Our weed control in grain sorghum this spring ranges from fields that are in pretty good shape to quite a few fields that are absolute grassy weed messes.  There have been a number of calls from folks wanting to rescue some of these grain sorghum fields from this grass. Unfortunately, once signalgrass, barnyardgrass, fall panicum, crabgrass, etc. gets taller than 2”, there is no herbicide that can help in grain sorghum.

Some have asked about Facet and atrazine.  This combination has the best chance to control borderline large (2”) annual grasses in grain sorghum.  The problem has been fields are often way too muddy to spray timely.  This has resulted in many fields with a good amount of grass weed pressure.

From a weed control standpoint, the best option for the fields that now are infested with a lot of annual grass that is 6 to 12” tall is to apply glyphosate and replant. Replant is never a popular option but for those with September grain sorghum delivery contracts it is a terribly unpopular option.

In those cases, the grower will need to determine if the locked in price for September delivery will offset the yield loss from the grass competition.  There is very limited research on annual grass weed competition effect on grain sorghum yield.   Research published from Arkansas stated that one can expect 20% yield loss if grass is allowed to compete with grain sorghum the first two weeks after emergence.  Research from Kansas State showed a 3.6% yield loss per week that a large infestation of grass competed with grain sorghum.   Perhaps this information will help with these replant decisions.