Suppression of Yellow Starthistle by Subterranean
Clover, Mowing and Grazing
C.D. Thomsen, W.A. Williams1,
L.M. Burkham, and D.W. Pratt
Yellow starthistle is one of California's worst noxious weeds, and is estimated to infest about 8 million acres in California. Although it is a well known weed in pastures, rangelands, and hayfields, it is also becoming increasingly troublesome in vineyards and orchards.
Properly timed mowing and grazing can reduce starthistle stands to tolerable levels, but even with large reductions in flowerhead densities, sufficient seed is still produced to maintain populations from year to year. Seeds from the seed bank also germinate under favorable conditions, adding to the difficulty in obtaining successful long term control.
To further reduce populations and enhance control we are testing subterranean clover plantings in combination with both mowing and grazing in two replicated experiments. The site is located on the Bio-integral Resource Center (BIRC) Field Station five miles west of Winters in a foothill ecosystem. Two subclover cultivars (Koala and Karridale) were chosen after on-site screening of 65 dryland legumes. These subclovers were among the best adapted to the site and remained competitive under periodic defoliation.
Our treatments include: 1) subclover planting with mowing, 2) mowing without subclover, 3) subclover planting with grazing and mowing, 4) grazing and mowing without subclover, and 5) a control without grazing, mowing, or subclover planting. Phosphorus is typically limiting for legume growth on range soils and a phosphorous fertilizer (0-20-0-12) was applied at 100 lbs/acre to the seeded portions.
The subclover is well established (planted
October 1993), and the first growth cycle of yellow starthistle
will be completed in July 1994. First year results related to
starthistle suppression will be available then.
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