Yellow nutsedge.
Yellow nutsedge.

Yellow nutsedge is a grass-like plant that has a well-earned reputation as one of the world's worst weeds. Not only does it grow aggressively in crops like rice and soybean that rely on moist soil, but it also has also developed resistance to the ALS-inhibitor herbicides used in its control. 

Two recent research studies featured in the journal Weed Science explore the biological changes associated with herbicide-resistant yellow nutsedge in order to inform the development of more effective management techniques.

The first study involved greenhouse experiments performed on herbicide-resistant yellow nutsedge found in Arkansas rice production. Researchers discovered that the weed produced a broader underground network of rhizomes and basal bulbs than yellow nutsedge plants susceptible to ALS inhibitor treatments. The resistant biotype also showed delayed emergence and relatively high levels of dormant tubers. In addition, resistant plants produced a greater above-ground biomass.

“This distinct growth pattern may mean that growers should avoid using tillage for yellow nutsedge control since it can disconnect and spread the underground network of rhizomes,” says lead researcher Muthukumar V. Bagavathiannan from Texas A&M University.

A second study involved herbicide-resistant yellow nutsedge found in rice and soybean crops in the Mississippi Delta. In contrast to the Arkansas study, researchers found that the resistant weed biotype produced fewer and lighter-weight tubers than yellow nutsedge plants susceptible to treatment. Researchers also found that seed plays a role in the persistence and spread of resistant yellow nutsedge – with up to 18 percent of its seeds germinating.

Both studies, though, shared one common finding.  Researchers characterized the growth habit of the resistant biotype as intermediate between yellow and purple nutsedge.

“Based on the similarity of our findings, we can conclude that the resistant biotype is likely a hybrid resulting from crossbreeding between yellow and purple nutsedge,” says Parsa Tehranchian of the University of Arkansas, lead researcher in the Mississippi Delta study.

Full text of the articles, “Acetolactate Synthase–Inhibitor–Resistant Yellow Nutsedge (Cyperus esculentus L.): I—Phenotypic Differences” and “ALS-Inhibitor Resistance in Yellow Nutsedge (Cyperus esculentus): II-Physiognomy and Photoperiodic Response” are now available in Weed Science Vol. 63, Issue 4, October-December, 2015.