Leafy spurge and grass response to picloram and intensive grazing
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Published source details
Lacey J.R. & Sheley R.L. (1996) Leafy spurge and grass response to picloram and intensive grazing. Journal of Range Management, 49, 311-314.
Published source details Lacey J.R. & Sheley R.L. (1996) Leafy spurge and grass response to picloram and intensive grazing. Journal of Range Management, 49, 311-314.
Summary
Leafy spurge Euphorbia esula (native to Europe) was accidentally introduced to USA in the early 1800’s. It is now highly invasive in natural and semi-natural grasslands. A study was conducted in pastures at the Crazy Mountain Ranch (45º45’N, 110º23’W) in Montana, northwest USA. Leafy spurge control by herbicide (picloram) application in combination with intensive short-duration sheep or cattle grazing, and responses of Kentucky bluegrass Poa pratensis and other native plants, were investigated.
Two pastures (16 and 24 ha; Kentucky bluegrass 75%, leafy spurge 20%, other plants 5%) were fenced in 1990 and split into three blocks. Picloram (which controls a range of broad-leaved weeds, most grasses are resistant) was applied to one-half of each block at a rate of 0.9 kg/ha. Three livestock exclosures (8 x 30 m) were erected in each pasture incorporating treated and untreated portions.
Grazing: There were one or two intense grazing periods of 1-2 days per year (other than this, livestock were excluded):
1) The 16 ha pasture was grazed by about 1,100 targhee ewes with lambs for two days in early July (when leafy spurge flowering). In two years, sheep regrazed for a day in early September.
2) The 24 ha pasture was cattle grazed. During the first two years, 500 cows with calves grazed for two days in early July. About 525 heifers similarly grazed in the latter three years.
Plant monitoring: Leafy spurge stem densities were counted annually (and grass cover estimated) in 0.5 m² quadrats placed along permanent transects incorporating grazed and ungrazed areas. In 1990-1993, spurge and bluegrass forage use was estimated immediately following grazing by clipping plots to ground level within and outside exclosures (i.e. to compare above-ground biomass yield after 1 year of no grazing vs. grazing). In 1994, additional quadrats within and outside were clipped (to estimate yield after 5 years). Clipping samples were separated by species, oven-dried and weighed.
Sheep selectively grazed leafy spurge (eating 65-86% annually) and their grazing significantly reduced stem density. Spurge stem densities were similarly significantly reduced by combined sheep grazing and picloram. Spurge (4.75 kg) and bluegrass (average 20.85 kg/ha) biomass was unaffected by sheep grazing alone. Bluegrass cover was not affected by grazing or picloram.
Picloram application alone, siginificantly reduced leafy spurge stem densities throughout the study in both pastures. Picloram significantly reduced spurge biomass from 5.7 to 3.7 kg/ha; in response Kentucky bluegrass increased from 17.5 to 24.3 kg/ha in the sheep pasture. Native bunchgrass (Stipa and Danthonia spp.) density initially increased in picloram treated areas but by 1994 no differences were apparent to those untreated (average 0.48 plants/m²).
Without sheep grazing or picloram, spurge stem densities more than doubled from 1990 to 1994 (c.85 to c.190/m²) and there was no evidence of native plant recolonisation. Cattle did not eat leafy spurge and did not affect stem densities.
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