We evaluated the use of ornamental plants as phenological indicators for predicting giant foxtail emergence and compared their performance with predictions based upon Julian day, cumulative growing degree–days (GDD), and the WeedCast program. From 1997 to 2001, we monitored giant foxtail emergence in a field experiment with and without fall and spring tillage to estimate the dates of 25, 50, and 80% emergence; we also recorded dates of first and full bloom of 23 ornamental plant species. Dates of weed emergence and ornamental blooming for 1997 to 2000 were compiled in a phenological calendar consisting of 54 phenological events for each year, and events were ordered by average (1997 to 2000) cumulative GDD (January 1 start date, 10 C base temperature). Bloom events occurring just before the giant foxtail emergence events were chosen as the phenological indicators for 2001. The Julian day method used the average (1997 to 2000) dates of foxtail emergence to predict 2001 emergence. The GDD model (October 1 start date, 0 C base temperature) was chosen by determining the combination of start date and base temperature that provided the lowest coefficient of variation for the 1997 to 2000 data. The WeedCast prediction was generated using local soil and environmental data from 2001. The rank order of the 54 phenological events in 2001 showed little deviation from the 4-yr (1997 to 2000) average rank order (R2 = 0.96). The phenological calendar indicated that, on average, 25% of giant foxtail seedlings had emerged when red chokeberry was in first bloom, and 80% of seedlings had emerged around the time multiflora rose was in full bloom. We compared the phenological calendar predictions for 25, 50, and 80% emergence with those based on Julian day, cumulative GDD, and WeedCast. The average deviation in predictions ranged from 4.4 d for the phenological calendar to 11.4 d for GDD. In addition to being generally more accurate, the phenological calendar approach also offers the advantage of providing information on the order of phenological events, thus helping to anticipate the progress of emergence and to plan and implement management strategies.

Perennial weeds constitute a serious problem in Greek cotton-growing areas, as they strongly competing against the crop and downgrade the final product. Monitoring weeds at a regional scale and relating their occurrence with abiotic factors will assist in the control of these species. Purple nutsedge, field bindweed, bermudagrass, and johnsongrass were studied in cotton crops for three consecutive growing seasons (2007 through 2009) in a large area of central Greece. Weed densities and uniformities per sampling site were assessed in relation to soil and climatic data. Abundance index (AI), which is highly dependent on abiotic factors, was also estimated, and revealed purple nutsedge to the most persistent and damaging species among the recorded weeds. Field bindweed showed the highest correlation with soil properties and especially with clay content. Furthermore, correlation analysis was used over the sampling years in order to assess the stability of weed occurrence in the sampling sites. Purple nutsedge, field bindweed, and bermudagrass proved to be stable in location and intensity. The weed density spatial distribution was evaluated by using local indicators of spatial autocorrelation (LISA) statistics, and was mapped by ordinary kriging and co-kriging interpolation methods. Only 1 to 3 spatial outliers were identified in each 1 of the 3 yr. Between the two interpolation methods co-kriging delivered better results for field bindweed and purple nutsedge, indicating that soil data could improve the estimation of weed occurrence. These co-kriging interpolated weed maps would be a very useful tool for decision makers in taking appropriate weed control measures.

The knowledge of weed distribution in a field is a key factor to manage weeds effectively. The feasibility of using weed distribution maps for site-specific weed control will largely depend on the stability of the spatial distribution of the populations. Seed banks are the most reliable way of telling the area's weediness, but the effect of regular herbicide applications on its stability is largely unknown. A field experiment was conducted during 3 yr in a winter wheat field under herbicide treatments with the aim of studying the seed bank's spatial distribution of prostrate knotweed and corn poppy and the spatiotemporal stability of their populations. Soil samples were taken each year on the same locations, and seed abundance was measured by germination in greenhouse. Both species accounted for more than 10% of the broad-leaved weed seed bank and they were selected for further analysis. Prostrate knotweed seed-bank density decreased 76% and corn poppy 88% in 3 yr. Spatial distribution was described by spherical isotropic semivariograms. Distance of spatial dependence (range) of prostrate knotweed and corn poppy decreased 33 and 11% respectively, and the spatial variability (sill) decreased 96 and 99%. Yearly spatial seed distribution was compared for each species and no temporal stability was observed over a 3-yr period. The lack of stability was attributed to the important decrease of seed density over time and the increase in the short-range variability (nugget). However, for prostrate knotweed, the location of minima and maxima were roughly the same between years, allowing farmers to extend the period of use of the weed distribution maps. Although spatial distribution of seed banks can be affected by processes that promote fast changes in the densities of weed populations, this fact does not mean that weed distribution maps could not be used in consecutive seasons.

