Field experiments were conducted in the Mediterranean conditions of the Ebro Valley, Spain during 1995 to 1996 and 1996 to 1997 to determine the effects of imazamethabenz and PP-604 on selected durum wheat Triticum turgidum var. durum cultivars grown under irrigation. Herbicides were applied at their recommended rates of 600 g ai/ha for imazamethabenz and 375 g ai/ha for PP-604 and at twice these rates. Herbicide treatment reduced the average wheat height in three of four trials. Wheat treated with imazamethabenz was almost 2 cm shorter than wheat treated with PP-604 and almost 3 cm shorter than untreated control plants. However, durum wheat yields were not significantly reduced by treatment with imazamethabenz or PP-604 in any of the four trials, and no visible plant injury was observed. These results differ from reported yield reductions under Mediterranean dryland conditions, suggesting that durum wheat can be affected by imazamethabenz and PP-604 but irrigation enhances recovery from herbicide injury.

Field studies were conducted in 1992 and 1993 to evaluate weed control by 15 herbicide treatments in wheat stubble and in the succeeding corn crop. Atrazine at 2.24 kg ai/ha plus several herbicide treatments were applied about 13, 21, and 33 d following winter wheat harvest on separate plots in 1992 and 1993 in a soybean–winter wheat–corn rotation. Atrazine with and without 2,4-D isooctyl ester at 1.46 kg ae/ha or dicamba at 0.36 kg ae/ha did not control barnyardgrass, green foxtail, horseweed, kochia, stinkgrass, tumble thistle, or witchgrass in the wheat stubble 30 d after treatment. Atrazine mixtures containing glyphosate or paraquat with or without 2,4-D or dicamba controlled most summer annual weed species. Atrazine plus paraquat at 0.43 kg ai/ha was more effective on redroot pigweed and tumble thistle than atrazine plus glyphosate at 0.43 kg ae/ha plus 2,4-D at 0.95 kg ae/ha. Atrazine plus glyphosate mixtures were more effective on barnyardgrass for the first and second application date than atrazine plus paraquat. Increasing the glyphosate rate from 0.43 to 0.67 kg/ha was necessary to control barnyardgrass 95% at the first date. With the first date of application, kochia control was greater when 2,4-D or dicamba was added to the atrazine plus paraquat (0.43 kg/ha) mixture. Although annual grass control was generally greater when weeds approached maturity, early applications are a more sound weed control strategy because of soil water conservation and prevention of weed seed production. However, corn yields in 1993 were greater on plots treated at the third application in 1992 because weed biomass in corn was less. In 1994, corn yields were highest for the first application in 1993, probably because of better weed control in the corn. Above average rainfall in 1993 and 1994 aided corn yields.

Weeded check plots are an integral part of most weed control experiments. They provide a measure of the maximum crop yield without weed competition in a given site-year environment. The traditional way to create weeded check plots is to hoe and pull weeds by hand in the row and hoe weeds between rows. But erratic heavy rainfall can prevent timely hoeing. The objective of this experiment was to compare faster, less-laborious mechanized ways to control weeds between crop rows as alternatives to hoeing in corn and soybean. Hoeing, the traditional method for controlling weeds between crop rows, was compared with either repeated mowing using a cord-mower or a string-trimmer or shallow tilling with a rototiller between rows. Weeds growing in rows were controlled by hand-pulling and hoeing because the focus of the experiment was on speeding weed control between rows. All four methods for controlling weeds between crop rows were equally effective when measured as either corn or soybean yield, visual rating of weed control, or weed ground cover in two years under contrasting rainfall patterns. Cord-mowing or string-trimming between rows was possible when soil was dry enough to walk upon but too wet to hoe or rototill.

Glyphosate was applied to pepper as single or sequential applications to assess the consequences of drift or other accidental exposures. Foliar injury increased and plant vigor declined with increased rates of glyphosate and were exacerbated by a second application. Single applications at flowering (stage 1) were more damaging than single applications after fruit set (stage 2). Decline in marketable yield with increased glyphosate rate was greater with stage 1 applications, except in spring 1987 when marketable yields with single applications of glyphosate at stage 1 or stage 2 were statistically similar. Sequential applications resulted in the lowest marketable yields. Total yields declined with increased glyphosate rate and decline was more pronounced with sequential applications than with single applications. Total yield was affected to a greater extent when glyphosate was applied at stage 1 than at stage 2. Yield was more sensitive to two successive exposures than to single applications. Mean fruit weight was reduced by glyphosate in two of the four experiments.

