Reduce Weed Competition Research Articles

Biological control of Senecio vulgaris in carrots (Daucus carota) with the rust fungus Puccinia lagenophorae

Senecio vulgaris is a troublesome weed in horticulture that is tolerant or resistant to a range of herbicides, and is therefore a candidate for biological control. The rust fungus Puccinia lagenophorae is a potential control agent, but being biotrophic, it is not suitable for use as a mycoherbicide. We tested the effects of induced rust epidemics on S. vulgaris, and investigated the resulting shading dynamics within this system. We sowed carrots at 267 seeds m−2 on five farms in western Switzerland in plots either with or without S. vulgaris seeds (also at 267 seeds m−2, within crop rows), and with or without strong sources of rust spore (four inoculum sources placed every 2 m along crop beds). Plots with S. vulgaris and no inoculum source produced low total carrot yields (18% of yield from S. vulgaris-free plots), whereas plots with S. vulgaris plus rust inoculum sources produced 48% of the yield from S. vulgaris-free plots. There were, however, no significant differences in several commercially important yield parameters such as the number of first grade carrots between S. vulgaris-free plots and those with S. vulgaris plus inoculum sources. Carrots grown with S. vulgaris were smaller and had skewed size distributions compared with the weed-free controls, but adding rust inoculum reduced this effect. This reduced size variability and reduced weed competition have important economic benefits to farmers. Carrots had longer leaves when grown with S. vulgaris, suggesting that carrots and S. vulgaris competed for light. Percent ground cover and height of S. vulgaris relative to carrots was reduced by the presence of rust, and these effects were most obvious one month after placing inoculum sources in the field. Our results are encouraging, even with artificially high weed competition, but further research is needed before this paradigm can be proposed for practical applications.

Herbicides are more cost-effective than alternative weed control methods for increasing early growth of Eucalyptus dunnii and Eucalyptus saligna

Effective weed control is an essential management task in establishing commercial tree plantations. Much of the current weed control strategies employed in Australian forestry relies on the use of available herbicides. However, given community concern regarding the use of herbicides, investigation of alternative weed control methods is warranted. We tested the ability and cost-effectiveness of mechanical (hand weeding and inter-row slashing), mulching (sawdust over newsprint, woodchips and jute), cover crops and herbicide applications for weed control in establishing eucalypt plantations. Jute matting and herbicide treatments reduced weed competition and increased seedling growth to age 2 years in plantations of Eucalyptus dunnii and Eucalyptus saligna in northern NSW, Australia. Growth increased by 269 % (Experiment 1) and 196 % (Experiment 2) in the Jute and by 216 % (Experiment 2) in the Herbicide treatments when compared to the control (no weed control) at 2 years age. As the Jute material deteriorated, after nearly 2 years, weed cover increased and there were significantly more weeds present in the Jute treatment compared to the Herbicide treatment. Jute matting costs approximately 15 times more than the herbicide regime used and, therefore, could not presently be considered a viable option for weed control in commercial eucalypt plantations. Other weed control treatments, including hand weeding, sawdust and woodchip mulches, slashing and sowing cover crops did not effectively control weeds and did not improve survival or increase seedling growth to age 2 relative to the control. We conclude that herbicides remain the most cost-effective weed control option available to commercial growers of eucalypt plantations.

Economics of weed control in mulberry (Morus indica)

