Seed Head Emergence Research Articles

Phenology and Population Differentiation in Reproductive Plasticity in Feathertop Rhodes Grass (Chloris virgata Sw.)

An understanding of phenology and reproductive plasticity of a weed species can provide valuable information to manage it precisely. This study evaluated the phenotypic plasticity of feathertop Rhodes grass (Chloris virgata Sw.) where cohorts of four different populations (two from cropping and two from roadside situations) were initiated in early spring (4 September), late spring (4 November), mid-summer (4 January), and early autumn (4 March) in southern New South Wales (NSW), Australia. The team grew individual plants in the absence of competition under natural conditions. Life-history and fitness-related traits of both phenology and morphology were measured, and dry biomass of vegetative and reproductive parts were determined at physiological maturity. Among the four sowing times, the late-spring sowing treatment took the longest time from emergence to the first seed head emergence (70–110 days), while it had the shortest seed maturity period (8–16 days). Length of reproductive and total life period of the four populations differed across the four sowing-time treatments. The plants that emerged in mid-summer had the longest reproductive period (30 days) whereas the early-autumn emerging plants died before the reproductive stage because of the cold temperatures during winter. The mid-summer cohort required slightly longer time (63–85 days) to achieve seed head formation and less time (19–24 days) for seed maturity than those plants that emerged in early or late spring. All the reproductive features were varied by sowing times and population. The number of seed heads (12–15 per plant) and spikelets (12–13 per seed head), as well as the seed head biomass, re-productive biomass allocation pattern, and seed production, generally increased in the mid-summer-emerged cohort. Seed production in the mid-summer (9942 seeds/plant) cohort was 10% and 70% higher than the late spring (8000 seeds/plant) and early spring (3240 seeds/plant) cohorts, respectively. The ratio of reproductive biomass to vegetative biomass increased in the mid-summer sowing times in all populations, and this species displayed true plasticity in reproductive allocation. Additionally, the four populations of feathertop Rhodes grass differed significantly in phenological, vegetative, and reproductive traits, depending on the sowing time. The reproductive fitness of the four populations varied, with the two roadside populations (FELT 04/20 and STURT/16–17) appearing to be better adapted than the two cropping populations (PARK 01/20 and GLEN 03/18). The results from our study could help construct a basic framework for a variety of weed-management tactics to achieve successful control.

Using local weather stations to generate growing degree‐day data to predict the flowering pattern of an annual bluegrass fairway in Michigan

AbstractSix 1‐yr observational studies were conducted from 2001 to 2006 at the Hancock Turfgrass Research Center in East Lansing, MI to characterize the timing, duration, and amplitude of annual bluegrass (AB) (Poa annua L.) seedhead emergence in a 10‐ to 15‐yr‐old AB fairway. The objective of this research was to collect data that could be used in the development of a growing degree‐day (GDD) model to predict AB seedhead emergence at other locations by using readily available weather station data. New GDD models were compared with previously published models. Plots were established on two adjacent perennial stands of AB maintained at 1.5 cm, receiving 0.5 to 0.6 cm of automatic daily irrigation throughout the growing season and 120 kg N ha–1 yr–1 from 2001 to 2006. The soil type is a Marlette sandy loam (fine‐loamy, mixed, semiactive, mesic Oxyaquic Glossudalf). Line intersects and visual estimations of seedhead cover were evaluated multiple times throughout the spring seedhead emergence period. A base temperature of –5 °C most accurately predicted the onset, peak duration, and completion of the AB seedhead emergence period for all 5 yr. The final model flowering rate = (–3.331599 × 10–6 × gdd2) + (6.968782 × 10–3 × gdd) + –2.841894, accurately predicted (R2 = .64) flowering stages of an AB fairway turf over 6 yr in Michigan.

Seedhead Development of Three Warm‐Season Turfgrasses as Influenced by Growing Degree Days, Photoperiod, and Maintenance Regimens

Seedheads of warm‐season grasses can reduce the quality of golf course turf. The objectives of this research were to evaluate environmental conditions associated with seedhead production of three warm‐season turfgrasses maintained at various mowing heights (0.6 or 1.3 cm 2 d wk−1, 3.8 cm wk−1, or no mowing) over a 3‐yr period. Photoperiod was more influential on initial seedhead development of ‘TifGrand’ bermudagrass [Cynodon dactylon (L.) Pers. ×Cynodon transvaalensis Burtt‐Davy] and ‘Sea Isle 1’ seashore paspalum (Paspalum vaginatum Sw.) than calendar date or growing degree day (GDD) accumulation. Across all mowing heights, initial seedhead emergence began at 13.5‐h photoperiod in 2013 and between 13.8 and 14.2 h in 2014 and 2015. Calendar date and GDD had stronger correlations than photoperiod with seedhead production from January until summer for bermudagrass and seashore paspalum at all mowing heights except for the 0.6 cm 2 d wk−1. ‘Diamond’ zoysiagrass [Zoysia matrella (L.) Merr.] exhibited two major flushes of seedhead emergence that began with photoperiods of ∼12.8 h in fall and spring. The GDD on dates of initial seedhead emergence in spring and fall ranged from 167 to 196 and 1949 to 2230 (base model 10°C on 1 January), respectively, in all years across mowing regimens. Zoysiagrass seedhead production had the highest correlation with GDD in spring and with photoperiod in fall. Overall, photoperiod triggers initial seedhead emergence of bermudagrass and seashore paspalum, but GDD is more influential on seedhead production in summer. The emergence of Diamond zoysiagrass seedheads in spring was associated with calendar date, GDD, and photoperiod, but emergence in fall was dependent on photoperiod.

Animal and Pasture Responses to Grazing Management of Chemically Suppressed Tall Fescue in Mixed Pastures

Treatment of toxic endophyte‐infected tall fescue [Lolium arundinaceum (Schreb.) Darbysh] with metsulfuran‐methyl {Methyl 2‐[[[[(4‐methoxyl‐6‐methyl‐1,3,5‐triazin‐2‐yl)‐amino]carbonyl]amino]sulfonyl] benzoate}, as delivered by Chaparral herbicide (Dow AgroSciences, Indianapolis, IN) can mitigate fescue toxicosis and enhance forage nutritive value by suppressing seedhead emergence. A grazing experiment was conducted with steers (2013) and heifers (2014) to evaluate animal and plant responses to grazing management of mixed cool‐season grass pastures treated with Chaparral. Continuous and rotational stocking treatments were assigned to six, 3.0‐ha pastures in a randomized complete block design with three replications in 2013 and two replications in 2014. Each pasture had six tester animals, and stocking rates were varied using put‐and‐take animals. Pastures were grazed from 16 April to 8 July 2013 and 20 May to 12 Aug. 2014. Pasture carrying capacity was 20% greater for rotational than continuous stocking. Calves on rotationally stocked pastures also had 26% greater average daily gain (ADG) and body weight (BW) gain per hectare than those on the continuous treatment. Pre‐grazed herbage had less neutral detergent fiber (NDF) and acid detergent fiber (ADF) than post‐grazed herbage and herbage from continuously stocked pastures in 2013, but they did not differ in 2014. Crude protein (CP) was lower in post‐graze rotational pasture than in continuous or pre‐graze rotational pasture. Fescue roots in rotationally stocked pastures had greater water soluble carbohydrates (WSC) and N concentrations than continuously stocked pastures following the second year of grazing. Results indicated that rotational stocking of Chaparral treated mixed pastures can improve animal performance and pasture productivity.

Growth and flowering inhibition of Paspalum notatum with application of trinexapac-ethyl and prohexadione-calcium

ABSTRACT This study aimed to evaluate the effect of sequential applications of plant regulators on growth and seedhead emergence of Bahiagrass (Paspalum notatum). The study was carried out on a 15-month-old lawn, in a randomized block design, with four replicates. The treatments consisted of the following plant-growth regulators and dose: trinexapac-ethyl in sequential application of 113 + 113, 226 + 113, 226 + 226, 452 + 113, 452 + 226, 452 + 452 g a.i. ha-1; trinexapac-ethyl in single application of 678 and 904 g a.i. ha-1; and prohexadione-calcium in sequential application of 100 + 100 and 200 + 200 g a.i. ha-1, besides a control, with no application. The effects of treatments were evaluated based on visual injury, plant height, height and number of flower rachises and total dry matter production of clippings. Sequential applications of prohexadione-calcium at 100 + 100 or 200 + 200 g a.i. ha-1 were efficient to reduce plant height, but did not show efficacy to reduce the number and height of seedheads or the total dry matter of clippings of Bahiagrass. However, Bahiagrass lawns can be managed by trinexapac-ethyl sequential applications of 452 + 452 g a.i. ha-1 or single application of 904 g a.i. ha-1, with reduction in the need for mowing for a period of up to 113 days after application, without causing any deleterious effect on the visual aspect of the lawn.