Reduced herbicide inputs can diminish pesticide movement into water supplies, enhancing environmental quality. A 3-yr study was conducted to evaluate the efficacy and economic viability of reducing herbicide inputs by using ultra-low rates (ULRs), consisting of one-eighth the normal use rates of nicosulfuron plus thifensulfuron, delayed planting (DP), or both in corn and soybean. We compared the ULR treatment at the assigned cost of $12.35/ha with three other traditional types of weed management systems in both chisel plow and no-till production schemes. The ULR weed management system suppressed weeds enough to allow economical soybean production all 3 yr of the study, but this system proved viable only during the wettest year for corn. DP was economically competitive with the best systems in both crops under chisel-plowed tillage only in the driest year of the study.

Herbicides registered for lima bean (Phaseolus lunatus L.) do not consistently control many troublesome weeds. Some herbicides registered for soybean (Glycine max) will control these weeds, but tolerance to lima bean is not known. Two field and two greenhouse studies were conducted to evaluate recently registered soybean herbicides for lima bean tolerance. Field studies were conducted in Delaware from 1996 to 1998, and in North Carolina during 1997 and 1998. The first field study evaluated the preemergence (PRE) herbicides cloransulam at 0.01, 0.02, 0.03, and 0.04 kg ai/ha; flumetsulam at 0.04, 0.05, 0.06, and 0.07 plus metolachlor at 1.3, 1.6, 1.8, and 2.1 kg ai/ha; sulfentrazone at 0.1, 0.15, 0.2, and 0.25 kg ai/ha; lactofen at 0.2 and 0.25 kg ai/ha; and the commercial standard treatment of imazethapyr plus metolachlor at 0.05 and 1.7 kg ai/ha, respectively. Lima bean injury 5 to 8 wk after emergence was lowest for imazethapyr plus metolachlor (standard treatment) and all four rates of cloransulam. Crop injury with flumetsulam plus metolachlor ranged from 0 to 18% and sulfentrazone ranged from 3 to 75% depending on location and rate. Lactofen treatments caused unacceptable lima bean injury. Yield in plots treated with cloransulam were consistently greater than in the plots treated with other herbicides. The second field study examined the postemergence (POST) herbicides cloransulam (0.013 or 0.02 kg ai/ha), bentazon (1.1 kg ai/ha), imazethapyr (0.035 or 0.053 kg ai/ha), and imazamox (0.018 or 0.036 kg ai/ha), applied when the crop was at the first trifoliolate stage. Cloransulam caused 0 to 13% crop injury and imazamox caused 3 to 25% injury depending on rate and location. In greenhouse studies, no differences were observed among eight common processing lima bean cultivars in tolerance to sulfentrazone applied PRE or to cloransulam, imazamox, imazethapyr, or bentazon applied POST.

Field experiments were conducted in 1997 and 1998 near Columbia and Novelty, MO, and at Urbana, IL, to evaluate corn injury, weed control, corn yield, and estimated economic returns with weed management programs in glufosinate-resistant corn. Herbicide programs included acetochlor preemergence (PRE) followed by glufosinate alone or with atrazine postemergence (POST) and total POST programs consisting of single and sequential applications of glufosinate alone or tank mixed with acetochlor, atrazine, or acetochlor plus atrazine. Metolachlor PRE followed by dicamba plus atrazine early POST (EPOST) and metolachlor plus atrazine PRE were included for comparison. In the total POST treatments, mid-POST applications controlled shattercane and common cocklebur better than EPOST applications. However, yield reductions as high as 23% occurred because of early-season weed interference, although weeds were controlled later in the season. Applying atrazine with glufosinate generally increased control of giant foxtail, common cocklebur, morningglory species, and common waterhemp compared to glufosinate alone, but did not increase control of common lambsquarters, velvetleaf, or Pennsylvania smartweed. Corn yield was positively correlated with weed control (r = 0.88) and more strongly dependent on grass (r = 0.82) than broadleaf (r = 0.70) weed control. Net incomes were positively correlated to corn yield (r = 0.73). Four of the top six net income-producing treatments included two herbicide applications. Three of the treatments were PRE followed by POST programs, and the fourth was a sequential POST treatment of glufosinate.

