Winter Annual Weed Research Articles

Winter Wheat (Triticum aestivum) Yield Response to Winter Annual Broadleaf Weed Control

Selected herbicide treatments from 25 winter annual broadleaf weed control experiments conducted across Oklahoma from 1979 to 1993 were examined for winter wheat yield response to weed control. All experiments contained one or two of the same three weeds (henbit, bushy wallflower, or cutleaf eveningprimrose) as the primary target(s). Herbicide treatments included chlorsulfuron at 8.8 or 17.6 g ai/ha, and/or 2,4-D at 420 g ae/ha, all broadcast POST to wheat. Most herbicide treatments controlled the weeds, but increased wheat grain yield at only one site, wherein bushy wallflower density was 830/m2. Correlation analysis found no relationship between weed densities and wheat yield when chlorsulfuron at 8.8 g/ha was applied for henbit or moderate levels of bushy wallflower or cutleaf eveningprimrose. There was a significant positive relationship favoring spraying of bushy wallflower when the correlation analysis included data from one site with a density of 830 plants/m2.

Evaluation of Weed Control Practices during Spring and Summer Alfalfa Establishment

Weed management during alfalfa (Medicago sativa L.) establishment is a major concern for producers in the northeast USA. The objectives of this research were to determine the yield, quality, and economic consequences of controlling weeds during the establishment of spring- and summer-seeded alfalfa. Alfalfa was band-seeded during spring (April and May) and late summer (August and September) into a conventionally tilled seedbed of Hagerstown silt loam (fine-loamy, mixed, mesic Typic Hapludalfs) at Landisville, PA, in 1991 and Murrill silt loam (fine-loamy, mixed, mesic Typic Hapludult) at Rock Springs, PA, in 1991 and 1992. Weed control treatments for the spring seedings included: (i) no herbicide or nurse crop (no weed control); (ii) oat (Avena sativa L.) nurse crop; (iii) benefin preplant incorporated; and (iv) sethoxydim and 2,4-DB postemergence. Weed control treatments for late-summer seedings were the same as those in the spring except that the nurse crop was replaced with a paraquat application to dormant alfalfa. Seeding alfalfa later, compared with earlier, in the spring tended to increase weed and decrease alfalfa dry matter (DM) yield but did not affect total DM yield or forage quality during the seeding year. For spring-seeded alfalfa, weed control treatment effects on alfalfa and weed DM yield during the seeding-year were sporadic, however, net economic return per acre was generally greatest when no weed control was used. Neither time of spring seeding nor weed control treatments produced consistent differences in yield, quality, or net economic return per acre after the seeding year. Delaying alfalfa seeding in the summer reduced first harvest alfalfa yield (704 Ib/acre less) and season total alfalfa yield (1121 Ib/acre less) compared with early seedings. Generally, weed control treatments in summer-seeded alfalfa did not improve alfalfa or total DM yield, forage quality, or net economic return per acre compared with no weed control. We conclude that when alfalfa is either spring or summer seeded, the weed control practices used in this study were not economically beneficial and may actually reduce net return per acre because of associated additional costs compared with seeding alfalfa with no companion crop or herbicide.

Downy Brome (Bromus tectorum), Jointed Goatgrass (Aegilops cylindrica) and Horseweed (Conyza canadensis) Control in Fallow

Jointed goatgrass, downy brome, and horseweed are increasingly troublesome winter annual weeds during fallow periods in conservation-tillage systems in the southern Great Plains. These experiments determined the optimum weed size, vigor, and minimum herbicide rate required for 95% or better control of these weeds on fallow land. Jointed goatgrass and downy brome were controlled best when plants were 10 cm or less tall and growing vigorously at time of treatment. Horseweed was controlled best when plants were 30 cm tall and growing vigorously. Based on local retail and application costs and assuming optimum conditions for control, the two most economical herbicide treatments that controlled each weed 95% or better were: jointed goatgrass, clethodim at 250 g ai/ha and glyphosate + 2,4-D at 249 + 479 g ae/ha; downy brome, quizalofop at 18 g ai/ha and glyphosate + 2,4-D at 582 + 950 g ae/ha; and horseweed, 2,4-D at 560 g ae/ha and metsulfuron at 5 g ai/ha.

Effects of Seeding Methods and Mowing on the Establishment of White Clover(Trifolium repens L.) Cover for Weed Suppression.

Maintainable clover cover is a desirable vegetation for suppression of noxious weeds. The effects of seeding times and rates of white clover (Trifolium repens L.) on the development of its stands, and on the weed populations therein were determined by a 2-year factorial experiment. Two cultivars (cv. Grasslands Huia, and cv. California Ladino), 2 seeding times (mid-September and mid-October) and 2 seeding rates (2.0kg/10a and 0.5kg/10a) were compared. In all treatment plots, clovers germinated and developed successfully. Early (September) seeding was more effective and dense (2.0kg/10a) seeding was also an important factor for establishing a good clover cover. Completion of clover cover was delayed most in the late (October) and sparsely (0.5kg/10a) seeded plots. Delayed completion of the clover cover allowed the invasion and/or emergence of winter annual weeds, especially Capsella bursa-pastoris and Erigeron sumatrensis. These annuals had little effect on clover dominance, although the plants of E. sumatrensis grew tall, suppressed under-growth of clover and presented unsightly stands when they were not mown. E. sumatrensis regrew after April mowing, but died after June mowing. Invasion of Rumex spp. and Lolium multiflorum was not prevented by the early completion of clover cover. Influences of seeding methods lasted through 1992, but dissipated in 1993. ‘Ladino’ maintained taller plant height and better continuous coverage than ‘Common’.

798 PB 074 CHANGES IN WEED SPECIES WITH DIFFERENT COVER CROPS IN TWO CALIFORNIA VINEYARDS

Cover crops are grown in vineyards for many reasons, including erosion control, maintaining organic matter and changing pest complexes. Changing a management practice from using resident vegetation as a cover to other planted cover crops will change the vineyard floor flora. The cover crops of `Olge' oat, `Olge' oat and purple vetch, and purple vetch alone were compared to resident vegetation as winter planted cover crops. The cover was harvested in April of each year and blown under the vine row; The cover crop remains were disked into the middles after mulching. Three varieties of subterranean clover were planted in the vine rows at each location in one-half of each of the cover crops. The winter annual weed species, black and wild mustard, common chickweed and annual bluegrass decreased in the inter-row areas. The perennial weed field bindweed increased in all cover crop treatments.

Fenarimol Tolerance of Roughstalk Bluegrass Overseeded in Bermudagrass Greens

AbstractBermudagrass (Cynodon spp.) putting greens are overseeded with cool‐season grasses in the fall to maintain a high‐quality putting turf throughout the southern USA. Perennial ryegrass (Lolium perenne L.) has been the predominant grass used for overseeding until recently, when roughstalk (Poa trivialis L.) has been increasingly used for overseeding. Annual bluegrass (Poa annua L.) is a problem winter annual weed that infests most overseeded bermudagrass greens and the weed must be controlled with a herbicide to maintain a high‐quality putting surface. Fenarimol [ɑ(2‐chlorophenyl)‐ɑ‐(4‐chlorophenyl)‐5‐pyrimidinemethanol] has preemergence herbicidal activity on annual bluegrass, but it may also reduce the germination and establishment of roughstalk bluegrass seedlings. A field experiment was conducted over a 2‐yr period to determine the time interval of fenarimol treatments necessary to avoid injury to roughstalk bluegrass overseeded on a bermudagrass green. Overseeded roughstalk bluegrass tolerated fenarimol when applied as (i) a single application at 2.7 kg ha−1, (ii) two applications of 2.0 kg ha−1 each, and (iii) three applications of 1.4 kg ha−1 each, provided the final application was made ≥ 2 wk before overseeding. Quality and density of roughstalk bluegrass were not influenced by fenarimol, provided the last application was made ≥ 2 wk before overseeding in 1991 and ≥ 1 wk before overseeding in 1992. When the final fenarimol application was made during this period, the transition of overseeded roughstalk bluegrass back to bermudagrass was not affected the following spring and early summer.

Cyclic oscillations between a summer-annual (C4) and a winter-annual weed grass in Waikato dairy pastures

Cyclic oscillations between a summer-annual (C4) and a winter-annual weed grass in Waikato dairy pastures

Life-history variation in the annual arable weed Diplotaxis erucoides (Cruciferae)

Variation in life-history traits such as emergence, survival, time of flowering, and fecundity were studied in Diplotaxis erucoides, a mediterranean winter annual weed, by analyzing cohorts that emerged in autumn, early spring, and spring. The response of the plants to the environment, as reflected by plant architecture and pattern of biomass allocation, was also studied. Seedlings that germinate in autumn produced from 3 to 10 times more seeds than those that germinated in spring. The main factor affecting the number of seeds produced appears to be the life-span. Reduction of the growing period led to a decrease in both number and length of modular units, which resulted in decreased numbers of leaves, flowers, and fruits of each module. In semelparous D. erucoides plants, differences in the pattern of biomass allocation to reproduction are related to plant size. Our field data indicate that an increase of reproductive effort with size occurs in small individuals; however, a decrease occurs for vegetative biomass greater than 2 g and less than 5 g. Little variation in reproductive effort occurs when vegetative biomass is greater than 5 g. From a strategic point of view, size-dependent variation of reproductive effort in D. erucoides can be interpreted as good tactics to favour a higher proportion of resources devoted to reproduction in small individuals, thus ensuring some offspring. However, structural, developmental, and physiological constraints lead to stabilization or even a decrease in reproductive effort above a certain threshold size, when production of offspring is already ensured. Key words: phenotypic plasticity, plant architecture, biomass allocation, Diplotaxis erucoides.

Post-harvest Management of Tobacco Thrips (Thysanoptera: Thripidae) Overwintering in Peanut Fields

A combination of fallow tillage and a March application of carbofuran were assessed as tactics for decreasing survival and reproduction of tobacco thrips overwintering in six harvested peanut fields. Large numbers of tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), developed in three fields on volunteer peanut, Arachis hypogaea L., and winter annual weeds. Adult tobacco thrips collected during the late winter were predominantly brachypterous, with percent brachyptery averaging 71–95% for females. Brachypterous adults tended to be more abundant in fields harvested in September than in those harvested in October. Disking during November and February greatly reduced the density of volunteer peanut and winter annual weeds but did not measurably decrease abundance of brachypterous tobacco thrips. Carbofuran application reduced abundance of brachypterous adults and thrips larvae on volunteer peanut by 85–100% during the early spring. Post-harvest tillage and carbofuran application did not measurably reduce incidence of tomato spotted wilt virus in the subsequent peanut crop. Implications for winter ecology and management of spotted wilt are discussed.

Improving Weed Control with 2,4-DB Amine in Seedling Alfalfa (Medicago Sativa)

2,4-DB ester had been widely used for winter annual broadleaf weed control in seedling alfalfa in the western United States, but was replaced commercially by the amine formulation in 1990. Field studies conducted in the high desert region of southern California confirmed previous reports that 2,4-DB amine is not as effective as the ester formulation. Two methods were found to improve the weed control performance of 2,4-DB amine: 1) application at earlier alfalfa growth stages and 2) the addition of adjuvant. Applications made at the three-trifoliate leaf stage of the alfalfa were more than three times as effective as applications made at the eight-trifoliate leaf stage. When adjuvants were added to the amine formulation, weed control was improved 50 to 97%.

Integration of Cereal Cover Crops in Ridge-tillage Corn (Zea mays) Production

Field experiments evaluating 11 cereal cover crops were established at two locations in Ontario over a two-year period. Cover crops were interseeded into a ridge-tillage corn crop and evaluated in terms of biomass production and winter annual, biennial, and perennial weed species suppression. Seedling establishment and aboveground biomass production of cover crops were variable between locations and years. At both locations over two years, ‘Danko’ winter rye, ‘OAC Halton’ winter barley and ‘Rodeo’ spring barley were the most consistent cover crops in biomass production. However, cover crop residues had no significant effect on weed biomass or density due to a high degree of spatial variability present in the weed populations. Corn grain yields were not reduced by the presence of inter-seeded cover crops when compared with the bare ground control treatment.

FALL, SPLIT, AND TANK-MIX APPLICATION METHODS AS ALTERNATIVES TO SPRING PREEMERGENT HERBICIDE APPLICATION

Preemergent herbicides were applied to vineyards in the southcentral Missouri Ozark region. These were applied at full label rate in the fall or in the spring, at half rate in the fall and again in the spring, and as tank-mixes in the spring. Days of acceptable annual weed control (30% or less cover) beyond the untreated control were determined for these application methods over three years. The fall applications were effective at controlling winter annual weeds and early summer annual weed growth the following season. By mid summer the fall applied preemergents lost residual activity. Splitting the label rate between fall and spring was no better than a full rate spring application at increasing the days of acceptable summer annual weed control. Single preemergent spring application performed as well as tank-mixes.

