We investigated the toxicity of MSMA (monosodium methanearsonate), fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], and propanil (3′,4′-dichloropropionanilide) to soybeans [Glycine max (L.) Merr. ‘Hill’]. Over-the-top treatments were applied to soybeans at four stages of growth using MSMA at 0.1, 0.2, and 0.4 kg/ha, propanil at 0.2, 0.4, and 0.9 kg/ha, and fluometuron at 0.05, 0.1, and 0.2 kg/ha. Each herbicide caused 10 to 30% soybean injury at the lowest rate, and 40 to 70% injury at the highest rate. Soybeans treated earliest in the growing season usually recovered from injury better than soybeans treated later in the season. Soybean yields were reduced 50 to 70% by MSMA at 0.4 kg/ha and 25 to 35% by propanil at 0.9 kg/ha. Yield losses increased with stage of soybean maturity at time of treatment. Fluometuron at 0.2 kg/ha significantly reduced yield only when applied to soybeans with 7 or 10 trifoliolates or in midbloom.

Greenhouse and field experiments were conducted to determine effects of light, water, and chlorsulfuron on growth of Canada thistle. In the greenhouse, shoot and root dry weight, leaf area, and number of inflorescences decreased as light and water levels decreased. In the field, shoot and root dry weight, leaf area, and number of Canada thistle inflorescences were positively correlated with light intensity from 1832 to 30 μmol m−2 s−1 photosynthetic photon flux density (PPFD). The greatest effect of light was on inflorescence production which was eliminated at 30 μmol m−2 s−1 (PPFD). The combined effect of water stress and chlorsulfuron decreased root and shoot growth but did not eliminate it.

The potential of mourning doves (Zenaida macroura L.) as dispersers of leafy spurge (Euphorbia esula L. # EPHES) seeds was investigated by examing digestive tract contents and feces. Very few intact seeds passed through the digestive systems of wild or captive adult mourning doves. An average of less than one intact leafy spurge seed/g was recovered from fecal material found in dove nests. These results suggest that adult mourning doves are primarily consumers of leafy spurge seeds and rarely act as dispersal agents. It appears that dispersal is only possible when seeds passing through the digestive tracts of nestlings are deposited in the nest and the nest later falls.

The penetration, translocation, and metabolism of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} in ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. ♯3 IPOHE], velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), and soybean [Glycine max (L.) Merr.] were studied. An application to plants of 0.3 kg ai/ha mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} 0, 3, 5, or 7 days prior to treatment with 14C-acifluorfen often altered one or more of the physiological processes under study. Pretreatment of ivyleaf morningglory with mefluidide 3, 5, or 7 days prior to application of 14C-acifluorfen increased penetration of 14C and decreased metabolism of acifluorfen, while translocation was unaffected. All mefluidide treatments increased penetration of 14C-acifluorfen into velvetleaf, while the 3-, 5-, and 7-day pretreatments decreased acifluorfen metabolism. Penetration of acifluorfen into common cocklebur was unaffected by pretreatment with mefluidide. However, the 7-day mefluidide pretreatment of common cocklebur increased translocation of 14C into the upper leaves and decreased acifluorfen metabolism. Penetration and translocation of the radiolabel from 14C-acifluorfen in soybean was unaffected by pretreatment with mefluidide. Metabolism of acifluorfen by soybean was decreased by the 0-day mefluidide treatment but was unaffected by the 3-, 5-, or 7-day mefluidide pretreatment.

Sicklepod (Cassia obtusifolia L. ♯ CASOB) was planted at six densities (0 to 39.4/m2) and six durations of competition (0 to 10 weeks after seeding) in lima beans (Phaseolus lunatus L. cv. ‘Jackson Wonder’). The yield of green lima beans was inversely proportional to the density of sicklepod. In general, weed densities at 2.7 to 10.8 sicklepod/m2 did not significantly reduce yields, but higher populations frequently did. The average yields generally decreased if the duration of competition exceeded six weeks.