Impact of deferred grazing and fertilizer on herbage production, soil seed reserve and nutritive value of native pastures in steep hill country of southern Australia

AbstractDeveloping sustainable grazing management systems based on perennial species is critical to preventing land degradation in marginal land classes. A field study was conducted from 2002 to 2006 to identify the impacts of deferred grazing (no defoliation of pastures for a period generally from spring to autumn) and fertilizer application on herbage accumulation, soil seed reserve and nutritive value in a hill pasture in western Victoria, Australia. Three deferred grazing strategies were used: short‐term deferred grazing (no defoliation between October and January), long‐term deferred grazing (no defoliation from October to the autumn break) and optimized deferred grazing (withholding time from grazing commenced between annual grass stem elongation and seed head emergence and concluded in February/March). These treatments were applied with two fertilizer levels (with or without fertilizer at 50 kg phosphorus ha−1 and 2000 kg lime ha−1 applied in year 1 only) in a factorial arrangement and two additional treatments: continuous grazing (CG) and no grazing (NG) in year 1. The deferred grazing treatments on average produced herbage dry matter of 4773 kg ha−1, the NG produced 4583 kg ha−1 and the CG produced 3183 kg ha−1 in year 4 (2005–06) of the experiment. Deferred grazing treatments with and without fertilizer application produced an average of 5135 and 4411 kg DM ha−1 respectively. Averaged over 4 years, deferred grazing increased the germinable seed pool of perennial grasses by 200% and annual grasses by 50% (except optimized deferred grazing that considerably decreased the annual grass seed pool) compared with the CG. The best of the deferred grazing strategies increased the digestibility of pastures by 7% compared with the CG. The results demonstrated that deferred grazing from spring to autumn followed by rotational grazing could be an effective tool to increase herbage production and soil seed pool and improve the digestibility of native pastures in the steep hill country of southern Australia.

Ergot Alkaloid Concentrations in High‐ and Low‐Moisture Tall Fescue Silage

ABSTRACTErgot alkaloids are mycotoxins found in foods and forage crops, including common tall fescue [Lolium arundinaceum (Schreb.) Darbysh. = Schedonorus arundinaceus (Schreb.) Dumort.], which hosts a fungal endophyte. The objective of this study was to determine changes in ergovaline and total ergot alkaloid concentrations in tall fescue silage produced at high moisture (650 to 680 g H2O kg−1) and low moisture (340 to 400 g H2O kg−1). The study was conducted on endophyte‐infected pastures of tall fescue in northern and southern Missouri. Tall fescue was clipped after seedhead emergence but before anthesis, wilted to high or low moisture, baled, and wrapped. After >100 d of ensiling, bales were cored and samples analyzed for ergovaline and total ergot alkaloid concentrations. Ergovaline concentration decreased (P < 0.05) during ensiling at both locations and moisture levels, and the decrease ranged from 24 to 58%. In contrast, total ergot alkaloid concentrations increased during ensiling in high moisture silage in northern (P < 0.10) and southern (P < 0.05) Missouri but did not change in low moisture silage. The opposing responses of ergovaline and total ergot alkaloids offer partial explanations for differences reported in studies involving tall fescue silage. These responses also caution against recommendations to ensile tall fescue to reduce toxins because one analyte indicates detoxification is possible, while the other analyte does not.

