Alfalfa Injury Research Articles

Genome Sequence Resource for Strains of Pseudomonas syringae Phylogroup 2b and P. viridiflava Phylogroup 7a Causing Bacterial Stem Blight of Alfalfa.

Genome Sequence Resource for Strains of Pseudomonas syringae Phylogroup 2b and P. viridiflava Phylogroup 7a Causing Bacterial Stem Blight of Alfalfa.

Evaluation of the summer slump application of saflufenacil on nondormant conventional alfalfa

AbstractAlfalfa (Medicago sativa L.) is an important crop for the low desert region of southwestern United States. A field study was conducted to evaluate tolerance of established nondormant conventional alfalfa to saflufenacil applied during the summer slump. Treatments consisted of saflufenacil applied alone at 0.7 or 1.4 oz ac−1, or saflufenacil at 0.7 oz ac−1 tank‐mixed with imazamox, bromoxynil, or metribuzin at 0.8, 6.0, or 16.0 oz ac−1, respectively. Methylated seed oil (as surfactant) and ammonium sulfate (as adjuvant) were tank‐mixed at 1 and 2.5% (v/v), respectively, to each herbicide treatment. At 2 d after treatment, alfalfa injury from saflufenacil at the lower rate was lowest (21%); whereas the injury was highest (48%) from saflufenacil plus bromoxynil treatment. The alfalfa injury progressed for 2 wk after treatment (WAT) and was >36% for all treatments except for saflufenacil at the lower rate. Crop recovery was observed about 2 WAT and minimal injury (<3%) occurred at 4 WAT. Alfalfa height was similar across herbicide treatments and the weed‐free (non‐treated) control. At 4 WAT, average alfalfa height for all treatments was 11 inches or greater. The alfalfa injury observed during the initial weeks did not translate into biomass yield reduction. Accordingly, there was no significant difference in alfalfa biomass yield among the treatments. Overall, alfalfa biomass yield was 0.57 and 0.47 ton ac−1 or greater at 4 WAT (1st cutting) and 8 WAT (2nd cutting), respectively, after herbicide application. Our results illustrate that saflufenacil and its tank‐mix with imazamox, bromoxynil, or metribuzin caused injury to nondormant conventional alfalfa during early weeks, but alfalfa recovered by 2 wk after herbicide application without height and biomass yield reduction.

Mapping Fall Dormancy and Winter Injury in Tetraploid Alfalfa

ABSTRACTAlfalfa (Medicago sativa L.) is a widely planted perennial forage crop. Fall dormancy is generally negatively correlated with winter injury in alfalfa. To understand the genetic basis of the two traits, we identified quantitative trait loci (QTL) controlling autumn growth and winter injury using a tetraploid alfalfa F1 population. In total, 601 marker alleles were scored from 78 restriction fragment length polymorphism (RFLP), 123 simple‐sequence repeat (SSR), and 48 single nucleotide polymorphism (SNP) markers. Linkage maps were constructed for each parent separately. Both maps contained eight linkage groups (LGs), with a length of 898 cM for WISFAL‐6 and 845 cM for ABI408. Using interval mapping, we identified 15 QTL from an across‐environment analysis and 71 QTL within individual environments for autumn plant height; winter injury; and autumn shoot, crown, and root biomass across four Iowa environments. Of the 71 QTL, 42 were identified at 18 chromosomal locations that were identified in multiple environments for the same trait. Possible pleiotropic QTL that contributed to dry weight of shoot, crown, and taproot were found, which partially explained the observed genetic correlations between those traits. However, few QTL were related to both autumn plant height and winter injury, supporting the observation of no genetic correlation between the two traits in this study. These results indicated that the two traits could be manipulated independently and, possibly, efficiently improved using marker‐assisted selection. Because most QTL identified in this study were mapped to intervals of at least 10 cM, validation and localization in additional populations is needed to facilitate application of marker‐assisted selection.

