Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Plant Sciences

Major Professor

James T. Brosnan

Committee Members

Michael D. Best, William E. Klingeman, Dean A. Kopsell


Options for controlling herbicide resistant weed species are severely limited; thus, the recent proliferation of these species is a significant concern to land managers. The discovery and development of novel herbicidally active compounds is one method proposed to manage herbicide resistant weed species. Novel herbicides would provide effective new options for control of existing weed species, and alleviate the narrow selection pressure that leads to the development of herbicide resistance.

Research examined analogs of the synthetic cytokinin thidiazuron (TDZ). TDZ is used as a pre-harvest defoliation of cotton (Gossypium hirsutum L.) and as a plant growth regulator. Although the use of TDZ as a plant growth regulator in tissue culture systems has been extensively studied there is no available data on weed susceptibility to TDZ. Twenty seven analogs of TDZ were synthesized at the University of Tennessee (Knoxville, Tennessee). Thidiazuron and these analogs were applied postemergence corn (Zea mays L.), large crabgrass (Digitaria sanguinalis (L.) Scop.), field bindweed (Convolvulus arvensis L.), barnyardgrass (Echinochloa crus-gali (L.) P.Beauv.), velvetleaf (Abutilon theophrasti Medik.), and redroot pigweed (Amaranthus retroflexus L.). at 250 g ha-1 [grams per hectare]. TDZ injured velvetleaf and redroot pigweed 80 to 96% while only inducing 0 to 2% injury to corn. Across all species tested, minimal injury was induced by any of the analogs synthesized. Results indicate that the synthetic cytokinin, TDZ, may have utility for weed management in corn.

Additional research examined preemergence control of large crabgrass (Digitaria sanguinalis (L.) Scop.), giant foxtail (Setaria faberi Herrm.), and common purslane (Portulaca oleracea L.) with analogs of the cellulose biosynthesis inhibitor dichlobenil. Treatments consisted of two pyridine and one pyrimidine heterocyclic analogs applied in comparison to dichlobenil. Japanese holly (Ilex crenata Thunb.) tolerance was monitored following postemergence over-the-top applications in addition to preemergence weed control efficacy. All treatments were applied at 1,5, and 10 kg ha-1. Only the pyrimidine analog controlled common purslane and large crabgrass similar to dichlobenil at all rates evaluated. Additional research should be performed to determine if this pyrimidine analog inhibits cellulose biosynthesis at sites of action similar to dichlobenil.

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