Managing Nutsedge In Vegetable Crops

 Nutsedges are perennial plants that survive as tubers and rhizomes in the soil. Their leaves and flower stems die back at the end of the season. The tubers can remain viable in the soil for several years and can be found as deep as 18 inches below the soil surface. Tubers are spread within the field by cultivation, moving water, and other forms of soil movement. Long-distance dispersal can occur with soil on equipment, in infested compost or topsoil, and on infested nursery stock.^3,4,7 

Yellow nutsedge plants can produce hundreds to thousands of tubers in a season. Most tubers are distributed in the upper six inches of the soil. Tubers up to eight inches deep can sprout and emerge, and an individual tuber can sprout as many as seven times before exhausting its reserves. Tuber sprouting is affected by soil temperature and moisture conditions. Tubers (and rhizomes) begin to sprout when soil temperatures rise above 43°F for yellow nutsedge and above 59°F for purple nutsedge. Tubers tend to have a staggered emergence, with not all tubers emerging simultaneously. Emerging nutsedge stems are strong enough to penetrate and emerge through plastic mulches and landscape cloth.^1,3,4,5,7 

Nutsedges thrive in waterlogged soils and become established most easily in areas with poor drainage, leaky irrigation systems, or over-irrigated areas. Once established, nutsedge plants can tolerate drier soil conditions. While nutsedge plants produce seeds, seed viability is usually fairly low, and nutsedge seeds do not contribute much to plant dispersal.^3,7,9 

Nutsedges are difficult to control, and no single measure will eliminate these weeds. The first priority should be to prevent nutsedge establishment in non-infested fields. Tillage and harvesting equipment should be cleaned of soil and plant debris before entering non-infested fields. Hay, straw, manure, and compost applied to the field should be obtained from reputable sources and free of nutsedge tubers and rhizomes.^3,4,5 Improve soil drainage, and eliminate other factors causing wet soil conditions^.3,9 Spot treat any nutsedge patches as soon as they appear to help prevent establishment. Avoid cultivating areas where nutsedge has emerged to limit the spread within the field.⁵ 

In fields where nutsedge has become established, multiple control strategies will be needed for long-term management, including cultural, mechanical, and chemical techniques.^5,9 

Cultural: Nutsedges are not shade tolerant, and promoting the rapid formation of dense crop canopies can help limit nutsedge development. Plant canopies 18 inches or taller usually provide enough shade to inhibit nutsedge growth.^1,3,4 Select varieties that are well adapted to the region and growing conditions. Plant early using narrow row spacings and high plant populations. Manage disease, insect, and weed problems to maintain a full, healthy canopy.⁵ Apply levels of nitrogen fertilizer that promote optimal crop growth. The added nitrogen will not stimulate nutsedge growth.^4,5 

Rotating to corn and soybean crops that provide abundant shade can help manage nutsedge problems. Rotating to these crops can also allow the use of herbicides that are effective against nutsedge but may not be registered for use on vegetable crops^.2 Rye cover crops also have some allelopathic effects against nutsedge and provide adequate soil shading.^2,4 

Mechanical: Tillage can be used to help manage nutsedge, but the timing is critical. Disking, chisel plowing, and moldboard plowing shortly after nutsedge seedlings have emerged can help destroy germinating tubers and kill young plants. However, this must be done before the plants start producing new tubers. Otherwise, tillage will spread the tubers and increase the area of infestation.^3,4,5 Cultivation should be done before nutsedges reach the five to six-leaf stage. Tubers can regerminate, but they consume resources each time they do. Repeated cultivation, every two to three weeks, can reduce tuber viability over time. Nutsedge plants can be pulled up or hoed by hand, and the rhizomes and tubers can be dug up. However, the soil needs to be dug down to at least ten inches and then sifted to remove the rhizomes and tubers.^3,9 

Soils can be cultivated in mid-summer when it is warm and dry, so that tubers brought to the surface will dry out and lose viability over ten to twelve days. Repeated cultivation to bring additional tubers to the surface can help reduce the number of viable tubers by about 80% over a month.^4,7 

Chemical: The application of herbicides can also help manage nutsedge, and herbicides are most effective when used with other control methods. Few herbicides are available to selectively control nutsedge, especially for vegetable crops^.1,3 Many of the herbicides available to selectively control grasses are not effective on nutsedge. Managing annual weeds with herbicides can actually increase problems with nutsedge because of reduced competition for resources.^5,9 

Several herbicides are registered for controlling nutsedge in corn and soybeans. These include products used for pre-plant incorporated (PPI), pre-emergence (PRE), and post-emergence applications. In corn, soil-applied herbicides often provided better control of nutsedge than foliar-applied products, and PPI applications are typically more effective than surface applications.⁵ Foliar treatments should be applied when nutsedge plants are actively growing but before they start to flower. Post-emergence products are often used as spot treatments to manage nutsedge plants missed by the soil treatments. Consult regional production and pest management guides for up-to-date recommendations on herbicides registered for controlling nutsedge on specific crops. Follow all label directions for rates, timing, restrictions and other application instructions. 

Glyphosate can be used as a non-selective post-emergent herbicide for both purple and yellow nutsedge. It is best to apply the product in the late vegetative to early flowering stages of nutsedge growth before tubers have fully formed. Glyphosate can be translocated from the leaves to the tubers if the tubers are still attached to viable rhizomes. In later stages of growth, the rhizomes become inactive, preventing translocation to the tubers. Repeated applications will likely be needed to achieve adequate levels of control.^1,5,7,9 

Soil fumigation under plastic mulch can also help control yellow and purple nutsedge. Some soil fumigants, such as chloropicrin and metam sodium, used for pathogen and nematode control, can also suppress nutsedge when applied prior to or during mulch application.¹⁰