Abstract:

Yellow starthistle is a highly invasive, noxious weed that infests much of California’s rangeland. Translineâ , a clopyralid herbicide effective as a yellow starthistle herbicide, was approved for use in California on January 1998. The effects of the herbicide on preferred forage species in eastern Butte County have not been documented. The study was conducted using a completely randomized design. Dry matter production and chlorophyll content was measured for yellow starthistle, grass and forbs. It was determined that Translineâ controlled yellow starthistle which allowed increased grass and forb production.

Introduction:

Yellow starthistle (Centaurea solstitialis L.) is one of California’s most noxious weeds. This annual plant is toxic to horses and becomes unpalatable as it matures. It is highly competitive and replaces native and desirable vegetation. Its large seed output, extended germination period, deep taproot and late spring and summer growth has allowed it to spread rapidly. More than 7.9 million acres of rangeland and pastures in California are infested with yellow starthistle (Maddox 1981). This infestation significantly reduces the amount of available forage decreasing stocking rates. In January 1998, Translineâ (Dow-Elanco), a clopyralid herbicide, was approved for use on California rangelands. Transline provides excellent control of yellow starthistle at low use rates (DiTamasso et al. 1998) and promises to increase edible forage production if it does not suppress preferred species. The effect of Transline on preferred forage species on the foothills Butte County has not been documented. A reduction in preferred forage species could be more detrimental than a yellow starthistle infestation. The objective of this study was to determine the effects of Transline on yellow starthistle control and production of preferred forage species in Eastern Butte County.
 

Materials/Methods: Study Site-

The study was conducted 10 miles east of Chico, California in the Foothill Pine series. The site is an open level area with uniform vegetation composition. The area has a history of seasonal, set stock grazing. Predominant grasses are soft chess (Bromus hordeaceus L.), Wild Oats (Avena fatua L.) and Ripgut Brome (Bromus diandrus Roth). Forbs are Subterranean Clover (Trifolium subterraneum L.), White-tipped Clover (Trifolium variegatum Nutt.) and Turkey-Mullein (Eremocarpus setigerus (Hook.) Benth.).

Experimental Methodology-

Twelve 6 by 14 foot plots were randomly established within a 180 by 80 foot area. Six of the plots were randomly assigned to the treatment group and six to the control group. On April 23, 1998 Transline® was applied to the treatment plots at a rate of 8 oz/ac with a calibrated hand sprayer using a timed application. Yellow starthistle was in the rosette stage at the time of application. More than 24 hours elapsed between application and the onset of rain. One week after herbicide application chlorophyll content was determined with a handheld chlorophyll meter (SPAD-502 Minoltaâ ). In each plot sixty random observations were taken, 20 for grasses, 20 for forbs and 20 for yellow starthistle. Community composition was visually determined. On August 8, after senescence of grasses, plots were sampled for biomass. A 0.96 ft² ring was randomly placed in each plot twice. Material within each ring was clipped at ground level and separated into grass, yellow starthistle and forbs. Because most forbs disintegrated they were not measurable. Clipped material was bagged, oven dried at 105^oF for 24 hours and weighed.

Data Analysis-

Data was checked for normality and analyzed using Analysis of Variance. Differences in biomass production and chlorophyll content of grasses forbs and yellow starthistle were analyzed.
 
  Results: 
  
 

Fig. 1. Chlorophyll content of grasses, forbs and yellow starthistle in treatment and control plots. Error bars indicate standard error of the mean

Chlorophyll Content-

Chlorophyll content in grasses and forbs showed no significant differences(p<0.05) between the treatment and control groups (Figure 1). Yellow starthistle had significant differences between the treatment and control groups (p=0.0009).
 

Fig. 2. Dry matter production of grass and yellow starthistle in treated and control plots.

Above Ground Biomass Produinction-

Analyzed data showed significant differences (p < 0.05) biomass production of both grass and yellow starthistle (Figure 2). Grass biomass treated plots was higher than control plots. Species composition in both the treatment and control plots was similar. Forbs were too deteriorated to collect but the same species were present in both treated and control plots. In the control plots yellow starthistle biomass was more than twice that of the grasses. In the Transline treated plots yellow starthistle was absent.

Discussion:

The study showed that Transline® had no detrimental effect on the preferred forage species in eastern Butte County. Species composition of grasses and forbs was similar in both the treated and control plots. Forage production was doubled in the treatment plots and there was 100% control of yellow starthistle in these plots. This study indicates that Transline® provides excellent control of yellow starthistle and increases forage production without altering community composition. A reduction in yellow starthistle population density will allow preferred forage species to increase. Increased forage species density will allow for greater stocking rates and increased revenue for livestock producers.
 
Literature Cited: