Three cultivars of wild rice (Zizania palustris L.) were grown with various densities of common waterplantain (Alisma triviale Pursh) established from seeds and from rootstocks during 1979 and 1980. Wild rice cultivars did not differ in their response to common waterplantain interference. Common waterplantain grown from seeds at densities up to 82/m2 did not significantly reduce wild rice yield. Common waterplantain established from rootstocks significantly reduced wild rice yield at densities as low as 3/m2. A density of 43/m2 reduced wild rice yield by 91%. The yield component most susceptible to interference from common waterplantain was panicles per plant. The number of seeds per panicle was reduced by densities as low as 11/m2 and seed weight was reduced by densities of 22/m2 or greater. Only a density of 43/m2 reduced the stand of wild rice. Common waterplantain established from rootstocks at a density of 17 plants/m2 did not reduce wild rice yield if removed by 7 weeks after planting. Interference from common waterplantain for 9 weeks or longer reduced wild rice yield by approximately 50%.

The development of 157 tanoak [Lithocarpus densiflorus (Hook. and Am.) Rehd.] and 130 Pacific madrone (Arbutus menziesii Pursh) sprout-clumps 1 to 6 yr after cutting or burning was studied on a range of sites in southwest Oregon. The width and area of sprout-clumps originating from trees ≥ 2-cm stem diameter at 1.4-m height of both species was related to the size of the parent stem and time since cutting (tanoak, r2 = 0.77 and 0.75; Pacific madrone, r2 = 0.84 and 0.83). The sprouting capacity of tanoak develops slowly, and 5 to 6 yr after cutting, sprout-clumps produced by small tanoak 40 to 50 yr old averaged only 37 cm in diameter. Prediction equations, along with stem-diameter distributions of these species in forest stands, can be used to estimate hardwood foliar cover up to 6 yr after cutting.

Benzoylprop ethyl [Ethyl N-benzoyl-N (3,4-dichlorophenyl)-2-amino-propionate] and WL 29761 [methyl-N-benzoyl-N-(3-chloro-4-fluorophenyl)-2-amino-propionate] were applied to wild oat (Avena fatua L.) in wheat (Triticum aestivum L. ‘Manitou’) to study the yield benefits occurring and the efficacy of the compounds on wild oat. Even though removal of the wild oat was at the later growth stages, benzoylprop ethyl and WL 29761 did produce significant yield increases at both rates tested. Efficacy on wild oat ranged from mediocre to virtually complete control. Crop tolerance was satisfactory throughout the study.

Cell suspension cultures of white clover (Trifolium repens L. ‘Regal Ladino’) were treated with 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], 2,4,5-TP [2-(2,4,5-trichlorophenoxy) propionic acid], and 2,4,5-TB [4-(2,4,5-trichlorophenoxy)butyric acid]. Cell population densities were monitored throughout the treatment period and herbicide remaining in the cells and culture medium was extracted and quantified at the termination of the treatment. Herbicide tolerance increased in cell populations which were conditioned by pretreatment with 2,4-DB and 2,4,5-T. However, 2,4-DB was rapidly degraded by all cell populations regardless of pretreatment. White clover cell suspension cultures treated with 2,4-D, 2,4-DB, 2,4,5-T, 2,4,5-TP and 2,4,5-TB metabolized the homologs, according to the following sequence: butyric acidåpropionic acidåacetic acid homologs. There was no difference in the rate of degradation of similar homologs of the 2,4-dichloro- and 2,4,5-trichloro- analogs.

Radicle length of barley (Hordeum vulgare L. ‘Larker’) seedlings was greatly reduced by the combination of the herbicide S-ethyl diisobutylthiocarbamate (butylate) applied in combination with the insecticide 2,2-dimethyl-2,3-dihydrobenzofuranyl-7-N-methylcarbamate (carbofuran). Corn (Zea mays L. ‘Michigan 400’) seedlings were not similarly affected. Carbofuran interacted with butylate to reduce synergistically the root and shoot growth of barley but not that of corn. The combination of these two carbamate pesticides synergistically increased respiration in barley. The basis for these interaction effects in barley appeared to be decreased metabolism of butylate and increased respiration in the presence of carbofuran. Although the same metabolism trend was apparent in tolerant corn, the butylate level was much lower since the absorption of butylate was reduced by the carbofuran seed treatment. The 14C from 14C-butylate preferentially accumulated in barley shoots and corn roots.

Leaching of dl-strigol at six rates between 0.3 and 4.5 kg/ha through columns of sandy loam soil was estimated using a witchweed [Striga asiatica (L.) Kuntze # STRLU] germination bioassay. After 21 days of leaching daily with 1.27 cm of simulated rainfall, about 86% of the applied chemical remained in the top 2.5 cm of the soil, about 6% in the zone between 2.5 and 7.5 cm, and less than 1% in the soil at depths between 7.5 and 30 cm. However, even with the lowest rate of the chemical application, sufficient dl-strigol was leached to a soil depth between 22.5 and 30 cm to cause most, if not all, of the witchweed seeds to germinate. These results suggest that dl-strigol has a potential for use as an effective tool for a witchweed control or eradication program. No significant degradation of the chemical occurred in moist soil during the 21-day period.

Retention, absorption, translocation, and metabolism of 2,4-D [(2,4-dichlorophenoxy)acetic acid] by common waterplantain (Alisma triviale Pursh. # ALSPA) at three growth stages were investigated to determine the basis for differential susceptibility of common waterplantain at different growth stages. Plants in the five-leaf and scape elongation stages retained more 2,4-D than plants in the early flowering stage. Absorption of 14C-2,4-D by the flower stalk was less than absorption by the treated leaves regardless of growth stage. The majority of the absorbed 14C translocated out of the treated plant part was recovered in the aerial portion of the plant younger than the treated leaves or in the corm, with greater movement of 14C into the corm at the older growth stages. Metabolism of 14C-2,4-D did not differ among the growth stages. The results suggest that the greater sensitivity of common waterplantain at the scape elongation stage to 2,4-D is due to greater translocation to the corm when compared to the five-leaf stage, and greater retention when compared to the early flowering stage.

Diffusion of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) through Mexico silt loam soil was measured in diffusion cells under laboratory conditions. Radiolabeled herbicide was extracted from each sample and counted by liquid scintillation. Fick's Second Law with a constant diffusion coefficient adequately describes trifluralin diffusion regardless of concentration or diffusing time. Solution diffusion increases directly with bulk densities to 1.1 g/cm3 and then decreases. Vapor diffusion is decreased approximately 50% for every 10% decrease in air-filled porosity. Vapor diffusion contributes the major portion of total diffusion at bulk densities of less than 1.2 g/cm3. For bulk densities between 1.2 and 1.4 g/cm3, the magnitudes of vapor and solution diffusion are similar.

Herbicides used in corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and soybeans [Glycine max (L.) Merr.] were applied in the spring and their persistence into late summer was determined during 1974 to 1976. Composite soil samples from the top 5 cm of field plots were taken each August and bioassayed in the greenhouse. Bioassay species used were winter wheat [Triticum aestivum L.) and soybeans for herbicides used in corn and sorghum, and winter wheat and white mustard (Brassica hirta Moench) for herbicides used in soybeans. Soil persistence of triazine herbicides caused more injury to winter wheat, soybeans, and white mustard than any other class of herbicides tested. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] showed the most soil persistence of the five triazines evaluated. At normal field application rates, herbicides other than the triazines showed little injury to the bioassay plants. Soil persistence of herbicides was further reduced when combinations of reduced rates of each herbicide were utilized. Herbicides used for spring applications in corn showed more soil persistence in August than did the herbicides for sorghum, while herbicides for soybeans generally were least persistent. Postemergence herbicide applications resulted in more injury in bioassay species than preplant incorporated or preemergence applications. Persistence of some herbicides will restrict certain options to the grower such as changing crops in case of crop failure, fall planting of winter wheat, double cropping, or certain crop rotations.

Organophosphate insecticides, which have the capacity to inhibit specific herbicide-degrading (cytochrome P450) enzymes, have been used to explore metabolic herbicide-resistance mechanisms in weeds. This study investigates the response of seven field-selected rigid ryegrass (Lolium rigidum Gaudin) populations to herbicides from three different sites of action in the presence or absence of the P450 inhibitor phorate. Phorate antagonized the thiocarbamate herbicides triallate and prosulfocarb (8-fold increase in LD50) in multiple resistant L. rigidum populations with resistance to three different site-of-action herbicides. In contrast, phorate synergized trifluralin and propyzamide in some populations, reducing the LD50 by 50%. Conversely, treatment with phorate had no significant effect on the LD50 for S-metolachlor or pyroxasulfone (inhibitors of very-long-chain fatty-acid synthesis). Phorate has diverse effects that are herbicide and population dependant in field-selected L. rigidum, suggesting P450 involvement in the metabolism of trifluralin and failure to activate thiocarbamate herbicides in these populations. This research highlights the need for implementation of diverse approaches other than herbicide alone as part of a long-term integrated strategy to reduce the likelihood of metabolism-based resistance to PPI herbicides in L. rigidum.

Research was conducted to determine the effect of starch encapsulation on soil dissipation and weed control with alachlor, metolachlor, and atrazine on an Estherville sandy loam in the field. Starch encapsulation increased persistence of alachlor in the surface 15 cm of soil compared to the emulsifiable concentrate formulation during the first 60 d after treatment More alachlor was detected 30 to 75 cm deep with emulsifiable concentrate than the starch-encapsulated formulation 30 d after treatment. Little alachlor was detected below 15 cm thereafter. Starch encapsulation also increased persistence of metolachlor in the surface 15 cm, but reduced concentrations at 15 to 30 cm compared to the emulsifiable concentrate 30 d after treatment. By 120 and 340 d after treatment, metolachlor concentrations at 15 to 30 cm were greater with starch-encapsulated than emulsifiable concentrate formulation. Starch encapsulation greatly increased atrazine persistence in the surface 15 cm compared to the dry flowable formulation. Although encapsulation increased atrazine concentration in the surface 15 cm, it reduced the concentration below 15 cm compared to the dry flowable formulation 30 and 60 d after treatment However, by 120 and 340 d after treatment, starch encapsulation often resulted in greater atrazine concentrations below 15 cm than the dry flowable formulation. Control of green foxtail and redroot pigweed with starch-encapsulated herbicides was similar or superior to the commercial formulations.

The noxious weed yellow starthistle is commonly controlled by the auxinic herbicide picloram. Induction of ethylene synthesis, epinasty, and reduction in shoot growth are typical symptoms of picloram treatment. Picloram did not induce ethylene evolution in the resistant accession RDW-1, though it caused a 250% increase in ethylene evolution in the susceptible wildtype SCI-1. The ethylene synthesis inhibitor aminoethoxyvinylglycine reduced the amount of ethylene induced by picloram in SCI-1 to control levels, but only reduced epinasty by 20% after 6 d. Aminoethoxyvinylglycine did not affect the reduction in shoot weight caused by picloram. The ethylene-releasing compound ethephon induced only a small amount of epinasty and had little effect on shoot weight in either accession. These results suggest that ethylene induced by picloram in wildrype plants plays only a minor role in the herbicidal effects of picloram. Furthermore, the resistance of the RDW-1 accession is not due to the lack of ethylene biosynthesis following picloram application to this accession.

Proso millet has become a major weed in North America during the past 20 yr. Experiments were conducted to assess the role of the soil seedbank in proso millet's success as a weed. Proso millet has at least eight distinct biotypes, all weeds, which exhibit a wide range of seedbank behavior. At one extreme, weed biotypes resembling crop varieties form transient seedbanks where all viable seed germinate or die before newly ripened seed enter the seedbank. In contrast, the black- and dark-red-seeded biotypes form persistent seedbanks that last several years in the soil. These latter seedbanks differ from those previously described in that there is always a fraction of the seedbank that is not capable of immediate germination. The black-seeded biotype of proso millet can establish a persistent seedbank quickly and that makes the weed very difficult to eradicate.