The dissipation of sodium azide (NaN3) from soil was significantly affected by pH, soil moisture, and relative humidity (RH). Loss was more rapid from acid than from alkaline soils. Moist soil (20 to 60% field capacity) or air dry soil in a moist environment (100% RH) lost NaN3 more rapidly than air dry soil in a dry (0% RH) environment. However, dissipation was decreased when soil moisture exceeded 60% field capacity. Degree of leaching and phytotoxicity of NaN3 was not affected by soil pH. Bioassay studies indicated that 10 ppm NaN3 in the soil significantly reduced germination and growth in plant species tested. At concentrations of NaN3 below 10 ppm, plant germination was often delayed but normal growth occurred after NaN3 dissipation.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 10−5 M applied to etiolated corn (Zea mays L. ‘Michigan 500′) seedlings 6 or 12 hr before the isolation of chromatin from the roots markedly reduced ribonucleic acid (RNA) synthesis supported by the chromatin. The addition of Escherichia coli RNA polymerase failed to overcome the inhibition. Trifluralin increased the melting temperature of the chromatin. The presence of trifluralin during the isolation and reaction procedure inhibited RNA synthesis indicating possible trifluralin binding to the chromatin with subsequent reduction of template availability for transcription. Trifluralin did not inhibit chromatin activity in soybean [Glycine max (L.) Merr. ‘Hark’] seedlings.

Pyrithiobac and imazaquin are persistent herbicides used in the midsouthern region of the United States. Certain rotational crops are extremely sensitive to each herbicide. Field studies were established near Brooksville, MS, and St. Joseph, LA, to examine crop injury from the previous year's application of pyrithiobac and imazaquin. In Mississippi, 690 g ai ha−1 of each herbicide was applied as a preplant-incorporated carryover treatment. The subsequent year, pyrithiobac-treated areas were planted with soybean, corn, and grain sorghum. Imazaquin-treated areas were planted with cotton, corn, and grain sorghum. In plots adjacent to the carryover treatment, pyrithiobac or imazaquin was applied at rates ranging from 0 to 173 g ha−1 as in-field bioassay plots. In Louisiana, pyrithiobac was applied at 70 and 240 g ha−1 as a postdirected broadcast layby treatment in cotton. The subsequent spring, pyrithiobac-treated areas were planted to corn. Assay rates of pyrithiobac ranging from 0 to 140 g ha−1 were established in areas adjacent to the carryover treatment. Grain sorghum was most sensitive to pyrithiobac soil residues, followed by corn and then soybean. Cotton was the most sensitive crop to imazaquin soil residues, followed by corn and then grain sorghum. Residual amounts of pyrithiobac and imazaquin were approximately 15 and 24 g ha−1, respectively. The approximated half-life of pyrithiobac and imazaquin was 61 and 71 d, respectively. Pyrithiobac applied at 280 g ha−1 as a layby treatment the preceding year injured corn and reduced yields in 1 of 2 yr. Pyrithiobac at 70 g ha−1 did not affect corn in either year. The difference in persistence between the 2 yr was attributed to reduced precipitation and lower soil temperatures in the year with observed carryover. Injury and yield reduction observed in the second year of the study correspond to an approximate pyrithiobac half-life of 60 d.

Field trials were conducted in 1986 and 1987 to determine the effects of moisture on cinmethylin activity. The herbicide was applied preemergence at rates of 0.0, 0.3, 0.6, and 0.9 kg ai ha−1 to both dry and moist sandy loam soil, followed by varying irrigation regimes. Plant species used in the study included soybean, snap bean, cotton, peanut, and cucumber. Peanut was the most tolerant to cinmethylin, followed by cotton, soybean, snap bean, and cucumber. When cinmethylin was applied to a moist soil, less crop injury resulted than when it was applied to a dry soil. If 7.6 cm of water was applied shortly after cinmethylin application to a dry soil, severe crop injury occurred. When 2.5 cm of irrigation was applied within 8 h or at 5 days after cinmethylin application to a dry soil, crop injury was reduced when compared to applying 7.6 cm irrigation.

Field studies were conducted at Morden, Manitoba, in 1994 and 1995 to investigate the effect of crop growth stages on canola and sunflower tolerance to sublethal doses of thifensulfuron:tribenuron (2:1). Thifensulfuron:tribenuron at doses of 0, 0.23, 0.45, 0.9, 1.8, and 3.6 g ai ha−1 plus a nonionic surfactant at 0.5% v/v were applied to canola and sunflower at the two- to three-leaf, four- to five-leaf, and six- to seven-leaf stages. Crop leaf stage at the time of application affected tolerance of both crops to thifensulfuron:tribenuron. Crop injury was lowest, and flowering, seed yield, and seed oil content were least affected when low doses of thifensulfuron:tribenuron were applied at the two- to three-leaf stage. At the highest dose, there was little practical difference among growth stages since yield of both crops was severely reduced. Producers with drift-affected canola or sunflower can expect less effect on crop yield when thifensulfuron:tribenuron injury occurs during early crop growth.

