College of Agriculture

Molasses Not Shown To Increase Palatability of Old Growth Yellow StarThistle

Gregory W. Allen


Red Angus heifers that had fasted for 24 hours showed no preference between yellow starthistle sprayed with molasses or not sprayed with molasses.


Yellow starthistle, Centaurea solstitialis, is a non-native, summer-maturing, aggressive weed that can displace many desirable plant species (Thomsen et al., 1996). In 1965 nearly 1.9 million acres in California were infested with yellow starthistle. By 1998 yellow starthistle infested over 10 million acres of pasture, rangeland, hay fields, orchards, and roadsides.

Grazing starthistle in early growth stages reduces starthistle densities (Thomsen et al., 1997). However, we found no research on enticing cattle to consume old growth (over one year old) yellow starthistle. The objective of this experiment was to test cattle’s acceptance of old growth yellow starthistle treated with a molasses and water mixture.

Materials and Methods

The experimental site, ½ mile east of Meridian Road in Butte County, had an extremely dense blanket of starthistle which was over one year old and had become hard and twig-like. The experiment was set up in a completely randomized block design. Nine blocks were used with two treatment plots per block totaling 18 plots. Each plot was 10’x12’. We separated plots with fencing and movable Powder River pipe panels. The treatments included a control, no molasses applied, and a second treatment in which a solution of 5 parts water to one part molasses was applied. A three gallon hand held pump sprayer was used to mix and apply the mixture to the nine plots at a rate of 120.90 gallons per acre.

Fourteen Red Angus heifers were held off feed for 24 hours then moved into the experimental area at 4 AM on May 18, 1998, where they grazed for 12 hours. The stocking rate was 283 heifers per acre. The estimated yellow starthistle biomass per plot was calculated by harvesting a 10' x 12' area of starthistle that was visually identical to the plots, then drying and weighing the clippings. This representative plot contained 4618 grams of starthistle. The consumption of starthistle per plot was calculated by subtracting the dry matter of starthistle, post grazing from 4618 grams. The data was analyzed using a single factor ANOVA to test for significant difference between treatments.


No significant difference was found between treatments. The heifers consumed nearly 70% of the yellow starthistle in both treatments.


The application of molasses to yellow starthistle did not increase consumption of old growth starthistle; therefore, it would not be profitable to apply molasses to starthistle to increase the palatability. Perhaps the results would have been different if the heifers had not been held off feed for 24 hours before they were introduced to the experimental plots.

Research conducted by the University of California, Davis has shown that grazing yellow starthistle during the late bolting stage does little to decrease starthistle densities. However, it does reduce plant height, canopy size, and seed production allowing seedlings of more desirable grasses to obtain essential sunlight for growth (Thomsen et al.,1989). After removing old growth starthistle using grazing techniques, additional grazing during the pre-bolting stage has shown in research conducted by UC, Davis to dramatically reduce yellow starthistle densities in following years (Thomsen et al., 1993). The grazing of old growth starthistle can be used to remove the weed canopy and allow light to reach small annual grasses below, helping them to establish themselves. Following the removal of old growth thistle additional grazing can be used to control the newly emerging starthistle plants.

Literature Cited

Thomsen, Craig D., Marc P. Vayssieres, William A. Williams; Mowing and Subclove Plantings Suppress Yellow Starthistle, California Agriculture Vol. 51, Number 6 1997.

Thomsen, Craig D., William A. Williams, Melvin R. George, W.B. McHenry, Fremont L. Bell, Ronald S. Knight; Managing Yellow Starthistle on Rangeland California Agriculture Vol.43, Number 5 1989.

Thomsen, Craig D., William A. Williams, Marc P. Vayssieres; California Exotic Pest Plant Council Symposium, Vol. 2, 1996.

Trinity County Resource Conservation District; Control of Yellow Starthistle, (PDF)