A field experiment during the rainy (khar9 and winter (rabi) seasons of 1991-92 on red sandy clay-loam soil on mulberry (Morus indica) revealed that the weed-free check significantly outyielded the herbicides-treated plots. However, considering the cost of weed-control treatments alone, all the herbicides under trial showed higher benefit : cost ratio than weed-free check. Out of the evaluated herbicides, diuron and metolachlor were found most economical compared with the rest of the herbicides. . - The final choice of any weed-control loam with high organic carbon (0.38%), low measure will depend largely on effectiveness in nitrogen (188 kgha) and phosphorus and economics. The cost of weed control (18.4 kglha) but .medium in available must be compared with the resulting in- potassium (224 kglha). The pH of the creased value of the crop. Mulberry (Morus experimental soil was 6.2. indica) is no exception to this. Although the The experiment was laid out in rand- age-old practices like intercultivation and omized complete-block design with 3 repli- hand-weeding controlled the weeds effec- cations. Seven herbicides, viz. diuron, tively, often they are tedious, labour con- butachlor, isoproturon, alachlor, metol- suming and expensive. On contrary, the her- achlor, pendirnethalin and oxyfluorfen, each - ra bicides usage offer an effective and econom- at 2 levels as pre-emergent sprays, were inte- ical means of reducing weed competition, grated with weed-free check and unweeded crop losses and production losses (Kasi- control, resulting in all 16 treatments. viswanathan et al., 1978). Hence an attempt Kanav 2 (M 5) was selected for the ex- was made to work out the comparative eco- periment and all the plots were uniformly nomics among different weed-control treat- fertilized at 300 kg N, 120 kg P,O, and 120 ments. kg K,Oha/year. Out of which, 60 kg Nfha was top-dressed after the harvest of each M A T E W S AM) METHODS crop in a year. Herbicides were applied on The field experiment was conducted at next day after bottom pruning by using - University of Agricultural Sciences, knap-sack sprayer. The herbicidal spray was --- Bangalore, during the rainy (kharfl and taken only for first crop. Irrigation was pro- winter (rabi) seasons of 199 1-92. The soil vided as per the schedule. The gross returns of the experimental site was red sandy-clay were calculated by pricing leaf yield at

638 Intercropping Buckwheat and Sweet Corn: Competition and Management Factors

Row intercropping sweet corn (Zea mays L.) with a living mulch of buckwheat (Fagopyrum esculentum Moench) may reduce weed competition without reducing sweet corn yields. The objective of this experiment was to examine competition for nutrients, crop water use, and plant growth between weeds, buckwheat, and organically grown sweet corn, and examine the impact of buckwheat on weed densities and corn yields. In 1999, `Bodacious' (sehybrid) sweet corn was planted to 41,000 plants/ha stand and the following treatments were applied: 1) `Manor' buckwheat planted at 0 kg·ha–1, 56 kg·ha kg·ha–1, and 112 kg·ha–1, 2) buckwheat planted at three times: planting corn, at four-leaf corn and eight-leaf corn stage. A RCB design with four replications including a weedy/weed-free split was used. Above ground biomass of buckwheat was measured within a 1/2-m2 quadrat 8WAP and analyzed for C and N. Weed densities were taken within a 1/2-m2 quadrat 4WAP and 8WAP following each buckwheat planting. Buckwheat and corn tissue samples were analyzed for total nutrient content 8WAP. Soil samples were taken in corn and buckwheat interrows at emergence, 4 WAP, 8 WAP, and at harvest, and evaluated for inorganic nitrogen and soil moisture. Within rate treatments, yield was highest in weed and buckwheat-free (16.3 MT·ha–1) and lowest in weed-free 112 kg·ha–1 buckwheat (8.5 MT·ha–1). Within buckwheat timing treatments, yield was highest in 8 leaf (18.2 MT·ha–1) relative to at plant buckwheat. Weed densities were highest in no buckwheat (281 no/m2) and lowest in 56 kg·ha–1 buckwheat (28 no/m2) compared to the controls. These findings indicate buckwheat rate influences yield and weed density more than timing of buckwheat plant.

Weed Seedbanks and Corn Growth following Continuous Corn or Alfalfa

AbstractSpecific crop rotations may reduce weed problems and supplement agrichemical inputs. This study, conducted from 1991 through 1994, compared weed densities and corn (Zea mays L.) growth in continuous corn rotation (C/C) and in an alfalfa (Medicago sativa L.)/alfalfa/corn rotation (A/C) among different input levels (tillage, herbicide, and fertilizer rates varied to achieve high, intermediate, and low treatments). Alfalfa suppressed weeds. During establishment, grass and broadleaf weeds made up about 36 and 10% of the forage biomass, respectively. During the second year, grass and broadleaf weeds made up no more than 17 and 4% of the forage biomass, respectively. Weed seed density in both A/C and C/C corn low‐input plots averaged about 15 000 seeds m−2 in 1993; however, grass seed comprised 73% of the C/C seedbank, but only 26% of the A/C seedbank. In 1994, weed seed density increased to 38 000 seeds m−2 in the low‐input A/C corn, and grass species made up 55% of the seedbank. However, grass densities in A/C and C/C low‐input corn averaged about 300 and 4000 shoots m−2, respectively, each year. No grain was harvested in C/C low‐input corn, due to intense weed competition. Grain yield in A/C low‐input corn was 37% of the A/C high‐input treatment in 1993, 66% of the yield in A/C high‐input treatment in 1994, and similar to yield in the C/C medium‐input treatment both years. Alfalfa in rotation with corn may be used to reduce weed competition while sustaining yield.

Evaluation of Nurse Crops for Weed Control and Plant Establishment in Prairie Restoration

Nurse crops are often recommended in prairie restoration planting. This work investigated several alternative nurse crops to determine their utility in prairie planting. Nurse crops were composed of increasing densities (900, 1800, or 2700 seeds/m2) of partridge pea, spring oats, spring barley, Canada wild rye, or equal mixtures of partridge pea and one of the grasses. The experimental design was a randomized complete-block set in two sites with three blocks per site and 48 treatments per block. Each 3 × 3-m plot contained 1 m2 planted in Dec. 1995 or Mar. 1996 with an equal mix of seven prairie species. The nurse crops were sown over each nine square meter area in April 1996. Plots lacking nurse crops served as controls. Evaluated data consisted of weed pressure rankings and weed and prairie plant dry weight. Nurse crop treatments had a significant effect on weed pressure in both sites. Barley (1800 and 2700 seeds/m2) as well as partridge pea + barley (2700 seeds/m2) were most effective at reducing weed pressure. When weed and prairie plant biomass values were compared, a significant difference was observed for site quality and planting season. Prairie plant establishment was significantly greater in the poorly drained, less-fertile site and spring-sown plots in both sites had significantly higher prairie biomass values. Overall, after two seasons, there was no advantage in using nurse crops over the control. Among nurse crop treatments, oats were most effective in reducing weed competition and enhancing prairie plant growth.

Orchard Floor Practices Affect Soil Compaction around Young Pecan Trees

Orchard floor treatments of total weed control with herbicides, disking, mowing, grass control only with herbicides, and no control of vegetation were maintained in a 3 × 3-m area underneath young pecan [Carya illinoinensis (Wangehn.) K. Koch] trees. Soil compaction in treated areas was compared to heavily trafficked row middles. Mean cone index (CI) readings obtained from a cone penetrometer for the heavily trafficked areas were higher, indicating greater compaction than all other treatments in the 4.7- to 11.8-cm soil depth range. Heavily trafficked areas had severe compaction (>2.0 MPa) at the 9.5- to 22.9-cm soil depths. Mowed plots had similar CI readings at 14.2- to 54.3-cm depth as those heavily trafficked. The mowed areas had severe compaction at the 14.2- to 22.9-cm depth range. Grass control only with herbicides and plots with no control of vegetation had low CI throughout the soil profile. Disking, grass control, and no control treatments had similar effects, except at the 4.7-cm depth, where disking reduced compaction. An orchard floor management practice that minimized traffic near young trees, but also reduced weed competition, appears to be the best choice.

