Maize cultivars differ in tolerance to imazethapyr

Abstract

The low tolerance of maize (Zea mays L.) to imazethapyr ((±)-2-[4,5-dihydro-4 methyl-4-(1 -methylethyl)-5-oxo 1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid) resulted in extensive crop damage in 1992/93 due to residue carry-over from resistant soybean (Glycine max L.). Pot experiments were conducted to assess the role of cultivar differences in maize tolerance, as well as the potential for synergistic interaction between imazethapyr and a fungicide. A selection of white and yellow maize cultivars were tested. The fungicide captab (3a, 4, 7, 7a- tetrahydro-2-[(trichloromethyl)thio]-1H-isoindole-1, 2(2H)-dione) was investigated in terms of its potential to exacerbate damage caused by imazethapyr to various maize cultivars. White cultivars were significantly more sensitive to imazethapyr than the yellow cultivars, with damage in shoot dry mass ranging from 13 to 63% at the lowest herbicide rate of 5 g ai ha−1. The ED50-values derived from linear regression equations for the relationship between imazethapyr rate and maize damage confirmed the differential tolerance of white and yellow cultivars, and indicated that the sensitivity of all six cultivars of the former type increased in the presence of captab. Except for one of six yellow cultivars, the same tendency was found in this group. The mechanisms involved in these differential plant responses are not known. Their elucidation could introduce flexibility into the safety (waiting) period specified for maize, through rational cultivar selection and promote the breeding of cultivars that are tolerant to the broad spectrum of acetolactate synthase (ALS)-inhibiting herbicides.