Producers in the semi-arid Great Plains are starting to grow corn in sequence with winter wheat and proso millet. However, volunteer proso millet (hereafter referred to as proso) is difficult to control in corn with conventional practices. This study characterized growth and interference of proso in corn to aid producers in developing control strategies. Proso seedlings began emerging May 18 with 78% of seasonal emergence occurring by June 22; initial proso emergence occurred within 2 wk of corn emergence in all years. Seed production was related to time of emergence; proso seedlings emerging in mid-May produced approximately 2,800 seeds per plant, whereas seedlings emerging 4 wk later produced 88% fewer seeds. Controlling proso in late June prevented loss of corn grain yield caused by competition. When corn was planted in early May, the height difference between corn and proso was sufficient to allow postemergence-directed applications of graminicides for proso control. Corn yield was highest when planted in early May.

Field studies were conducted to evaluate the tolerance of peanut cultivars ‘Florunner’, ‘Georgia Green’, ‘Sunoleic 95R’, ‘AgriTech GK7’, ‘NC-7’, ‘ViruGard’, and ‘Spanco’ to sulfentraone. Herbicide treatments included sulfentrazone applied as a single treatment preemergence (PRE) at 0.14, 0.21, 0.28, 0.35, or 0.42 kg ai/ha or as a PRE followed by (fb) an at cracking (AC) application (0.14 kg ai/ha PRE fb 0.14 kg ai/ha AC, 0.21 kg ai/ha PRE fb 0.14 kg ai/ha AC, 0.21 kg ai/ha PRE fb 0.21 kg ai/ha AC, 0.28 kg ai/ha PRE fb 0.07 kg ai/ha AC, or 0.28 kg ai/ha PRE fb 0.14 kg ai/ha AC). Imazapic and paraquat applied early postemergence (EPOT) were included along with a weed-free control. NC-7 exhibited higher early-season injury (ranging from 1 to 29%) than other cultivars across all sulfentrazone applications. However, this injury did not affect yield when compared with the untreated weed-free check. Overall, peanut tolerance to sulfentrazone was high across all varieties.

Field experiments were conducted to study the competition effect of winter wheat planted in a square arrangement and Italian ryegrass planted randomly on biomass yields of both species, ryegrass seed yield, N use efficiency, and progeny seed germination. Increases in wheat density up to 800 plants/m2 reduced ryegrass seed yield by 87% but increased its harvest index up to 42% compared to its monoculture yield. Species densities and their interactions accounted for 66 to 73% of the total variation in per-unit area biomass of species, and their association was more favorable to ryegrass biomass than wheat. Seeds of each species had three times greater nitrogen percentage than did shoots. Intra- and interspecific competition increased nitrogen percentage in wheat seeds. In Italian ryegrass, only interspecific competition increased N percentage in seeds. Although total nitrogen uptake by winter wheat was three times greater than in Italian ryegrass, Italian ryegrass was two times more efficient than wheat at producing biomass per unit of N taken up and specific leaf area at heading stage in mixture. Germination percentages of progeny seeds of both species in mixtures were greater in presence of high densities of the companion species than in their monocultures. Nitrogen was not the main limiting factor for competition between winter wheat and Italian ryegrass in this study.