Physiological Behavior of Ethephon in Five Turfgrasses

ABSTRACTTurfgrass seedhead emergence often warrants plant growth regulator (PGR) use for suppression, but practitioners have limited chemistries available for warm‐season species. Ethephon effectively suppresses turfgrass seedheads, but injury to bermudagrass and seashore paspalum is often excessive. Experiments were conducted to evaluate differential behavior of ethephon in bermudagrass and seashore paspalum, compared with annual bluegrass, creeping bentgrass, and zoysiagrass. In greenhouse experiments, ethephon was most injurious to bermudagrass and seashore paspalum, ranging 19 to 40% from 3 to 28 d after treatment (DAT), while annual bluegrass, creeping bentgrass, and zoysiagrass had less injury, ranging 9 to 21%, across three application rates (1.9, 3.8, or 7.6 kg a.i. ha–1). In laboratory experiments, foliar absorption of 14C‐ethephon generally increased from 24 to 96 h after treatment (HAT), but differences among species were not detected. Creeping bentgrass and zoysiagrass retained >90% of foliar applied 14C in treated leaves, but bermudagrass and seashore paspalum distributed ∼25% more 14C to nontreated shoots. From root absorption, bermudagrass and seashore paspalum distributed ∼25% less 14C to shoots than creeping bentgrass at 72 HAT. Annual bluegrass 14C distribution after foliar and root absorption was similar to all species, except creeping bentgrass. There were no meaningful differences in turfgrass metabolism levels of 14C‐ethephon at 1, 4, or 7 DAT. Results suggest differential levels of distribution after root and shoot absorption could be associated with bermudagrass and seashore paspalum sensitivity to ethephon compared with turfgrasses with less injury potential.

FORAGES AND PASTURES SYMPOSIUM: Managing the tall fescue–fungal endophyte symbiosis for optimum forage-animal production12

Alkaloids produced by the fungal endophyte (Neotyphodium coenophialum) that infects tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] are a paradox to cattle production. Although certain alkaloids impart tall fescue with tolerances to environmental stresses, such as moisture, heat, and herbivory, ergot alkaloids produced by the endophyte can induce fescue toxicosis, a malady that adversely affects animal production and physiology. Hardiness and persistence of tall fescue under limited management can be attributed to the endophyte, but the trade-off is reduced cattle production from consumption of ergot alkaloids produced by the endophyte. Improved understanding and knowledge of this endophyte-grass complex has facilitated development of technologies and management systems that can either mitigate or completely alleviate fescue toxicosis. This review discusses the research results that have led to development of 5 management approaches to either reduce the severity of fescue toxicosis or alleviate it altogether. Three approaches manipulate the endophyte-tall fescue complex to reduce or alleviate ergot alkaloids: 1) use of heavy grazing intensities, 2) replacing the toxic endophyte with nonergot alkaloid-producing endophytes, and 3) chemical suppression of seed head emergence. The remaining 2 management options do not affect ergot alkaloid concentrations in fescue tissues but are used 1) to avoid grazing of tall fescue with increased ergot alkaloid concentrations in the late spring and summer by moving cattle to warm-season grass pasture and 2) to dilute dietary alkaloids by interseeding clovers or feeding supplements.

Steer and Plant Responses to Chemical Suppression of Seedhead Emergence in Toxic Endophyte‐Infected Tall Fescue

ABSTRACTChaparral herbicide has been shown to suppress seedhead emergence in tall fescue [Lolium arundinaceum (Schreb.) Darbysh] and potentially mitigate the effects of fescue toxicosis. A two‐year grazing experiment evaluated steers grazed on endophyte‐infected fescue–Kentucky bluegrass (Poa pratensis L.) pastures either treated or untreated with Chaparral herbicide to determine if seedhead suppression alleviates fescue toxicosis and increases average daily gain (ADG). Treatments were assigned to six, 3.0‐ha fescue‐bluegrass pastures in a randomized complete block design with three replications. Pastures were grazed with 48 steers (2.7 steers ha−1) from 9 Apr. to 1 July 2009 and 6 Apr. to 7 July 2010. Reproductive tiller densities in treated pastures were low in both years (<7 m−2) in comparison with untreated pastures (113 and 69 tillers m−2 in 2009 and 2010, respectively). Ergovaline and ergovalinine concentrations were three‐ to sixfold greater in seeds than in leaf blades and sheaths of vegetative and reproductive tillers. Crude protein, water soluble carbohydrates, and in vitro digestible dry matter concentrations of tillers declined over time at a greater rate in untreated than in treated pastures. Steers on treated pastures had greater (P < 0.01) ADG, lower (P < 0.10) rectal temperatures, and greater (P < 0.01) serum prolactin concentrations. Results indicated that Chaparral herbicide can suppress reproductive development of fescue to increase ADG and reduce the severity of toxicosis.

