Imazapyr, imazaquin, and imazethapyr were evaluated for control of leafy spurge. Herbicides were applied at 70, 140, and 280 g ae/ha in Fall 1989, 1990, or 1991 on a sub-irrigated meadow near Ainsworth, NE and a tallgrass prairie near Columbus, NE. Imazapyr, imazaquin, imazethapyr at 280 g/ha controlled leafy spurge 58, 82 and 73%, respectively, 9 mo after treatment (MAT) at Ainsworth. Leafy spurge control averaged 49% 9 MAT at Columbus where 280 g/ha of the imidazolinone herbicides were applied. Leafy spurge yields were reduced at Ainsworth by 29 and 78% where the imidazolinones were applied at 140 and 280 g/ha. By 11 MAT, leafy spurge control on areas treated with 280 g/ha declined to less than 60% at Ainsworth and 10% at Columbus. Perennial forage grass yields at both sites were generally unaffected by imazaquin or imazethapyr, but imazapyr at 280 g/ha reduced yields by 69 and 44% at Ainsworth and Columbus, respectively. Imidazolinone herbicides applied in the fall partially controlled leafy spurge, but did not increase perennial forage grass yields.

Greenhouse cage studies were conducted to determine the influence of shoot morphology and genetic variation on establishment of Spurgia esulae gall midge on seven leafy spurge genotypes. The genotypes were collected from South Dakota, North Dakota, Nebraska, Montana, Wyoming, Manitoba, and Austria. Genotypes from South Dakota and Nebraska were most susceptible to gall formation and had the highest larvae survival, while the genotypes from Montana and Manitoba were most resistant. Morphological characteristics of the leafy spurge stem tips, such as stem diameter, leaf length, width, and area did not correlate with gall formation or larvae survival. Chloroplast DNA restriction fragment length polymorphism analysis of the genotypes identified six chloroplast types among the seven leafy spurge genotypes. The two genotypes most resistant to galling by S. esulae, Manitoba and Montana, had the same chloroplast genotype, but also were closely related to the two most susceptible genotypes. Because eggs were laid on all genotypes, it appears that adult females were not preferentially selecting appropriate host genotypes, but that egg and larvae survival was strongly influenced by genotype.

Efforts to screen and mass-rear insects and diseases for leafy spurge biocontrol agents have been hampered by low success in propagation and slow growth of leafy spurge in the greenhouse. The optimum greenhouse conditions for leafy spurge growth were determined. Leafy spurge was propagated from stem tip cuttings, with the basal end treated with 0.2% NAA, and the plants misted with water for 10 d. Optimum conditions for growth were 27 C air temperature, application of a complete fertilizer at 70 kg ha−1 weekly or 135 kg ha−1 biweekly 20 d after stem tip propagation, in a peat/perlite/vermiculite growth medium at pH 7 and a 16-h photoperiod. Regrowth from roots of parent plants was improved when cuttings were taken from plants at least 60 d old, and plants grew nearly twice as rapidly when the medium was maintained at 30 C compared to 22 C. Refrigeration of stem tip cuttings or roots before planting did not affect survival or growth vigor. Only gibberellic acid of nine plant growth regulators evaluated increased growth, but plants were etiolated. Biotypes from Nebraska and South Dakota were shorter than five others from the United States or Austria but had similar root and shoot dry weight. The time required to propagate vigorous leafy spurge was reduced to 2 mo compared to 6 mo required prior to the study.

Weed population models can serve as a framework to organize weed biology information and to develop weed control strategies. Models help to identify information gaps, to set research priorities, to develop hypotheses pertinent to weed population regulation, and to suggest control strategies. A population simulation model of leafy spurge (Euphorbia esula L. # EPHES) was used to demonstrate the applicability of population models to weed science. Sensitivity analysis of an existing leafy spurge model indicated that transition from basal buds to vegetative shoots, survival of vegetative shoots, and survival of basal buds over winter were important transition parameters influencing population growth of this weed species. Possible mechanisms (intraspecific competition and environmental factors) that influence the transition from basal buds to vegetative shoots were shown. Intraspecific density effects on basal bud transition and production were included to show model refinement and second-generation model development. Four control strategies were simulated and were compared to field studies to show the predictive and management potential of the modeling approach. Simulations of population response to foliage feeding herbivores was highly correlated (r = 0.98) with field data for sheep grazing on leafy spurge. Simulation of picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) applied to leafy spurge also was correlated (r = 0.97) with field results.