The diversity of resistance among wild oat collected before and after commercial introduction of imazamethabenz, difenzoquat, diclofop, fenoxaprop-P, sethoxydim, and tralkoxydim was evaluated. Wild oat sampled in 1964 and 2000 from the Red River Valley of Minnesota and North Dakota were screened for resistance. Nearly 43% of the 1964 collections were susceptible (S) to all six herbicides, whereas only 9% were S by 2000. The frequency of resistance in 2000 compared with 1964 increased for all six herbicides, and 27 phenotype response groups to the six herbicides occurred in 2000 vs. 14 phenotype response groups for the 1964 collection. The proportion of resistant (R) plants increased faster for the aryloxyphenoxypropionate (APP) herbicides, diclofop and fenoxaprop-P, than for the cyclohexanedione (CHD) herbicides, sethoxydim and tralkoxydim. High diversity of resistance responses was observed in wild oat to acetyl-coenzyme A carboxylase–inhibitor herbicides, suggesting that there may be multiple APP herbicide– or CHD herbicide–specific resistance mechanisms in addition to those that confer cross-resistance. The trend of resistance response generally indicates that increased exposure to herbicides in wild oat may confer resistance to newly introduced but unrelated herbicides.

Pitted morningglory seed were collected in the fall of 2003 from Blackville, SC, and 2004 from Pendleton, SC, to assess the effect of After-Ripening and burial on light and temperature requirements for germination. Pitted morningglory germination was evaluated over a 12-mo period after maturation. Germination was neither stimulated by red light or inhibited by far-red light, nor was it reversible by red or far-red light. Light was not essential for germination of buried seed. Direct exposure to sunlight prevented germination of recently mature seed, but not once seed had sufficiently after-ripened. Pitted morningglory was capable of germination in darkness over a wide range of constant and fluctuating temperatures immediately after maturation. Germination in response to temperature varied with time of year after maturation, with the population from Pendleton having increased germination in May. Thermal fluctuations increased germination of both populations at suboptimal temperatures. Thermal amplitude regulation of germination varied over time and appeared to play a more important role in germination of after-ripened seed than recently mature ones. The ecological significance of changes in germination requirements with After-Ripening is discussed.

The advancement of biological weed control is limited by the slow development of effective, broader-spectrum biological control agents. Protoplast fusion was carried out between the Helminthosporium gramineum subsp. echinochloae (HGE) strain, HM1, and Curvularia lunata (CL) to breed new strains with improved biocontrol efficiency. The HM1 strain was derived from HGE by ultraviolet (UV) treatment. Conditions for protoplast fusion were optimized, including lytic enzyme mixtures and incubation time. The efficacy of lytic enzyme mixtures on cell wall digestion was also compared. The most effective lytic enzyme mixture for CL was 2% lywallzyme plus 2% snailase and for HM1, 2% cellulase plus 2% snailase. The optimum incubation time was 16 h for CL and 24 h for HM1. All fusant strains exhibited similar morphological and conidial properties to the HM1 parent. A total of 1,360 fusant strains were produced, 136 of which were randomly selected for characterization. Seven fusant strains showed improved spore productivity and four fusant strains had increased production of the phytotoxin ophiobolin A, compared with HM1. Random amplified polymorphic DNA (RAPD) analysis of the fusant strains showed that the seven phytoactive fusant strains had a high similarity index (95 to 99%) to the parent HM1, but low similarity (22 to 26%) to the parent CL. Ethyl acetate extract of the culture broth and mycelia effectively controlled major weeds in rice production.

