Fall panicum

Fall panicum (Panicum dichotomiflorum) is a summer annual grass that can grow to about three feet tall with a characteristic growth habit: the stems bend sharply at swollen nodes near the base, producing a zigzag, kinked appearance, and the lower stems often have a waxy or smooth, shiny look. Leaf blades and sheaths are typically smooth (glabrous) with a prominent light-colored midrib down the blade, and the ligule is a fringe of hairs (membranous-fringed). The seedhead is a large, open, branching panicle. The bent-at-the-nodes habit, hairy ligule, smooth sheaths, and conspicuous whitish midrib help separate fall panicum from crabgrass and other summer annual grasses.

Fall panicum degrades the stand by forming coarse, upright clumps that grow taller and faster than surrounding turf, creating an uneven, weedy texture between mowings and contrasting in color with finer turfgrasses. As it competes for light, water, and nutrients it thins the desirable turf, and its large, branching seedheads mar appearance and shed enormous quantities of seed, ensuring repeated infestations. After frost the dead clumps leave open spots that invite further weed encroachment.

Fall panicum is a warm-season summer annual that reproduces entirely by seed. It emerges in late spring as soils warm, grows vigorously through summer, flowers from roughly July through October, and is killed by the first hard frost. It is an extraordinarily prolific seed producer, with large plants capable of producing huge numbers of highly persistent seeds that remain viable in the soil for many years, so a single uncontrolled season can replenish the seed bank for a long time and drive recurring infestations.

Fall panicum invades thin, open, or disturbed turf and is common in landscapes, roadsides, nurseries, and noncrop areas as well as managed turf. It favors warm conditions and moist, fertile soils, and it readily colonizes gaps in the stand from its abundant, long-lived seed. Because it emerges somewhat later than crabgrass and is so prolific, it tends to persist where preemergence timing is missed or where the stand is weakened by stress, scalping, or low density.