Seasonal Timing of a Range of Rates of Amicarbazone for Efficacy Against Poa Annua in Desert Turfgrasses.

Amicarbazone at 0.13, 0.18, and 0.22 lb a.i./A was initially evaluated to control P. annua in winter overseeded perennial ryegrass in February 2010. Sequential applications of the higher rates at 3 weeks apart gave up to 90% control of P. annua for only 2 months. Timings of applications in the fall of 2011 after ryegrass overseeding were injurious to the ryegrass when applied during December and January when temperatures were very cold.  Amicarbazone at 0.13 or 0.18 lb a.i./A were not efficacious against P. annua. In late January to early February 2012, the activity of amicarbazone at 0.09, 0.13, and 0.18 lb a.i./A was enhanced by the addition of a non-ionic surfactant compared to no surfactant added to the spray. In February 2015, amicarbazone at 0.09 and 0.18 lb a.i./A showed that the higher rate was visibly more effective against P. annua.  A late spring 2015 application in May showed the sequential applications of 0.09 lb a.i./A to be effective in giving complete control of P. annua with acceptable ryegrass safety.  Amicarbazone at 0.18 lb a.i./A was also effective by providing complete control of P. annua but ryegrass injury was not acceptable. In the desert, very early spring timings in February showed that sequential applications of amicarbazone at 0.09 to 0.18 lb a.i./A with an adjuvant were effective against P. annua with adequate safety to the overseeded ryegrass turf.