A study of factors effecting the herbicidal control of yellow nutgrass (Cyperus esculentus L.)

The objective of this research was to determine if tuber scarification and potassium gibberellate treatment improved the effectiveness of four herbicides in killing yellow nutgrass (Cyperus esculentus L.). Scarification was studied as a method for improving herbicidal penetration into the nutgrass tuber. Potassium gibberellate was evaluated for its effectiveness in promoting starch hydrolysis in the mother tuber. It was applied as a soak to the germinating tubers alone and in combination with soil applications of s-ethyl dipropylthiocarbamate (EPTC) or 2'chloro-2,6-diethyl-n-methoxymethyl acetanilide (alachlor). Potassium gibberellate was also applied alone as a foliar spray and in combination with a foliar application of 3-amino-s-triazole (amitrole) or 3-(3,4- dichlorophenyl)-1-methoxy-1-methylurea (linuron). Plant height, fresh and dry weight, total air dry root weight, and free glucose and starch content of the mother tubers were determined at one, five, and nine weeks after herbicide treatment. Tuber scarification did not improve herbicidal effectiveness in killing yellow nutgrass. The tuber soak of potassium gibberellate did not influence plant growth or form of tuber carbohydrate content. Foliar applications of potassium gibberellate increased plant height, but the increase was not associated with a change in type of carbohydrate of the mother tuber, and did not improve the herbicidal effectiveness in killing nutgrass. EPTC greatly inhibited nutgrass plant and root growth. There was a delay in the availability of free glucose in EPTC treated tubers. Starch utilization in the mother tubers was greatly inhibited, but hydrolysis occurred over the nine week period. Alachlor inhibited nutgrass foliage and root growth for four weeks after treatment. Starch utilization was inhibited by alachlor, but hydrolysis occurred over the nine week period. Foliar applications of amitrole and linuron were effective in reducing nutgrass plant growth. Free glucose decreased in tubers treated with these chemicals. There was no significant difference in the initial and final starch content of the amitrole. or linuron treated tubers. However, starch content in amitrole and linuron treated tubers was significantly lower than that of the nontreated control at the termination of the experiment. Neither the amitrole nor the linuron treated tubers appeared viable at the termination of the experiment.