Field studies were conducted to assess weed control and potato (Solanum tuberosum) tolerance to ethalfluralin. Ethalfluralin applied preemergence (PRE) alone at 1.05 kg ai/ha generally did not control weeds adequately. However, ethalfluralin at 1.05 kg/ha combined with either metribuzin at 0.28 kg ai/ha or rimsulfuron at 0.018 kg ai/ha controlled common lambsquarters (Chenopodium album), redroot pigweed (Amaranthus retroflexus), and green foxtail (Setaria viridis) ≥ 98%, which was similar to control observed with several currently registered herbicide mixtures. Volunteer oat (Avena sativa) control with either ethalfluralin at 1.05 kg/ha plus EPTC at 3.4 kg ai/ha or ethalfluralin plus metribuzin was equal to registered two-way mixtures. Ethalfluralin plus metribuzin did not adequately control hairy nightshade (Solanum sarrachoides), but ethalfluralin mixtures with either rimsulfuron or EPTC controlled hairy nightshade equal to or better than the registered two-way mixtures evaluated. A sequential application of ethalfluralin PRE followed by rimsulfuron or rimsulfuron plus metribuzin postemergence (POST) did not improve hairy nightshade control compared to ethalfluralin plus rimsulfuron applied PRE. Potato tolerance to herbicide treatments applied PRE or POST to potato was evaluated in weed-free studies. Ethalfluralin alone or with metribuzin was compared to mixtures of metribuzin with either pendimethalin or EPTC. Initial visual injury with ethalfluralin PRE was ≤ 4% both years. In 1996, initial injury with ethalfluralin POST was ≤ 4% and U.S. No. 1 and total tuber yields were not affected by herbicide treatment or application timing. However in 1997, initial injury from POST ethalfluralin at 1.05 or 2.1 kg/ha was 2 or 8% and increased to 9 or 17%, respectively, at potato row closure. Averaged over all herbicide treatments, POST applications reduced U.S. No. 1 and total tuber yield 7% relative to PRE applications in 1997.

Field experiments were conducted in southern Wisconsin from 1996 to 1998 to evaluate the effects of acetochlor applied preemergence (PRE) followed by nicosulfuron or sethoxydim applied postemergence (POST) and of cultivation on woolly cupgrass control, corn grain yield, and woolly cupgrass seed production. Sethoxydim treatments provided greater woolly cupgrass control than nicosulfuron treatments in 1997 and similar control to nicosulfuron treatments in 1996 and 1998. However, neither herbicide killed all emerged woolly cupgrass plants, regardless of herbicide rate or POST application timing. Late postemergence treatments provided greater season-long control than early postemergence treatments in 1996 and 1998, but there was no difference in control between timings in 1997. Acetochlor applied PRE at 1,800 g ai/ha (1×) followed by nicosulfuron (35 g ai/ha) or sethoxydim (213 g ai/ha) at the registered rate (1×) or at one half of the registered rate (0.5×) consistently provided sufficient woolly cupgrass control to maximize corn yield, regardless of cultivation or POST herbicide application timing. Acetochlor PRE treatments, cultivated and noncultivated, followed by sethoxydim POST and cultivated acetochlor PRE treatments followed by nicosulfuron POST treatments provided sufficient control in each year to limit woolly cupgrass seed production to a level that decreased the predicted future seedbank density, regardless of herbicide rate or POST herbicide application timing. However, noncultivated acetochlor treatments followed by nicosulfuron applied at 1× followed by 0.5× or at 0.5× followed by 0.5× did not consistently reduce seed production to a level that decreased the predicted future seedbank density. These results suggest that the rate of sethoxydim can be reduced to 0.5× if a full rate of acetochlor is applied PRE with little effect on corn yield or woolly cupgrass seedbank density. However, reducing the rate of nicosulfuron to 0.5× following an application of acetochlor at the full rate or reducing both the acetochlor and nicosulfuron or sethoxydim rate to 0.5× is recommended only if a cultivation is planned.