Green algal cell suspensions are used in agrochemical research for screening herbicides. This paper reports on the inhibitory effects of 39 herbicides from 19 different chemical classes with nine different modes of action on green algae cultured in liquid media. The results show that herbicide screening using Chlorella as a model organism is simple, quick, and sensitive. In vitro systems can be a second screening net to ensure that potential new structures are not missed. A set of biotests using cell suspension cultures of Chlorella are suggested as a herbicide prescreen to eliminate inactive compounds before testing on higher plants in the greenhouse. The method has been shown to be suitable for the requirements of microscreen and high-throughput screening (HTS) in vitro. A large-scale microscreen has been devised, which cultures algal cells using self-made Erlenmeyer flasks containing 5 ml of liquid medium. They are particularly useful for HTS compounds with dissimilar modes of action.

London rocket is hypothesized to be the most important overwintering host of the beet leafhopper in southern New Mexico. Knowledge of the environmental factors affecting the emergence of this plant is essential to developing a predictive model for London rocket and leafhopper populations. The temperature and moisture optima for London rocket germination and emergence were assessed using growth chamber studies. Temperatures of 5 to 35 C and soil water tension treatments of − 0.01 to − 1.5 MPa were tested. Optimal seed burial depth also was assessed. Optimal London rocket germination occurred at approximately 15 C and maximum emergence was achieved at 15 to 20 C with soil moisture tensions of − 0.01 to − 1.2 MPa. London rocket emergence occurred best at a seed burial depth of 2 mm.

Studies conducted from 1964 to 1967 on three soil types indicated that α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), dimethyl tetrachloroterephthalate (DCPA), and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) applied preplant and incorporated with two tandem diskings in March or April prior to bedding, gave excellent control of a mixture of Amaranthus sp. and volunteer sorghum (Sorghum bicolor (L.) Moench) in cotton (Gossypium hirsutum L.) planted in early May. Cotton was not stunted and yields were not appreciably reduced. When trifluralin was applied, soil residues the next year dictated that sorghum planting be delayed until May.

We evaluated nine systems of weed control over a 3-year period for cotton (Gossypium hirsutum L.) tolerance and control of weeds on Tifton loamy sand soil. Cultivation with sweeps did not control weeds effectively, which allowed weed competition to reduce cotton yields. Five cultivations plus an annual average of 185 hr/ha hand-hoeing was required to keep cotton relatively free of weeds for 7 to 8 weeks after planting. The use of herbicides offered certain economic advantages over systems using only cultural practices in controlling weeds. A preplant application of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) reduced annual hand-hoeing requirements by 66 hr/ha. The level of weed control at harvest time increased each year in all systems that used a herbicide program, but not where only cultivation or hand-hoeing was used. The continuous use of specific weed-control systems shifted weed populations. Systems that achieved 100% control by the end of the third year included all of the following: (a) a preplanting or at planting treatment of trifluralin or EPTC (S-ethyl dipropylthiocarbamate) plus (b) a preemergence application of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], (c) two directed postemergence sprays with MSMA (monosodium methanearsonate), and (d) diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. Large crabgrass [Digitaria sanguinalis (L.) Scop.] and Florida pusley (Richardia scabra L.) were nearly eliminated where we used trifluralin. Systems that did not include a postemergence application of MSMA allowed common cocklebur (Xanthium pennsylvanicum Wallr.), Florida beggarweed [Desmodium tortuosum (Sw.) DC], and other weeds to emerge and remain in the crop row, reducing yield of lint cotton. Cotton yield appeared to be directly related to the level of early-season weed control. We did not detect biologically active soil residues at harvest time each year. Our weed-control systems did not affect cotton fiber length, strength, or color.

Studies were conducted to determine the relative competitive ability and productivity of an atrazine-resistant biotype (WRB1) and an atrazine-susceptible accession (WSA1) of velvetleaf from Wisconsin. Noncompetitive productivity studies conducted in the field and greenhouse during 1992 and 1993 showed that instantaneous relative growth rate, net assimilation rate, and leaf area ratio of the WRB1 biotype and WSA1 accession were similar. There were no consistent differences between the WRB1 biotype and WSA1 accession in plant height, shoot dry biomass, and leaf area over time. The WRB1 biotype and WSA1 accession did not differ in noncompetitive seed yield. A replacement series experiment conducted in the field in 1992 and 1993 showed that the WRB1 biotype and WSA1 accession did not differ in shoot dry biomass or seed yield at densities of 36, 64, and 100 plants m−2. Results suggest that resistance to atrazine has not reduced the noncompetitive productivity or the intraspecific competitive ability of the WRB1 biotype relative to the WSA1 accession. Thus, even in the absence of atrazine selection intensity, the frequency of atrazine resistance gene(s) is unlikely to decrease in the velvetleaf population from which the WRB1 biotype was selected.