Soybean (Glycine max), common cocklebur (Xanthium strumarium), and sicklepod (Senna obtusifolia) sap flow in interspecific competition

Two field experiments were conducted to examine the competitive effect of common cocklebur and sicklepod in soybean. Factors examined included sap flow of both the weed and the crop, as well as the traditional parameters of weed and crop growth and crop yield. The intent was to determine to what extent competitive effects could be attributed to differential water utilization. In the first study, soybean planted at 20 plants m−1row was infested with either sicklepod at 10 plants m−1row or common cocklebur at two plants m−1row. Sicklepod reduced soybean sap flow and yield 53 and 49%, respectively. Common cocklebur reduced soybean sap flow and yield 31 and 38%, respectively. Within a weed species, weed-induced yield and sap flow reductions were comparable, indicating that water deprivation was the primary detriment that these weeds inflicted on soybean. Individual common cocklebur plants were 3.9 times more competitive than sicklepod with respect to reducing soybean yield. However, sap flow of individual common cocklebur plants was only 1.4 times more than that of sicklepod, indicating that water deprivation was not the only causal factor in weed-crop competition. In the second experiment, sicklepod was planted in soybean (fixed density) and clipped to either half the height, same height as soybean, or left unclipped, in an attempt to simulate herbicide-induced stunting. Clipping sicklepod had a positive effect on soybean sap flow and yield. Thus, the benefits of reduced weed competition were achieved without killing sicklepod.

Effect of Planting Patterns and Inter-row Cultivation on Competition Between Corn (Zea mays) and Late Emerging Weeds

Narrower corn row widths, higher crop densities, and interrow cultivation may be used as part of integrated weed management (IWM). During a three-year study, we tested whether these factors affected corn growth, development and grain yield at final harvest, and weed biomass when weeds were late-emerging (after the three-leaf stage of corn). Increasing corn density from 7 to 10 plants m−2or decreasing row width from 75 to 50 cm significantly increased corn leaf area index (LAI), and reduced photosynthetic photon flux density (PPFD) available for a mixture of weed species located below the corn canopy. Narrower rows and higher corn density significantly reduced biomass of late-emerging weeds. Corn yields increased significantly (10 to 15%) only when narrower rows were used. Intraspecific competition between corn plants in the higher density significantly reduced early corn growth and offset any gain in yield from reduced weed competition. In comparison to plots where late-emerging weeds grew uncontrolled, interrow cultivation did not decrease biomass of late-emerging weeds, hence did not increase corn yield. We recommend using narrower row widths to reduce weed competition and increase corn yield. Increased corn densities had no net yield benefit. Early-season weed management is crucial as the later-emerging weeds were less important in terms of their effect on yield.

Intercropping Annual Medic with Conventional Height and Semidwarf Barley Grown for Grain

AbstractInterseeding annual legumes with grain crops has been proposed as a cropping strategy to enhance ground cover, thereby reducing weed competition, suppressing soil erosion, and providing N for use by subsequent crops. The potential of annual medics (Medicago spp.) for intercropping in small‐grain cropping systems has not been adequately assessed for the north‐central United States. Our objective was to evaluate a spring barley (Hordeum vulgare L.)‐annual medic intercrop system for barley grain yield, fall biomass production, suppression of fall weeds, and quantity of N available for incorporation into the soil. Field experiments were conducted in four Minnesota environments (Becker, Morris, Rosemount, and St. Paul). Conventional height ‘Robust’ and semidwarf ‘Royal’ barley were intercropped with each of three medic species [‘George’ black medic (M. lupulina L.), ‘Mogul’ barrel medic (M. truncatula Gaertn.) and ‘Santiago’ burr medic (M. polymorpha L.)]. Intercropping with medics reduced barley yields by an average of 6% at Rosemount, 30% at St. Paul, and 76% at Becker, compared with monoculture barley fertilized with N. Medics increased yields by 9% at Morris. Intercropping with medic reduced fall weed mass by an average of 65% across environments, compared with the fertilized Royal monoculture. Nitrogen available for incorporation from the barley‐medic intercrops ranged from 66 to 140 kg ha−1 over the environments, whereas N available for incorporation from fertilized barley monoculture ranged from 22 to 80 kg ha−1. We conclude that the prospects for successfully intercropping with annual medic in a barley grain production system are mixed and depend in part on the medic species used and barley stature. A wider array of medic types should be evaluated for their suitability in intercropping with small grains.