Experiments were conducted to determine the efficacy of imidazolinone and sulfonylurea herbicides applied alone or in combination to control leafy spurge. Imazapyr (840 g ai/ha), imazethapyr (140 g/ha), sulfometuron (100 g/ha), and chlorsulfuron (20 g/ha) were applied in the fall on rangeland sites near Ainsworth and Columbus, NE. Imidazolinone and sulfonylurea herbicide combinations did not improve leafy spurge control nor affect forage grass yields when compared with herbicides applied alone. Imazapyr and sulfometuron were the most efficacious, providing greater than 80% leafy spurge control 9 mo after treatment (MAT). Imazethapyr provided 80% control of leafy spurge 9 MAT when applied to a coarse textured, low organic matter soil. In contrast, leafy spurge control was only 15% when imazethapyr was applied to a fine textured soil. Chlorsulfuron did not control leafy spurge, regardless of site characteristics. Imazapyr reduced perennial grass yields by more than 60%.

The addition of chlorflurenol (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate) at 0.6 kg ai/ha or mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]amino]phenyl] acetamide} at 0.3 kg ai/ha to picloram (4-amino-3,5,6-tricloropicolinic acid) at 0.3 kg ae/ha increased leafy spurge (Euphorbia esula L. # EPHES) control compared to picloram alone. Application of 84 kg/ha nitrogen in the fall prior to a spring treatment of 0.3 kg/ha picloram decreased the original stand (75%) compared to no nitrogen (18%). In greenhouse experiments, chlorflurenol and mefluidide increased the amount of 14C-picloram absorbed approximately twofold when applied in combination but not when applied independently. Based on 14C-picloram absorbed, chlorflurenol and mefluidide each increased the amount of 14C translocated to the root system, whether applied independently or in combination with picloram. An increase in root bud numbers was observed following an application of 0.6 kg/ha chlorflurenol or nitrogen.

R230, an isolate of Rhizoctonia solani anastomosis group 5 from leafy spurge, caused root and crown rots on leafy spurge when inoculated via soil in greenhouse experiments. The fungus grew through soil over a wide range of matric potentials (–0.01 to −1 MPa). When applied to leafy spurge foliage, the fungus blighted young adventitious shoots, but not mature stems. Foliar infection required high relative humidity. Mycelial growth on plant surfaces stopped at below 92% relative humidity. Pathogenicity of R230 was not limited to leafy spurge. The fungus caused stem and foliar lesions on all crops tested (alfalfa, smooth bromegrass, corn, Kentucky bluegrass, soybean, tall fescue, and wheat) when plants were kept under high humidity. It reduced seedling emergence and survival in soybean, Kentucky bluegrass, and tall fescue. R230 also caused a foliar blight on spotted spurge. The potential for R230 to damage crops will limit application of the fungus to noncultivated areas and to sites where it is endemic.

The Spurgia esulae gall midge was introduced in North Dakota in 1986 as a biocontrol agent for leafy spurge. Spurgia esulae causes stem tip galls thereby decreasing seed production and it has been most successful near wooded areas. However, a second control method is needed to reduce the leafy spurge infestation and prevent spread from roots. Imazethapyr, 2,4-D, or picloram application did reduce the number of S. esulae galls but not the number of larvae per gall. Long-term S. esulae population was not affected by herbicide application. The integration of herbicides with S. esulae would prevent leaf spurge spread from a wooded area and would reduce seed production within an area where herbicides generally cannot be used.

Relative humidity after application, spray additives, and solution pH affected both foliar absorption and translocation of 14C-picloram to leafy spurge roots. 14C-picloram absorption increased from 11 to 34% and translocation increased from 5 to 21% as time at posttreatment humidity increased from 0 to 48 h. Absorption and translocation were not different when pre- or posttreatment temperatures were 30/18 or 18/10 C (day/night). 14C-picloram absorption and translocation to the roots were 18 and 6%, respectively, when applied alone, and increased to 46 and 12%, respectively, when applied with ammonium sulfate at 2.5 kg/ha. Absorption and translocation were unaffected by ammonium nitrate. Foliar absorption and translocation of 14C-picloram in leafy spurge were unaffected by pH of unbuffered spray solution but increased at least 50% when applied in a solution buffered at pH 4.8 with trisodium citrate. Foliar absorption in detached leafy spurge leaves increased from 26 to 51% of applied 14C as the citrate buffer concentration increased from 0.01 to 0.1 mM, respectively.

Wells and streams in 10 North Dakota counties were surveyed for picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), the major herbicide used to control leafy spurge (Euphorbia esula L. # EPHES). Three rivers and 144 wells were sampled in 1985. Picloram concentration ranged from <0.1 to 12.4 ppb in the water from five wells in five counties and from <0.1 to 6 ppb in two rivers. An additional 44 wells were sampled in 1986; they were located within 2 km of the five wells where picloram was detected in 1985. Picloram concentrations in 1986 ranged from non-detectable to 6.7 ppb in the original contaminated wells and was 0.97 ppb in water from one of the additional 44 wells. Picloram concentration in the river water was lower in 1986 than in 1985 but was detected farther downstream. All contaminated wells were within 1.5 km of an area treated for leafy spurge, but picloram had been spilled accidentally or misapplied near all but one of the wells. The concentrations detected were at least 100 times below suggested tolerance levels for water.