Laboratory studies were conducted to evaluate flumetsulam adsorption and mobility in seven Mississippi soils of different organic matter content, pH, and texture. Adsorption isotherms were determined for all soils using a 1:1 (soil: water) technique. In six of seven soils, Freundlich n constants were close to unity, suggesting a partitioning-like adsorption mechanism for flumetsulam. Mobility was examined using packed soil columns. 14C-flumetsulam recoveries in leachate ranged from 1 to 70% and were influenced by both organic matter content and soil pH. However, the effects of organic matter content and soil pH were not independent. Consequently, clear relationships between flumetsulam mobility and either organic matter content or soil pH were not established across all soils. However, among soils of similar pH (7.5 ± 0.3), mobility decreased linearly (R 2 = 0.75) as organic matter content increased from 0.7 to 3.6%. Across soils with similar organic matter content (3.9 ± 0.3%), mobility increased linearly (R 2 = 0.98) as soil pH increased from 5.3 to 7.2. Net adsorption constants (K d ) provided a more accurate assessment of flumetsulam mobility across all soils than K oc .

Canada thistle [Cirsium arvense (L.) Scop.] and field bindweed (Convolvulus arvensis L.) were controlled in asparagus (Asparagus officinalis L. ‘Mary Washington’) fields by repeated applications of dicamba (3,6-dichloro-o-anisic acid) at 0.6 kg/ha or 2,4-D [(2,4-dichlorophenoxy)acetic acid] + dicamba at 1.1 + 0.3 or 1.1 + 0.6 kg/ha. Applications of 2,4-D + dicamba at 1.1 + 0.6 kg/ha in early May and again in mid-June controlled 97% of the Canada thistle in asparagus fields. A third application about August 1 was required to give similar control of field bindweed. Rates of dicamba exceeding 0.6 kg/ha injured the asparagus.

The effects of weed species on the anatomy of roots of cabbage (Brassica oleracea L.) and tomato (Lycopersicum esculentum Mill.) were studied. One crop seed was placed on agar in a test tube to germinate in association with four additional seeds of a weed species. All the weed species caused abnormal changes in the anatomy of cabbage and tomato roots. Jimsonweed (Datura stramonium L.) inhibited cell elongation and caused disruption of epidermis and disorganization of the root tissue in cabbage. Green foxtail (Setaria viridis (L.) Beauv.) also caused disruption of cabbage roots. Mustard (Brassica kaber DC.) and velvetleaf (Abutilon theophrasti Medic.) induced enlarged parenchyma cells of cabbage roots. The combination of tomato and jimsonweed resulted in disorganized root tissue or large roots with large parenchyma cells.

Studies were conducted at Grand Rapids, MN, to determine the effect of giant burreed (Sparganium eurycarpum Engelm. # SPGEU) planted at 6, 12, and 24 corms/m2 on wild rice (Zizania palustris L. ‘K2′) growth and yield. Giant burreed, a spreading perennial, had shoot densities of 21, 29, and 42/m2 at harvest for the 6, 12, and 24 corms/m2 treatments, respectively. Wild rice yield and panicle number were reduced approximately 60% when giant burreed shoot density was 40/m2 or higher when compared to the weed-free control. Giant burreed did not interfere with nutrient uptake of wild rice on a whole-plant basis, and increased N fertilizer application did not reduce losses in dry weight. Giant burreed reduced penetration of photosynthetically active radiation (PAR) from 2 to 35% in the wild rice canopy from the early tillering to the anthesis stage of wild rice development. In growth chamber studies, wild rice dry weight and panicle number were reduced by 46 and 65%, respectively, when wild rice was shaded for 12 weeks and compared to a full light treatment. Reduction of PAR penetration into the wild rice canopy appears to be the major mechanism of giant burreed interference with wild rice.

