Epicuticular wax is a major barrier to the movement of foliar-applied herbicides into plant leaves. Many researchers have evaluated the penetration of herbicides in plants using similar methods. However, the methods used to remove unabsorbed herbicide from the leaf surface have been inconsistent among scientists. Laboratory experiments were conducted to evaluate the effectiveness of various compounds as a leaf wash for removing unabsorbed 14C-labeled herbicides from shattercane and velvetleaf leaves. Product B and Product C provided poor results as a leaf wash compared with water, chloroform, methanol, and Product A. Product A increased the amount of 14C-bentazon removed from velvetleaf by 26% compared with the amount removed by chloroform, methanol, or water. Removal of 14C-nicosulfuron was not different between chloroform, Product A, methanol, or water. Although water was the best treatment for the two salts of 14C-glyphosate, Product A was as good or better than chloroform and methanol.

Two field studies evaluating horsenettle control were conducted from 1997 to 1999 to examine the efficacy of various fall-applied herbicides and rates and to evaluate the effect of the stage of horsenettle senescence on the effectiveness of fall glyphosate applications. The herbicides and rates evaluated in the fall herbicide efficacy study included 1.1, 2.2, or 3.4 kg ai/ha glyphosate, 1.7, 2.2, or 3.4 kg ai/ha glyphosate-trimesium, 0.6, 1.1, or 2.2 kg ai/ha dicamba, 0.06 plus 0.16, 0.09 plus 0.2, or 0.17 plus 0.44 kg ai/ha BAS 654 plus dicamba, respectively, or 2.2 kg ai/ha glyphosate plus 0.6 kg ai/ha dicamba. The highest horsenettle control in the following spring was observed with all rates of glyphosate or glyphosate-trimesium, the highest rate of BAS 654 plus dicamba, or glyphosate plus dicamba. In the study on the horsenettle stage of senescence, 2.2 kg ai/ha glyphosate was applied at stages of senescence in the fall. The presenescence stage reduced horsenettle shoot density from fall to spring and provided the highest level of control in June and July of the following year compared with plants that had already begun leaf color change and leaf drop.

Field studies were conducted over 2 yr in Louisiana to evaluate entireleaf morningglory and hemp sesbania control by glyphosate isopropylamine salt applied alone at 420, 560, and 700 g ae/ha and in combination with chlorimuron at 4, 6, 9, and 11 g ai/ha. Comparison treatments included glyphosate alone at 840 g/ha, glyphosate at 1,400 g/ha plus chlorimuron at 13 g/ha, and sethoxydim at 210 g ai/ha plus chlorimuron at 11 g/ha. Entireleaf morningglory and hemp sesbania were controlled no more than 77% with glyphosate rates as high as 840 g/ha. Chlorimuron added to glyphosate increased entireleaf morningglory control in two of the three experiments to 83 to 88% and hemp sesbania control to 86 to 98%. Response to chlorimuron was not rate dependent. In most cases, glyphosate–chlorimuron mixtures did not antagonize barnyardgrass control, and increasing rate of glyphosate did not always increase control. Soybean was injured no more than 6% by chlorimuron at one location, but injury was as great as 30% at another location, which was possibly due to smaller soybean size. Differences in weed control and soybean injury among the glyphosate and glyphosate–chlorimuron combinations were not reflected in soybean yields. Because injury occurred early season, sufficient time remained for soybean to recover and produce acceptable yields. Weed control by sethoxydim plus chlorimuron was less consistent than that by glyphosate plus chlorimuron, and soybean yield in most cases was inferior to the glyphosate treatments.

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.

