Wet or dry, hot or cold, nutsedge (also known as nutgrass) seems sure to survive. As one of its common names (nutsedge) indicates, nutgrass is a type of sedge which grows most vigorously under fairly wet conditions. Seasons with excessive rains, heavy irrigation, or low fields or lawns with abundant moisture are ideal situations for nutgrass spread if it is present. There are two types of nutgrass that are serious weed problems, yellow nutsedge and purple nutsedge. Our main problem in lawns and gardens is yellow nutsedge. As a weed, whether in lawns or cropland, these nutgrasses rank among the most serious weed pests in the world. It was originally not native worldwide, but has been spread by man throughout most of the world.
In the lawn, or elsewhere, nutgrass is easy to spot. If it exists in the lawn, its grass-like blades grow faster than most desirable grasses. A few days after a lawn has been mowed, the nutsedge will be visibly taller than the other grass. The leaves are coarser than blades of lawn grasses and generally a lighter green color. The edges of the leaves are rougher and more saw-toothed. If the plants are not mowed, they will eventually produce flower stems which are triangular in cross section. The flowers have leaf-like bracts below them, giving the appearance of a small umbrella on each stalk. If allowed to develop under good growing conditions, plants may grow as much as 15 to 30 inches tall including flower stalks.
This weed spreads easily by several methods. In May, a plant will begin to grow from the underground tubers which are generally called nutlets. This young plant will soon initiate rhizomes which spread through the soil and give rise to other plants, forming a clump. These may appear above the ground several inches from the original plant. As the days begin to shorten in late summer, existing plants will each form nutlets which will allow them to survive the winter. Under excellent soils and ideal growing conditions, one plant was reported to have formed 1,900 plants in a single season with 6,900 nutlets formed underground by the end of the growing season. Few plants have the ability to reproduce so abundantly. Although nutsedge under competition with other plants will not grow as vigorously or produce as many nutlets, there will still be enough to make it a real pest.
Nutlets may remain dormant in the soil for several years after they have formed if growing conditions are not suitable for growth. Treating existing tops with any type of herbicide may not necessarily eliminate the pest in one season. Repeated treatments over several years are necessary if the pest is to be totally eliminated. Herbicides, even though translocated to roots of treated plants, will not be translocated to dormant nutlets.
Nutgrass is weakened by shade and by competition from more vigorous plants. Often in a healthy lawn, nutgrass will not appear to be present. When a spot thins or dies from disease or some other cause, any nutlets present will start to grow in that spot. If only a few nutgrass plants exist in a lawn or garden, pull or dig them out promptly as soon as they are seen. If pulled early in the summer, they have not yet formed nutlets. If plants are let grow too long, they will soon produce nutlets which will remain in the soil when plants are pulled. The greatest number of nutlets will form in later summer when day lengths are 12 hours or less and night temperatures begin to cool.
Herbicides suitable for controlling nutgrass are generally not readily available to home gardeners in small amounts. One herbicide that has proven fairly effective for nutgrass control is bentazon (Basagran). Other materials for post-emergence control include Image (a registered name) as well as a very new herbicide which is available under the registered name ‘Manage’. It shows promise as a good control. Professional lawn care services are more likely to be able to get these materials for treating the smaller home lawn.
There are a few other materials that may be used to suppress and control nutgrass in home lawns that are currently more available to home gardeners. These materials are known as organic arsenates and include DSMA and MSMA. These require two or more applications at weekly intervals. Best time for treatment is a few weeks after the nutgrass first appears in the lawn, but before nutlets are forming. These materials may cause some temporary discoloration of the grass, but it will recover. Pets or small children should be kept off the lawn immediately after treatment. Apply any herbicide carefully and only in accordance with the manufacturer’s directions.