A 3-yr (1982, 1983, and 1984) study was conducted to determine the relationship between tillage and six weed control treatments for soybean [Glycine max (L.) Merr. ‘Williams 79′] production on silt loam (Udollic and Mollic Ochraqualfs). Conventional tillage consisted of spring moldboard plowing and secondary tillage with a combination tool just before planting. No-tillage consisted of a foliar application of glyphosate [N-(phosphonomethyl)glycine] at the time of planting. Weed control treatments included combinations of no weed control with and without soybean plants, preemergence herbicide application only, postemergence herbicide application only, and combined preemergence and postemergence applications with and without additional handweeding. In 1982, a year of above-normal seasonal rainfall, conventional tillage had significantly greater soybean grain yields than no-tillage for all weed control treatments except the preemergence-only treatment. Yields within tillage systems and between weed control treatments in 1982 were not significantly different because adequate rainfall reduced the effect of weed competition for soil moisture. Soybean seed yields in 1983 and 1984 in no-tillage were equal to or significantly greater than those of conventional tillage. No-tillage treatments had greater soil moisture conservation and soil moisture availability resulting in less plant water stress during podfilling in periods of drought in 1983 and 1984. In all 3 yr, conventional tillage had significantly greater early weed growth than no-tillage in the treatments with and without soybean plants where no preemergence or postemergence herbicides were used. Comparing treatments with and without soybean plants indicated an average increase of 36 and 38% weed control for no-tillage and conventional tillage, respectively.

Based on chlorophyll content, hydroponically cultured soybean seedlings were 254, 66, and 13 times more tolerant to clomazone than velvetleaf, corn, and smooth pigweed, respectively. Clomazone, at concentrations that inhibited chlorophyll, did not affect fresh weight accumulations of any species except velvetleaf. However, in velvetleaf, fresh weight accumulation was only half as sensitive to clomazone as the leaf chlorophyll content. Uptake of 14C-clomazone from nutrient solution by 72 h after treatment (HAT) (pigweed > velvetleaf > soybean > corn) indicates that differential absorption cannot account for selectivity. Shoot:root ratios of 14C recovered from soybean, corn, velvetleaf, and pigweed by 72 HAT were 0.39, 0.84, 1.67, and 2.37, respectively. The limited acropetal clomazone translocation in soybean seedlings may account to a small degree for soybean tolerance to clomazone. Conversion of clomazone to more polar metabolites was rapid in all four species. There were no significant differences among species in the percentage of 14C activity recovered as clomazone from root tissue by 72 HAT. Of the 14C activity recovered from shoots of soybean, corn, pigweed, and velvetleaf seedlings by 72 HAT, 46, 59, 35, and 54%, respectively, was clomazone. Differences in clomazone uptake, distribution, and metabolism among the four species were either insignificant or poorly correlated to selectivity, and therefore cannot account for the tremendous differences in clomazone sensitivity among these species. These observations indicate, indirectly, that differences at the site of action may account for selectivity.

