Density of seed of three species of locoweed, salt milkvetch [Astragalus lentiginosus var. salinas (Howell) Barneby], Lambert locoweed (Oxytropis lambertii Pursh. # OXRLA), and white locoweed (O. sericea Nutt ex. T.&G. # OXRMA) in the soil was determined at four locations in New Mexico, Wyoming, and Utah. Seed density ranged from 50 to 2820/m2. Greater than 77% of the seed were viable as determined by tetrazolium tests. Longevity of white locoweed seed was determined by sewing seed into nylon mesh packets and returning them to the site of origin in northwestern Utah. Greater than 50% of seed buried 1 cm deep in the soil were still present after 6 yr, but only 33% of seed placed on the surface remained. Germinability of the buried seed was less than 5%, but an average of 14% of seed placed on the soil surface germinated each year. Viability of retrieved seed ranged from 89 to 99%.

Leaflets of 1690 species of Old World and South American Astragalus collected from herbaria at Kew, England; Edinburgh, Scotland; Munich, Germany; and Vienna, Austria were analyzed qualitatively for toxic aliphatic nitro compounds. The catabolites of nitro compounds found in species of Astragalus (nitro-bearing), 3-nitro-1-propanol and 3-nitropropionic acid, are especially toxic to cattle and sheep. A total of 190 of 1624 (12%) Old World species, 30 of 66 (45%) South American species, and a single species of one Astragalus subgenus were positive for nitro compounds. Most Old World species that contained aliphatic nitro compounds were collected in the Middle East and the Union of Soviet Socialist Republics. Nitro compounds were detected in specimens of eight species collected between 1822 and 1836. The nitro-bearing species were chemotaxonomically related and grouped within taxonomic sections. The presence of two or three nitro-bearing species within a section indicated that other species within the same section might also be nitro-bearing.

Plots of western false hellebore (Veratrum californicum Durand), treated in 1968 and 1969 with 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 kg/ha, were reexamined in July 1979 to determine vegetative changes, especially any increases in the production of desirable species and long-term control of western false hellebore. Grass, sedge, and rush production had doubled, and broadleaved plant production, excluding western false hellebore, which was eliminated, decreased on treated plots. Western false hellebore had not reinvaded the treated plots; control remained at 100% for 10 yr. Removal of the western false hellebore on treated plots allowed an increase in grass, sedge, and rush production of 1,500 kg/ha over check plots.

Poisonous plants and noxious weeds are often chemically examined to determine concentrations of secondary metabolites which are responsible for their toxic or biological activity. This study examined sample size requirements and sample methods necessary to quantify accurately the concentrations of individual and total toxic alkaloids in two tall larkspur populations. A high performance liquid chromatography analytical method was utilized to determine toxic alkaloid concentrations in all leaves from three individual plant stems and leaves from the remaining stems (remainder) from each of 50 plants in each population. To obtain high precision in quantifying toxic alkaloids in the larkspur populations (within 2.5 to 5% of the population mean, 0.95 confidence), very large numbers of samples (>50–200) were required. However, lower precision (within 10% of the population mean, 0.90–0.95 confidence) required only 20 samples. Similarly, testing parameters relating to toxin concentration in tall larkspur populations within 5 or 10% of the population mean also required hundreds of samples at power levels of 0.95 and α-levels of 0.05. Relaxing power and α-level requirements to 0.80 and 0.1 respectively, reduced sample size to about 30. The means obtained by four different sampling methods were similar (P>0.05). Alkaloid concentrations in leaf samples from single stems were highly correlated to whole-plant leaf (remainder) samples (r2≥0.76), indicating that harvesting leaves from single stems provided representative samples of the entire plant. The results indicate the difficulty in obtaining accurate information about toxins in poisonous plant populations for risk assessment by livestock producers or extension agents and demonstrate the necessity for efficient analytical methodology. Researchers evaluating concentrations of plant compounds in other weeds or toxic plants should consider variability, sampling procedure, and sample size before experiments begin.

Purposefully introduced plants that have become weeds cost the United States millions of dollars annually by reducing yields of crops and livestock, clogging navigable and recreational waterways, reducing productivity and value of grazing lands, poisoning humans and livestock, and increasing weed control costs. Research is in progress to develop methods of intercepting foreign plants that might be toxic to livestock if introduced on western ranges and pastures. Methods of intercepting include identifying poisonous plants from seed inventories, chemical analysis, chemotaxonomic investigations of biochemical relationships between related taxa, and feeding suspected plants to laboratory and domestic animals.

Locoweed poisoning of livestock is the most widespread poisonous plant problem in the western United States. This paper presents a historical review of control methods to reduce locoweed plant density. Hand grubbing, the most common method of control before phenoxy herbicides, was practical in small pastures considering the number of livestock saved. Trials in the 1950s indicated that 2,4-D and 2,4,5-T generally controlled locoweeds effectively if applied when plants were actively growing and soil moisture was not limiting plant growth. Picloram, dicamba, clopyralid, and triclopyr provide more consistent control than 2,4-D and 2,4,5-T when applied at less than optimum environmental conditions.

Conditioned food aversion is a powerful experimental tool to modify animal diets. We have also investigated it as a potential management tool to prevent livestock from grazing poisonous plants such as tall larkspur (Delphinium barbeyi), white locoweed (Oxytropis sericea) and ponderosa pine (Pinus ponderosa) on western US rangelands. The following principles pertain to increasing the strength and longevity of aversions: mature animals retain aversions better than young animals; novelty of the plant is important, although aversions can be created to familiar plants; LiCl is the most effective emetic, and the optimum dose for cattle is 200 mg/kg body weight; averted animals should be grazed separately from non-averted animals to avoid the influence of social facilitation which can rapidly extinguish aversions. Social facilitation is the most important factor preventing widespread application of aversive conditioning. When averted animals see other animals eat the target food they will sample it, and if there is no adverse reaction they will continue eating and extinguish the aversion. However, if averted animals can be grazed separately, aversions will persist. Aversive conditioning may provide an effective management tool to prevent animals from eating palatable poisonous plants that cause major economic loss.