Effects of Adjuvants, Halosulfuron, and Grass Herbicides onCucurbitaspp. Injury and Grass Control

Abstract

Greenhouse experiments were conducted to evaluate pumpkin cultivar injury and control of three grass species from tank-mixtures of halosulfuron with either clethodim or sethoxydim in combination with nonionic surfactant (NIS), crop-oil concentrate (COC), methylated seed oil (MSO), and high-surfactant oil concentrate (HSOC). Pumpkin injury, in the form of chlorosis and visual growth reduction, was 13 to 21% by 7 d after treatment (DAT) for all pumpkin cultivars. The specific adjuvant used with halosulfuron did not influence pumpkin injury or final plant dry weight. Pumpkin growth reduction at 21 DAT from halosulfuron was less than 9% for all pumpkin cultivars with the least growth reduction (5% or less) observed withCucurbita pepo‘Howden’,C. pepo‘Appalachian’, andCucurbita moschata‘Libby's Select’. The efficacy of sethoxydim or clethodim on large crabgrass was antagonized by the addition of halosulfuron with NIS or COC. However, only combinations of sethoxydim and halosulfuron with COC or MSO were antagonistic on smooth crabgrass. Giant foxtail dry weight reduction was decreased 4 to 24% by the addition of halosulfuron to sethoxydim with NIS and clethodim regardless of adjuvant. Although the frequency and magnitude of grass antagonism was variable, the use of clethodim and MSO with halosulfuron most often provided the greatest level of grass control compared with sethoxydim or other adjuvants.