Overwintering Hosts and Wingform of Thrips, Frankliniella spp., in Georgia (Thysanoptera: Thripidae): Implications for Management of Spotted Wilt Disease

Forty-five plant species were surveyed for thrips during the winter and spring in Georgia. The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), was collected from 44 plant species, and the tobacco thrips, Frankliniella fusca (Hinds), was collected from 25 plant species. Adults of both species were 60–100% female in most samples. Thrips larvae were collected from 37 plant species, but were relatively uncommon until mid-March. Western flower thrips and tobacco thrips were most abundant during the spring on Trifolium spp. and volunteer peanut, Arachis hypogaea L., respectively. Volunteer peanut was intensively sampled for thrips during the fall and spring. Adults were 60–95% tobacco thrips in most samples, with western flower thrips comprising the remainder. Thrips larvae were collected in all samples, but were more numerous during the spring. Adult tobacco thrips were predominantly brachypterous during the late fall and early spring, suggesting that some populations of tobacco thrips overwinter in old peanut fields. Brachypterous adults were rarely observed on peanut transplanted during late March into an old pearl millet, Pennisetum americanum (L.), field, but were common on peanut transplanted into an adjacent old peanut field. The potential of tobacco thrips, western flower thrips, and their plant hosts as winter reservoirs for tomato spotted wilt virus (TSWV) is discussed. Destruction of overwintering thrips, volunteer crops, and winter annual weeds in cultivated fields is suggested as a potential strategy for TSWV management.

Effects of Topsoil Thickness On Winter Annual Weed Biomass Production and Nutrient Flux

The effects of topsoil thickness on winter annual weed growth and nutrient concentration were assessed for three consecutive years in soybean plots. The topsoil treatments had high fertility levels, uniform textures, and no herbicides were used in the study. Common chickweed composed 75% of the winter annual weed species. Weed biomass production decreased as topsoil thickness decreased from 22.5 cm to 0. Topsoil thickness of 22.5 cm produced 800 kg ha–1 more weed growth than 0 cm topsoil. The weed biomass grown in thicker topsoil had higher total amounts of N, K, Mg, and Ca.

Biology and Control of Jointed Goatgrass (Aegilops cylindrica), a Review

Jointed goatgrass is a winter annual grass weed which is believed to have been introduced into North America as a contaminant in winter wheat seed. Although jointed goatgrass was first discovered in some states early in the 20th century, changing wheat production practices during the past 25 yr have encouraged its spread and increase. Winter wheat producers in the western United States are concerned about the lack of adequate selective control measures for this weed. Jointed goatgrass and wheat share the D chromosome in common and have similar growth habits. Jointed goatgrass lowers winter wheat yield by competing for growth requirements, reducing harvesting efficiency, and lowering crop quality by contaminating harvested grain. Jointed goatgrass is well adapted to stubble-mulch or reduced tillage crop production, particularly in regions where climate limits cropping options to the winter wheat-fallow rotation or continuous wheat. This review summarizes jointed goatgrass seed germination, dormancy, physiology, yield loss estimates in winter wheat, and both herbicidal and non-chemical methods of managing jointed goatgrass.

Selection and Characterization of a Gibberellin-Deficient Mutant of Thlaspi arvense L.

Field pennycress (Thlaspi arvense L.) is a winter annual weed with a cold requirement for reproductive development. Previous work in this laboratory has demonstrated that the bolting aspect (rapid stem growth) of reproductive development is mediated by gibberellins (GA). The present paper describes the selection and characterization of a mutant lacking the capacity for thermoinduced stem growth. Seeds of an inbred field pennycress line (CR(1)) were treated with the chemical mutagen ethyl methane sulfonate, germinated, and allowed to produce seed. Plants derived from these seeds were screened for reduced stem growth. A mutant line, EMS-141, in which the lack of stem growth can be fully overcome with exogenous GA(3), was selected for further analysis. Other phenotypic abnormalities exhibited by the mutant line include reduced petiole growth, slightly delayed floral initiation, and failure of flowers to develop fully. These are also reversed with exogenous GA(3). Evidence is presented indicating that all of the alterations in growth and development exhibited by EMS-141 are conferred by a recessive mutation of a single nuclear gene. Through quantitative analysis of endogenous GA and GA precursors and a comparison of the abilities of various compounds to restore normal growth when applied to plants of EMS-141, the physiological basis for the mutant phenotype was determined to be the result of highly reduced endogenous GA levels. Moreover, the affected site in GA biosynthesis appears to be the accumulation of ent-kaurene, probably at the level of ent-kaurene synthase. The relative abilities of exogenous GA and GA precursors to restore normal growth of petioles and stems are compared, and the results are used to make inferences on the functions of the two different pathways of GA metabolism that exist in field pennycress.

Comparison of Biological Activities of Gibberellins and Gibberellin-Precursors Native to Thlaspi arvense L.

