Can Nicosulfuron plus Metsulfuron Effectively Control or Suppress King Ranch Bluestem?

Abstract

Core Ideas Nicosulfuron plus metsulfuron combinations failed to effectively control KR bluestem even when used in consecutive years. Lack of control in permanent plots was due to the high populations and also the crown bud bank, which were not entirely killed by herbicide treatments. Glyphosate provided effective control at the end of each growing season and provided 55 to 60% control the following spring. The use of herbicides alone is probably not an effective method for control or suppression for KR bluestem. Research was conducted in south-central Texas to evaluate nicosulfuron plus metsulfuron combinations or glyphosate for King Ranch (KR) bluestem (Bothriochloa ischemum var. Songarica) control. In one study, at one location, where KR bluestem was interspersed in a Tifton 85 bermudagrass [Cynodon dactylon (L.) Pers. × C. nlemfuënsis Vanderyst] pasture, control up to 9 weeks after an early fall application was 98% for nicosulfuron plus metsulfuron combinations and 99% for glyphosate. At another location, with a solid stand of KR bluestem, control was 60% or less for nicosulfuron plus metsulfuron combinations. When evaluated the following spring, control at either location was no better than 25% for nicosulfuron plus metsulfuron combinations and 60% for glyphosate. In another 2-year study with permanent plots having a solid stand of KR bluestem, control was ineffective for nicosulfuron plus metsulfuron combinations applied in either late spring, mid-summer, or early fall. When evaluated in mid- to late December, the best control was provided with sequential applications, either in late spring plus mid-summer or mid-summer plus early fall while in another year, the mid-summer plus early fall sequential applications were best. However, none of these sequential applications had greater than 45% control. Applying nicosulfuron plus metsulfuron combinations reduced KR bluestem herbage yields up to 10% as compared with the untreated check.