Comparison of Conventional and Alternative Nursery Weed Management Strategies

Soil cultivation (3 to 5 times/yr) and herbicide management (oxadiazon, 3.92 kg ai/ha), agricultural standards for reducing weed competition, were compared to three alternative nursery field management systems regarding weed suppression: ‘Norcen’ bird's-foot trefoil companion crop, ‘Wheeler’ winter rye cover crop/mulch, and grass sod (80% ‘Eton’ perennial ryegrass and 20% ‘Ruby’ red fescue). Field management treatment had a significant effect on observed weed populations. Weed densities were also subject to yearly variations caused by climate and endogenous weed life cycles. Herbicide management (oxadiazon) consistently provided the best control of undesired vegetation (0.3 weeds/m2) followed by the grass sod (0.7 weeds/m2), Wheeler rye cover crop/mulch (1.7 weeds/m2), Norcen bird's-foot trefoil companion crop (8.6 weeds/m2), and cultivated (55.7 weeds/m2) treatments, respectively. Although the grass sod treatment provided excellent control of undesired vegetation, as an alternative to cultivation and herbicide use, it proved to be excessively competitive with the nursery crop. The bird's-foot trefoil treatment quickly became infested with broadleaf weeds the eradication of which proved difficult. The Wheeler winter rye cover crop/mulch field management system provided acceptable weed control combined with other beneficial effects on the plant/soil environment. Results support the effectiveness of Wheeler winter rye and perhaps other allelopathic cover crop/mulch systems in controlling undesired vegetation in horticultural field production systems.

Okra production with pine straw mulch

Conventional planted okra in Booneville, Arkansas and Lorman, Mississippi were mulched with loblolly pine straw (Pinus taeda L.) and longleaf pine straw (P. palustris Mill.), respectively, at a rate of 11 t/ha or left bare. At Booneville, plant stand, season yields (18.6 t/ha), pod weight (16.3 g), plant dry weight (2.3 kg), or stem diameter (3.5 cm) were not affected by the loblolly pine mulch. However, mulch application increased pod number (1.22 vs. 1.06×106/ha) and plant height (1.5 vs. 1.6 m), while reducing weed competition (0.05 vs. 0.40 t/ha) and visible plant stress, during periods of soil moisture deficits. Soil temperatures at 5 and 15 cm depth were reduced by mulch until mid-August when plant canopies covered the rows. Seasonal moisture at 30 and 45 cm depths was similar between mulched and bare soils, based upon unreplicated neutron probe measurements. At Lorman, season okra yield (29.8 vs. 24.6 t/ha), number of pods per ha (1.24 vs. 1.07×106) and weed competition were reduced and soil pH lowered 0.56 units by longleaf pine straw mulch. Mulch reduced early season yield at both locations.

Performance of conventional and alternative cropping systems in cryoboreal subhumid central Alberta

SUMMARYA 3-year field study (1986–88) was conducted in central Alberta to discover how diverse soil-plant systems function under cryoboreal subhumid conditions. Barley, fescue, faba (field) bean and a barley/field pea intercrop were grown continuously on different soils at Ellerslie and Breton using two distinct tillage methods. The agronomic performance, weed-crop interactions and below-ground productivity of these cropping systems were examined. The main findings were as follows: different soil properties did not affect yields of barley, barley/field pea and fescue fertilized with N and P; silage yield of faba bean at Breton was greater than at Ellerslie; barley/field pea and faba bean could be grown without tillage at Ellerslie; barley/field pea plots had the lowest weed counts; fescue root biomass was greatest at all depths followed by faba bean and barley; and soil properties appeared not to induce differences in root production of a cereal, an annual forage legume and a perennial grass. Increasing the use of annual legumes into rotations, either as sole crops or as intercrops with cereals, may be a viable alternative to continuous cereal cropping because annual legumes contribute N through biological N fixation, reduce weed competition and increase the input of root mass in soil.