Field pennycress (Thlaspi arvense L.) is a winter annual weed with a cold requirement for stem elongation and flowering. The relative abilities of several native gibberellins (GAs) and GA-precursors to elicit stem growth were compared. Of the eight compounds tested, gibberellin A(1), (GA(1)), GA(9), and GA(20) caused stem growth in noninduced (no cold treatment) plants. No stem growth was observed in plants treated with ent-kaurene, ent-kaurenol, ent-kaurenoic acid, GA(53), or GA(8). Moreover, of the biologically active compounds, GA(9) was the most active followed closely by GA(1). In thermoinduced plants (4-week cold treatment at 6 degrees C) that were continuously treated with 2-chlorocholine chloride to reduce endogenous GA production, GA(9) was the most biologically active compound. However, the three kaurenoid GA precursors also promoted stem growth in thermoinduced plants, and were almost as active as GA(20). No such increase in activity was observed for either GA([unk]) or GA(53). The results are discussed in relation to thermoinductive regulation of GA metabolism and its significance to the initiation of stem growth in field pennycress. It is proposed that thermoinduction results in increased conversion of ent-kaurenoic acid to GAs through the C-13 desoxy pathway and that GA(9) is the endogenous mediator of thermoinduced stem growth in field pennycress.

Summer Annual and Winter Annual Weed Control in Field Soil and Soilless Media with Gallery (lsoxaben)

Abstract Field and container experiments were conducted to evaluate Gallery (isoxaben) efficacy on several common nursery and landscape weeds. Gallery was applied at rates from 0.14 to 1.1 kg ai/ha (0.125 and 1 lb ai/A). Annual grass control with Gallery generally was poor at application rates below 0.84 kg/ha (0.75 lb/A). Higher rates were needed for consistent foxtail and annual bluegrass control. Gallery controlled most broadleaf weeds at ≤0.56 kg/ha (0.5 lb/A) in field soil and a soilless potting medium. The exception was velvetleaf, which was not controlled with 1.1 kg/ha (1 lb/A). Combining Gallery with Surflan (Snapshot) at 1.1 + 3.4 kg/ha (1 + 3 lb/A) provided excellent control of all weeds tested. Equivalent weed control was obtained with a tank mix of Gallery plus Surflan at 0.28 + 3.4 kg/ha (0.25 + 3 lb/A) in 1989, suggesting that when used in combination with Surflan the rate of Gallery may be reduced relative to the comparable Snapshot rate, without sacrificing weed control.

Relationship of Herhivore- Imposed Stress to Weeds in Alfalfa

The relationship of selected herbivores and herbivore complexes to the incidence of winter and summer annual weeds associated with alfalfa was evaluated over a 3-yr period. Winter annual weed populations in the first cutting, second production year, were associated with aphid stress imposed during the previous fall and exacerbated by a severe infestation 6–8 wk before harvest. A significant (P < 0.05) interaction between Egyptian alfalfa weevil and aphids affected winter annual weed percentages in the first harvest of the third production year. Summer annual grass populations did not develop until the third year. Egyptian alfalfa weevil had a significant effect on grass percentages in three of the four cuttings in which grasses were present.

Interference of Annual Weeds in Seedling Alfalfa (Medicago sativa)

Barnyardgrass [Echinochloa crus-galli(L.) Beauv. #4ECHCG] and pigweeds (mixture ofAmaranthus retroflexusL. # AMARE andA. powelliiS. Wats. # AMAPO) seeded separately with alfalfa (Medicago sativaL.) in mid-August suppressed alfalfa severely before frost killed them in October and November. Some alfalfa was killed, and yield of alfalfa forage was reduced in each of three harvests the following year. These weeds did not harm alfalfa seeded in mid-September. Downy brome (Bromus tectorumL. # BROTE) and tumble mustard (Sisymbrium altissimumL. # SSYAL) suppressed alfalfa seeded in August and September. They reduced alfalfa stands and reduced yield of alfalfa forage in each of three harvests the following year. Alfalfa seeded August 27 and allowed to compete with a mixture of these species for various periods was injured most by weeds that emerged with the alfalfa and remained uncontrolled until forage harvest in May. These weeds did not reduce alfalfa yields if removed by 36 days after alfalfa emergence. Thereafter, yield decreased as the period of weed interference increased. Interference was most damaging in early spring, when growth of winter annual weeds was rapid and vigorous. Weeds seeded 65 or more days after alfalfa emergence did not reduce alfalfa yields but sometimes produced enough biomass to reduce the quality of the first-cutting alfalfa hay.