflectance sensors were modified to allow selective interrogation of the near infrared–red ratio to estimate differences in plant biomass. Sampling was programmed to correspond to the forward movement of the field of view of the sensors. There was a linear relationship (r 2 > 0.80) between actual biomass and crop canopy analyzer (CCA) values up to 2,000 kg/ha for winter wheat sequentially thinned to create different amounts of biomass and up to 1,000 kg/ha for spring wheat sampled at different stages of development. At higher amounts of biomass the sensors underestimated the actual biomass. A linear relationship (r 2 = 0.73) was obtained with the CCA for the biomass of 76 chickpea cultivars at 500 growing degree days (GDD500). The reflectance sensors were used to determine differences in the herbicide response of soybean cultivars sprayed with increasing rates of herbicides. The CCA data resulted in better dose–response relationships than did biomass data for bromoxynil at 0.8 kg ai/ha and glyphosate at 1.35 kg ai/ha. There was no phytotoxicity to soybean with imazethapyr at 1.44 kg ai/ha. The method offers a quick and nondestructive means to measure differences in early-season crop growth. It also has potential in selecting crop cultivars with greater seedling vigor, as an indicator of crop nutrient status, in plant disease assessment, in determining crop cultivar responses to increasing herbicide dose rates, in weed mapping, and in studying temporal changes in crop or weed biomass.

Field studies were conducted from 1995 through 1998 to evaluate citronmelon control in peanut with various preplant and preemergence combinations of dimethenamid, flumioxazin, imazethapyr, lactofen, metolachlor, oxyfluorfen, and pendimethalin. Pendimethalin alone or in combination with imazethapyr, metolachlor, or dimethenamid did not control citronmelon. Flumioxazin alone, pendimethalin plus flumioxazin, or pendimethalin followed by (fb) lactofen controlled citronmelon at least 85% early season. Pendimethalin fb lactofen controlled citronmelon at least 75% late season, whereas all other herbicide treatments controlled less than 70%.

Studies were conducted at one location in 1997 (W97) and in two locations in 1998 (E98 and W98) near Garden City, KS, to evaluate the impact of Palmer amaranth at densities of 0, 0.5, 1, 2, 4, and 8 plants/m of row on forage yield and quality of irrigated corn and to determine if harvesting Palmer amaranth–infested corn for forage rather than for grain would reduce losses. Weed-free corn, Palmer amaranth alone, and corn–Palmer amaranth harvested together were evaluated for forage yield and quality. Forage quality was determined by evaluating in vitro dry matter digestibility (IVDMD), acid detergent fiber (ADF), neutral detergent fiber (NDF), and crude protein (CP). Corn grain and forage yield declined with increasing Palmer amaranth density. However, decline in forage yield ranged from 1 to 44% of the weed-free yield at Palmer amaranth densities of 0.5 and 8 plants/m of row, whereas decline in grain yield ranged from 11 to 74% of the weed-free yield at the same densities. Digestibility of weed-free corn forage, expressed as IVDMD, was significantly higher than that of Palmer amaranth alone at W97 and W98. The CP of weed-free corn forage was similar to that of Palmer amaranth forage at W98, but it was lower at the other two locations. In contrast, CP did not differ between corn–Palmer amaranth harvested together and weed-free corn. The IVDMD of weed-free corn forage was greater than that of corn–Palmer amaranth mixture at W98, but no differences were observed at the other two locations. The relative feeding values of weed-free corn and corn–Palmer amaranth mixture were similar, and greater than that of Palmer amaranth in monoculture. These results indicate that Palmer amaranth interference in corn may not affect forage quality but can cause a decline in yield. This decline in yield is less when harvesting corn and Palmer amaranth together for forage rather than for harvesting corn grain alone.

Field experiments were conducted in Greece during 1997, 1998, and 1999 to study the efficacy of various preemergence and postemergence herbicides against red rice. Tolerance of rice seeded 15 and 6 d after preemergence and postemergence herbicide application was also examined. Control of red rice with alachlor, dimethenamid, metolachlor, or acetochlor applied preemergence was 92, 84, 92, and 92%, respectively. The corresponding control with postemergence applications of paraquat, glyphosate, glufosinate, or quizalofop-ethyl to emerged red rice seedlings was 92, 89, 81, and 100%, respectively. None of the herbicides had any phytotoxic effect on rice cultivars planted after the herbicide application, and grain yield produced in treated plots was higher than that in untreated plots. These results clearly showed that red rice can be effectively controlled by applying the previously mentioned preemergence or postemergence herbicides and that rice could be safely seeded 15 and 6 d after treatment, respectively.

Field research conducted over 3 yr evaluated the utility of preemergence (PRE), soil-applied herbicides at half- and full-label rates in glyphosate-resistant soybean. Soil-applied herbicide treatments at full-label rates included pendimethalin plus imazaquin (0.84 + 0.14 kg ai/ha), pendimethalin (1.12 kg/ha), metolachlor (1.68 kg ai/ha), dimethenamid plus imazaquin (1.0 + 0.14 kg ai/ha), sulfentrazone plus chlorimuron (0.22 + 0.04 kg ai/ha), and metribuzin plus chlorimuron (0.36 + 0.06 kg ai/ha). Weed density and growth were reduced when PRE herbicides were used, and in many cases for broadleaf weeds, half-label rates were as effective as full rates. None of the herbicides provided complete control of all weeds. Sulfentrazone plus chlorimuron reduced ivyleaf morningglory density an average of 90%. For hemp sesbania, metribuzin plus chlorimuron reduced weed emergence over 3 yr at least 95%. The initial glyphosate application was made when the largest weeds, barnyardgrass or hemp sesbania, reached 10 cm. In 1998 all soil-applied herbicide treatments extended the time period of glyphosate application by 3 to 5 d when compared with the nontreated control. In 1999 the full rate of metribuzin plus chlorimuron delayed the application of glyphosate by 6 d, and an extension of 7 d was noted for the full rates of sulfentrazone or metribuzin plus chlorimuron in 2000. When soil-applied herbicides were used each year, only a single application of glyphosate was needed. A second glyphosate application was needed in only 1 yr when soil-applied herbicides were not used. Even though differences in weed control were observed among the herbicide treatments, soybean yield was the same.

Field experiments were conducted from 1997 to 1999 at the University of Minnesota Southern Research and Outreach Center in Waseca to evaluate the (1) effect of corn row spacing on grass and broadleaf weed species density and height, (2) optimal herbicide application timing in narrow- and wide-row systems, and (3) corn grain yield response to row spacing and herbicide application timing. Corn was planted in 51- and 76-cm row spacings. Within each row-spacing treatment, there were five herbicide application timings: a formulated mixture of acetochlor plus atrazine applied preemergence or a formulated mixture of imazethapyr and imazapyr tank-mixed with bromoxynil applied postemergence at 5-, 10-, 20-, or 30-cm giant foxtail plant height. Reducing the row spacing in corn from 76 to 51 cm did not influence early-season weed emergence or growth. Similarly, late-season weed density and growth were not influenced by row spacing except in 1997. But corn grain yield increased when corn was planted in narrow rows compared with wide rows in 2 out of 3 yr when averaged over herbicide application treatments. Herbicide application timing had a significant effect on late-season weed density and grain yield. But there was no interaction between herbicide application timing and row spacing on grain yield. Potential increases in crop competitiveness resulting from narrow-row corn did not appear to affect weed density or growth in this study.

The failure of glyphosate to control all weeds throughout the entire growing season has sometimes prompted growers to use herbicides other than glyphosate on glyphosate-resistant soybean. Field studies were conducted in 1999 and 2000 to investigate potential crop injury by several herbicides in glyphosate-resistant soybean and to determine the relationships between soybean maturity group, planting date, and herbicide treatment on soybean injury, leaf area index (LAI), and yield. Glyphosate-resistant soybean generally recovered from early-season herbicide injury and LAI reductions; however, some treatments reduced yield. Yield reductions were more common in double-crop soybean than in full-season soybean. In full-season soybean, most yield reductions occurred in the early-maturing ‘RT-386’ cultivar. These yield reductions may be attributed to reduced developmental periods associated with early-maturing cultivars and double-crop soybean that often lead to reduced vegetative growth and limited LAI. Reductions in LAI by some herbicide treatments were not necessarily indicative of yield loss. Further yield reductions associated with herbicide applications occurred, although soybean sometimes produced leaf area exceeding the critical LAI level of 3.5 to 4.0, which is the minimum LAI needed for soybean to achieve maximum yield. Therefore, LAI response to herbicide treatments does not always accurately indicate the response of glyphosate-resistant soybean yield to herbicides.

Field and greenhouse studies were conducted to evaluate sulfentrazone and flumioxazin as preemergence (PRE) herbicides for broadleaf weed control in potato. Sulfentrazone and flumioxazin were applied alone and in combination with s-metolachlor to determine the crop response and the weed spectrum controlled. These treatments were compared with metribuzin or rimsulfuron plus s-metolachlor treatments. Potato variety response to sulfentrazone and flumioxazin was evaluated in a separate field study. Sangre, Chipeta, Russet Norkotah, and Russet Nugget were treated with sulfentrazone from 0.14 to 0.28 kg/ha or flumioxazin from 0.035 to 0.07 kg/ha. Sulfentrazone and flumioxazin provided excellent broadleaf weed control at all the rates tested, whereas grass control increased as rate increased. Grass control improved when combined with s-metolachlor. Sulfentrazone and flumioxazin treatments were comparable with metribuzin and rimsulfuron treatments in weed control and total yield. Flumioxazin was safe when applied PRE to four selected varieties, whereas sulfentrazone produced initial phytotoxicity to Sangre and Chipeta at high rates but did not affect yields. Sulfentrazone increased the yield of U.S. No.1 potatoes compared with other treatments in the variety response study. Dose–response curves were used to generate the sulfentrazone, flumioxazin, and metribuzin herbicide rates required to reduce biomass by 50% (I50) for eight common weed species. Herbicides were applied PRE at several rates, and plant response was recorded. Log-logistic analysis was performed on bioassay data generated to estimate species sensitivity to each herbicide. Sulfentrazone reduced the biomass of hairy nightshade, black nightshade, redroot pigweed, kochia, common lambsquarters, and redstem filaree by more than 90% at 0.0175 kg/ha (the lowest rate evaluated), whereas flumioxazin had a similar effect on all broadleaf species except on kochia at 0.004 kg/ha (the lowest rate evaluated). Therefore, it was not possible to calculate I50 or even I80 values for most broadleaf species. Metribuzin I50 values could be calculated for most of the species tested. The metribuzin I50 value for hairy nightshade was 0.28 kg/ha, which was 16 and 70 times higher than the sulfentrazone and flumioxazin rates, respectively, that reduced hairy nightshade biomass by more than 90%. Sulfentrazone and flumioxazin appeared to be sufficiently safe when applied on potato and controlled several weed species common to potato production in the western United States.

Annual, cylindric, and globe sedges were controlled > 90% with a single application of MSMA at 2.2 kg ai/ha in field studies. But this same treatment controlled fragrant and green kyllingas only 69 and 52%, respectively. Control was increased to 82 and 81%, respectively, with a repeat application. Other postemergence-applied (POST) herbicides evaluated included bentazon, halosulfuron, imazapic, imazaquin, and CGA-362622. Postemergence-applied herbicides were applied either once or twice, as well as alone and in combination with MSMA. In general, a sequential application of MSMA, either alone or in combination with any of the aforementioned herbicides, except bentazon, provided maximum control of the sedge and kyllinga species evaluated. Preemergence-applied (PRE) oxadiazon and S-metolachlor, controlled annual sedge ≥ 94% at 7 wk after treatment (WAT) in field studies and 96 and 70% at 9 WAT, respectively. Dithiopyr and prodiamine provided 86 to 80% control of annual sedge over the 9-wk rating period. In a hydroponic-type laboratory study, oxadiazon and S-metolachlor were more effective than atrazine, bensulide, imazaquin, oryzalin, or simazine, in reducing seedling development of annual, cylindric, and globe sedges, and green kyllinga.

Field research was conducted for a period of 2 yr to evaluate the response of soybean and cotton to simulated drift rates representing 12.5, 6.3, 3.2, 1.6, and 0.8% of the usage rates of 1,120 g ai/ha glyphosate (140, 70, 35, 18, and 9 g/ha, respectively) and 420 g ai/ha glufosinate (53, 26, 13, 7, and 4 g/ha, respectively). Early-postemergence applications were made to 2- to 3-trifoliate soybean and 2- to 3-leaf cotton, and late applications to soybean at first flower and cotton at early bloom. A mid-postemergence application was also made to cotton at pinhead square (first flower bud development). Soybean and cotton injury and height reductions occurred in most cases for only the two highest rates of the herbicides with variation noted between years. Soybean height was reduced by no more than 11%, regardless of herbicide rate or timing. On the basis of visual injury, soybean was more sensitive to glyphosate than to glufosinate when applied early in 1998, but sensitivity was equal for both the herbicides in 1999. When herbicides were applied late, soybean was more sensitive to glufosinate in the first year. Cotton was more sensitive to glufosinate 7 d after application in both years, regardless of timing, but by 28 d differences between herbicides were less apparent. Cotton maturity was not delayed by either herbicide, on the basis of days to first square or flower and nodes above white flower. Both crops were able to recover rapidly from herbicide injury, and yields were not affected negatively.

