Author: Extension Brush and Weed Specialist, Department of Extension Animal Sciences and Natural Resources, New Mexico State University.
The groundsels are woody-stemmed, native, perennial plants that often cause livestock poisoning in winter and early spring. Poisoning of cattle and horses is reported most often, with sheep and goats being poisoned less frequently.
Two groundsel species occur in New Mexico. Threadleaf groundsel (Senecio longilobus) is a gray-white half-shrub, 1–3 ft tall with leaves deeply divided into three to seven segments. It is usually covered with long white hairs, giving the plant a woolly appearance, but can also be nearly smooth in appearance. Riddell's groundsel (Senecio riddellii) is much the same as threadleaf groundsel, except leaves are pinnatifid and relatively hairless, revealing its bright green leaf color. Both species have bright yellow flowers on the stems at about the same height above the ground. This gives the plants a flat-topped appearance during bloom. Threadleaf groundsel can produce flowers any time of the year, and often remains green year-round. Riddell's groundsel produces flowers in late summer to early fall and dies back to ground level after frost. Threadleaf groundsel typically grows on dry slopes and mesas across southern New Mexico. Riddell's groundsel grows on the dry, sandy soils of southeast New Mexico. Both plants can be found anywhere in New Mexico at elevations of 3,000–7,000 ft.
The poisonous agents in groundsels are pyrrolizidine alkaloids, which primarily affect the animal's liver and the nervous system. Toxic agents are distributed throughout the plant, but younger plant tissue appears to be more toxic than older tissue. Toxins are present in fresh, dry, and dead plant material.
Numerous types of alkaloids occur in plants, and each must be treated separately. There are no antidotes. Once symptoms of poisoning appear, it is too late to save the animal.
Toxicity is cumulative and the animal may not show symptoms for several months after eating the plant. Affected animals may have a rough coat and dry scaly nose, and will frequently void small amounts of liquid and bile-stained feces after painful straining.
Poisoned animals usually walk constantly with a slight stagger, and have a fixed, staring expression. The direction of travel indicates no specific itinerary. The head will droop, and the animal may walk into other animals, fences, or buildings. Death is sometimes caused by exhaustion or injury. Affected animals may attack any moving object.
Other symptoms of groundsel poisoning are jaundiced mucosal tissues, an accumulation of up to several gallons of clear liquid in the peritoneal cavity, hardening and cirrhosis of the liver, and distention of the gall bladder, often to an enormous size. Death may occur within two to four days after the onset of symptoms. Lesions may progress resulting in losses over several months. Further intake of plants must be avoided.
Management and Prevention
Because it is unpalatable, groundsel is usually not a serious problem, except during extended drought on severely overgrazed areas, or at times when forage is extremely limited. Supplemental feeding on forage-depleted areas is a management practice that may prevent some losses.
Sheep and goats are less susceptible than cattle. Intake of large quantities of groundsel is required to poison sheep and goats, and poisoning occurs infrequently on the range.
Threadleaf groundsel is highly susceptible to the herbicides listed in Table 1, and good kill has been obtained when the plants are growing vigorously with good soil moisture. Spraying is effective from April through June with ground or aerial equipment. Satisfactory control of Riddell's groundsel has been obtained by spraying during late summer and fall after effective rainfall.
Table 1. Herbicides Currently Labeled for Groundsel Control on Rangeland
|Common name||Trade name||Rate||Time of application|
|Dicamba||Banvel||0.5 lb/ac||When plants are growing vigorously and before seeds mature|
|Dicamba + 2,4-D||Weedmaster||1.0 lb/ac|
|Aminopyralid + 2,4-D||Grazon Next||2–2.6 pt/ac|
|Picloram||Tordon 22K||1.0 lb/ac|
|Picloram +2,4-D||Grazon P+D||1.0 lb/ac|
|2,4-D||Esteron 99 and others||1.0 lb/ac|
|Tebuthiuron||Spike 20P||1 tbsp/plant||Prior to rainfall|
|Note: Reference to commercial products or trade names is made with the understanding that no endorsement by the Cooperative Extension Service is implied and no discrimination is intended.|
High priority should be given to rangeland where groundsel numbers are high and where desirable forage can be reestablished after control. Removal of groundsel makes soil moisture and nutrients available to desirable forage, and reduces the potential for livestock poisoning. Sparse groundsel stands are most economically treated with a knapsack or power sprayer. Herbicide-treated areas should be deferred from grazing for the remainder of the growing season to prevent further poisoning.
Pelleted formulations of soil-active herbicides including tebuthiuron (Spike 20P) effectively control groundsel when applied at 1 tbsp per plant. Application timing is less restrictive with pelleted herbicides than with foliar sprays, and risk of herbicidal drift to susceptible crops is eliminated. Pelleted herbicides are most effective when applied in summer before peak rainfall.
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Revised and electronicaly distributed June 2008, Las Cruces, NM.