Imazethapyr at 0.05 to 0.14 kg ai/ha applied preplant incorporated, preemergence, and postemergence was evaluated alone and with complementary herbicides in the field for weed control in soybean. Imazethapyr controlled 90% or more smooth pigweed regardless of application method or herbicide rate. Imazethapyr at 0.05 kg/ha controlled jimsonweed 30% better postemergence compared to soil applications. Imazethapyr at 0.10 kg/ha controlled 90% or more velvetleaf regardless of application method. The addition of alachlor to soil-applied imazethapyr enhanced giant foxtail, jimsonweed, and velvetleaf control. Adding acifluorfen or bentazon to postemergence imazethapyr antagonized weed control. Adding sethoxydim to postemergence imazethapyr was not beneficial.

Experiments with similar experimental design, soil, and planting date were conducted between 1975 and 1979 to evaluate the interference of jimsonweed on soybeans and cotton in Alabama (AL), Arkansas (AR), and Mississippi (MS). Jimsonweed densities were 0, 4, 8, 16, 32, and 64 plants 12 m−1 of row. Because of variation in rainfall patterns, geographic region influenced jimsonweed interference in cotton but not in soybeans. Even though jimsonweed interference was reduced by lack of rainfall, jimsonweed was more competitive in the less competitive cotton than in soybeans. Jimsonweed at 64 plants 12 m−1 of row was more competitive with cotton than soybeans, causing a 56 and 16% yield reduction, respectively. Position of jimsonweed to the soybean row did not influence competitiveness. Interspecific interference with soybeans caused one-third more reduction in jimsonweed fresh weight and capsules per plant than interspecific interference with cotton. The potential for jimsonweed to become a problem in southern soybeans is less than its potential in cotton because of the competitive ability of soybeans to reduce the growth and reproductive potential of jimsonweed.

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

The weed control spectrum of clomazone, the influence of clomazone on the performance of other herbicides, and the performance of tank mixtures containing clomazone were evaluated from 1985 through 1987. Clomazone applied preemergence at 280 g ai/ha controlled 90 to 100% of barnyardgrass, giant foxtail, goosegrass, large crabgrass, seedling johnsongrass, prickly sida, and velvetleaf. Clomazone at reduced rates was more effective applied preemergence than preplant-incorporated for 10 of 23 weed species. Clomazone enhanced imazaquin activity on entireleaf morningglory and sicklepod in 1986. A tank mixture of clomazone, imazaquin, and metribuzin at half the labeled rates reduced soybean injury, increased soybean yield, and controlled weeds as well as the mixture at labeled rates.

Seed capsules of field-grown jimsonweed were harvested 2, 4, 6, and 10 weeks after anthesis. Degree day accumulation from anthesis and weeks after anthesis were equal in predicting the time required for nondormant jimsonweed seed production and seed dry weight. Seed germination increased as capsule age increased from 2 to 6 weeks. No additional increase in germination was observed in seed from capsules collected 10 weeks after anthesis. Maximum seed weight was obtained from capsules 6 and 10 weeks old in 1986 and 1987, respectively. Germination was correlated highly with seed weight.

Photosynthesis and growth responses to irradiance level during growth were compared in soybean (Glycine max L. Merr. ‘Century’) and three broadleaf weeds to determine if these responses were associated with differences in shade tolerance among species. In response to reduced irradiance during growth, leaf thickness of all species decreased, while chlorophyll content per unit leaf volume and photosynthetic rate per unit leaf volume, measured at low irradiance, increased. Soybean and common cocklebur (Xanthium strumarium L. #3 XANST) also exhibited a decrease in soluble proteins on a leaf volume basis under reduced irradiance, and common cocklebur further exhibited a decrease in ribulose-1,5-bisphosphate carboxylase (RuBPcase) protein per unit leaf volume. Decreased irradiance during growth did not alter the content of RuBPcase or other soluble proteins per unit leaf volume in jimsonweed (Datura stramonium L. # DATST) or velvetleaf (Abutilon theophrasti Medic. # ABUTH). The superior shade tolerance of common cocklebur compared to the other species was attributed in part to the levels of RuBPcase and other photosynthetic proteins in leaves developed at low irradiance.

