Herbicide sensitivity of Echinochloa spp. accessions in Italian rice fields

Echinochloa species are listed among the major weeds in rice worldwide. A greenhouse study was carried out on 80 accessions of Echinochloa collected in Italian rice fields to assess difference in response to azimsulfuron, bensulfuron-methyl, cyhalofop-butyl, molinate, propanil and quinclorac. The accessions were classified as Echinochloa crus-galli (L.) Beauv. (48 accessions; 60% of total), E. erecta (Pollacci) Pignatti (23 accessions; 29%) and E. phyllopogon Stapf (Koss) (9 accessions; 11%). The herbicides were applied at 0×, 0.5×, 1×, and 2× the field rate. The sensitivity of the collected accessions was variable, even within each species. The variability was inversely related to the rate of application and hormesis occurred mainly in the case of bensulfuron-methyl at 0.5× and 1× the field rate. With the exception of quinclorac, the accessions classified as E. crus-galli were, on the whole, more sensitive to most of the herbicides. Discriminant analysis pointed out that differences in herbicide sensitivity among accessions were of limited usefulness for accession classification. The results of this study suggest that the structure of Echinochloa populations in Italian rice fields, and the connected relationships with the effects of the use of herbicides are much more complex than previously thought.