Grain Yield and Returns from Intercropping Wheat and Flax

Intercropping hard red spring wheat (Triticum aestivum L.) with flax (Linum usitatissimum L.) could offer advantages over monocropping in dry regions of northern latitudes. Our objective was to determine if wheat yield could be maintained while also producing an economic yield of flax. Two high yielding wheat cultivars, ‘Amidon’ and ‘Grandin’, were sown at 65 lb/acre in a monoculture and intercropped with ‘Linton’ flax sown at 32 lb/acre. North Dakota dryland management was used in 1989 and 1990, but supplemental irrigation also was evaluated in 1990. Intercrop patterns included establishment of both crops in the same row, in alternate rows, and in plots where flax was broadcast seeded into wheat. An additional intercrop pattern was included during 1990; flax and wheat were seeded in rows perpendicular to each other. Compared with sole cropping, intercropping reduced flax yield more than 90%, and sometimes reduced wheat yield by almost 25% (P < 0.05). Economic returns were generally greater for a monoculture of wheat or flax than for intercrops. Land equivalent ratios (LERs) failed to indicate any advantage for intercropping. This study shows that an economic flax yield is not produced when a monoculture wheat population (app. 20 plants/sq ft) is established in a wheat-flax intercrop. Work is needed to determine if the economic performance of wheat-flax intercrops is improved when the seeding rate for wheat is considerably less than in a monoculture. Research Question Flax (Linum usitatissimum L.) is a difficult-to-grow but important oil-seed crop in portions of the Great Plains and upper Midwest. Intercropping flax with small grain crops could alleviate production problems encountered when growing flax alone. This study compared the economics of intercropping flax and wheat (Triticum aestivum L.) to growing each crop in a monoculture. Literature Summary Research in the 1920s indicated that intercropping flax and spring wheat reduced weed competition and improved wheat grain quality. Intercropping, however, tended to reduce flax and wheat yield compared with sole cropping, particularly during periods of environmental stress. The tendency of intercropping to reduce yields, along with technological constraints, resulted in abandonment of the practice. Intercropping flax with wheat may compare favorably with sole cropping because of cultivar improvements and farm machinery developments since the 1920s. Study Description Two spring wheat cultivars were each planted at 65 lb/acre alone and intercropped with flax planted at 32 lb/acre in 1989 and 1990 at Carrington, ND. Spring wheat cultivars: Amidon and Grandin Flax Cultivar: Linton Soil: Heimdal Weed control: Hoelon and Bronate Seeding row width: 6-in. Treatments: Flax planted alone Wheat planted alone Flax and wheat planted in the same row Flax and wheat planted in alternating rows Flax broadcast planted and then harrowed into wheat Flax planted in perpendicular rows to the wheat (in 1990 only) Applied Question Were flax and wheat yields reduced by intercropping? Intercropping reduced flax yields more than 90%, and sometimes reduced wheat yields by almost 25% (Fig. 1). Intercropping reduced flax yield partially because the wheat plants shaded flax plants. Competition between crops for water also helped explain why intercropping reduced flax and, in some instances, wheat yields. Did the economics of intercropping flax and wheat compare favorably with sole cropping either crop? Figure 1Open in figure viewerPowerPoint Grain yield of wheat and flax grown alone and intercropped in alternating 6-in. rows (Alt), in the same row (Mix), and with flax broadcast seeded and then harrowed into wheat (Broad). Economic returns were generally greater when wheat and flax were grown alone than when growing both crops together. Therefore, little incentive exists for intercropping flax and wheat under economic assumptions made in this study, which included a cost of $0.65/bu of wheat for separating mixed grain following harvest. If mixed grain could be separated on the farm, however, then returns from intercropping could compare favorably with sole cropping. Reducing wheat populations in intercrops compared with a sole crop may also improve the performance of flax-wheat mixtures.