Experiments were conducted in 1985 and 1986 to determine and compare the efficacy, phytotoxicity, and soil persistence of imazquin, imazethapyr, and clomazone in no-till double-crop soybeans. All herbicides controlled 93% or greater jimsonweed, velvetleaf, and giant foxtail. Imazaquin and imazethapyr controlled more common cocklebur and ivyleaf morningglory than clomazone. Soybeans were injured from imazaquin and imazethapyr applications in 1986 but yields were not reduced. First-order kinetics described the dissipation of each herbicide. Imazaquin and imazethapyr were more persistent in the soil than clomazone. Averaged over both years, half-lives of 10, 43, and 60 days were calculated for clomazone, imazaquin, and imazethapyr, respectively. Clomazone was not detected 10 to 20 cm in the soil profile. More imazethapyr was detected 10 to 20 cm in the soil profile than imazaquin in 1985. Slight corn injury (≤10%) was observed in 1987 following previous year applications of imazaquin to no-till double-crop soybeans but corn yields were not reduced.

Common cocklebur, jimsonweed, and velvetleaf were grown with soybeans in the field to determine how soybean interference affects weed canopy architecture. Common cocklebur had more leaves within the soybean canopy than jimsonweed or velvetleaf. At the end of the season, common cocklebur leaf area was distributed evenly below and above the top of the soybean canopy, while nearly all the jimsonweed and velvetleaf leaf area was above the soybean canopy. Common cocklebur exhibited more shade tolerance than jimsonweed or velvetleaf by also maintaining leaves in the shade within the soybean canopy. Differences among these weeds in leaf distribution within the soybean canopy were not related to differences in abscission of the lower leaves but to a differential response of lower axillary buds to soybean shading. Growth from lower axillary buds in jimsonweed and velvetleaf was strongly inhibited by soybean interference, but interference had little effect on lower axillary bud growth in common cocklebur. Axillary bud growth in the lower canopies of both common cocklebur and soybeans, and their similarity in height, caused these plants to compete for the same aboveground niche. However, common cocklebur had more extensive axillary growth along the lower stem than soybeans, which may allow it to compete for resources in this niche more aggressively than soybeans. Velvetleaf and jimsonweed did not share the same aboveground niche with soybeans due to the placement of their leaves above rather than within the soybean canopy. The lower branching characteristics and apparent shade tolerance of common cocklebur may be important factors in the superior competitive ability with soybeans compared to jimsonweed and velvetleaf.

Tolerance of direct-seeded pepper under clear plastic mulch to herbicides applied pre- and post-emergence was investigated in 1991 and 1992. Weed control of herbicides applied preemergence was also studied. Paprika cultivar ‘Buketen’ and canning cultivars ‘Piquillo de Lodosa’ and ‘Pico de Mendavia’ were seeded in the field in Zaragoza, Spain, in a loamy soil. Percent emergence, plant mortality after the postemergence treatment, dry weight of plants, and fruit weight were recorded. Pepper was tolerant to diphenamid and napropamide applied preemergence but these herbicides did not control broadleaf weeds. Clomazone, when applied preemergence resulted in chlorotic seedlings and at 2 kg ai/ha reduced the final stand, but was selective when applied at the 6 to 8-leaf stage of the crop. Pepper was tolerant to diethatyl-ethyl when applied preemergence. However, diethatyl-ethyl applied postemergence caused severe phytotoxicity symptoms, and when mixed with diphenamid, fruit ripeness in 1992 was delayed. Weed control during the crop emergence period was better when diethatyl-ethyl was used mixed with diphenamid or napropamide.

Field and laboratory studies were conducted in 1985 and 1986 to determine the effect of herbicide application timing and level of corn residue on metribuzin plus metolachlor for weed control in soybean. Herbicides were applied early preplant (35 days before planting), sequentially (early preplant and preemergence), or preemergence. Giant foxtail control was better with sequential application than early preplant herbicide application in both years. Control of velvetleaf, smooth pigweed, and jimsonweed was independent of application timing, except in 1986, when jimsonweed control was less from herbicides applied early preplant compared to sequentially. Metribuzin reaching the soil was less when applied to high levels of corn residue compared to low residue levels. However, corn residue level had no effect on weed control.

Activity, adsorption, mobility, and field persistence of one emulsifiable concentrate (EC) and three microencapsulated (ME) formulations of alachlor were studied with petri dish bioassay, based on root response of oats grown in sand or soil. Both bioassays indicated that activity of all formulations was increased with increasing herbicide concentration. EC-alachlor in sand showed the highest activity, while ME-alachlorL and ME-alachlorA, the lowest; the activity of ME-alachlorC was intermediate. In silty clay loam soil, EC-alachlor had the highest activity, while ME-alachlorL had the lowest; and ME-alachlorA showed intermediate activity and was similar to that of ME-alachlorC More alachlor was adsorbed on the soil or remained encapsulated (not biologically available) after ME-alachlorL and ME-alachorA application compared to EC-alachlor. An intermediate amount of alachlor was adsorbed or remained inside the capsules when the ME-alachlorC formulation was applied. Greater amounts of alachlor were leached through a silty clay loam after EC-alachlor application compared to the three ME-alachlor formulations. Biologically available alachlor was not detected below 15 or 10 cm after application of EC- and ME-alachlor formulations, respectively. All alachlor formulations applied alone or in mixture with atrazine showed similar field persistence. Biologically available alachlor was not detected in the 0- to 10-cm soil depth 30 d after their application. All alachlor formulations applied alone gave excellent control of redroot pigweed and black nightshade, but only partial control of jimsonweed. None of the herbicide treatments showed any detrimental effect on corn, and all of them increased corn yield to the level of weed-free control.

Field experiments were conducted in 1986, 1987, and 1988 to evaluate imazethapyr rate and time of application on postemergence control of 24 weed species. Contour graphs were developed that predicted imazethapyr rates required for various levels of weed control based upon weed leaf number at application. Rates below the labeled rate (70 g ha−1) provided 90% or greater control of common cocklebur, smallflower morningglory, and smooth pigweed if applied to 3 true-leaf or smaller weeds and of barnyardgrass, seedling johnsongrass, and Palmer amaranth if applied while weeds were in the cotyledon or 1 true-leaf stage. A rate of 70 g ha−1 provided 90% control of large crabgrass in the 1 true-leaf stage. Entireleaf morningglory, red rice, pitted morningglory, and velvetleaf are not susceptible enough to imazethapyr for 90% or greater control to be obtained with rates lower than 70 g ha−1 at the 1 true-leaf growth stage. These data demonstrate how control data can be used for developing effective reduced-rate herbicide recommendations based on weed leaf number.

In 1992 and 1993, rimsulfuron alone at 17, 35, and 70 g ai/ha, and at 35 g/ha plus metribuzin at 280 g ai/ha, respectively, was evaluated PRE and POST for weed control in potato. Rimsulfuron at 35 g/ha PRE and POST controlled common lambsquarters and giant foxtail and when combined with 280 g/ha metribuzin, controlled common ragweed and jimsonweed. Rimsulfuron and rimsulfuron with metribuzin caused slight to moderate chlorosis in new terminal growth of potato but chlorosis disappeared within 3 wk. Potato height, tuber yields, and tuber quality were not affected by rimsulfuron alone or with metribuzin.

Interference between jimsonweed and soybean was investigated. Jimsonweed growing within the soybean row had little influence on vegetative characteristics of soybean during the first 12 wk of the growing season. The influence of an individual jimsonweed plant was first detected 10 wk after planting and extended 20 cm within the row. At harvest, interference extended 50 cm from individual jimsonweed plants, and yield within the 1.2 m of row surrounding a single jimsonweed plant was reduced 12%. Jimsonweed spaced 60 cm apart within the row reduced yield 18%. Soybean interference with jimsonweed growth increased steadily during the season, reducing the size of jimsonweed plants within the soybean row 80 to 93% compared with jimsonweed plants free of soybean interference. Jimsonweed grown within the soybean rows produced an average of 4900 seeds per plant whereas jimsonweed grown crop-free produced nearly 69 000 seeds per plant.

Field experiments were conducted in 1994 and 1995 to evaluate weed control in imidazolinone-resistant corn with postemergence applications of imidazolinone and sulfonylurea herbicides. Imazethapyr controlled 100% of redroot pigweed, jimsonweed, and eastern black nightshade. Control of fall panicum with imazethapyr was inconsistent, with control ranging from 42 to 85%. Imazethapyr provided less than 55% control of common lambsquarters and 43% of large crabgrass. Imazethapyr plus either atrazine, 2,4-D, or dicamba increased control of common lambsquarters compared to imazethapyr alone. Fall panicum control was > 95% with nicosufluron. CGA-152005 and MON 12000 did not control eastern black nightshade. In 1995, corn yield was greater with the hand-weeded check compared to all herbicide treatments. The greatest return over herbicide cost with imazethapyr was obtained with imazethapyr plus atrazine. Nicosulfuron plus CGA-152005 provided the greatest return over herbicide cost when averaged across years.

