MCPA resistance in hemp-nettle, Galeopsis tetrahit L., and bentazon-Na antagonism of tritosulfuron toxicity

In this thesis, two phenomenon related to herbicide physiology were investigated, resistance and antagonism. The resistant (R) and susceptible (S) biotypes of hemp-nettle ('Galeopsis tetrahit') were found in Alberta. Dose-response experiments revealed that the resistance ratios were 3, 8, 1.7, 1.6, 0.7 and 0.6 in response to MCPA, fluroxypyr, dicamba, 2,4-D, glyphosate and chlorsulfuron, respectively. The uptake of [14C]MCPA was not different in R and S, however, 45% and 58% of the absorbed 14C was exported from the treated leaves, with 32 and 38% moving to the roots in R and S, respectively, 72 hours after treatment (HAT). In the root, 55 and 42% of the recovered 14C was MCPA metabolites in R and S, respectively. A lower amount of MCPA translocation along with a higher rate of metabolism in the roots may protect the hemp-nettle R biotype from MCPA injury. The MCPA-resistance trait is nuclear encoded, and probably governed by at least two genes with additive effects. The addition of Na-bentazon to tritosulfuron (482.5 and 10 g ai ha -1, respectively) plus DASH HC (0.156%) reduced tritosulfuron toxicity to white bean ('Phaseolus vulgaris' L.) by 86% (i.e. antagonism ratio [AR] was 1.86). Addition of (NH4)2SO4, (NH4)2HPO4 or NH4NO3 (0.2 N) to the aforementioned mixture eliminated the antagonism (ARs were 1.2, 1.1 and 1.2, respectively), while addition of NH4CH3 COOH did not (AR 2.0). Replacing Na-bentazon with NH4-bentazon or H-bentazon (471.4 and 532 g ai ha-1, respectively) eliminated the antagonism (AR 1.1 and 1.1, respectively). Addition of 0.2 N Na2 SO4 or NaCH3COOH to mixtures that contained NH 4-bentazon resulted in ARs of 1.20 and 1.95, respectively. DASH at 0.625%, or separate applications of Na-bentazon and tritosulfuron reduced the antagonism. Na-bentazon caused 60% and 80% reduction in the uptake and the translocation of [14C]tritosulfuron, respectively. The addition of (NH 4)2SO4, replacement by NH4-bentazon or DASH (0.625%) eliminated Na-bentazon antagonism on [ 14C]tritosulfuron uptake but did not affect the translocation of tritosulfuron. Scanning electron microscopy revealed that a mixture of Na-bentazon, tritosulfuron plus DASH formed a layer of grainlike crystals on the leaf surface, whereas, the addition of (NH4)2SO4 or replacement with NH4-bentazon resulted in an amorphous deposit.