BIOLOGICAL-CONTROL OF RUMEX-OBTUSIFOLIUS L BY GOAT GRAZING

Effect of goat grazing on the growth, propagation and survival of a dock, Rumex obtusifolius L. was investigated during a period of 3 years in a permanent pasture divided into 2 parts. Three cows were grazed on one part (namely, cow-grazing plot) and 3 cows plus 4 goats were grazed on the other part (mixed-grazing plot). In both plots, 3 belt transects were set up to determine the degree of defoliation, plant height, maximum leaf length and the number of bolting stalks of adult docks. Apart from the transects, typical adults were collected to determine the dry weight of seeds in both plots in late July. Five permanent quadrats were set up to take a census of the seedlings of the dock. The adult docks were defoliated more severely up to August in the mixed-grazing plot than in the cow-grazing plot. In the former plot, the leaf length was shortened to 67%, the plant height was lowered to 26% and the number of bolting stalks was reduced to 41% of the respective ones in the latter plot in July. Moreover, the adults formed shorter bolting stalks in the mixed-grazing plot. This suppression of reproduction of the dock led to a decrease in the number of seedlings. In the mixed-grazing plot, the seedlings emerged at a rate of 18% of that in the cow-grazing plot in the autumn of the first grazing year and 30% in the spring of the second year. There were few differences between the survivorship curves of the dock in the two plots. A low percentage of seedlings survived during one year, although with a slightly higher rate in the mixed-grazing plot than in the cow-grazing plot. The established individuals could set numerous seeds in the latter plots. It was concluded that goats controlled Rumex obtusifolius effectively through a process of defoliation, suppression of the propagation and decline of the population of the dock. Mixed-grazing could afford both weed control and improvement of pasture production.