An intensive survey of two farmer-managed corn and soybean fields in eastern Nebraska was conducted to investigate parametric sequential sampling of weed seedling populations using a multistage procedure to estimate k, of the negative binomial distribution. k is a nonspatial aggregation parameter related to the variance at a given mean value. Mean weed seedling density ranged from 0.18 to 3.11 plants 0.38 m−2 (linear meter of crop row) based on 806 sampling locations. The average value of k, derived from 200 multistage estimation procedures, ranged from 0.17 to 0.32. A sequential sampling plan was developed with the goal of estimating the mean with a coefficient of variation (CV) of 10, 20, 30, and 40% of the sample mean. A sampling plan was also constructed to estimate the mean within a specified distance H of the true mean (H(x̄)= 0.10, 0.50 and 1.0 plants 0.38 m−2) with 80, 85, and 90% confidence. Estimating mean weed seedling density within a specified CV of the true mean CV(x̄) using parametric sequential sampling techniques was superior to estimating the mean within a specified distance (H(x̄)) of the true mean when considering the frequency of sampling and probability of error, especially at intermediate k values. At a k: value of 0.32 and 0.25, the difference between the actual CV(x̄) obtained from sampling and the CV(x̄) specified by the sampler was minimal. However, the accuracy of weed seedling density estimates was reduced with decreasing k values below 0.25, especially as the specified CV(x̄) increased.

Greenhouse and laboratory studies were conducted to determine the effects of bentazon on the crop safety, efficacy, foliar absorption, and translocation of thifensulfuron when it is applied to soybean, velvetleaf, and common lambsquarters. A metabolism study was conducted on soybean. Thifensulfuron applied at 1.1 g ai ha−-1 with 28% urea ammonium nitrate (2.5% v/v) and BAS-0904805 (Dash) adjuvant (0.63% v/v) reduced the growth of velvetleaf and common lambsquarters by an average of 91 and 84%, respectively. The addition of 420 g ai bentazon ha−-1 had no effect on thifensulfuron efficacy in the weed species. Soybean dry weights were decreased by 58% when thifensulfuron was applied at 2.2 g ha−-1 but were decreased by only 36% when bentazon, at 420 g ha−-1, was added. In the absorption study, the addition of bentazon reduced foliar absorption of 14C-thifensulfuron into velvetleaf and common lambsquarters 8 and 24 h after treatment (HAT), but absorption into soybean was not affected. Bentazon reduced the translocation of 14C from thifensulfuron out of the treated leaves of velvetleaf and common lambsquarters by at least 16 and 11%, respectively, beyond 24 HAT. Soybean translocated 18, 29, and 26% of absorbed 14C out of the treated leaflets 24, 72, and 168 HAT, respectively. These translocation values were reduced to 7, 12, and 11%, respectively, when bentazon was tank-mixed with thifensulfuron. Soybean metabolized 35% of recovered 14C-thifensulfuron by 24 HAT. Addition of bentazon did not change this level of metabolism. These studies suggest that the physiological basis for the decrease of soybean injury from thifensulfuron, when it is tank-mixed with bentazon, is decreased thifensulfuron translocation.

Applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.1 kg/ha at the start of each growing season severely damaged established alfalfa (Medicago sativa L. ‘Beaver’) and reduced seed yield 32% over a 4-yr period. Dandelion (Taraxacum officinale Weber) populations were reduced but perennial sowthistle (Sonchus arvensis L.) increased in frequency. Dichlobenil (2,6-dichlorobenzonitrile) applied at 2.1 kg/ha controlled both dandelion and perennial sowthistle. Alfalfa was damaged initially but rapid recovery resulted in an increase in seed yield in 2 yr out of 4. Terbacil (3-tert-butyl-5-chloro-6-methyluracil) applied at 1.1 kg/ha also controlled dandelion and perennial sowthistle. No alfalfa damage was evident and seed yields were increased 34% over a 3-yr period. Seed yield increased 30% where asulam (methyl sulfanilylcarbamate) was applied at 4.5 kg/ha, but there was no visible effect on the growth of either alfalfa or weeds. Simazine [2-chloro-4,6-bis (ethylamino)-s-triazine], propham (isopropyl carbanilate) + PCMC (p-chlorophenyl-N-methyl carbamate), pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide], and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], did not affect alfalfa seed production significantly, although simazine and diuron did reduce dandelion populations.

