It competes with the soybeans for nutrition and sunlight. But nutgrass is neither beautiful like ginger nor useful like corn. It is simply a pest. It probably grew in the sugar and pineapple fields, but there it wasn't a problem. It was shaded by the cane or the pineapples.
Nutgrass grows rapidly in full sunlight, provided adequate water and nutrients are supplied.
However, its growth is severely restricted when shaded. This explains why it thrives in plantings of mondo grass which is not tall enough to offer shade but languishes in borders around shade trees. With its lanky leaves and wimpy little purple flowers, nutgrass is unattractive but that isn't its major drawback. The tubers, the little nuts on the roots that give the plant its name, are the primary source of growth. Left undisturbed, Nishimoto said, an infestation will spread by growing laterally, several yards each year.