The beetle Oberea erythrocephala, whose larvae mine stems and roots of leafy spurge (Euphorbia esula L. # EPHES), was introduced into Oregon, Montana, and Wyoming between 1980 and 1984. Although it was not recovered in Oregon and Wyoming, it became established at two of three release sites in Montana and appears to be accepting leafy spurge plants at a fourth.

Response of clones of Canada thistle from North America and leafy spurge from North America and Eurasia to treatment with chlorsulfuron, clopyralid, and glyphosate was determined. Roots of Canada thistle plants from different locations responded differentially to injury from chlorsulfuron and clopyralid but not to glyphosate. Clones of Canada thistle varied significantly in response to all herbicide treatments. Roots of leafy spurge plants from different locations were differentially susceptible to injury from glyphosate. Clones of leafy spurge varied significantly for all responses to each herbicide. The differential effects of chlorsulfuron, glyphosate, and clopyralid on clones of Canada thistle and leafy spurge suggest that genetically-based differences may account for the failure of the herbicides to kill all plants within collection locations or between collection locations. Cross tolerance to the herbicides was not found in leafy spurge or Canada thistle.

Herbicide treatments containing the butoxyethanol ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid], the dimethylamine salt of dicamba (3,6-dichloro-o-anisic acid), the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid), and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] were applied for 6 yr to a pasture in east-central South Dakota containing leafy spurge (Euphorbia esula L. ♯ EPHES). Several treatments resulted in leafy spurge control exceeding 90%. Mean herbage dry-weight yield in treated plots was 2340 kg/ha, a 67% increase over untreated plots. Forage yields did not significantly differ among treatments controlling 90% or more leafy spurge. Marginal net return over marginal cost from herbicide treatments ranged from $35 to –$63/ha. Treatments providing satisfactory leafy spurge control with minimum economic risk were annual spring applications of 2,4-D at 1.7 kg ae/ha or dicamba + 2,4-D at 0.6 + 1.1 kg ae/ha and the biannual application of 2,4-D at 0.8 kg ae/ha.

Levels of inter- and intrapopulation genetic variation were determined in five North American populations of leafy spurge using chloroplast DNA (cpDNA) RFLPs and RAPD markers. Thirteen plastome types were identified among 123 individuals collected from five geographically separated populations. Number of plastomes within a population ranged from one to seven, with four of the populations having a predominate type plus one or more rarer types. Some plastome types were shared by populations, but plastome distribution among populations was nonrandom. RAPD markers indicated greatest relatedness among individuals within a population. Relatedness among populations as established through RAPDs was greater for geographically closer populations; this relationship was not observed for cpDNA markers. Differences in the range of movement for pollen and seed may account for differences between results of the cpDNA and RAPD analyses. The high degree of genetic variability among North American leafy spurge suggests possible multiple introductions or a high degree of variability within leafy spurge populations in its native range.

Phytotoxicity of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in cell cultures of Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] was approximately 30-fold greater than in leafy spurge (Euphorbia esula L. # EPHES) cultures. Differences in chlorsulfuron phytotoxicity in these two species were attributed to large differences in cellular metabolism of the herbicide. Leafy spurge cells metabolized all of the applied 14C-chlorsulfuron within 72 h of treatment, while Canada thistle metabolized less than 2%. Acid hydrolysis of the metabolic products isolated from leaf disks and cell cultures of leafy spurge yielded a radioactive product that cochromatographed with a 2-chlorobenzenesulfonamide standard. Therefore, metabolic transformation occurred on the heterocyclic portion of the molecule. A major metabolite was further characterized as 2-chloro-N-[[4-(hydroxymethyl)-6-methoxy-1,3,5-triazin-2-yl]aminocarbonyl]-benzenesulfonamide by cochromatography with the authentic standard.

