Effects of Monuron on Halogeton and Associated Salt-Desert Shrub Vegetation

Abstract

ALOGETON (Halogeton glomeratus) is an introduced, poisonous 11 annual plant which is rapidly invading the salt-desert ranges of western North America (6). The poisonous constituent of this plant is water-soluble oxalic acid, which varies from 17 to more than 30 percent of the dry weight in its leaves during the growing season.3 Because of the poisonous property of halogeton and its dense population on disturbed site, it is of considerable importance to the livestock industry (1, 2, 3, 8, 12). The borrow pits of highways in the Great Basin usually have a large population of halogeton. (The borrow pits are drainage areas immediately adjacent to the road shoulders and the soil used to build up the roadbed is borrowed from these pits.) The additional moisture derived from drainage of the roadbed substantially increases the vigor and densities of these populations. Halogeton is a prolific producer. Germination, establishment and survival studies indicate that an inch of seed-producing stem can potentially produce from 3 to 39 plants during the following growing season. These calculations are based on the potential of the black seeds. Data on the germination of brown seed (5, 12, 13, 14) and the establishment and survival of their seedlings are not available. The disturbed and denuded soils of livestock and game trails, railroad rights-of-way, and highway rights-of-way have provided some of the major avenues by which halogeton has spread into new habitats. Highway rights-of-way are probably one of the more important routes to new infestations because of the profusion of both brown seeds and black seeds in and on the soil of the borrow pits and man's intense use of roads and the immediately adjacent areas (6, 11). Sterilization of the soil surface appeared to have promise as a means for reducing the spread of the weed. Available data indicate that embryos which escape from the coat below a depth of ?4 inch do not emerge from the soil. The vegetation bordering the borrow pit is often weak in vigor or reduced in density to a degree that halogeton can invade. Therefore, closing of highway rights-ofway as a pathway of incursion by halogeton necessitates sterilization of the soil surface under the adjacent perennial vegetation until vigor and density of the vegetation would prevent the growth and development of invading plants. Soil sterilization under the perennial vegetation would not accomplish its purpose in the event it