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Project description

Management Practices for Long-Term Yellow Starthistle Control and Enhanced Rangeland Productivity. (97CC018)
Program UC IPM competitive research grants program
S.B. Orloff, Cooperative Extension, Siskiyou County
J.M. DiTomaso, Vegetable Crops, UC Davis
D. Drake, Cooperative Extension, Siskiyou County
Host/habitat Rangeland
Pest Yellow Starthistle
Discipline Weed Science
Cultural Controls
Start year (duration)  1997 (Three Years)
Objectives Using IPM principles, develop a long-term sustainable approach to controlling yellow starthistle and improving the quality and productivity of California rangeland.

Test the effectiveness of 1, 2, or 3 years of herbicide treatment (clopyralid) on yellow starthistle management and seed bank depletion and on rose clover and wheatgrass establishment in a rangeland system in Siskiyou County.

Measure and contrast rangeland productivity, forage quality, and water infiltration rates in unimproved yellow starthistle infested rangeland with no chemical control, unimproved rangeland with chemical control, and rose clover or wheatgrass improved rangeland treated with clopyralid for 1, 2, or 3 years.

Evaluate all treatment combinations to determine the most cost-effective method of yellow starthistle management in rangeland.

Yellow starthistle is the most troublesome weed in northern California rangeland. Available control measures have been largely ineffective due to a failure to eliminate the seedbank and prevent reinvasion. The use of clopyralid for elimination of yellow starthistle seed production in conjunction with reseeding for conversion of the annual range type to perennial grasses has been hypothesized to be an effective long-term control strategy. Studies established in 1997 have provided valuable information for testing this hypothesis. Excellent control of yellow starthistle was achieved at low clopyralid rates between 1 and 4 oz ae/A. Early applications (February and March) were more effective than April and May treatments. The February application timing also produced the highest forage quantity and this decreased significantly with each month delay in clopyralid application. These results suggest that an early season treatment is preferred for cattle ranchers where the desired outcome is both yellow starthistle control and improved forage quality and quantity.

Evaluations of the long-term clopyralid / reseeding study have shown that a single year of clopyralid treatment did not provide long-term control of yellow starthistle. However wheatgrass could be established with only one application. Where no reseeding program is used, at least two consecutive years of treatment are necessary. Over three years, wheatgrass has established to 50% cover and appears to vigorously compete with yellow starthistle. Rose clover has not consistently performed to expectation and may not be a suitable choice when yellow starthistle control is desirable.

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