Field experiments were conducted in 1997 and 1998 near Columbia and Novelty, MO, and Urbana, IL, to evaluate crop injury, weed control, corn yield, and net economic returns provided by weed control programs in glyphosate-resistant corn. The herbicide programs evaluated included acetochlor preemergence (PRE) followed by (fb) glyphosate with or without atrazine postemergence (POST) and total POST programs consisting of single and sequential applications of glyphosate alone and tank-mixed with actochlor, atrazine, or both. Metolachlor PRE fb dicamba plus atrazine POST and metolachlor plus atrazine PRE were included for comparison. In the total POST treatments, mid-post (MPOST) applications provided better control than early-post (EPOST) applications on weeds that germinated throughout the growing season such as shattercane and common cocklebur, but also resulted in yield reductions of up to 23% caused by early-season weed competition. The addition of atrazine to glyphosate POST generally increased control of common cocklebur, morningglory species, and common waterhemp. EPOST or PRE fb EPOST applications generally provided higher yields than MPOST treatments, although MPOST treatments often provided equal or greater weed control at midseason. Treatments including two herbicide applications tended to provide greater weed control, yield, and profit than those with a single application. Input costs for glyphosate-resistant corn are slightly higher than nontransgenic hybrids. However, net economic returns are similar and the use of glyphosate POST allows greater flexibility in POST weed management decisions.

Eurasian watermilfoil, an aquatic invasive weed, has been identified recently at a number of sites in western Nevada and northeastern California, including Lake Tahoe. Because Eurasian watermilfoil is easily spread by fragments, transport on boats and boating equipment plays a key role in contaminating new water bodies. This is an important means of the potential spread of this weed throughout key recreational and agricultural areas surrounding Lake Tahoe. Unless the weed is controlled, significant alterations of aquatic ecosystems, with associated degradation of natural resources and economic damages to human uses of those resources, may occur. This research uses the economic valuation approach known as benefits transfer to estimate the value of a portion of the recreational service flows that society currently enjoys in the Truckee River watershed below Lake Tahoe. The lower-bound estimates of baseline water-based recreation value at a subset of sites in the watershed range from $30 to $45 million/yr. Impacts from the continued spread of Eurasian watermilfoil in the watershed could be significant; for example, even a 1% decrease in recreation values would correspond to roughly $500,000/yr as a lower bound.

The influence of four tillage systems, varying from intensive to zero tillage, on weed populations and the vertical distribution of weed seeds in the soil was determined at Alliance, Hairy Hill, and Wainwright in northeastern Alberta. The soil was sampled at two depths (0 to 5 and 5 to 10 cm) in fall. Weed seedling emergence in the greenhouse over the winter was assumed to represent the type and amount of weed seeds present in the soil seedbank. Emerged weed seedlings were also identified and counted in the field in spring. In the zero-tillage system, most of the weed seeds were close to the soil surface (0 to 5 cm) at Alliance and Wainwright but were deeper (5 to 10 cm) at Hairy Hill. The winter annuals, field pennycress, shepherd's-purse, and flixweed, and the summer annuals, wild buckwheat and common lambsquarters, increased in the soil seedbank as tillage was reduced, but the higher populations in the soil seedbank did not always result in higher spring seedling populations under zero tillage. In contrast to the seedbank, spring seedling populations of common lambsquarters at Alliance and field pennycress and ball mustard at Hairy Hill were lowest in the zero-tillage system, suggesting that the requirement for herbicides for controlling these weeds in the crop may be least under zero tillage. Both soil seedbank and spring seedling populations of shepherd's-purse at Wainwright and Alliance and of flixweed at Alliance were highest in the zero-tillage system. At Alliance, wild buckwheat seedling emergence in the spring tended to be highest in the minimum-tillage system (one tillage operation prior to seeding). Both soil seedbank and spring seedling populations of green foxtail decreased as tillage was reduced, indicating that green foxtail should become less of a problem under reduced tillage.