Mixed‐weed infestations: Prediction of crop losses for economic weed management in rice

Abstract Weed control in Latin America is costly and heavily dependent upon herbicides. Often irrigated rice farmers spray herbicides in late post‐emergence at 30–44 days after emergence (d.a.e.). The economic benefits from such late applications are often unclear. Two experimental approaches involving density series of Eclipta alba, Leptochloa filiformis, Eleusine indica a 1:1 mixture of Echinochloa colona and E. crus‐galli and a range of rice densities were used to estimate crop losses for late weed infestations, and the benefit of increasing rice densities to reduce weed competition. The experiments were conducted in Colombia, and current values of rice and fanning inputs were used for economic analysis. With farmers obtaining average yields (5600 kg/ha) only weed densities larger than about 20 plants/m2would justify herbicide applications after 30 d.a.e. Opportunities to reduce herbicide use are even greater in low‐yielding farms (3500 kg/ha), where herbicides would pay off only at weed densities larger than about 30 plants/m2. Hand‐weeding could be an alternative to herbicide use at weed densities higher than about 25 plants/m2. Using high rice densities, providing large numbers of tillers/m2, was economical even at large weed infestations (> 100 plants/m2). Omitting the late post‐emergence herbicide application would reduce weed control costs in Colombia by 28%.

Addressing Real Weed Science Needs with Innovations

Weed science is responsible for reducing weed competition with crops, within constraints, allowing food production for a growing world population. We have been successful, but with an increasing reliance on the fantastic arsenal of herbicides. Heavy herbicide usage and the concomitant loss of control due to changing weed species spectra, as well as evolved herbicide resistance, along with cancellations of registrations, limit chemical options. Old “innovations” such as well-conceived rotations and various mechanical procedures partly alleviate chemical dependency. We must try innovative, meaningful herbicide mixtures, whether synergistic or additive, mixtures of crop varieties, more competitive varieties, including allelopathic varieties, which could all help to lower chemical dependency. Three cases where innovative genetic-engineering coupled with chemistry seem to be needed are: (a) for the control of parasitic higher plant weeds such as broomrapes (Orobanchespp.), dodders (Cuscutaspp.), witchweeds (Strigaspp.) that cannot be controlled by mechanical or selective chemical means with a sufficient margin of user error; (b) for the control of weeds in wheat (Triticumspp.) that are evolving multiple and cross resistances toallwheat-selective herbicides; and (c) to replace the majors-triazine and chloroacetamide herbicides in corn (Zea maysL.) that are under attack and where many local restrictions and cancellations have been imposed. We need better replacements than the resistance-prone inhibitors of acetolactate-synthase and acetyl-CoA-carboxylase. Much of the long-term innovative planning and research must come from the public sector as no one else seems willing to fill the needs.

Meyer Zoysiagrass Regrowth from Sod Debris as Influenced by Herbicides

In this field study, five preemergence and two postemergence herbicides were evaluated for their ability to hasten Meyer zoysiagrass (Zoysia japonica Steud.) sod development when sod was established from the regrowth of rhizomes, sod strips, and loosened plant debris. Herbicide influence on zoysiagrass re-establishment was examined using two postharvest field preparation procedures as follows: area I was raked to remove most above-ground sod debris, whereas in adjacent area II sod debris was allowed to remain in place. Herbicides that controlled smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl.] generally enhanced zoysiagrass cover by reducing weed competition. Meyer established from rhizomes, sod strips, and loosened plant debris, and treated with herbicides, had a rate of sod formation equivalent to that expected in conventionally tilled, planted, and irrigated Meyer sod fields. Effective smooth crabgrass control was achieved when the rates of most preemergence herbicides were reduced in the 2nd year. Chemical names used: dimethyl 2,3,5,6-tetrachloro-1,4-benzenedicarboxylate (DCPA); 3,5,-pyridinedicarbothioic acid, 2-[difluromethyl]-4-[2-methyl-propyl]-6-(trifluoromethyl)∼S,S-dimethyl ester (dithiopyr); [±]-ethyl 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy] propanoate (fenoxaprop); 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); N-[1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine(pendimethalin);N3,N3-di-n-propyl-2,4-dinitro-6-[trifluromethyl)-m-phenylenediamine (prodiamine); and 3,7-dichloro-8-quinolinecarboxylic acid (quinclorac).