Field studies were conducted in 1995 and 1996 at three locations in North Carolina to evaluate weed control and soybean injury with postemergence (POST) treatments of cloransulam-methyl alone or in tank-mixture with acifluorfen, fomesafen, or lactofen compared with a commercial standard of acifluorfen plus bentazon. Soybean injury was 2 to 3% 7 d after treatment with cloransulam-methyl applied alone and 11 to 46% when applied with fomesafen, lactofen, acifluorfen, or acifluorfen plus bentazon. Cloransulam-methyl applied alone controlled 95% of entireleaf morningglory and ivyleaf morningglory. Control was not increased by the addition of acifluorfen, fomesafen, or lactofen. Cloransulam-methyl improved the control of common lambsquarters to at least 81% compared with dimethenamid applied preemergence alone (69% control). All diphenyl ether herbicide treatments controlled common lambsquarters at least 91%. Prickly sida control by cloransulam-methyl ranged from 14 to 73% 8 wk after treatment. Control of prickly sida was varied by diphenyl ether herbicides (73 to 100% control). Tank-mixtures of cloransulam-methyl + fomesafen and cloransulam-methyl + acifluorfen increased the control of prickly sida over either herbicide applied alone. Soybean yield was greater for all tank-mixtures than for any diphenyl ether herbicide or for cloransulam-methyl treatment applied alone. But only the acifluorfen + cloransulam-methyl treatment had higher economic returns than the cloransulam-methyl treatment alone. All other POST systems, with the exception of lactofen applied alone, had similar economic returns. Tank-mixtures of cloransulam-methyl and diphenyl ether herbicides increased the spectrum of control and soybean yield compared with these herbicides applied alone.

Plot-scale field studies were conducted to evaluate the efficacy of steam for the control of cropland weeds in comparison with common herbicides. Weed densities, biomass, or emergence after treatment were measured. Steam (3,200 kg/ha, energy dosage equivalent to 890 kJ/m2, speed of 0.8 m/s) and glyphosate (560 g ai/ha) gave similar control (> 90%) of seedling common lambsquarters and seedling redroot pigweed. Applied at heading, steam was comparable to glyphosate in reducing green foxtail biomass at heading 2 wk after application. Steam applied at a rate of 3,200 kg/ha significantly reduced weed biomass (mixed stand, treated at seedling stage) 9 wk after application compared with the control, whereas steam applied at a rate of 1,600 kg/ha (1.6 m/s) did not. Biomass of downy brome treated with steam was reduced more at anthesis than at the seedling growth stage. Emergence of common lambsquarters, redroot pigweed, and black nightshade was not affected by steam application. Amount of steam applied, weed species, and growth stage are key factors in determining control effectiveness.

Diminished control of goosegrass was observed in tomato fields located in Manatee County, FL, after years of repeated paraquat use. Tolerance of the Manatee biotype to paraquat was confirmed by its comparison in greenhouse studies with a susceptible biotype from the Alachua County, FL. A 30-fold increase in paraquat rate was required to reach the 50% growth reduction level of the resistant biotype over the susceptible biotype. The Manatee biotype was not tolerant to clethodim, metribuzin, or sethoxydim. These herbicides provided adequate control of all the goosegrass biotypes tested.

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%.

Auxin-type herbicides such as 2,4-D and dicamba are commonly used to control kochia in small grain production areas, but poor kochia control with these herbicides has been reported. Several auxinic herbicide-resistant kochia inbreds were evaluated for their response to 2,4-D or dicamba and to alternative herbicide treatments. Values of the dose of the herbicide causing 50% visible injury to test plants (I50) from week 1 to week 4 after treatment with 2,4-D were unchanged for six of the seven 2,4-D–resistant inbreds, indicating that these plants may recover to produce seeds. In contrast, the corresponding I50 values for dicamba decreased for five of the six dicamba-resistant inbreds, indicating that kochia was not recovering from the treatment. Postemergence treatments with atrazine, carfentrazone, fluroxypyr, bromoxynil plus MCPA, nicosulfuron plus dicamba, and nicosulfuron plus dicamba plus atrazine, all provided adequate to excellent control of resistant kochia inbreds. Alternative chemical control options are available for managing auxinic herbicide-resistance in kochia.

Crop response to carfentrazone–ethyl can be affected by environmental conditions. Field research was initiated to determine the effect of irrigation and light intensity prior to herbicide treatment on crop response to carfentrazone–ethyl. Wheat, corn, and soybean response was evaluated in 1996 and 1997, 2 yr that differed significantly in rainfall. It was difficult to distinguish differences in visible crop injury between irrigated and nonirrigated crops within the same year; however, injury was much higher in 1996 than in 1997. In 1996, the study area received timely rainfall prior to treatment of each crop, but in 1997, no precipitation was recorded during the treatment period. Overall, irrigated plants appear to be slightly more sensitive than nonirrigated plants. In contrast, crop injury was significantly higher in response to low light intensity prior to herbicide treatment. Soybean plants covered with 80% shade cloth for 5 d prior to carfentrazone–ethyl application were injured 24 to 41% more than nonshaded plants. Corn was relatively insensitive to either condition. Soybean plants were very sensitive to carfentrazone–ethyl and were highly influenced by both light intensity and irrigation. Wheat response to carfentrazone–ethyl was not influenced within 1 yr by irrigation, but injury in 1996 was four times higher than in 1997. Light intensity prior to treatment influenced wheat response to carfentrazone–ethyl, where shading before treatment increased visible injury in wheat, but by less than 10%. The risk of crop injury increases when carfentrazone–ethyl is applied to irrigated plants or to crops following several cloudy days.

