Leafy spurge Euphorbia esula (native to Europe) was accidentally introduced to the USA in the 1840s. It has become invasive in many grasslands. In this study, leafy spurge herbicide control to facilitate establishment of native grasses and legumes on range sites near Mason City (41°17'N, 99°17'W) and Tilden City (42°00’ N, 97°53’W), Nebraska, northern USA, was investigated.
Both sites were dominated by leafy spurge, Kentucky bluegrass Poa pratensis and smooth bromegrass Bromus inermis. The experiment was a randomized block design (four replicates per treatment combination).
Treatments were: standing crop management in the main plot (10 x 48 m at Mason; 16 x 30 m at Tilden); herbicide application in (8 x 5 m) subplots; and native seed mixes in sub-subplot (8 x 1.6 m).
In October 1995, glyphosate (at 1,600 g a.i. (active ingredient)/ha) was applied alone or with imazapic (140 or 210 g a.i./ha), using a tractor mounted sprayer.
In April 1996, standing crop was burned, or mown with stubble removed by raking (and disking where litter remained thick). Mixes of native grasses (big bluestem Andropogon gerardii, indiangrass Sorghastrum nutans, switchgrass Panicum virgatum, little bluestem Schizachyrium scoparium and sideoats grama Bouteloua curtiplendula) were sown (with a seed drill) with or without native legumes: leadplant Amorpha canescens, Illinois bundleflower Desmanthus illinoensis and purple prairieclover Petalostemum purpureum, at a rate designed to achieve 440 plants/m².
Imazapic was applied (70 g a.i./ha) in June 1996 to half the previously imazapic-treated plots, to determine if additional suppression of spurge and less desirable warm-season grasses would enhance sown species establishment. Frequency, dry matter yield, and spurge density were measured 14 to 16 months after sowing.
Overall, leafy spurge density and yield were least, and frequencies and yields of sown grasses usually greatest in imazapic plus glyphosate treated plots. At Mason, spurge density averaged 147 shoots/m² where no herbicide was applied and 62 shoots in imazapic (210 g/ha) plus glyphosate plots. At Tilden, densities averaged about 97 shoots/m² where no herbicide or glyphosate was applied; and 14 shoots/m² in imazapic plus glyphosate plots. At both sites, spurge yields were reduced by over 65% in imazapic plus glyphosate plots compared to plots with no herbicide. Imazapic spraying in June 1996 did not improve spurge control or enhance planted species yields.
Purple prairieclover was the only sown legume surviving after 14 months; highest yields were in imazapic plus glyphosate plots. After 14-16 months, total vegetation yields were greatest in imazapic plus glyphosate plots.
Existing standing crop removal followed by autumn herbicide application to suppress weeds enabled establishment of spring sown native species and suppressed leafy spurge.
If using or referring to this published study, please read and quote the original paper, this can be viewed at: https://www.uair.arizona.edu/holdings/journal/issue?r=http://jrm.library.arizona.edu/Volume54/Number5/