Corn Tim Trower and Chris Boerboom Sr. Weed Scientist Making the best weed control decisions depends on knowledge of weed populations, the biology of those weeds, and the limitations of the available herbicides. Large and smooth crabgrass are weeds that are best managed in field corn with preemergence herbicides but have very limited herbicide options after corn emergence. The following article contains information on weed biology and how to best manage large and smooth crabgrass infestations in field corn, soybeans, and alfalfa. Smooth - Digitaria ischaemum.
Large crabgrass has a membranous ligule that is truncate and has a jagged appearance.
The inflorescent consists of a panicle of branches with spikelets arranged in two rows of a flattened rachis. Large crabgrass may grow up to 3 feet in height. Smooth crabgrass has a membranous ligule that is truncate and often has a smooth appearance. The sheath has no hairs. The inflorescent consists of a panicle of digitate branches with spikelets arranged in two rows of a flattened rachis.