Greenhouse studies determined the influence of 14 adjuvants and desmedipham plus phenmedipham on velvetleaf control and sugarbeet injury by triflusulfuron. A second study determined if six adjuvants, or desmedipham plus phenmedipham, influenced 14C-triflusulfuron absorption by cotyledon or first true leaves of velvetleaf. Triflusulfuron applied twice at 4.4 g ai ha−1 (split application), alone or in combination with any adjuvant, did not reduce sugarbeet dry weight. Desmedipham plus phenmedipham applied twice at 370 g ai ha−1 (split application) reduced sugarbeet dry weight 3%. The addition of an adjuvant to desmedipham plus phenmedipham reduced sugarbeet dry weight 21 to 66% depending on the adjuvant. Sugarbeet injury was not greater when triflusulfuron was applied with any adjuvant (except urea ammonium nitrate (UAN)) plus desmedipham plus phenmedipham compared to desmedipham plus phenmedipham plus the respective adjuvant alone. Velvetleaf was most easily controlled in the cotyledon stage of growth. Velvetleaf control by triflusulfuron increased from 0 (no adjuvant) to 80% by the addition of Scoil or Sylgard 309 plus UAN. Cotyledonary leaves of velvetleaf absorbed 28% more 14C-triflusulfuron than first true leaves. Adjuvant increased 14C-triflusulfuron absorption by cotyledonary leaves from 15% (no adjuvant) to 48 to 90%. Desmedipham plus phenmedipham decreased velvetleaf control by triflusulfuron plus X-77 or X77 plus UAN compared to triflusulfuron plus the adjuvant alone. Velvetleaf control by triflusulfuron plus other adjuvants was not reduced by desmedipham plus phenmedipham. Absorption of 14C-triflusulfuron by cotyledonary and first true leaf velvetleaf decreased when desmedipham plus phenmedipham was added to triflusulfuron plus Dash, Dash plus UAN, X-77, X-77 plus UAN, and Sylgard 309 plus UAN.

Ludwigia is an important broadleaf weed of direct-seeded rice in Asia. Crop interference that relies on shading may have potential as a component of integrated weed management strategies but it requires understanding the extent to which rice can interfere with weed growth and how these weeds may respond. The growth of ludwigia was studied when grown alone and in competition with 4 and 12 rice (cv. IR72) plants. Rice interference reduced ludwigia height, number of branches, and shoot and root biomass. However, ludwigia showed the ability to reduce the effects of rice interference by increasing leaf weight ratio, increasing stem and leaf biomass in the upper half of the plant, and increasing specific stem length. At 11 wk after seeding, for example, ludwigia grown with 12 rice plants had 38% greater leaf weight ratio compared to plants grown alone. When grown with 12 rice plants, the weed had 82% of its leaf biomass in upper half of the plant compared to only 25% in weeds grown alone. The results showed that ludwigia responded to rice interference with a combination of adaptations typical of many weed species. Despite such plasticity, the control of ludwigia may be achieved by dense rice stands and increasing interference.

The effect of mowing regime on lateral spread and rhizome growth of dallisgrass and bahiagrass was determined in field studies conducted in 2003 and 2004 in North Carolina over 5 mo. Treatments were selected to simulate mowing regimes common to intensively managed common bermudagrass turfgrass and include 1.3-, 5.2-, and 7.6-cm heights at frequencies of three, two, and two times per week, respectively. A nonmowed check was included for comparison. Lateral spread of dallisgrass was reduced 38 to 47% regardless of mowing regime when compared with the nonmowed check. Rhizome fresh weight of dallisgrass was reduced 49% in 2003 and 30% in 2004 when mowed at the 7.6-cm regime after 5 mo, whereas the 5.2-cm mowing regime caused a reduction of 31%. Rhizome fresh weight of dallisgrass was most negatively affected by the 1.3-cm regime, which caused reductions of 57% in 2003 and 37% in 2004. Lateral spread of bahiagrass was more strongly affected by mowing height and frequency than dallisgrass, with reductions of 21 to 27%, 40%, and 44 to 62% when mowed at 7.6, 5.2, and 1.3-cm regimes, respectively. Rhizome fresh weight of bahiagrass was reduced 24 to 33%, 55%, and 70 to 73% when mowed at 7.6, 5.2, and 1.3 cm, respectively. Based upon these results, areas mowed at a golf course rough height (≥ 5.2 cm) may be more conducive to bahiagrass spread, whereas dallisgrass may tolerate areas mowed at a fairway height (1.3 cm). Mowing at the shorter heights examined in this study clearly reduced the potential of Paspalum spp. vegetative spread and may help to explain observed distributions of Paspalum spp. infestations in bermudagrass turfgrass.