Evaluations were made of the α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) distribution patterns produced by eight incorporating implements. The power rotary cultivator concentrated the trifluralin in the top inch when operating at a 4-inch depth, while the disk, operated at the same depth, concentrated the trifluralin at a point 2 to 3 inches below the surface. All the remaining implements resulted in more than 80% of the recovered trifluralin in the top inch, except for isolated treatments with the Richardson and Lilliston tools. Surface applications resulted in less trifluralin recovery than from any implement. The disk resulted in the highest recovery and was two to three times greater than the recovery from the surface application. The recovery from the Richardson, Lilliston, and Ro-Wheel was 1.5 to 2 times greater than the recovery from the Mix-A-Product, field cultivator, and spike harrow.

Greenhouse and field trials were conducted at the Aberdeen Research and Extension Center to determine the effect of hairy nightshade competition on two potato varieties with different growth habits. Greenhouse replacement trials included treatments of three plants total in each pot with potato : hairy nightshade ratios of 3 : 0, 2 : 1, 1 : 2, or 0 : 3. Varieties tested were ‘Russet Burbank’ and ‘Russet Norkotah’. Greenhouse-grown hairy nightshade (cotyledon to one-leaf stage) were transplanted into pots earlier than or at the same time as potato plant emergence. As the number of Russet Burbank plants per pot decreased, potato plant biomass dry weight (average per plant) increased, regardless of hairy nightshade number or transplant time. When hairy nightshade were transplanted before Russet Norkotah emergence, potato plant biomass dry weight per plant was similar, regardless of potato : nightshade ratio. Field trials were conducted with Russet Burbank and Russet Norkotah in 2004 and 2005. At potato emergence, greenhouse-grown hairy nightshade plants (one- to two-leaf) were transplanted in between potato rows at densities of 0, 1, 2, or 3 plants m−1 row, and solid-seeded at approximately 100 plants m−1 row. Hairy nightshade biomass, stem and berry number, and seeds per berry were reduced by competition from Russet Burbank due to the amount and duration of shading, as compared with Russet Norkotah. Russet Burbank U.S. No. 1 and total tuber yields in plots with 1 hairy nightshade plant m−1 row were similar to weed-free control yields, whereas yields in plots with 2, 3, or 100 m−1 row were reduced in comparison. In contrast, Russet Norkotah yields were reduced when only 1 hairy nightshade plant m−1 row was present. Overall, Russet Norkotah were less competitive with hairy nightshade than Russet Burbank in both the greenhouse replacement and field trials.

The escalating evolution of weed species resistant to acetolactase synthase (ALS)-inhibitor herbicides makes alternative weed control strategies necessary for field crops that are dependent on this herbicide group. A fully integrated strategy that combined increased crop seeding rates (2X or 4X recommended), mechanical weed control with a minimum-tillage rotary hoe, and reduced-rate non–ALS inhibitor herbicides was compared with herbicides, rotary hoe, and seeding rates alone as a method of controlling ALS inhibitor–tolerant Indian mustard as a model weed. The full-rate herbicide treatment had the lowest weed biomass (98% reduction) and the highest yield of all treatments in 3 of 4 site-years, regardless of seeding rate. The fully integrated treatment at the 4X seeding rate had weed suppression rates equal to the full herbicide treatment at the recommended seeding rate. The fully integrated and reduced-rate herbicide treatments at the 4X seeding rate reduced weed biomass by 89% and 83%, respectively, compared with the control at the recommended seeding rate. The rotary hoe treatment alone resulted in poor weed control (≤38%), even at the highest seeding rate. Fully integrated and reduced-rate herbicide treatments at 2X and 4X seeding rates had yields equal to those of the full herbicide treatment at the recommended seeding rate. Partially or fully integrated weed control strategies that combine increased crop seeding rates and reduced-rate non–ALS inhibitor herbicides, with or without the use of a rotary hoe, can control weeds resistant to ALS-inhibitor herbicides, while maintaining crop yields similar to those achieved with full-rate herbicides. However, combining increased seeding rate, reduced-rate herbicides, and mechanical rotary hoe treatment into a fully integrated strategy maximized weed control, while reducing reliance on and selection pressure against any single weed control tactic.