Amicarbazone is a photosystem II (PSII) inhibiting herbicide of the triazolinone herbicide family. Greenhouse experiments were conducted to compare the effects of amicarbazone and atrazine on annual bluegrass control and quantum yield (ΦPSII) when applied at three treatment placements (soil-only, foliage-only, and foliage soil). Herbicide rates for amicarbazone and atrazine were 0.53 and 2.25 kg ha−1, respectively. Amicarbazone applied soil-only and foliage soil controlled annual bluegrass 57 and 59%, respectively, 1 wk after treatment (WAT). Atrazine applied to foliage soil controlled annual bluegrass 48% at 1 WAT. All soil-only and foliage soil treatments were similar 2 WAT. Foliage-only application of amicarbazone provided significantly less control than other amicarbazone treatments throughout the study. Amicarbazone applied soil-only and foliage soil controlled annual bluegrass 100% at 3 WAT. Soil-only and foliage soil applications of atrazine and amicarbazone had similar reductions in quantum yield (ΦPSII) at 1 to 3 WAT. Foliar-applied amicarbazone reduced ΦPSII 78, 84, and 86% at 1, 2, and 3 WAT, respectively. The rapid reduction in annual bluegrass ΦPSII and the increase in control resulting from soil contact of amicarbazone indicate root exposure of amicarbazone is beneficial for annual bluegrass control.
Nomenclature: Amicarbazone, 4-amino-N-(1,1-dimethylethyl)-4,5-dihydro-3-(1-methylethyl)-5-oxo-1H-1,2,4-triazole-1-carboxamide; annual bluegrass, Poa annua L.