Seed Production Characteristics of Prairie Junegrass Germplasm Accessions

Prairie junegrass [Koeleria macrantha (Ledeb.) Shult.] is a perennial, short‐grass prairie species distributed throughout the northern hemisphere. This species is known to require fewer inputs than other cool‐season turfgrasses and it demonstrates tolerance to many environmental stresses found in Minnesota. In June 2007, 48 K. macrantha accessions from the U.S. National Plant Germplasm System (NPGS) were grown and evaluated for seed production characteristics in 2 locations (St. Paul, MN, and Becker, MN). Significant variation was found among accessions for several seed production traits including harvest date, plant height, seedhead number, and seed yield. A significant correlation between seedhead number and seed yield was found, which can be utilized for indirect selection in the production nursery. Plant growth and seed yield were highest at the Becker location, demonstrating the species' preference for well‐drained soils. Flowering times were significantly different between the locations; however, there were no significant differences in the duration from seedhead emergence to harvest between the locations. Multivariate analysis did not reveal clustering of accessions based on geographic origin, suggesting a diversity of material within collection regions.

Chemical control of blind seed disease in perennial ryegrass (Lolium perenne) in Victoria

Seven fungicides were evaluated in field trials for control of blind seed disease (caused by Gloeotinia temulenta) of Lolium perenne in southern (Birregurra) and northern (Mansfield) Victoria. Propiconazole (125 g a.i./ha), flutriafol (125 g a.i./ha) and benomyl (250 g a.i./ha) gave the best control. The incidence of blind seed was significantly reduced by urea applications at Birregurra, but not at Mansfield. The fungicides were most effective when applied at seed head emergence and at anthesis stages of crop growth. Alternating applications of benomyl and propiconazole, which could be a strategy to minimise the chance of G. temulenta developing fungicide resistance, provided satisfactory control of the disease. Propiconazole is currently registered for control of blind seed disease in Victoria.

Efecto de la fitohormona esteroidal cidef-4 en el rendimiento y calidad de semilla

The objective of this study was to evaluate the effect of the steroidal compound cidef-4 on guinea grass (Panicum maximum Jacq.) cv. Tanzania seed yield and quality. The experiment was carried out in the field under rainfed conditions during 2000 in Tejupilco, State of Mexico, Mexico. Two treatments were evaluated, i) before seed head emergence and ii) at the beginning of anthesis at four product concentrations (0, 2, 4 and 6 mg kg-1 active ingredient of cidef-4), distributed in a randomized complete block design, and arranged in split plots with three replicates. Variables evaluated were: pure germinable seed harvested yield (PGSHY), number of panicles per square meter, number of seeds produced and harvested per panicle, 1000-seed weight, and seed purity and germination. PGSHY varied between treatments (P<0.05) and the greatest yield (128 kg ha-1) was obtained when cidef-4 was applied at the beginning of anthesis. All concentrations of cidef-4 increased PGSHY, however, the greatest seed yield (132 kg ha-1) was obtained with the highest cidef-4 concentration (6 mg kg-1). Number of panicles showed an increase with the application of cidef-4 compared to the control (P<0.05). 1000-seed weight, purity and germination of the harvested seed were not significantly affected by any of the treatments applied. It can be concluded that the yield of guinea grass seed can be increased through application of 6 mg kg-1 active ingredient of cidef-4 at the beginning of anthesis.

