Glyphosate-Resistant Johnsongrass Management In Corn

DR. LARRY STECKEL

JACKSON, TENN.
   A number of questions have arisen on how to manage the glyphosate-resistant (GR) Johnsongrass that is very prevalent in some corn fields of south west Tennessee. Much of this corn is now in the V2 to V3 corn growth stage so some decision has to be made fairly quickly before the fields dry.
   Of course most of the corn premixes applied POST in Tennessee rely on glyphosate to control grass.  Traditional corn herbicides most commonly used in Tennessee like atrazine and more recently the mesotrione-containing premixes can help provide control of GR annual grass species like goosegrass but provide little help on Johnsongrass. Therefore with the GR Johnsongrass we need to go with a Plan “B”. The most viable option is Steadfast Q or Accent Q. Either one of these herbicides should do a good job cleaning up the Johnsongrass.
   The cut off in corn to apply Accent Q in corn is V6.  The cut off in corn to apply Steadfast Q is V7 or 20” tall corn, whichever comes first. So we still have some time to get either of these herbicides applied.
   Another question that has been asked is about the utility of Capreno on GR Johnsongrass. Capreno will provide good control of seedling Johnsongrass and about 50 to 60 percent control of rhizome Johnsongrass. So it is a better GR Johnsongrass herbicide than the many of the premixes sold but not as good as Steadfast Q or Accent Q, which should provide 80 to 90 percent control in most situations. ∆
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee