Published online by Cambridge University Press: 12 June 2017
Field and greenhouse studies have shown that dinitroaniline herbicides suppress root rot of peas (Pisum sativum L.) caused by the fungus Aphanomyces euteiches Drechs. This investigation was conducted to identify factors which could enhance root rot suppression. In a temperature-soil moisture growth chamber study, dinitroaniline herbicides significantly reduced disease severity symptoms at all temperature and soil moisture regimes except 32 C and 0.75 field capacity. Dinitroaniline herbicides increased pea fresh weight significantly only under those conditions which favored severe disease development. Maximum root rot suppression occurred at 24 C and 1.25 field capacity. In a greenhouse study of the interaction of root rot suppression with pea varieties, dinitroaniline herbicides significantly increased growth of all 12 pea varieties tested including a root rot tolerant wild type of pea. A series of experiments explored the effect of uniformity, time, and depth of dinitroaniline herbicide incorporation on root rot suppression. In greenhouse studies, non-uniform incorporation significantly reduced root rot suppression indicating the need for thorough incorporation to achieve maximum root rot suppression. The combination of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) + oryzalin (3,5-dinitro-N4,N4 dipropylsulfanilamide) was more effective than either trifluralin or oryzalin alone under non-uniform incorporation conditions but not under uniform incorporation conditions. Field studies showed that herbicide incorporation 2 weeks prior to planting may improve pea yield by 1.12 kg/ha of trifluralin or 0.56 + 0.56 kg/ha of trifluralin + oryzalin but not by 0.56 kg/ha of trifluralin. Herbicide incorporation to 15.2 cm rather than the normal 7.6 cm, increased pea yield at the 1.12 kg/ha rate of trifluralin or oryzalin or at 0.56 + 0.56 kg/ha of trifluralin + oryzalin. At the 0.56 kg/ha rate of trifluralin or oryzalin, herbicide dilution offset any benefit from deeper soil incorporation.