Effects of Johnsongrass (Sorghum halepense) Density on Sugarcane (Saccharum officinarum) Yield

The effects of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] infestations were determined during a 2-yr study on sugarcane (Saccharum officinarum L. ‘CP-65-357’) yield. Both cane and sugar yields were lower (36 and 31%, respectively) in plots heavily infested with johnsongrass than in weed-free plots. Sugarcane yields were inversely influenced by johnsongrass equivalents (the sum of the values obtained by multiplying the number of clumps by their corresponding importance value for each plot). In 1983, both johnsongrass standing crop and johnsongrass equivalents correlated negatively with cane yield much better than any other factor combinations, while in 1984, the same was true for stalk population. Substantial yield reductions from johnsongrass interference were observed at johnsongrass infestation levels higher than 15 to 35%.