Identification of tolerance to metribuzin and imazethapyr herbicides in faba bean

Weeds cause serious constraint to faba bean (Vicia faba L.) productivity. Broad
weed control is hampered by the availability of postemergence herbicides to control
them, as the current faba bean cultivars are highly susceptible to them. Therefore,
the deployment of postemergence herbicide tolerance is desirable in faba bean. To
address this, 130 accessions were screened for their response in mature plants under
field conditions to the recommended dosage of two herbicides, metribuzin at 250 g
a.i. ha−1 and imazethapyr at 75 g a.i. ha−1 at Marchouch and Terbol stations. The
recorded herbicide damage score (HDS) varied from 1 (no visual damage) to 5 (full
damage with death of more than 50% of plants) at both locations. Low but highly significant (p < .01) and positive correlation (+0.26) was obtained between the recorded
HDS at both locations. Both herbicides significantly delayed flowering and maturity time occurrence, reduced plant height and grain yield, and increased number of
branches. Reduction index (RI) correlated positively with HDS score at Terbol station
in different seasons and at Marchouch in 2016–2017 seasons. Eleven tolerant accessions were identified and further evaluated to 1×, 1.5×, and 2× of recommended dose
of both herbicides. The results indicated that the harmful effect of herbicides on grain
yield reduction intensified from 13.4 to 27.2% and from −7.6 to 1.8% as the dose of
metribuzin and imazethapyr increased respectively from 250 to 500 g a.i. ha−1 and
from 75 to 150 g a.i. ha−1. Tolerance to metribuzin and imazethapyr in eight faba
bean accessions was confirmed with no significant reduction in grain yield