Canada Thistle (Cirsium arvense) Control in Established Alfalfa (Medicago sativa) Grown for Seed Production1

Canada thistle is one of the most troublesome and difficult weed species to control in established alfalfa grown for seed production. Current tools available for control are limited because of cultural management strategies associated with seed production. Alfalfa seed losses due to Canada thistle interference include both reduced yields from competition and increased seed loss during seed cleaning operations. Additional tools are needed to alleviate these losses. Field experiments were conducted in 1998, 1999, and 2000 at two locations in Park County, WY, to evaluate Canada thistle control and alfalfa tolerance to several postemergence herbicides. Bentazon, imazamox, imazethapyr, and MCPB were applied, alone or in combination, at different Canada thistle growth stages. Methylated seed oil (MSO) was added at 1.5% v/v to the treatments containing imazamox or imazethapyr. MCPB applied alone when Canada thistle was 7.5- or 15-cm tall caused severe alfalfa injury (28 to 40%) and resulted in less Canada thistle control (23 to 27%). Imazamox or imazethapyr applied alone when Canada thistle was 15-cm tall did not cause any significant alfalfa injury but resulted in unsatisfactory Canada thistle control (29 to 35%). Bentazon was the only treatment containing a single herbicide that provided more than 50% Canada thistle control. The treatments providing the best balance between Canada thistle control (>80%) and alfalfa injury (<13%) were a single application of bentazon combined with either imazamox or imazethapyr. These two treatments also yielded the highest, more than 800 kg/ha. Split applications of bentazon combined with imazamox or imazethapyr were similar to single applications.Nomenclature: Bentazon; imazamox; imazethapyr; MCPB; Canada thistle, Cirsium arvense (L.) Scop. #3 CIRAR; Alfalfa, Medicago sativa L.Additional index words: Application timing, herbicide mixtures, methylated seed oil, MSO, postemergence, weed management, CIRAR.Abbreviations: IMI, imidazolinone-resistant; MSO, methylated seed oil.

Interaction between Waterlogging Injury and Irradiance Level in Alfalfa

This study investigates the interaction between irradiance and waterlogging injury in alfalfa (Medicago saliva L.) at various plant developmental stages. Alfalfa was subjected to flooding for 8 to10 d under high or low irradiance levels in controlled environmental chambers. Treatments were imposed on alfalfa 8 and 21 d after planting (DAP) and during regrowth following clipping at 31 DAP. Hooding significantly reduced dry matter accumulation regardless of growth stage, although damage was most severe when flooding was imposed on plants during regrowth after clipping. Irradiance levels primarily affected shoot and root dry matter in 21- and 31-DAP treatments. Much greater shoot dry matter accumulation in nonflooded high irradiance plants was observed relative to low irradiance plants. A flooding × irradiance interaction was found at every growth stage except for root dry weight in the regrowth stage after clipping. The flooding interaction was due to greater injury of flooded high-irradiance plants relative to flooded low-irradiance plants when injury was expressed as a percentage of the unflooded control. Results indicate that the irradiance level during flooding can influence damage rating when expressed as a percentage of control. Assimilate supply to roots was sharply reduced by low irradiance as evidenced by reduced root growth and carbohydrate concentration in unflooded controls. Flooding damage, however, was not enhanced under low irradiance, lending support to the hypothesis that carbohydrate (i.e., energy supply) is not a limiting factor in survival of alfalfa roots during short-duration flooding stress.

Modeling Freezing Injury in Alfalfa to Calculate Forage Yield: II. Model Validation and Example Simulations

AbstractFreezing injury can cause extensive yield loss in alfalfa (Medicago sativa L.) exposed to severe winters in cold climates. Alfalfa models must simulate freezing injury effects in a cumulative way, so that forage dry matter (DM) yield can be accurately calculated during multiple years of a crop. A companion paper presents ALFACOLD, an alfalfa simulation model developed by integrating functions of cold tolerance, fall dormancy, and freezing injury into the ALSIM 1 (Level 2) alfalfa model. The ALFACOLD model calculates forage yield on a daily basis, while simulating freezing injury across multiple years of the same crop. The objective of this study was to test the ALFACOLD model's ability to calculate field‐measured forage DM yield. The model was tested against measured forage yield from 39 cultivars seeded in two years and managed under a 4‐cut system for 3 yr after the seeding year at two sites in Wisconsin. Averaged across the sites, cultivars, and years, the ALFACOLD model calculated annual forage DM yield to within 12% of the measured yield, compared with an error of 35% with the ALSIM model. A regression of field‐measured yield of individual harvests (n = 874) on the corresponding ALFACOLD calculated yield indicated that 70% of the measured variability in forage yield was explained by the model. The average difference between measured and calculated DM yield for Harvests 1, 2, and 3 was &lt;7%, but the model overcalculated fourth‐cut yield by 38%. Averaged across all sites, cultivars, years, and cuts, the ALFACOLD model calculated yield with an average SD of 600 kg ha−1 cut−1.

Modeling Freezing Injury in Alfalfa to Calculate Forage Yield: I. Model Development and Sensitivity Analysis

AbstractFreezing injury can cause extensive yield loss in alfalfa (Medicago sativa L.) exposed to severe winters in cold climates. Existing simulation models for alfalfa either do not account for freezing injury effects or do not differentiate cultivars for their varying response to freezing stress and subsequent effects on crop productivity. The objective of this project was to incorporate cultivar‐specific effects of freezing injury on forage dry matter (DM) yield into an existing alfalfa growth model to calculate annual forage yield during the life of an alfalfa crop. Numerical functions of cold tolerance, fall dormancy, and freezing injury were developed and integrated with the growth processes in the ALSIM 1 (Level 2) alfalfa model. The new model, ALFACOLD, requires input of: daily solar irradiance, maximum and minimum air temperature, and precipitation; latitude; dates of harvest; cultivar's fall growth score (FGS); initial plant density; and maximum plant‐available water in the root zone. The plant components modeled were leaf, stem, buds, and total nonstructural carbohydrates accumulated in the crown and root tissue. The model integrates the effects of soil moisture deficit, temperature, solar irradiance, and plant density on alfalfa growth, and the effects of subzero (°C) temperature on freezing injury and associated yield loss. Sensitivity of calculated forage DM yield to a ±25% change in selected model parameters was measured in cultivars of FGS 2, 3, and 4 during three production years of a 4‐yr alfalfa crop. The model did not simulate growth during a seeding year. A cultivar's rate of cold hardening and lowest temperature tolerance during autumn and winter influenced forage yield more than did the rate of dehardening in the spring. Field validation of ALFACOLD calculations of forage yield is presented in a companion paper.

Influence of Seedling Growth Stage on Flooding Injury in Alfalfa

AbstractTemporary flooding of alfalfa (Medicago sativa L.) seedings frequently occurs in the midwestern USA, often resulting in total or partial stand establishment failures. This study evaluated the effect of seedling growth stage on the severity of flooding injury in alfalfa grown in the greenhouse. Alfalfa seedlings of ‘WL 323’, rated as highly resistant to root rot caused by Phytophthora medicaginis E.M. Hans. &amp; Maxwell and resistant to root rot caused by Aphanomyces euteiches Drechs., were flooded for 14 d at three vegetative growth stages: (i) early seedling development (1–2 trifoliolates), (ii) eaely vegetative (3–6 trifoliolates), and (iii) mid to late vegetative (5–11 branches on the main stem). Root and shoot dry weights (DW) were recorded at the initiation of flooding, 0 days after flooding (DAF), 18 DAF (shoots only), and 36 DAF (18 d of regrowth from the 18 DAF harvest). The experiment was conducted twice. Flooding significantly (P &lt; 0.01) reduced root and shoot DW, regardless of growth stage, and adversely impacted regrowth potential of alfalfa. There was a growth stage × flooding treatment interaction (P &lt; 0.01) for root DW at 0 and 36 DAF in Trial 1, and at 0 DAF in Trial 2. Generally, flooding reduced root DW the least when seedlings were in the mid to late vegetative growth stage. Averaged over experimental trials, flooding reduced root DW at 36 DAF by 78% for early seedling, 73% for early vegetative, and 64% for mid to late vegetative growth stages, compared with unflooded controls. There was a growth stage × flooding treatment interaction (P &lt; 0.01) for shoot DW at 0, 18, and 36 DAF in Trial 1, and at 36 DAF in Trial 2. Averaged over trials, flooding reduced alfalfa shoot DW measured at 36 DAF by 57% for early seedling, 40% for early vegetative, and 19% for mid to late vegetative growth stages, compared with unflooded controls. We conclude that older and more vegetatively advanced alfalfa seedlings recover shoot regrowth potential after temporary flooding better than do seedlings in the early trifoliolate stages.

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.

Weed Control in Oat (Avena sativa)-Alfalfa (Medicago sativa) and Effect on Next Year Corn (Zea mays) Yield

Field experiments were conducted from 1985 through 1989 to evaluate herbicide selectivity and impact on seeding-year yields of spring oat and underseeded alfalfa, and carryover weed control benefits from increased legume-fixed N for second-year dryland no-till corn. PRE metolachlor, pendimethalin, and prodiamine controlled green foxtail and POST bromoxynil or 2,4-DB controlled broadleaf weeds. These herbicides caused 0 to 20% alfalfa injury and 0 to 17% oat injury, and increased oat yield one of three years but did not increase the yield of underseeded alfalfa. POST pyridate, thifensulfuron, and tribenuron were too injurious to either oat, alfalfa, or both crops. Forage yields of annual ‘Nitro’ and perennial ‘Wrangler’ alfalfa seeded alone were greater than when they were underseeded in oat, with herbicides applied in both systems. As a result of drought in 1988 and 1989, yield of second-year corn planted after one-year alfalfa was not increased from potentially greater legume-fixed N. Dryland corn yield following monoculture oat or corn was 254% higher than corn following alfalfa.

Leakage of Intracellular Substances as an Indicator of Freezing Injury in Alfalfa

Alfalfa (Medicago sativa L.) freezing tolerance is commonly determined by measuring ion leakage (by electrical conductivity) after freezing. This study was conducted to evaluate other measurements of freeze‐induced leakage of intracellular substances as indicators of freezing tolerance in alfalfa cultivars varying in fall dormancy and winterhardiness. Alfalfa crowns and roots were harvested in late fall of the seeding year and subjected to a −8 °C freezing treatment. Freezing injury was determined by measuring electrical conductivity, ultraviolet (UV) light absorbance, and oxidized nicotinamide‐adenine dinucleotide (NAD+)‐malate dehydrogenase (MDH) activity of leakage from roots after freezing. The optimal wavelength for determining freeze‐induced leakage of intracellular substances and for delineating differences in leakage among cultivars was 265 nm (A265). Percent electrical conductivity was linearly related to A265 (r2 = 0.92). Quadratic relationships were found between MDH activity and percent electrical conductivity (R2 = 0.88) and A265 (R2 = 0.90). Differences among cultivars were significant and cultivar rankings were similar for all leakage measurements. These data demonstrate that A265 and MDH activitiy of plant leakage after freezing are useful indicators of freezing injury, and that cellular rupture results from the −8 °C freezing treatment commonly used in alfalfa freezing tolerance tests. The MDH assay is more timeconsuming and variable than A265 or electrical a conductivity and is probably most useful when absolute measures of cellular rupture are important. Measuring A265 was quick and provided a good alternative to measuring electrical conductivity.

Bentazon for Annual Weed Control in Newly Seeded Alfalfa (Medicago sativaL.)

Preplant-incorporated (PPI) herbicides were applied to suppress annual weeds in new seedings of alfalfa, then additional annual weed control and crop tolerance from selected bentazon treatments were evaluated. Bentazon applied at 0.8 kg ai ha-1without an adjuvant caused an average of 8% visual injury to newly seeded alfalfa but did not reduce first-harvest alfalfa yields. Bentazon improved common lambsquarters control in newly seeded alfalfa and reduced weed biomass in first-harvest forage. No significant difference in crop injury, weed control, alfalfa yield, or weed yield was observed when bentazon was applied at 0.6, 0.8, or 1.1 kg ha-1. Greater alfalfa injury occurred when bentazon was applied with 1.25% v/v oil-emulsifier mixture, than when applied alone or with 5% v/v 28% liquid nitrogen fertilizer (28% N). Ten alfalfa cultivars did not differ in sensitivity to bentazon applied early postemergence (POST) or POST.

