By Dennis Oda, Star-Bulletin
Roy Nishimoto cultivates nutgrass, growing up to
2 feet tall, in an effort to eradicate the weed.
IF you have ever looked at a stubborn stand of nutgrass in your garden border and thought, "This is the worst weed in the world," you're right. By unpopular acclaim of professionals in the field, it is. Weed out nutgrass myths
According to Roy K. Nishimoto, "scientists who have assessed the world's major weeds have designated nutsedge (nutgrass) as the world's worst weed."
It ought to have its picture hanging in the post office. Nishimoto, a professor of horticulture at the University of Hawaii, doesn't exactly like weeds, but he understands them and teaches courses in their control. He explained that the term "weed" is subjective, that there is no real definition beyond the classic one, "the wrong plant in the right place." Ginger, for example, is overrunning the slopes of Tantalus, but does that make white ginger a weed? "Corn becomes a weed in a soybean field if it is growing where it wasn't intended to be," Nishimoto said. "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 is native to India, and has been in Hawaii since well before 1900," Nishimoto said. "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. "In addition to being unsightly, nutgrass can restrict the establishment and growth of groundcovers and other landscape plants," he said.
"Although it flowers profusely, very few seeds are formed, and nearly all of the seeds are not viable (will not sprout.)" 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. Most grow no deeper than 6 inches.
New infestations can occur when the tubers are moved from one location to another on garden tools or in soil brought into the garden from nursery plants. The tubers will live for as long as two years in the soil as long as they have water and shade.
If brought to the soil surface for one week of sunlight, however, they dry out and die. This is why golf courses and commercial plantings are repeatedly plowed before lawn or a crop is installed. When preparing a new planting bed where nutgrass has grown, it is a good idea to follow this practice. Turn the soil over and leave it for a week without water, rake up the dried weeds and repeat the process once more before planting.
In an otherwise deserted UH greenhouse, Nishimoto is cultivating nutgrass in plastic pots. One collection contains plants of the size that grow in local gardens, in the other collection the nutgrass has grown to 2 feet tall. The latter plagues golf courses and large fields of crops or flowers where there is sunlight and water.
Unlike just about every other professor in the horticulture department, who is trying to increase the production of a plant, Nishimoto and his students are dedicated to eradication. "We are trying to find out what gets the grass to sprout," he said. "Tuber dormancy is one of the most important factors that enables the plant to persist.
"Dormancy means that not all of the tubers in the soil will sprout at any one time, so a potential reservoir of new plants always exists. This is the reason you will find nutgrass plants emerging after you thought you controlled them with a herbicide or a hoe."
And that brings us to the question of how to get to rid of them. In a home garden, you either pull 'em out or knock 'em down. If you are using a weeder, be sure to dig deep enough to get the whole root with the nuts on it, otherwise you are just accomplishing a temporary cosmetic effect.
Nishimoto, while pointing out that there may be other products equally suitable, suggests that Manage or Image, or a combination of Image and MSMA, all available at garden shops, will sort of control nutgrass. "But these herbicides must be repeatedly applied to emerged nutgrass shoots, probably every three months," he said.
He emphasized that the instructions on the container must be followed to the letter. He emphasized that the instructions on the container must be followed to the letter. "Say that twice," he said.
But until Nishimoto and his colleagues discover a permanent cure or a biological control, nutgrass will probably always be with us. And that's how it earned the distinction of the world's worst weed.
Gardening Calendar
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