Weeds are plants that grow along with cultural plants, both groups making up a community. The prevalence of weed species becomes adjusted to cultural management practices and often, they are not able to survive without their cultivated counterpart. In this way, some weeds become more or less domesticated plants (e.g. Bromus secalinus L.).

The objective of this study was to evaluate weed control, crop yields, potential soil loss, and net returns to management of an integrated weed management system in no-till corn and soybean compared to an herbicide-based strategy. The integrated weed management system reduced herbicide inputs by delayed cover crop termination, herbicide banding, and high-residue cultivation (reduced herbicide [RH]), while the other system used continuous no-tillage and herbicides to control weeds (standard herbicide [SH]). Research was conducted within the Penn State Sustainable Dairy Cropping Systems Experiment, where corn and soybean are each planted once in a 6-yr crop rotation. In this 3-yr study, weed density and biomass were often greater under RH management, but weed biomass never exceeded 19 g m–2 in corn and 21 g m–2 in soybean. Corn yield and population did not differ in any year, and net returns to management were $33.65 ha–1 higher in RH corn due to lower herbicide costs and slightly, though not significantly, higher yields. Soybean yield was lower in RH compared to SH in 2 of 3 yr, and was correlated with soybean population and cover crop residue. Net financial returns were $43.69 ha–1 higher in SH soybean compared to RH. Predicted soil loss never exceeded T (maximum allowable soil loss) for any treatment and slope combination, though soil loss was 100% greater on a 10% slope under RH management (vs. SH) due to cultivation.

Sesbania [Sesbania cannabina (Retz.) Pers.] is a problematic emerging weed species in Australian cotton-farming systems. However, globally, no information is available regarding its seed germination biology, and better understanding will help in devising superior management strategies to prevent further infestations. Laboratory and glasshouse studies were conducted to evaluate the impact of various environmental factors such as light, temperature, salt, osmotic and pH stress, and burial depth on germination and emergence of two Australian biotypes of S. cannabina. Freshly harvested seeds of both biotypes possessed physical dormancy. A boiling-water scarification treatment (100±2 C) of 5-min duration was the optimum treatment to overcome this dormancy. Once dormancy was broken, the Dalby biotype exhibited a greater germination (93%) compared with the St George biotype (87%). The nondormant seeds of both biotypes showed a neutral photoblastic response to light and dark conditions, with germination marginally improved (6%) under illumination. Maximum germination of both biotypes occurred under an alternating temperature regime of 30/20 and 35/25 C and under constant temperatures of 32 or 35 C, with no germination at 8 or 11 C. Seed germination of both biotypes decreased linearly from 87% to 14% with an increase in moisture stress from 0.0 to −0.8 MPa, with no germination possible at −1.0 MPa. There was a gradual decline in germination for both biotypes when imbibed in a range of salt solutions of 25 to 250 mM, with a 50% reduction in germination occurring at 150 mM. Both biotypes germinated well under a wide range of pH values (4.0 to 10.0), with maximum germination (94%) at pH 9.0. The greatest emergence rate of the Dalby (87%) and St George (78%) biotypes was recorded at a burial depth of 1.0 cm, with no emergence at 16.0 cm. Deep tillage seems to be the best management strategy to stop S. cannabina’s emergence and further infestation of cotton (Gossypium hirsutum L.) fields. The findings of this study will be helpful to cotton agronomists in devising effective, sustainable, and efficient integrated weed management strategies for the control of S. cannabina in cotton cropping lands.

Barnyardgrass seeded in field plots at monthly intervals from March through October at Shatter, CA, began to emerge in March when soil temperatures reached 17 C at a depth of 5 cm. For all plantings, most of the seeds germinated and produced seedlings within 2 weeks. Increasing day lengths favored vegetative growth, with April, May, and June plantings producing the tallest plants, the most dry matter, and the largest number of tillers. July and August plantings, the first to flower, began flowering and producing seeds within 5 to 6 weeks after planting, but the greatest number of seeds (15 000 to 25 000/plant) was produced by the larger plants of the April, May, and June plantings. September plantings produced few seeds/plant (37), when compared to March (5900), July (9800), and August (9700) plantings. The earliest that seed production would be expected from seedlings emerging in March and April would be early June, and seedlings emerging in September could produce seeds before killing frosts.