Lally, Nathan Gerard2011-08-112011-08-112011-08-11http://hdl.handle.net/2097/12002Postemergent herbicide options for grain sorghum are limited and increasingly challenged by the development of herbicide resistant weeds. The herbicide pyrasulfotole & bromoxynil (P&B) was evaluated for potential use in grain sorghum and for control of a suspected HPPD-resistant Palmer amaranth population. Field experiments were conducted near Manhattan and Rossville, KS, to evaluate grain sorghum response to P&B with and without 2,4-D applied to growth stages from 1-leaf through the flag leaf stage and tankmixed with 2,4-D ester, amine, or dicamba applied to 3- and 6-leaf sorghum. The addition of 2,4-D ester did not reduce sorghum injury from P&B alone. Increasing the rate of P&B increased injury. Treatments applied to 1- and 4-leaf sorghum were injured the most. All P&B treated sorghum, regardless of timing, yielded 8 to 20% less than the untreated check. Pyrasulfotole & bromoxynil applied alone or with dicamba injured sorghum less than 2,4-D applied at 3- or 6-leaf. Increasing the rate from 140 to 280 g ha[superscript]-1 2,4-D amine or ester increased injury by 6 to 11%. Yields were lowest when P&B was applied with 2,4-D amine at 140 g ha[superscript]-1 and 2,4-D amine or ester at 280 g ha[superscript]-1 compared to all other treatments. Increasing the rate of growth regulator herbicides decreased yields by 8% and did not reduce crop injury from P&B alone. Greenhouse and field experiments were conducted to evaluate the response of two suspected P&B-resistant (R1 & R2) and one susceptible (S) Palmer amaranth population to P&B, atrazine, and tembotrione. Herbicides were applied when plants were 7 to 19 cm tall. The S population was controlled with less than field use rates. A resistance index (RI) of 4.8 to 11.0 was determined for R1 and R2 in greenhouse and field experiments. Tembotrione controlled 100% of S in all experiments, while providing 63 to 86% injury to R1 and R2 populations. Atrazine did not control the resistant populations. Pyrasofotole & bromoxynil will be an valuable tool for weed control in sorghum, however, Palmer amaranth populations exist that will not be controlled.en-US© the author. This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).http://rightsstatements.org/vocab/InC/1.0/Pyrasulfotole & bromoxynilHPPD inhibitorsPalmer amaranthGrain sorghumThesisAgronomy (0285)