The 6-hydroxy derivative of picloram (4-amino-3,5,6-trichloropicolinic acid) is not on the main pathway of the soil microbial decomposition sequence for picloram. Rather it may be formed in very small amounts in a competing reaction. Decarboxylation of picloram cannot be the initial reaction in this sequence and, in fact, does not occur.

Laboratory experiments were conducted to determine the effects of optimum temperature, depth of planting, and simulated moisture stress on smellmelon germination and subsequent emergence. Smellmelon germination increased with temperatures ranging from 20 to 30 C, with the highest germination of 83% occurring at 30 C. Germination percentages decreased to 49 and 15% with temperatures of 35 and 45 C, respectively. Emergence from depths of 9 to 15 cm was less than 25% for all temperatures. Highest emergence from depths of 1 to 6 cm occurred with 30 and 35 C. Smellmelon germination was reduced from 81 to 61% when the osmotic potential was reduced to − 0.2 MPa and was further reduced to 48 and 7% with solutions of − 0.4 and − 0.6 MPa, respectively. Field studies were conducted to evaluate smellmelon biomass production in 1999 and 2000 when competing with cotton (Gossypium hirsutum L.). End of season-smellmelon leaf area values were 16,280 and 22,053 cm2 per plant in 1999 and 2000, respectively, or 67 and 117 g of leaf dry weight per plant for 1999 and 2000, respectively. In 1999, smellmelon produced 60 g of stem dry weight per plant, and it increased to 75 g in 2000. Optimum germination temperature for smellmelon coincides with those for many annual crops. These data indicate that smellmelon germination and emergence can occur under a wide variety of environmental conditions. On the basis of biomass production values, smellmelon may also be a very efficient competitor with many cultivated crops.

Other research has shown that a roller applicator can selectively control weeds that protrude above the crop, conserve over 80% of the herbicide, eliminate spray drift and splash, and obviate recirculation of the spray solution. The carpet on the roller applicator must be moist enough to transfer ample herbicide to the weeds it contacts but dry enough to prevent dripping of herbicide solution from the carpet. An electronic moisture sensor and solenoid valve system was designed to permit operation of the roller applicator through various weed densities while automatically maintaining a proper level of herbicide solution in the carpet of the roller.

Wind-erodible soil sediments are classified as aggregates and particles < 1 mm in diameter. Aggregate size has been reported to influence pesticide retention and behavior in the soil. Atrazine sorption and desorption isotherms were determined using batch equilibration methods for six aggregate sizes of Barnes loam (fine-loamy, mixed, superactive, frigid Calcic Haplodol) and Brandt silty clay loam (fine-silty, mixed, superactive, frigid Calcic Haplodol) soils. Aggregate and particle sizes used in this study ranged from < 0.11 to > 1.7 mm, and atrazine concentrations ranged from 0.65 to 39.2 μmol L−1. The Kf values for the isotherms were calculated using the Freundlich equation. In the Barnes loam, Kf values were strongly positively correlated to aggregate size, particle size, and organic carbon (OC) content (P = 0.01 for each parameter), whereas in the Brandt silty clay loam, Kf values were less correlated to size and OC content (P ≥ 0.1) but were better correlated to clay content and estimated specific surface area (P = 0.05 for each parameter). Desorption was hysteretic with about 18% more atrazine desorbed from smallest than from largest size fractions. At a concentration of 13.0 μmol L−1, the amount desorbed ranged from 9 to 13.7% of the initial amount of adsorbed atrazine after 5 d, whereas at 39.2 μmol L−1, the amount desorbed ranged from 10.3 to 16% of the amount adsorbed. These data indicate that wind-erodible size aggregates and particles could be a source of herbicide contamination of surface water.