The Botanophila–Epichloë association in cultivated Festuca in Oregon: evidence of simple fungivory

AbstractWe investigated the Botanophila (Diptera: Anthomyiidae)–Epichloë (Ascomycetes: Clavicipitaceae) interaction in cultivated Festuca spp. (fine fescue) in Oregon in western USA. Epichloë spp. are endophytic fungi of grasses in the subfamily Pooideae. They develop a felt‐like stroma on the surface of grass culms and a dense mycelium within the culms that typically prevents seed head emergence. As a result, seed yields are suppressed, and hence the disease is known as choke. Studies of Epichloë spp. on wild grasses indicate that the fly–fungus interaction is an obligatory mutualism. During oviposition, Botanophila transfers Epichloë spermatia between stromata of opposite mating types, and the perithecia that develop after fungal fertilization serve as food for Botanophila larvae. In the current study, we surveyed 19 cultivated fields of Festuca spp. in Oregon, and observed choke caused by Epichloë festucae Leuchtmann, Schardl and Siegl in 10 of these. However, perithecia were observed in only four fields, and on only 1.0–2.6% of stromata. Perithecial development was also low, and rarely covered 50% of the stroma surface. Despite the absence or low frequency of fertilized stromata, Botanophila lobata Collin larvae were present in all choke‐infested fields. Infestation levels ranged from 2.5 to 70.7%, based on an examination of 175–200 stromata from each field. Only eight (= 2%) of the 450 stromata with B. lobata had perithecia, and the greater majority of B. lobata larvae completed development and exited from unfertilized stromata. This is the first report of the B. lobata–E. festucae association in the USA, and of B. lobata larvae developing successfully on unfertilized Epichloë stromata. The average pupal weight (0.0032 g) did not differ significantly from pupae (0.0030 g) originating from larvae that had developed on fertilized stromata of E. typhina on Dactylis glomerata in a neighboring field. This result indicates that in cultivated fine fescue fields in Oregon, B. lobata forages on E. festucae, but fly development is not dependent on the fertilized stromata of Epichloë.

Effects of Postemergence Herbicides on Centipedegrass Seed Production1

Field studies were conducted in 2001 and 2002 to determine the effect of clethodim, sethoxydim, and halosulfuron on centipedegrass seedhead suppression, seed yield, and seed germination. Clethodim (0.28 kg/ha), sethoxydim (0.31 kg/ha), and halosulfuron (0.06 kg/ha) applications were made at −2, 0, 2, 4, and 6 wk after mowing stopped (WAMS) in each year. Seedhead suppression varied in severity between 2001 and 2002, with increased suppression in 2001. Clethodim reduced seedhead emergence 50 and 33% when applied at 2 and 4 WAMS, respectively, in 2001. Sethoxydim reduced seedhead emergence by 21 and 18% when applied at 2 and 4 WAMS, respectively, in 2001. Halosulfuron had no effect on seedhead emergence in either year and did not reduce seed yield at any application timing. Clethodim reduced seed yield between 22 and 44% at all application timings. The pattern of yield reduction from sethoxydim was similar to that caused by clethodim; however, yield reduction with sethoxydim ranged between 7 and 48% for all application timings. The greatest reduction in seed yield occurred when clethodim and sethoxydim were applied 4 WAMS. Seed germination was not affected by halosulfuron or sethoxydim at any application timing. Clethodim, when applied at 4 and 6 WAMS, decreased seed germination by 17 and 20%, respectively.Nomenclature: Clethodim; halosulfuron; sethoxydim; centipedegrass, Eremochloa ophiuroides (Munro) Hack. ‘Tifblair’ #3 ERLOP.Additional index words: Seed germination.Abbreviations: WAMS, weeks after mowing stopped; WAT, weeks after treatment.

Rice (Oryza sativa) Response to the Microencapsulated Formulation of Clomazone1

Experiments were conducted in 1996 and 1997 in water-seeded and drill-seeded production systems to determine rice response to clomazone applied at rates ranging from 0.28 to 2.2 kg ai/ha on silt loam and silty clay soils. Clomazone-induced bleaching of rice seedlings was 15% or less when clomazone was applied at 0.28 or 0.56 kg/ha. Increasing the rate of clomazone increased bleaching in most experiments. Clomazone at 0.84 kg/ha or higher delayed seed head emergence in five of eight experiments. Clomazone at lower rates did not delay seed head emergence. Although clomazone at 0.28 and 0.56 kg/ha did not reduce grain yield, clomazone at 0.84 and 1.1 kg/ha reduced grain yield in one experiment while clomazone at 1.7 and 2.2 kg/ha reduced yield in two experiments. The influence of soil type and seeding method on rice's tolerance to the microencapsulated formulation of clomazone could not be demonstrated in these experiments. Clomazone was more injurious in drill-seeded production than in water-seeded production.Nomenclature: Clomazone, 2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone; rice, Oryza sativa L. ‘Cypress’.Additional index words: Crop injury.Abbreviations: PRE, preemergence.