A study was conducted to evaluate flumioxazin preemergence (PRE) at 71 and 105 g ai/ha, when used with dimethenamid PRE, dimethenamid preplant incorporated (PPI), or ethalfluralin PPI, for crop injury, weed control, and yield. Peanut injury from treatments including flumioxazin 2 wk after soil-applied treatment (WAST) was less than 2% at two locations and 50 to 67% at a third location. Peanut injury increased with flumioxazin rate. Soil-applied treatments that included flumioxazin at either rate controlled common lambsquarters and prickly sida at least 96 and 89%, respectively. Addition of postemergence (POST) herbicides to any soil-applied program controlled prickly sida and ivyleaf morningglory at least 94 and 98%, respectively. Treatments that included ethafluralin or dimethenamid controlled goosegrass at least 82%. With a few exceptions, peanut yields were not improved by use of POST herbicides. Where peanut injury occurred, increased flumioxazin rate resulted in lower peanut yield when averaged over PPI and POST herbicide treatments.

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 1998 and 1999 at two locations in Mississippi to determine weed control efficacy of postemergence soybean herbicides alone or following pendimethalin + imazaquin preemergence in glufosinate-tolerant soybean planted in 38- or 76-cm rows. Glufosinate applications controlled pitted morningglory better than conventional herbicide treatments, regardless of row spacing. Pendimethalin + imazaquin did not increase the efficacy of glufosinate on pitted morningglory. Pitted morningglory control was increased in narrow rows when compared to wide rows with all treatments. Sicklepod control ranged from 90 to 100% in narrow rows with glufosinate, regardless of rate. Residual herbicides alone controlled sicklepod 54%, regardless of row spacing. With grass species, two applications of 420 g ai/ha glufosinate controlled weeds 82 to 100%. Residual herbicides followed by 420 g/ha glufosinate controlled grass species 80% or more, regardless of row spacing. Hemp sesbania control ranged from 80 to 92% in 76- and 38-cm rows with one application of 560 g/ha glufosinate. Glufosinate at 420 g/ha used as sequential applications controlled hemp sesbania better than the conventional treatment in 76-cm rows. Residual herbicides in combination with glufosinate did not increase hemp sesbania control. There were no differences in yield due to row spacing at Stoneville in either year due to extremely dry growing conditions during pod set. At Starkville, two applications of 420 g/ha glufosinate resulted in higher yields than pendimethalin + imazaquin followed by 420 g/ha glufosinate in both years. Pendimethalin + imazaquin followed by 420 g/ha glufosinate increased yield in narrow rows compared to wide rows at Starkville in 1998.

Field studies were conducted from 1998 to 2000 in Beltsville, MD, to evaluate the effects of preemergence (PRE) applications of BAY FOE 5043 + metribuzin, s-metolachlor, and diclofop on crop injury, yield, and control of diclofop-tolerant Italian ryegrass in winter wheat. No injury was observed in 1999. In 2000, minor stunting of wheat plants was observed where high rates of BAY FOE 5043 + metribuzin and s-metolachlor were utilized. Wheat plants outgrew the stunting and grain yields were not affected. High rates of BAY FOE 5043 + metribuzin and s-metolachlor provided equally effective Italian ryegrass control in 1999, averaging 85% or greater in June. In 2000, all rates of BAY FOE 5043 + metribuzin provided 93% or greater Italian ryegrass control, whereas s-metolachlor at 0.43 kg/ha or greater provided 85% Italian ryegrass control or greater when evaluated in June. In 1999, wheat yields from plots treated with BAY FOE 5043 + metribuzin, or s-metolachlor at 0.43, 0.56, or 0.84 kg/ha, were higher than from the nontreated control. In 2000, all wheat yields from plots treated with BAY FOE 5043 + metribuzin and s-metolachlor were higher than from the nontreated control.