Potassium Fertilizer and Potato Leafhopper Effects on Alfalfa Growth

AbstractPotassium nutrition can alter plant resistance to environmental stresses. In two glasshouse experiments, the objectives were to assess the effects of K fertility and potato leafhopper (PLH) [Empoasca fubae (Harris)] feeding on mature and young (seven and four regrowth periods prior to PLH infestation, respectively) alfalfa plant (Medicago sativa L.) growth, regrowth, and carbohydrate reserves. Mature plants were grown on Claiborne (fine‐loamy, siliceous, mesic, Typic Paleudult) and young plants on Doniphan (clayey, mixed, mesic, Typic Paleudult) top soil treated with 0, 50, 100, and 200 mg K kg−1 soil. Three harvests were allowed to give K nutrition differences. Female PLHs were released into half of the caged plants for 3 wk for two subsequent harvests. Alfalfa herbage yield, shoot height, root weight, and root total nonstructural carbohydrates (TNC) increased with increasing K fertilizer. With mature plants, herbage yield, root weight, and TNC were reduced by PLH over K rates by 0.3 g plant−1 , 0.36 g plant−1 , and 22 g kg−1 , respectively. Reduction by PLH to young‐plant root TNC was an average of 44 g kg−1 . At the same time, reduction in herbage yield and root weight increased with K fertility. Alfalfa maturity was delayed by the PLH. Susceptibility to PLH injury was greatest with young alfalfa plants. Increased K fertility did not reduce PLH injury in alfalfa; however, alfalfa growth and persistence improved, with or without PLH, with increasing K fertility.

Effect of Atrazine and Tillage on Alfalfa (Medicago sativa) Establishment in Corn (Zeaways)-AlfaIfa Rotation

The effect of atrazine rate and subsequent tillage on seedling alfalfa injury from atrazine carry-over was examined at two locations in Michigan. Atrazine concentration and alfalfa injury 1 yr after treatment were greater in the northern location than in the central Michigan location. At both locations, alfalfa injury was significantly greater under no-tillage than moldboard plowing. With no-tillage, alfalfa was injured more in the area between the previous corn rows than within the rows. Analysis of soil samples collected from within corn rows and between rows showed higher atrazine concentration between the corn rows.

Selective Control of Downy Brome in Alfalfa

Selective control of downy brome (Bromus tectorumL.) in alfalfa (Medicago sativaL.) was studied in 1971 and 1972. Herbicidal efficacy and alfalfa tolerance, yield, and percent and total protein were observed. The weed population was composed of almost 100% downy brome in 1971 and 1972. Herbicide treatments were applied early and late winter when both alfalfa and downy brome were dormant. Five herbicides afforded virtually complete downy brome control in 1971: pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl) benzamide] at 0.84 and 1.40 kg/ha, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 1.12 kg/ha, terbacil (3-tert-butyl-5-chloro-6-methyluracil) at 0.84 kg/ha, paraquat (1–1′-dimethyl-4,4′-bipyridinium ion) at 0.56 kg/ha and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} at 3.4 kg/ha. All herbicide treatments reduced downy brome yields in 1972. Significantly higher alfalfa yields were closely related with lower downy brome yields. In 1972, alfalfa treated with propham (isopropyl carbanilate), cyanazine, pronamide and terbacil also was higher in second cutting yields than the control. Twelve of the 23 treatments, including all triazine herbicides, increased first harvest alfalfa protein percentage in 1972 although differences were not observed in 1971. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide] spring-applied in 1971 at 5.62 kg/ha was the only treatment causing visual alfalfa injury.

Control of Volunteer Oat in Alfalfa1

AbstractSimazine, atrazine and terbacil were applied to alfalfa (Medicago sativa L.) stands, established with oat (Avena sativa L.) as a companion crop, after the oat was harvested at maturity. Herbicides were applied before the germination of volunteer oat or after both oat and alfalfa had made substantial growth. Excellent control of volunteer oat, without significant alfalfa injury, was obtained with all three herbicides. Control generally was better if the herbicides were applied in September rather than in August. Root carbohydrate reserves of alfalfa may have provided some physiological protection against herbicide injury.

Dodder Control in Alfalfa by Dichlobenil

The herbicide, 2,6-dichlorobenzonitrile (dichlobenil), applied to the soil surface at 2 lb/A controlled dodder (Cuscutaspp.) and other weeds for 4 to 6 weeks in the field, and did not injure established alfalfa (Medicago sativaL.) significantly. Soil incorporation increased the herbicidal effect of dichlobenil on alfalfa and dodder, but alfalfa injury was increased more than dodder control. Dichlobenil was effective when applied just before sprinkler irrigation, or on moist soil after irrigating. In the greenhouse, dichlobenil vapors moved from a wettable powder formulation mixed with moist soil or from granules on the surface of moist soil, and killed dodder in adjacent untreated soil.