Spray-topping annual grass pasture with glyphosate to delay loss of feeding value during summer. III. Quantitative basis of the alkane- based procedures for estimating diet selection and herbage intake by grazing sheep

Previous papers in this series have demonstrated that, when annual pastures were sprayed at seed head emergence with low rates of the herbicide glyphosate, the nutritive value of the sprayed herbage was improved. Housed sheep preferred sprayed herbage to unsprayed herbage and, within sprayed herbage, appeared to have a preference for stem material. The housed sheep ate more of the sprayed material and their weight gains were improved. If such responses occurred in grazing animals, they could result in substantial improvements in animal liveweights or wool production. The present paper describes the alkane-based procedures used to investigate diet selection and herbage intake in grazing animals, with the emphasis placed on methodological and statistical issues. The alkane concentrations in the plant fractions (leaf, leaf sheath, stem, seed head) of sprayed and unsprayed herbage are reported. Similarly, the alkane concentrations in extrusa samples collected by oesophageally fistulated sheep given access to the grazed areas, and in the faeces of sheep grazing the areas, are reported. Patterns of alkane concentrations in extrusa and faeces were similar and indicated that, in the short term, oesophageally fistulated animals consumed a diet of similar composition to that selected by the animals resident on the plots. Using these data for alkane concentrations, multivariate statistical analyses are presented which provide an objective basis for selecting the alkanes to be used in the estimation of diet selection. The results of the first of 4 grazing periods are presented, as an example of the application of the alkane-based procedures for estimating herbage intake and, in particular, diet composition. Use of these techniques indicated that, when given access to sprayed senescent pasture, sheep consumed more digestible dry matter and selected more of it from the stem fraction than was the case with unsprayed herbage. These results are similar to those found with housed animals and demonstrate that patterns of herbage and faecal alkane concentrations can be used to estimate diet composition of grazing animals in terms of the plant parts on offer

Spray-topping annual grass pasture with glyphosate to delay loss of feeding value during summer. IV. Diet composition, herbage intake, and performance in grazing sheep

We report the effects of spray-topping annual grass pasture with glyphosate (180 g a.i./ha as Roundup CT, at the seed head emergence stage) on the nutritive value of herbage and on subsequent performance of grazing sheep. Eight 1-ha plots, consisting of 4 sprayed and 4 unsprayed (control) plots, were set-stocked with Merino wethers (18 months old, 12 sheep/ha) from 8 days after anthesis in the control plots (late spring) until 165 days after anthesis (mid-autumn). In 4 periods (15–20, 36–41, 71–76, and 99–104 days after anthesis; Periods 1–4, respectively) sheep were dosed with synthetic alkanes and herbage and faecal samples were taken, in order to estimate diet composition (in terms of plant parts), faecal output, herbage intake, and the digestibility of the whole diet. As described in our earlier papers, spray-topping reduced the yield of pasture dry matter, but also slowed the loss of water-soluble carbohydrate (WSC) and digestibility during pasture senescence. The present paper shows that as a result, sheep grazing sprayed herbage in Periods 1 and 2 consumed significantly more organic matter (OM) and digestible OM (DOM) than sheep grazing the control pasture. Their diet contained a higher proportion of stem with a higher WSC concentration than that of the sheep grazing the control plots. The proportions of different plant parts (leaf blade+sheath, stem, seed head) in the diet of both the plot sheep and oesophageally fistulated (OF) sheep, which grazed treatments for short periods, differed significantly between treatments in all periods. However, the compositions of the diets selected by plot and OF sheep were similar. These results confirmed diet preferences measured using housed sheep and demonstrate the usefulness of alkane-based procedures for quantifying diet composition and intake in grazing animals. As a result of their higher intake of DOM, sheep grazing sprayed herbage had a significantly higher liveweight gain over the first 2 periods (40 g/day). In Period 3, sheep grazing sprayed herbage consumed more OM than sheep grazing control herbage. However, DOM intakes from sprayed or control plots were not significantly different in either Period 3 or Period 4, and were lower than in Periods 1 and 2. Sheep grazing both treatments lost liveweight at a similar rate over this time. Wool growth in sheep grazing sprayed herbage was improved by 10% during the experimental period; wool strength was also improved significantly. The implications for the management of sheep grazing spray-topped pastures over summer are discussed.