In field studies in 1991, 1992, and 1993, rimsulfuron at 26 and 35 g ai/ha, sequentially at 26 g/ha, at 26 g/ha plus metribuzin at 280 g ai/ha, and metribuzin at 280 g/ha were evaluated POST for weed control in transplanted ‘Agriset’ tomato. Common lambsquarters was controlled by rimsulfuron at 35 g/ha. Rimsulfuron plus metribuzin gave consistent control of common ragweed, but jimsonweed control was inconsistent and goosegrass control was generally low. Rimsulfuron treatments caused slight (< 12%) temporary injury to new terminal growth of tomato. Yield of tomato fruit was consistently high in the metribuzin, metribuzin plus rimsulfuron, and rimsulfuron sequential treatments. In greenhouse studies, giant foxtail and large crabgrass control by rimsulfuron was above 95 and 85%, respectively, but goosegrass was not controlled. Height of four tomato cultivars was not reduced, but dry weight of ‘Floradade’ and ‘Sunbeam’ was reduced by rimsulfuron.

Field studies were conducted to determine response of ‘Atlantic’ and ‘Fontenot’ potato varieties and eight weed species to rimsulfuron and metribuzin. Rimsulfuron was applied at 9, 18, 27, 35 and 70 g ai/ha and metribuzin at 69, 140, 210, 280 and 560 g ai/ha. Each herbicide was applied PRE or POST alone or in 1:8 combinations of rimsulfuron to metribuzin. Yield of either variety was not reduced by any treatment. Rimsulfuron applied PRE or POST at the suggested field use rate of 35 g/ha controlled smooth pigweed, redroot pigweed, ivyleaf morningglory, and common cocklebur 100%, common lambsquarters 90%, and jimsonweed 60%. Large crabgrass and fall panicum were controlled 92% by rimsulfuron at 35 g/ha. Reduced rates of 9 g/ha rimsulfuron plus 69 g/ha metribuzin, applied PRE or POST, controlled all weeds 100% except jimsonweed, fall panicum, and large crabgrass. For complete control of these weeds, rimsulfuron at 35 g/ha plus metribuzin at 280 g/ha was required.

In field experiments conducted from 1985 to 1987 in Mississippi and Arkansas, jimsonweed was successfully controlled with the fungus Alternaria crassa (Sacc.) Rands. Conidial applications of the fungus provided an average of 96% control in Mississippi, and 87% control in Arkansas. Mycelial formulations were less effective than conidial applications overall, but during periods of favorable environmental conditions, weed control provided by the mycelial formulations was similar to that provided by conidial preparations. These results indicate that Alternaria crassa has potential as a mycoherbicide for controlling jimsonweed.

Experiments were conducted in 1985 to 1987 to evaluate the effects of conventional and no-tillage systems on the weed control provided by clomazone applied preemergence in soybeans. The persistence of clomazone in soil of the two tillage systems was also determined. Increasing the clomazone rate from 0.8 to 1.4 kg/ha did not increase weed control. Clomazone controlled 80% or more of jimsonweed, velvetleaf, and giant foxtail. Common cocklebur control ranged from about 50 to 70% in no-till and from 80 to 90% in conventional tillage. Generally, soybean pods/plant and yields were lower from clomazone treatments than from handweeded treatments due to inadequate common cocklebur control. Over 40% of the clomazone applied did not reach the soil surface; it was either intercepted by wheat straw, volatilized, or both. Clomazone persisted longer in conventional tillage than in no-tillage in. However, in 1986, clomazone was equally persistent in the two tillage systems. The half-life of clomazone was 34 and 6 days in 1985 in conventional and no-tillage, respectively, and in 1986, 18 and 16 days in conventional and no-tillage, respectively. Significant clomazone concentrations were not found below 10 cm in the soil profile. Corn planted without tillage (no-till) approximately 1 yr after clomazone application was not injured and yields were not reduced due to prior clomazone use.

Common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), and jimsonweed (Datura stramonium L. ♯ DATST) are weeds that grow taller than soybeans [Glycine max (L.) Merr.] and compete for limited resources such as light. These weeds have an average area of influence of 0.5 m2, thus a density of 1 to 2 plants/m2 forms a full canopy of weed leaves above the soybeans that intercept 44 to 56% of the sunlight. Shade of 44 to 56% without weeds, placed above soybeans late in the season corresponding to times of weed shading, reduced soybean yield 19 to 26%. Since reported soybean yield reductions at weed densities of 0.7 to 2.5 plants/m2 were 18 to 54% for common cocklebur and 12 to 31% for jimsonweed and velvedeaf, it was concluded that most of the interference from jimsonweed and velvetleaf infestations in soybeans could be ascribed to competition for light, but only about one-half the interference was due to competition for light for common cocklebur. Soybean photosynthesis in the field was reduced about twice as much as soybean yield at equivalent levels of shading.