Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


The responses of soybeans {Glycine max (L.) Merr. 'Bragg'} and red rice (Oryza sativa L. 'Strawhulled') to postemergence applications of mefluidide {N-{2,4-dimethyl-5-{{(trifluoromethyl)=sulfonyl}amino}phenyl}acetamide} and bentazon {3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide} alone and in combinations were evaluated in greenhouse studies. Soybeans and red rice were tolerant to bentazon, but their heights were reduced by mefluidide. When these two herbicides were combined, soybeans were not injured at any tested rates, but a synergistic interaction occurred that killed red rice. The changes in degradation, uptake, translocation, metabolism, and loss of these two herbicides due to combinations with each other were studied in order to establish the basis for synergistic interactions of this herbicide combination on red rice. The combinations of these herbicides resulted in decreased degradation and uptake of both herbicides and decreased loss of only mefluidide as compared to either used alone. The translocation of both herbicides was primarily acropetal with limited basipetal movement. The translocation of ('14)C from mefluidide from the treated-middle leaf was reduced by bentazon sprayed over-the-top, however, the entire plant showed necrosis. Mefluidide, sprayed over-the-top, increased the translocation of ('14)C from bentazon, but necrotic symptoms appeared only on the bentazon-treated middle leaf. There were no significant changes in the metabolism of mefluidide due to addition of bentazon. Mefluidide reduced the rate of metabolism and conjugation of bentazon by red rice, and consequently high levels of free bentazon were maintained within the plant. Application of mefluidide 32 h following that of bentazon also resulted in a synergistic response to red rice. Although all the bentazon absorbed by red rice prior to delayed application of mefluidide was conjugated within 32 h, the mefluidide treatment prevented further conjugation of bentazon which continued to enter the plant. The identified metabolites of these two herbicides in red rice were not toxic to the plant. The inhibition of bentazon detoxification by mefluidide in red rice appears to result in the apparent synergistic interactions between the herbicides. Free bentazon remaining in the plant probably caused necrosis and death of red rice.