In traditional simulated herbicide drift research, dose response is evaluated using a constant carrier volume. The influence of carrier volume was evaluated in field experiments with drift rates representing 12.5 and 6.3% of the use rates of 1,120 g ai/ha glyphosate (140 and 70 g/ha, respectively) and 420 g ai/ha glufosinate (53 and 26 g/ha, respectively). Corn and soybean were exposed to herbicide rates applied in constant carrier volume of 234 L/ha and in proportional carrier volumes of 30 L/ha for the 12.5% rate and 15 L/ha for the 6.3% rate. Averaged across herbicides, corn height reduction 14 d after treatment (DAT) was greater for the 12.5% rate when applied in proportional 30 L/ha carrier volume (45%) compared with constant 234 L/ha carrier volume (28%). The 6.3% rate reduced corn height 38% when applied in proportional 15 L/ha carrier volume but not when applied in 234 L/ha carrier volume. When carrier volume was changed from constant to proportional, corn injury 14 DAT increased from 33 to 51% for the 12.5% rate and 18 to 38% for the 6.3% rate. Compared with constant spray volume, corn yield reduction was 1.5 times greater for the 12.5% rate but 4 times greater for the 6.3% rate when spray volume was varied proportionally to the herbicide rates. Differential response due to carrier volume was not observed when herbicides were applied to soybean. Soybean was injured more by glyphosate than by glufosinate, but recovery was rapid and yield was not negatively affected. Results suggest that drift research using constant spray volume may underestimate the yield reduction expected for sensitive crops exposed to glyphosate or glufosinate.

Field studies were conducted in 1999 and 2000 to evaluate the response of three runner market-type peanut cultivars to diclosulam applied preplant incorporated at 0,18, 27, or 54 g ai/ha in a weed-free environment. Peanut cultivars evaluated included ‘Georgia Green’, ‘C-99R’, and ‘MDR-98’. Peanut injury was not observed with diclosulam at any rate or with any cultivar. Diclosulam did not affect peanut canopy development, percentage extra-large kernels, sound mature kernels, sound splits, total sound mature kernels, other kernels, or yield for any cultivar.

Preemergence (PRE) herbicides may affect the ability to reestablish warm-season turfgrasses in winter-injured areas. Experiments were conducted in 1996 and 1997 to evaluate the effects of fall or spring applications of six PRE herbicides on the vegetative establishment of Tifway bermudagrass, and Meyer and El Toro zoysiagrass. PRE herbicides were applied at the recommended rates during the fall of 1995 and 1996 and at recommended or reduced rates during the spring of 1996 and 1997. Oxadiazon, benefin plus trifluralin, or oryzalin did not inhibit Tifway bermudagrass or zoysiagrass sprig establishment. Fall applications of prodiamine and dithiopyr at full rates suppressed Tifway bermudagrass establishment as much as 25%, but recovery was evident by the end of the growing season. Reduced spring rates of prodiamine diminished its suppressive effects on Tifway establishment. Zoysiagrass establishment was suppressed as much as 20% by full or reduced rates of prodiamine but was less affected by dithiopyr. Pendimethalin had lesser and briefer suppressive effects than prodiamine and dithiopyr had on either species. Results suggested that avoidance of or reduced rates of prodiamine or dithiopyr may be warranted in areas prone to winter injury.

This article presents an approach to managing and evaluating soil survey data that can aid in soil-applied herbicide decision making. Field experiments were used to quantify the dose responses of corn, shattercane, and velvetleaf to isoxaflutole over a range of soil conditions within an agricultural field. Isoxaflutole doses eliciting crop injury (20% greenness reduction) and weed control (80% biomasss reduction) were projected for a county located in Nebraska based on associations between the plant response and the soil properties. The biologically effective dose of isoxaflutole increased with increasing organic matter and mineral surface area. Mean biologically effective doses for velvetleaf (1 to 27 g/ha) were considerably lower than that for shattercane (42 to 206 g/ha). Over 60% of the surface texture is silty clay loam for Saunders County, suggesting that 17 and 158 g/ha are the minimal doses required to suppress velvetleaf and shattercane, respectively, for a majority of the county. Conceivably, this approach could be used as an initial step to assess the relative value of field-specific applications and variable dose application technologies.