Nutsedge (June 10, 2015)

Nutsedge has long been one of our most difficult to control weeds. It is often misunderstood and progress in controlling it has been slow. Nutsedge is often referred to as nutgrass although it is neither a grass nor a nut and is very different from both. It is a monocot, like grasses, but is in the sedge or Cyperaceae family. The nut refers to the below ground tubers which are not nuts but do have nutritional value and are sometimes eaten in famine stricken areas of Africa. There are more than 5,000 separate species of sedges that exist worldwide. Some of the most widely known sedges are water chestnut and papyrus sedge which was used to make the ancient writing material. Sedges are easily distinguished from grasses by their solid triangular flower stems. Sedges are almost all perennials while grasses, which have round stems, are most frequently annuals. It has been called the “world’s worst weed” because it can be found in every continent and in every state. The two sedges that are a problem here are purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus). While both are here, purple probably accounts for 75 to 80%. They are not hard to identify but people sometimes have trouble distinguishing them. They are both perennials and grow actively at the same time. Both grow from tubers and rhizomes. The seed is rarely viable and they spread vegetatively from these tubers and rhizomes. They spread so rapidly and are so prolific that people are often surprised that less than 5% of the seed they produce is viable. The leaves do not have ligules or auricles and have a ridge along the midvein. Yellow and purple nutsedge are similar at early growth stages but are not hard to distinguish later on. The leaves of purple are blunt and less pointed than yellow. As expected, the seedheads of purple are purple and yellow are yellow. The tubers of purple are much larger than yellow. They are irregular shaped, connected by chains, bitter in taste and have a distinctive almond odor. Yellow nutlets are small, round, not connected and have a more sweet taste. Nutsedge is one of those weeds that gets worse each year because of the absence of highly effective herbicides and because cultivation spreads it. Remember that the seed is not viable and the only way this weed spreads significant distances is mechanically. Soil movement should be minimized as much as possible where nutsedge is a problem. This is contrary to the belief that repeatedly bringing the nutlets to the surface to desiccate will control it. Many techniques have been used to try to control it over the years ranging from hand pulling to soil fumigants. Almost all herbicides that have activity on this weed are only partially effective and require multiple applications over multiple years. It is necessary to control the below ground nutlets and rhizomes and they can persist for many years and continually put out new growth. Nutsedge is so prolific that if an herbicide is not highly effective, the infestation is back to where you started one year later. Several herbicides have nutsedge on the label and range in control from 20 - 90%. Twenty of these herbicides are contained in the table "Herbicides with Activity on Nutsedge".

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To contact Barry Tickes go to: btickes@ag.arizona.edu.