Greenhouse and laboratory studies were conducted to determine kochia resistance to a spectrum of acetolactate synthase (E.C.4.13.18) (ALS)-inhibiting herbicides. The chlorsulfuron-resistant biotype plants were resistant to six herbicides: triflusulfuron, thifensulfuron, halosulfuron, imazamethabenz, chlorsulfuron, and nicosulfuron. But, the resistant biotypes showed sensitivity similar to the susceptible biotypes to three herbicides: metsulfuron, imazethapyr, and imazaquin. The resistant biotypes were slightly less sensitive to primisulfuron, chlorimuron, and flumetsulam than the sensitive biotypes. The I50 values for 50% inhibition of the ALS enzyme indicated that the resistant biotype was 22, 18, and 16 times more resistant to primisulfuron, chlorsulfuron, and thifensulfuron than the susceptible biotype. In contrast, the I50 ratios (resistant/susceptible) were 3, 2, and 1 for flumetsulam, nicosulfuron, and imazethapyr, respectively. The altered ALS enzyme system of the resistant biotype showed a differential response for the ALS-inhibiting herbicides. Addition of a mixed function oxidase inhibitor, piperonyl butoxide (PBO) at 2 kg ha−1, to primisulfuron and thifensulfuron increased visual injury and reduced plant height of the chlorsulfuron-sensitive kochia biotype plants. The addition of PBO to primisulfuron enhanced visual injury of the resistant biotype at low rates of primisulfuron.

Experiments were conducted to determine the inheritance of resistance in a Wisconsin accession of eastern black nightshade to acetolactate synthase (ALS) inhibitors. ALS-inhibitor–susceptible (S) and ALS-inhibitor–resistant (R) plants were crossed (S × R), and inheritance was characterized in F1 and F2 generations. Inheritance was characterized further in progeny of reciprocal crosses (R × S) and backcrosses (BCs) (S × F1 and R × F1). In dose–response experiments, three- to four-leaved F1 plants were intermediate in response to imazethapyr compared with parent R and S plants. The imazethapyr ED50 value (the effective dose that reduced shoot dry biomass by 50% compared with nontreated plants) was 99.6 ± 13.6, 32.5 ± 8.9, 24.5 ± 3.3, and 0.6 ± 0.1 g ae ha−1 for R, F1 (R × S), F1 (S × R), and S plants, respectively. Similarly, the response of in vivo ALS activity in F1 plants to imazethapyr was intermediate compared with that of parent R and S plants. To differentiate among phenotypes in F2 generations and in BC generations, the response of three- to four-leaved plants to imazethapyr applied in a single dose was scored 21 d after treatment as R (no imazethapyr symptomology), S (total plant necrosis), or intermediate (I, severely stunted plants with chlorotic and twisted leaves at the apical meristem). R, I, and S phenotypes segregated in a 1:2:1 ratio in the F2 generation. S and I phenotypes segregated in a 1:1 ratio in progeny from F1 BCs to the S parent. Similarly, R and I phenotypes segregated in a 1:1 ratio in progeny from BCs to the R parent. Eastern black nightshade resistance to ALS inhibitors is associated with a single, nuclear, incompletely dominant allele, which codes for an insensitive form of the target ALS enzyme.

Weed populations, weed control with imazethapyr, and Glycine max yields were affected by a 4-yr history of different weed control practices. A range of chemical and mechanical practices were applied in separate field experiments initiated under high and low weed densities. In the high-density experiment, plots kept weed free for 4 yr averaged 24 Setaria faberi plants m−2 compared with 200 to 600 plants m−2 with the various weed control treatments. In plots with a history of mechanical control, weeds not controlled by imazethapyr reduced G. max yield by 340 kg ha−1 compared with plots that were kept weed free during the same period. In the low-density experiment, weed control history had less effect on weed densities. For example, S. faberi densities ranged from 19 plants m−2 for the weed-free plots to 195 plants m−2 with mechanical control. Weed control history had little effect on weed control with imazethapyr or G. max yields in imazethapyr-treated plots. While weed-free conditions for 4 yr greatly reduced weed densities, imazethapyr application still increased G. max yields 22% in the low-density experiment and 51% in the high-density experiment. Differences in densities of individual annual broadleaf species also developed in response to weed control history in both experiments.