Spray-topping annual grass pasture with glyphosate to delay loss of feeding value during summer. II . Herbage intake, digestibility, and diet selection in penned sheep

The treatment of annual ryegrass–silver grass pasture with the herbicide glyphosate at seed head emergence delayed the loss of soluble carbohydrates and improved herbage digestibility. The present study investigated whether this improvement in nutritive value had any influence on the diet preference, intake, and performance of housed sheep. Since the effects of glyphosate on digestibility were most marked in stem tissue, preference was examined not only in relation to sprayed v. unsprayed herbage, but also in terms of preference for individual plant parts. In the preference testing, sheep showed a marked preference for sprayed rather than unsprayed herbage. They also consumed more of it, such that their digestible dry matter intake from sprayed herbage was nearly twice that from unsprayed herbage. When sheep were offered different plant fractions from the control herbage, they selected against stem material and preferred leaf or seed head. By contrast, when offered fractions from the sprayed material, they preferred stem to leaf, but showed no strong preference for stem over seed head. Preference was related more to the soluble carbohydrate content of a plant part than its digestibility, and only when soluble carbohydrate contents were similar was there preference for the more digestible material. The consumption of sprayed herbage, compared with control herbage, led to higher concentrations of rumen volatile fatty acids in the period 4 h after feeding. Moreover, the feeding of these herbages over a 6-week period resulted in significant reductions in pre-feeding plasma urea and β-hydroxybutyrate concentrations. When control herbage was fed with supplements of fructose, urea, or fructose+urea, in an attempt to mimic the possible differences in nutritive value between control and sprayed herbage, the responses in rumen and blood metabolites were less marked than when sprayed herbage was fed. As a consequence of the higher nutritive value of the sprayed herbage and the higher intakes by the animals fed this material, sheep fed sprayed herbage were able to maintain weight over the feeding period, whereas those offered the control herbage lost weight at 130–150 g/day

Johnsongrass (Sorghum halepense) Control and Rainfastness with Glyphosate and Adjuvants

Glyphosate and adjuvant combinations were applied to rhizome johnsongrass at vegetative and reproductive growth stages to evaluate control and rainfastness in field studies. Using a rainfall simulator delivering 1.3 cm of water in 15 min, plots received either no rainfall or rainfall 15 or 60 min after glyphosate was applied at 2.1 kg ai/ha in combination with the nonionic surfactants Kinetic®HV at 0.25% (v/v) or Induce®at 1.0% (v/v) or the silicone surfactant Break-Thru®at 0.125% (v/v). Regardless of adjuvant, rainfall 15 or 60 min after application reduced johnsongrass control compared with no rainfall. Johnsongrass control 14 d after treatment at the reproductive stage was at least 89% with no rainfall, but no more than 53 and 65% with rainfall at 15 and 60 min, respectively. Based on initial weed control, adjuvants did not consistently improve rainfastness. Johnsongrass regrowth did not occur when glyphosate was applied with either adjuvant. In contrast, for glyphosate applied to johnsongrass in the vegetative stage, addition of Break-Thru improved control over Induce at both 15- and 60-min rainfall timings in one of two experiments. With no rainfall, addition of Kinetic HV and Break-Thru increased johnsongrass control in only one experiment. For application at the vegetative stage, johnsongrass regrowth averaged across rainfall timings was no more than 10%. In other field experiments, glyphosate at 1.4 kg/ha plus nonionic surfactants, silicone surfactant, crop oil concentrate, methylated seed oil, or a blend of silicone surfactant and methylated seed oil were equally effective in reducing johnsongrass regrowth when applied after seedhead emergence. Improved control of vegetative johnsongrass with some adjuvants was not reflected in decreased regrowth.