Rapid publication Diuron-resistant Poa annua is resistant to norflurazon

Poa annua control with norflurazon was different between two field trials i n 1999. At the field site with suspected diuron-resistant I! annua, control was less than at the site with known diuron-susceptible I! annua. Diuron-r esistant and -susceptible biotypes of P. annua were subjected to a range of norflurazon rates in the greenhouse. The diuron-resistant P. annua biotype (R/S ratio of 2.5) was collected in 1995 from a Lolium perenne L. seed pro duction field near Tangent, OR. The RIS ratio for norflurazon in these expe riments was 4.8; thus, confirming that diuron-resistant P. annua is resista nt to norflurazon.