Field studies were conducted in 1997 and 1998 to evaluate weed control and soybean (Glycine max) yield with cloransulam and diclosulam. Cloransulam at 35 g/ha applied preplant incorporated (PPI) and preemergence (PRE) controlled at least 91% of hyssop spurge (Euphorbia hyssopifolia) and prickly sida (Sida spinosa) and at least 82% of entireleaf morningglory (Ipomoea hederacea var. integriuscula) and pitted morningglory (Ipomoea lacunosa) at 7 wk after planting. Control of these species with cloransulam was not affected by method of soil application. Control of prickly sida with cloransulam PPI or PRE was better than with cloransulam postemergence (POST) at 18 g/ha. Soybean yields were similar with cloransulam PPI (2,880 kg/ha) or PRE (3,110 kg/ha) and were comparable to imazaquin PRE at 140 g/ha (3,080 kg/ha). Weed control and soybean yields with cloransulam POST were similar to that with chlorimuron POST at 11 g/ha. SAN 582 plus cloransulam PRE followed by cloransulam POST provided the highest soybean yield (3,450 kg/ha). Diclosulam PPI or PRE provided similar levels of control of hyssop spurge, Ipomoea morningglories, and prickly sida. Overall, control of these species with diclosulam PPI or PRE was similar to that obtained with sulfentrazone plus chlorimuron PRE. Soybean yields (≥ 3,290 kg/ha) were similar regardless of method of diclosulam application, and yields were equivalent to that of sulfentrazone plus chlorimuron PRE (3,270 kg/ha).

Dose–response curves for acetochlor with and without timely rotary hoeing (two passes) were derived for corn (Zea mays) fields over 2 yr. The fields were dominated by green foxtail (Setaria viridis), which constituted 73 to 86% of the weed vegetation, but also contained minor populations of common lambsquarters (Chenopodium album), Pennsylvania smartweed (Polygonum pensylvanicum), and redroot pigweed (Amaranthus retroflexus). In the absence of herbicide, rotary hoeing achieved about 50% weed control. In the absence of rotary hoeing, weed control averaged > 90% at the full label rate of acetochlor (3 kg ai/ha on clay loam soil). With two timely rotary hoeings, however, this same level of control was achieved with only 1 kg/ha acetochlor. Given the suite of weed species present in these experiments, timely rotary hoeing substituted for 67% of the label rate of acetochlor. Timeliness of rotary hoeing operations also provided consistency of results from one year to the next.

In field experiments, nicosulfuron at 35 g ai/ha controlled itchgrass in corn 28 d after treatment better than primisulfuron at 39 g ai/ha (80 vs. 44%). Control with both herbicides was greater when applied to six-leaf itchgrass than to 10-leaf and with the addition of nonionic surfactant than with an organosilicone surfactant and methylated seed oil blend. Weed control for nicosulfuron plus nonionic surfactant resulted in corn yield approximately 1.5 times that of primisulfuron plus nonionic surfactant and 1.6 times that of nicosulfuron plus an organosilicone surfactant and methylated seed oil blend. When primisulfuron was applied with organosilicone surfactant and methylated seed oil rather than nonionic surfactant, corn yield was reduced by 25%. For nicosulfuron with nonionic surfactant, corn yield averaged approximately twice that of the nontreated check. In other field experiments, itchgrass control 28 d after treatment with nicosulfuron was enhanced with addition of an organosilicone and nonionic surfactant blend or methylated seed oil (83 and 78%, respectively) compared with nonionic surfactant (69%). Nicosulfuron was less effective when applied with crop oil concentrate or organosilicone surfactants compared with nonionic surfactant.

Differential response of wild carrot to 2,4-D was found in seeds collected from 10 locations in Michigan, three in Ohio, one in Illinois, and one in Ontario, Canada. Greenhouse studies were conducted on plants grown from the collected seeds to confirm resistance of wild carrot to 2,4-D, and to study variations among and within populations. The differential response of wild carrot to 2,4-D in field research was due to resistant individuals. Among the 14 locations, wild carrot control with 2,4-D ranged from 18 to 91%. Wild carrot varied in its response to 2,4-D among and within populations as well as within individual umbels. In 69% of the tested samples, at least one wild carrot plant was resistant to 2,4-D.

Studies were conducted from 1995 to 1997 near Tifton, GA, to evaluate shallow tillage implements and tillage frequency for stale seedbed weed control in peanut. Tillage implements evaluated were a power tiller, disk harrow, field conditioner, and sweep cultivator. Plots for each implement were tilled once or twice prior to planting peanut. Results from midseason weed counts and peanut yield showed similar responses among implements and frequency of tillage. These results indicate no advantage of any shallow tillage implement for stale seedbed weed control, although peanut yields were generally greater in plots with tilled stale seedbeds than in the nontilled control. The implement of choice should be based on cost of operation and compatibility with the overall peanut production system.