|Koger Iii, Clifford|
Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2005
Publication Date: 11/8/2005
Citation: Koger III, C.H., Walker, T.W., Krutz, L.J. 2005. Response of three rice (Oryza sativa) cultivars to pendimethalin application, planting depth, and rainfall. Crop Protection 25:684-689. Interpretive Summary: Pendimethalin is a herbicide that controls weeds such as annual grasses in rice. However, the chemical must be applied prior to the rice seed sprouting because it may damage older rice varieties. Newer rice varieties have greater seedling vigor which may allow these varieties to be planted deeper in order to avoid damage from pendimethalin. Regardless of timing of pendimethalin application, the Wells rice variety was more sensitive to pendimethalin that the rice varieties Cocodrie or Lemont. Emergence of all rice varieties was reduced by pendimethalin when planted at depths less than one and one-half inches deep. However, optimal planting depth for emergence and reduced injury was one-fourth to three-fourth of an inch deep. 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 is more important than a depth that will minimize injury caused by pendimethalin.
Technical Abstract: Pendimethalin provides preemergence (PRE) control of annual grasses in rice but must be applied delayed-PRE because older rice cultivars exhibit injury when the herbicide is applied prior to the seed imbibing moisture and sprouting. New rice cultivars exhibit greater seedling vigor and can be planted deeper. Planting new cultivars deeper may allow for pendimethalin comes in contact with seed, thus reducing the potential for injury. 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 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 as 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 to 1.9 cm. Rainfall after pendimethalin application, regardless of rainfall 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.