Extending the frontiers of aerially sown pastures in temperate Australia: a review

Over the past 40 years large areas of pastures on hill country in temperate Australia have been improved through aerial distribution of herbicides, pesticides, seed, and fertiliser, which has increased animal production and helped to control weeds. Refinements detailed in this review could extend the use of these techniques to promote sustainable systems by the establishment of perennial pasture species on unploughed land. It is argued that the most urgent requirement is ensuring that aerial spraying is not abolished by government regulation in response to demands by specialist groups, because perennial pasture species will not establish on hill country without prior aerial spraying of herbicides. The major technical refinement needed is the reduction of losses of establishing plants due to weed competition and dry periods during their first spring and summer. This could be accomplished by increasing the spectrum of weeds controlled by the most widely used herbicide, glyphosate; applying new herbicides that give longer weed control in spring than the presently used herbicides; using herbicides that can selectively remove annual grass weeds from establishing perennial grasses; or using strategic grazing with cattle or goats to reduce weed competition. Breeding, selecting or importing pasture species specifically designed for establishment from surface sowing has never been attempted. Attributes that could improve establishment include germination that occurs only under favourable conditions; seeds resistant to weathering on the soil surface; seedlings with fast radicle entry, hairs on the radicle, fast root development, and better seedling vigour; and for subtropical species sown in semi-arid New South Wales, tolerance of low winter temperatures. Improved distribution of herbicides, seeds and fertilisers, particularly in the more rugged hill country, is needed to ensure complete cover of the treated area with minimum drift. Techniques that allow establishment of aerially sown pastures on hill country with very acid soil are needed to facilitate the development of further, large areas of Australia.

The Role of Weeds in the Productivity of Amazonian Bush Fallow Agriculture

SummaryThree effects of herbaceous weeds on the productivity of a bush fallow system cropped with maize, cassava and plantain were identified in four experiments carried out in Central Amazonian Peru. First, early weed control is needed to minimize crop yield reductions. Weeds reduce plantain raceme weight and days to flowering, but not cassava yield, if weeding is done early. Second, fallows must be long enough to reduce weed seed banks to levels tolerable to farmers. While fallows of between two and five years eliminate herbaceous weed biomass present at the beginning of the fallow, weed seed banks decline linearly through ten years of tree cover. Third, with successive clean-weedings to reduce weed competition, tree and shrub numbers and their proportion of total non-crop biomass decline, while the amount and proportion of herbaceous weeds increase. Tree and shrub regeneration is reduced by longer cropping periods, more frequent weedings, greater crop cover, and shorter fallow periods.

Herbicides and planting date affect early performance of container-grown and bare-root loblolly pine seedlings in Alabama

The survival of bare-root and container-grown loblolly pine (Pinus taeda L.) seedlings exceeded 90% when outplanted in March at two sites in Lee County, Alabama. At both sites, soil moisture and seedling survival were greater in March than in May. A March herbicide application reduced weed biomass by 75–80% at both sites. At the moist site, herbicide application did not affect survival. However, at the drier site, a reduction in weed biomass increased both the percent soil moisture and the survival of May-planted bare-root seedlings. When soil moisture at planting time was less than 13% on a dry weight basis container-grown seedlings survived better than bare-root seedlings. At both sites, reduced weed competition resulted in greater seedling heights and diameters.