Response of three rice (Oryza sativa) cultivars to pendimethalin application, planting depth, and rainfall

Greenhouse experiments were conducted to evaluate the response of three rice cultivars (Lemont, Cocodrie, and Wells) to pendimethalin as a function of planting depth, herbicide application timing, and timing of simulated rainfall after herbicide application. In the absence of pendimethalin, emergence of Wells was greater than that of either Cocodrie or Lemont. However, regardless of application timing, Wells was more sensitive to pendimethalin compared to either Cocodrie or Lemont. Emergence of all cultivars was reduced by pendimethalin at planting depths <3.8 cm. For all cultivars, optimal planting depth for emergence and reduced injury was 0.64–1.9 cm. Rainfall after pendimethalin application, regardless of amount or timing, had no effect on rice emergence or plant health. Root biomass was not affected by planting depth or pendimethalin application, regardless of application timing. Based on these data, pendimethalin should be applied at labeled rates between 3 and 7 days after planting of certain cultivars, and should not be applied to fields planted to the Wells cultivar. A planting depth that will optimize rice emergence should take precedence over a depth that will minimize injury caused by pendimethalin.