ORNAMENTALS NORTHWEST ARCHIVES

Transcription

1 ORNAMENTALS NORTHWEST ARCHIVES Summer 1985 Vol. 9, Issue 2 Pages 4-6 Ray D. William Extension Horticultural Weed Specialist Oregon State University Corvallis, OR CONTROL OF YELLOW NUTSEDGE IN NURSERIES Yellow nutsedge (Cyperus esculentus) is fast becoming the most important weed in cultivated fields in the Pacific Northwest. In the U.S., yellow nutsedge ranks fifth in seriousness among all weeds and second only to quackgrass as a perennial weed problem (2). FIGURE 1: A mature yellow nutsedge (Cyperus esculentus) with the major plant parts identified. Yellow nutsedge is a persistent weed, especially in intensively cultivated fields (3). The plant thrives in a wide variety of habitats, soil types, and moisture conditions including seasonal flooding (1). Infestations are characterized by numerous small, but densely populated areas within cultivated fields. If not controlled or suppressed, yellow nutsedge will infest entire fields, making them unfit for production of ornamentals or other field crops. Identification The plant is 8 inches to 3 feet in height. If cut across (cross-sectioned), the stem is triangular-shaped. The leaves are attached to the stem in groups of three (at a given height on the stem, a leaf attached to each of the three sides, 3-ranked). The spikelets (seed heads) are yellowish to goldenbrown and flattened. The basal bulb is the principal site of vegetative activity and gives rise to leaves, roots, rhizomes. The rhizomes (fleshy roots) give rise to secondary basal bulbs that eventually produce tubers.

2 Sedges are often confused with plants in the grass and rush families. Yellow nutsedge is also distinguished from annual sedges found in the Pacific Northwest by its tubers. Nutsedge tubers are small, brown, peanut-sized, underground organs. Since production of viable seed is extremely low, tubers are the major means of reproduction and spread of yellow nutsedge. Life Cycle When soil temperatures exceed F, one or more buds on a parent tuber sprout to form a rhizome that develops into a basal bulb with leaves near the soil surface (1, 3, 5). As growth continues, new rhizomes develop from the basal bulb forming secondary and tertiary bulbs with leaves and the potential to produce a flower stalk. About midseason, when daylength has reached its maximum and is decreasing (after June 21), rhizomes or tubers, instead of basal bulbs, form. Generally, tubers germinate readily in fall and spring. On the other hand, they may not germinate for several years - making control a long term program. Infestation Tubers are often moved from contaminated fields on equipment, in soil for container media, or in balled-and-burlapped plants. Wild ducks dig up and eat the starchy tubers, and growers have sometimes suspected that these ducks transport. viable tubers to previously uninfested fields. However, Oregon wildlife specialists state that viable tubers do not survive the grinding action of the gizzard. Again, the major distribution occurs on infested planting materials and equipment. Once infestation has occurred, nutsedge populations often explode when fields are cultivated routinely or when competition from other weeds is reduced by repeated herbicide applications For example, in quackgrass infested orchards, nutsedge was rarely noticed until dramatic increases occurred following control of quackgrass and other weeds. Although yellow nutsedge will reduce growth of nursery seedling or liner plants, the greatest threat is the possibility of the infested plants being destroyed by quarantine officials in other states. Yellow nutsedge is considered a noxious weed in many states and should not be shipped with plants. It should be included on Oregon's noxious weed list for inspection purposes. Controls Controls should be applied when the nutsedge is at susceptible states of its life cycle, i.e. between tuber germination in the spring and formation of the first new tubers by mid-june. A

3 year-round control program incorporating tillage, soil fumigants, herbicides and crop rotations may be required to reduce infestations. Tillage - Preplant tillage in the spring stimulates tuber germination and reduces tuber energy reserves by 60% (7). Subsequent rhizomes are weaker and utilize another 10% of the carbohydrate reserves. By delaying spring planting, additional tillage can be used to reduce nutsedge populations; rapid development of the crop canopy favored by the warmer temperatures associated with delayed planting will shade and further reduce nutsedge infestations. Frequent fallow tillage for 2 to 4 years reportedly reduces tuber populations by 90% (1) or 99% (4). Even so, 1 ton of tubers remained following fallow tillage (4). At least two seasons are required to decrease infestations to manageable levels (1). Multi-purpose soil fumigants - Although costly, multi-purpose soil fumigants correctly applied, can nearly eliminate nutsedge infestations. Fumigants are volatile and require both aerated soil for penetration and a tarp to maintain proper concentration at the soil surface. The soil should be at a moisture level suitable for planting, whereas dry conditions increase tuber dormancy and the fumigant will not move uniformly through water saturated soils. Herbicides - Dual and Casoron are the most effective herbicides for yellow nutsedge control in ornamentals. Repeated applications for perhaps three to four years may be required to bring yellow nutsedge under control. Preemergence Herbicide Applications Perhaps the most effective herbicide treatment at present is a preemergence application of metolachlor (Dual) which inhibits root and shoot growth from tubers and prevents new tubers from forming. Parent tubers seem to be weakened and some die, but the infestation remains and requires retreatment after 2-3 months. Repeat applications for several years in a row have reduced infestations to minimal levels in midwest corn and soybean fields (7). Applications of dichlobenil (Casoron or Norosac) the year after crop establishment also provides excellent control of nutsedge growth, again by inhibiting tuber, root, and shoot growth. Casoron or Norosac are best for winter application: Wait until winter rains start and soils are cool before applying either of these herbicides. Both are volatile and will escape into the atmosphere unless they are tied to the soil by being leached in with water.

4 Postemergence Herbicide Applications Spot treat small patches as soon as they are discovered. In the past, 2,4,-D and organic arsenicals (MSMA and DSMA) provided erratic control of yellow nutsedge in some crops. More recently, postemergence applications of glyphosate (Roundup) were thought to control yellow nutsedge. However, recent evidence suggests that tubers remain viable if the plants are treated after tuber enlargement begins (sometime near July 1). Late herbicide applications may result in a false sense of accomplishment followed by an explosion of the nutsedge population. Nutsedge population can be reduced by application of postemergence herbicide (i.e. glyphosate) when nutsedge is actively growing, but before new tubers have matured. Applications should be made before the first tubers are beginning to enlarge. Year-Round Management of Nutsedge in Ornamentals Left photo: Yellow nutsedge, Cyperus esculentus, photograph of mature plant showing 3-angled stems bearing long leaves from near the base and a whorl of leaf-like bracts just below the flower cluster. Top photo, right: Reproduction is primarily by the small tubers found on the rhizomes. Lower photo, right: Leaf sheaths close (fuse) around the stem near its base. Although it may seem impossible, yellow nutsedge can be suppressed (2, 4, 6, 8, 9) and should be eradicated from nursery production areas. First, we must recognize that nutsedge infestations are increasing due to carelessness. New patches should be eliminated immediately by spot treating with herbicide. Continuous monitoring is required, and if regrowth occurs, retreatment is required. Cultivation or plowing of infested areas should be avoided to reduce spread of the tubers within the field. Equipment and transplants should be inspected and cleaned before moving to other fields.

5 It may be necessary to plant the field with another crop or leave it fallow in order to implement a season-long combination of tillage and herbicide practices. Apply preemergence herbicides that inhibit new tubers, plant crops that form a full canopy to shade the weed. Following harvest, consider tilling and applying metolachlor. Maintenance of an aggressive, year-round weed management program with frequent scouting can reduce and maintain nutsedge infestations at a minimal level similar to that of other weeds in the noxious weed list for nursery inspections. References 1. Bell, R.S., W.H. Lachman, E.M. Rahn and R.D. Sweet Life history studies as related to weed control in the Northeast: 1-Nutgrass. Bul Hansen, E.W., C.C. Dowler, M.D. Jellus, and S.R. Cecil Effects of herbicide-crop rotation on nutsedge, annual weeds and crops. Weed Science. 22: Holm, L.G., D.L. Plucknett, J.V. Pancho, and J.P. Herberger The world's worst weeds: Distribution and biology. The Univ. Press of Hawaii, Honolulu. 4. Keeley, P.E., R.J. Thullen, J.H. Miller, and C.H. Carter Comparison of four cropping systems for yellow nutsedge (Cyperus esculentus) control. Weed Science. 27: Mulligan, G.A. and B.E. Junkens The biology of Canadian weeds. 17. Cyperus esculentus L. Can. J. Plant Sci. 56: Simkins, G.S. and J.D. Doll Effects of crop rotations and weeding systems on yellow nutsedge control and tuber population. Northcentral Weed Control Conference (Abstract). 7. Stoller, E.W Yellow nutsedge: A menace in the corn belt. USDA Tech. Bul. No p. 8. Wax, L.M., E.W. Stoller, F.W. Slife, and R.N. Andersen Yellow nutsedge control in soybean. Weed Science. 20: William, R.D Purple nutsedge: Tropical scourge. HortScience. 11: Pesticide Use - Due to constantly changing laws and regulations, no liability for the suggested use of chemicals in this Newsletter is assumed by the ONW Newsletter. Pesticides should be applied according to label directions on the pesticide container. Permission to Reprint material appearing in the ONW Newsletter is granted with the request that you credit the source: Ornamentals Northwest Newsletter, date, volume, issue, page numbers. Do not excerpt or reprint in such a manner as to imply the author's endorsement or criticism of a product or concept. Nondiscrimination - The information in the Ornamentals Northwest Newsletter is provided with the understanding that no discrimination is intended and that listing of commercial products implies no endorsement by the authors. Criticism of products or equipment is neither intended nor implied.