Theses and Dissertations

Issuing Body

Mississippi State University


Reynolds, Daniel B.

Committee Member

Shaw, David R.

Committee Member

Willers, Jeffrey L.

Committee Member

Massey, Joseph H.

Committee Member

Cox, Michael S.

Date of Degree


Document Type

Dissertation - Open Access


Weed Science

Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Plant and Soil Sciences


Bispyribac-sodium is an acetolactate synthase (ALS) inhibiting herbicide introduced for control of grasses, broadleaves, and sedges in rice and turf. However, Mississippi and Arkansas rice producers have reported inconsistent barnyardgrass (Echinochloa crus-galli Beauv.) control with bispyribac-sodium. Experiments were conducted to determine if inconsistent barnyardgrass control with bispyribac-sodium could be alleviated through adjuvant technology. Absorption of 14C-bispyribac-sodium was greatest with a proprietary blend of methylated seed oil/organosilicone (MSO/OSL) (0.37 L ha-1) plus urea ammonium nitrate (UAN) (2% v/v) and the proprietary blend of MSO/OSL/UAN (2% v/v) at 80 and 74% of applied 14C-bispyribac-sodium, respectively. The addition of 32% UAN to MSO/OSL and non-ionic organosilicone (OSL/NIS) adjuvant systems resulted in a four- to fiveold increase in absorption compared to treatments without UAN. Maximum absorption was achieved 12 h after application and therefore, bispyribac-sodium should be rainfast at this time. MSO/OSL adjuvants supplied from multiple manufacturers were also examined to determine which provided the highest levels of 14C-bispyribac-sodium absorption as well as herbicidal efficacy and rainfastness. The addition of Rivet® plus UAN or Sil-MES 100® plus UAN to 14C-bispyribac-sodium resulted in the highest levels of absorption among adjuvants supplied. Bispyribac-sodium applied with no adjuvant or with 32% UAN only resulted in significant reductions in control compared to MSO/OSL adjuvant formulations. Addition of MSO or MSO/OSL adjuvants and UAN to bispyribac-sodium resulted in greater than 85% freshweight reduction of barnyardgrass. Bispyribac-sodium applied with MSO or Dyne-A-Pak® was rainfast by two and four hours after application, respectively. Addition of Sil-MES 100® plus UAN or Inergy® plus UAN to bispyribac-sodium reduced the rainfastness interval to 30 minutes and one hour after herbicide application, respectively. Further experiments were conducted to determine if individual components of 32% UAN as well as ammonium sulfate (AMS) would provide control similar to that of 32% UAN. The addition of ammonium chloride, calcium nitrate, and ammonium sulfate at selected rates provided barnyardgrass control similar to that of 32% UAN.