Sterile oat (Avena sterilis L.) cross-resistance profile to ACCase-inhibiting herbicides in Greece

Sterile oat (Avena sterilis) is the most widely distributed, abundant and harmful weed in the winter cereals grown in Greece. Its effective control has relied for the past three decades upon the ACCase-inhibiting herbicides. However, recently many growers in northern and central Greece have experienced reduced sterile oat control after the application of fenoxaprop-p-ethyl or clodinafop-propargyl. Preliminary screening indicated that less than 80% of the treated plants in 36 and 43 out of 125 sterile oat accessions were killed (R, resistant) by the application of the four times the recommended dose of fenoxaprop-p-ethyl (R-Fx) or clodinafop-propargyl (R–Cd), whereas less than 80% of the treated plants in 29 of them were killed by both herbicides applied at four times the recommended dose. Also, more than 80% of the treated plants in 42 and 35 accessions were killed by the four times the recommended dose (r, partially resistant) of fenoxaprop-p-ethyl (r-Fx) or clodinafop-propargyl (r-Cd), respectively. Finally, more than 80% of the treated plants in 47 and 47 accessions were killed (S, susceptible) by the recommended dose of fenoxaprop-p-ethyl (S-Fx) or clodinafop-propargyl (S-Cd), respectively, whereas more than 80% of the treated plants in 36 of these accessions were killed by the recommended dose of both herbicides. The whole-plant dose-response method used to evaluate 17 R-Fx and five S-Fx accessions showed that 16, 17, 11, and two R-Fx accessions were cross-resistant to clodinafop-propargyl, diclofop-methyl, tralkoxydim, and pinoxaden, respectively. In particular, more than 50% of the treated plants in 12, 12, 17, and three accessions survived the respective application of the four times the recommended dose of fenoxaprop-p-ethyl, clodinafop-propargyl, diclofop-methyl, and tralkoxydim. Regarding pinoxaden, 3, 17 and 20% of the treated plants in three accessions survived its application at four times the recommended dose. All R and the S accessions were effectively controlled by the recommended dose of imazamox and mesosulfuron-methyl + iodosulfuron methyl-sodium. These results strongly suggest that cross-resistance to ACCase-inhibiting herbicides has been developed for sterile oat. Therefore, measures should be taken for crop rotation when possible or rotational use of the available ALS- and ACCase-inhibiting herbicides in order to reduce the potential for development of sterile oat multiple resistance. Regarding the accessions with cross-resistance to APP, CHD and PPZ, these could be effectively controlled by the application of mesosulfuron-methyl + iodosulfuron methyl-sodium.

► We evaluated 125 sterile oat accessions for herbicide resistance.
► We used the whole-plant response method.
► We detected cross-resistance to ACCase- inhibiting herbicides.
► Multiple resistance to ALS- inhibiting herbicides was not detected.
► Resistant accessions were susceptible to mesosulfuron.