The productivity and native species diversity of Great Plains grasslands have been substantially reduced by past management that facilitated the establishment of invasive exotic weeds and displacement of native species. Management strategies are needed to rapidly restore the productive capacity and biological diversity of these degraded grasslands. Critically important phases of the grassland restoration process are the reintroduction and establishment of native species. Weed interference is the primary constraint to successful establishment of native plants. The goal of our research is to develop strategies that use multiple technologies, including herbicides, to expedite grassland revegetation with native grasses and forbs. Imidazolinone herbicides (AC 263,333, imazapyr, and imazethapyr) were used successfully to improve establishment of native perennial grasses (big bluestem, switchgrass, little bluestem) and selected forbs (blackeyed-susan, purple prairieclover, Illinois bundleflower, trailing crownvetch, and upright prairie coneflower) on cropland and as components of a strategy to revegetate leafy spurge-infested rangeland with native tallgrasses. Imazethapyr at 70 or 110 g ai/ha applied at planting resulted in stands of big bluestem and little bluestem that were similar or superior to stands established where atrazine was applied. Seedling grasses were susceptible to imazapyr at two of three study sites. Imazapyr at 560 g ai/ha plus sulfometuron at 100 g ai/ha applied in fall was the optimum treatment for suppression of leafy spurge and exotic cool-season grasses and establishment of big bluestem and switchgrass on degraded rangeland sites. Establishment of selected forbs was improved by PRE treatment with AC 263,222 or imazethapyr at 70 g ai/ha. This research provides evidence that the imidazolinone herbicides can be important components of integrated weed management strategies designed to reverse deterioration of grasslands by reestablishing native species, improving grassland productivity, and decreasing the prevalence of exotic weeds.

Leafy spurge is an exotic perennial weed that infests more than 1 million ha in North America and reduces rangeland carrying capacity. Experiments were initiated on range sites in Nebraska and North Dakota in 1994 and 1995 to determine the response of leafy spurge and other vegetation to AC 263,222. Herbicide treatments evaluated included AC 263,222 at 0 to 280 g ai/ha, picloram at 560 g ai/ha plus 2,4-D at 1,120 g ae/ha, and quinclorac at 1,120 g ai/ha. In Nebraska, a single application of AC 263,222 in the fall at 140 g/ha provided ≥ 90% leafy spurge control 11 to 12 mo after treatment. At Jamestown, ND, leafy spurge control increased to almost 90% and stem density declined to two shoots/m2 12 mo after the second consecutive fall application of AC 263,222 at 140 g/ha. At Hankinson, ND, leafy spurge control was ≤ 50% when AC 263,222 was applied in the fall only, but increased to > 80% when AC 263,222 was applied in the fall and again at 70 or 140 g/ha in the spring. There were no differences in herbage biomass of established cool- and warm-season grasses where AC 263,222 at 140 g/ha, picloram plus 2,4-D, quinclorac, or no herbicide was applied in the fall. In contrast, application of AC 263,222 in the fall and again in the spring usually reduced cool-season grass biomass.

Leafy spurge, a long-lived perennial, grows in many habitats, from floodplains to grasslands and mountain slopes. The plant emerges in early spring and produces showy, yellow bracts that appear in late May. The true flowers emerge in mid-June. The plant spreads by both seeds and roots and contains a white sticky latex that deters grazing by many animals. Dicamba, 2,4-D, glyphosate, and picloram have commonly been used to control leafy spurge. Picloram plus 2,4-D is frequently used for leafy spurge control in North Dakota. Ten insect species for leafy spurge biocontrol have been released in North Dakota; the most successful have been the flea beetles, Aphthona nigriscutis, A. czwalinae, and A. lacertosa. The leafy spurge gall midge (Spurgia esulae) has been most successful near wooded areas. Herbicides combined with either the leafy spurge flea beetles or gall midge have controlled leafy spurge better than either method used alone. Grazing with sheep or goats is a cost-effective method for controlling leafy spurge top growth in large infestations. Grazing combined with fall-applied picloram plus 2,4-D reduced leafy spurge density more rapidly and maintained control longer than either method used alone. Several grass species are competitive with leafy spurge including ‘Rebound’ smooth brome, ‘Rodan’ western wheatgrass, ‘Pryor’ slender wheatgrass, and ‘Manska’ pubescent wheatgrass. Cultivating twice each fall after harvest for 3 yr in cropland completely controlled leafy spurge. A successful long-term management program should be designed for specific situations and should include combinations of herbicides, insects, grazing, and/or seeding competitive species.

Leafy spurge is a serious problem because of the speed with which it spreads and the difficulty of controlling it with available means. A rangeland economics model was developed to estimate the economic impacts of leafy spurge infestation on both ranchers and regional economies. A leafy spurge-induced carrying capacity reduction of about 580 000 animal unit months (AUMs), or enough for 77 000 cows, reduced ranchers' annual net income nearly $9 million. Ranchers did not spend another $14 million on input costs, which reduced regional business activity. The regional impacts are about $75 million in reduced business activity for all sectors. These impacts on rancher incomes and regional economies suggest the potential economic returns of leafy spurge control could be substantial.

Larvae of the leafy spurge hawk moth were sprayed with and/or were fed leafy spurge plants sprayed with 2,4-D or picloram. Larval survival was not affected from contact with the chemicals, from feeding on contaminated foliage, or from a combination of both. Viable second-generation adult moths were produced in all treatments. Thus, leafy spurge infested with the leafy spurge hawk moth can be sprayed with 2,4-D or picloram without injury to larvae that have reached the fourth or fifth instar stages.