Field and greenhouse experiments were conducted to evaluate clethodim, CGA-362622, mixtures thereof, and sequential treatments for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. In greenhouse experiments, clethodim alone provided 93 and 100% control of three- to four-leaf goosegrass at the low (105 g ai/ha) and high (140 g/ha) rates, respectively, whereas CGA-362622 did not control grasses in greenhouse or field experiments. Control of six- to eight-leaf goosegrass in the greenhouse with clethodim was 75% for the low rate and 89% for the high rate. Control of goosegrass in greenhouse studies was reduced at least 43 percentage points with CGA-362622 and clethodim at the high rate in mixture compared with control provided by clethodim at the high rate alone. When CGA-362622 and clethodim were applied in mixture in field studies, the effectiveness of the graminicide was decreased from > 97 to < 57% control for all annual grasses. Antagonism of clethodim activity was greater than that of the tank mixture when clethodim was applied 1 d after CGA-362622 on large crabgrass, goosegrass, and fall panicum. Clethodim applied 7 d before or after CGA-362622 controlled the four grass species as well as did clethodim applied alone. When CGA-362622 was applied to goosegrass alone, fresh weight accumulation stopped for a period of 4 d compared with untreated plants. Normal growth resumed after 4 d.

A bioassay, based on seedling shoot inhibition with difenzoquat at 10 mg/L, provides a rapid means of predicting hard red spring wheat (HRSW) cultivar response to foliar-applied difenzoquat. The tolerance of several cultivars to difenzoquat was determined by shoot length inhibition in the laboratory, and by visible crop injury and shoot dry weight in the greenhouse. Of the 19 cultivars tested, one cultivar that was susceptible in the laboratory assay was intermediate in tolerance to difenzoquat in the greenhouse assay; two cultivars that were tolerant in the laboratory bioassay were of intermediate tolerance in the greenhouse assay. Results from laboratory and greenhouse studies both identified cultivars distinctly susceptible to difenzoquat. Shoot inhibition indicated that HRSW cultivar susceptibility to difenzoquat involves continuous variation from tolerant to susceptible. This may explain why some cultivars show differential responses to difenzoquat under different environmental conditions.

Control of common waterhemp in corn with chloroacetamide and dinitroaniline herbicides can be inconsistent. Common waterhemp control by dimethenamid, S-metalochlor, pendimethalin, and three formulations of acetochlor, applied alone or with atrazine as single preemergence (PRE) or sequential PRE followed by postemergence (POST) treatment, was determined. The manufacturer's suggested use rate (1 time) of PRE herbicides was compared with sequential applications (0.66 time PRE followed by 0.34 time POST) of herbicides. POST applications included dicamba to control emerged common waterhemp. Single and sequential herbicide applications controlled common waterhemp at least 98%, 28 d after planting (DAP). But herbicides applied sequentially were more effective than PRE treatments by 56 DAP. Encapsulated acetochlor formulations controlled common waterhemp at least 85% by 56 DAP regardless of application method. Sequential applications of S-metolachlor controlled common waterhemp greater than 83%. Atrazine improved common waterhemp control regardless of herbicide or application method 56 DAP. Sequential applications of dimethenamid or S-metolachlor alone or with atrazine were more effective than single PRE applications of these herbicides.

Field studies were conducted in 1998 and 1999 to evaluate the efficacy of glufosinate on Palmer amaranth, redroot pigweed, and common waterhemp at different growth stages in soybean planted at early, normal, and late dates. At 2, 4, and 8 wk after treatment, common waterhemp control was greater than Palmer amaranth and redroot pigweed control with single glufosinate applications of 410 g ai/ha at 2- to 5-, 7- to 10-, or 15- to 18-cm Amaranthus height or with two sequential applications of 293 g/ha at 2- to 5-cm height and 2 wk later. Only the sequential applications of 410 and 293 g/ha resulted in more than 80% control of Palmer amaranth and redroot pigweed, but all five treatments controlled common waterhemp more than 80%. All glufosinate treatments reduced the dry weight of all Amaranthus species by more than 65%. However, the sequential applications resulted in the greatest dry weight reductions.

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.