Mapping of herbicide resistant weeds in Italy

In the last three decades, herbicides resistance has become a worldwide problem. In Italy 18 species and the most important herbicide modes of action are involved. The Italian herbicide resistance working group (GIRE- www.resistenzaerbicidi.it) has been active since 1997 with the mission communication between public and private researchers as well as all involved stakeholders. The main aims are: to encourage a responsible use of herbicides, to improve the knowledge about this topic, to devise and communicate resistance management guidelines and strategies. One of the outcomes of the work done by GIRE is the continuous update and mapping of herbicide resistant weeds in Italy. With the collaboration of the major agro-chemical companies a complaint monitoring of putative resistant populations of different weed species is regularly carried out. Sampled populations were screened in greenhouse experiments with 3-4 specific herbicides. Plant survival in relation to the untreated check was recorded. A population was considered resistant when survival was >20% at the recommended field dose (1x) and highly resistant when survival was >10% at 3x. The data were stored in a database and weed resistance maps were drawn using ArcExplorer2 software. In northern Italy the most diffuse biotypes found in rice crops belong to A. plantago-aquatica, C. difformis, S. mucronatus and E. crus-galli resistant to ALS-inhibiting herbicides. Furthermore, S. halepense resistant to ACCase-inhibitors and E. crus-galli resistant to ALS- inhibitors were found in other summer crops. In the central-southern parts, many cases of Lolium spp., P. paradoxa and A. sterilis resistant to ACCase-inhibitors were found in autumn- winter crops, mainly durum wheat. Resistance maps allowed to analyse the distribution and the evolution of resistant weed biotypes in different Italian regions. The data maps were communicated to regional phytosanitary decision makers and published in the GIRE website.