Shattercane (Sorghum bicolor) Interference in Soybean (Glycine max)

Abstract
Shattercane interference in irrigated soybean was evaluated during 1987, 1988, and 1989 at Clay Center, NE, using ‘Rox’ forage sorghum to simulate shattercane. Soybean yield reduction did not occur if shattercane was removed by 2 wk after emergence in 1987 and 6 wk after emergence in 1988 and 1989. Shattercane interference with soybean began when shattercane height exceeded soybean height. Soybean yield was reduced up to 25% before the height differential reached 30 cm, the minimum difference required for selectively applying glyphosate with a wiper applicator. Soybean nodes per stem, pods per stem, and beans per pod decreased as duration of interference increased. A direct relationship between soybean yield loss and shattercane density fit a rectangular hyperbolic function. Yield loss per shattercane plant was highest at low shattercane densities. Soybean plant height, biomass, nodes per stem, pods per stem, pods per node, and beans per pod decreased as shattercane density increased. An interference model for estimation of soybean yield and economic loss based on shattercane density was developed.