Theses and Dissertations

Issuing Body

Mississippi State University


Reddy, K. Raja

Committee Member

Shankle, Mark W.

Committee Member

Massey, Joseph H.

Committee Member

Reddy, Krishna N.

Committee Member

Arancibia, Ramon A.

Date of Degree


Document Type

Dissertation - Open Access



Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Plant and Soil Sciences


S-metolachlor is an effective herbicide used to control/suppress annual grasses, nutsedges and several broadleaf weeds in sweetpotato. However, a decline in storage root quality and yield has been reported under certain environmental conditions. Information is limited on the effect of S-metolachlor application followed immediately by rainfall on sweetpotato growth and development under different temperatures, as well as the optimum application time. Therefore, the objectives of this study were to evaluate sweetpotato responses to interactive effects of S-metolachlor, temperature and rainfall, and to determine S-metolachlor optimum application time. A sunlit, controlled environment experiment was conducted to investigate sweetpotato response to S-metolachlor and rainfall immediately after application under different temperatures. Sweetpotato slips were transplanted into sandy soil filled pots. Treatment combinations included five levels of S-metolachlor, 0.00, 0.86, 1.72, 2.58 and 3.44 kg ha-1, two levels of rainfall, 0 and 38 mm and three temperatures, 25/17, 30/22 and 35/27 °C, day/night. After POST application of S-metolachlor and rainfall, all plants were transferred to sunlit growth chambers that were maintained at their respective temperatures and ambient CO2 concentration for 60 days. In another experiment, S-metolachlor application time was varied to investigate sweetpotato growth and development. Two levels of S-metolachlor 0.0 and 1.0 kg ha-1 and three application times 0, 5 and 10 days after transplanting (DAT) were used and plants were harvested five times, 5, 10, 15, 20 and 80 DAT to estimate plant growth and development. Shoot, root and total plant biomass yields declined with increasing concentration of S-metolachlor across temperatures. In addition, storage root yield and quality decline was S-metolachlor rate dependent and aggravated by rainfall immediately after herbicide treatment across temperatures. S-metolachlor was more injurious on most plant component parameters in the optimum and high temperatures where plant growth was vigorous than in the low temperatures. S-metolachlor application at 0 and 5 days affected sweetpotato growth, including storage roots, but delaying until 10 days minimized the injury. These results can be used to weigh the risk of crop injury against the weed control benefits of S-metolachlor when making management decisions, and to determine application time based on weather information.



evapotranspiration||slips||transplanting||post-transplant||Herbicide injury||storage roots||weed interference||yield reduction.