Halosulfuron reduced purple nutsedge (Cyperus rotundus) tuber production and viability

Authors: Webster, Theodore; GREY, TIMOTHY - University Of Georgia

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2014
Publication Date: 10/1/2014
Citation: Webster, T.M., Grey, T.L. 2014. Halosulfuron reduced purple nutsedge (Cyperus rotundus) tuber production and viability. Weed Science. 62:637-646.

Interpretive Summary: Purple nutsedge is a persistent weed of multiple crops throughout the world and is also one of the most difficult to control weeds of fresh-market vegetable crops in the Southern U.S. Many of these high-value vegetables are grown with polyethylene mulch tightly covering the soil surface of raised beds; aside from the holes in the mulch where the vegetables are transplanted, this provides a barrier through which most weeds cannot overcome. However, purple nutsedge is a species that is capable to piercing through the mulch and actually thrives in a black polyethylene mulch system. In the past, fresh-market vegetables in the Southeast U.S. relied on methyl bromide to control multiple pests, such as, soil-borne plant pathogens, insects, and weeds, including purple nutsedge. However, due to its link to ozone depletion, methyl bromide was restricted to critical-use exemption for preplant soil fumigation, while effective alternatives were developed and implemented. This research demonstrated that halosulfuron is an effective herbicide that controls purple nutsedge foliage, but also reduces the number of new tubers produced and overall tuber viability. This could be an important component used to reduce the long-term population density of this weed. Halosulfuron also reduced the viability of these tubers. The standard use rate of halosulfuron reduced purple nutsedge tuber production 93%, with only 14% viability of the tubers that were produced. Halosulfuron, and other herbicides used strategically to minimize weed reproduction, could be an important component used to reduce the long-term population density of purple nutsedge and similar weeds that are difficult to manage.

Technical Abstract: Weeds persist and cause economic losses in agricultural systems because they exploit an underutilized portion of that system. Reducing the impact of weeds on agroecosystems begins with minimizing the number of propagules (e.g, seeds and tubers) that are produced and returned to the soil. Purple nutsedge is a problematic weed around the globe, persisting between growing seasons as tubers in the soil. Halosulfuron is an effective means of controlling purple nutsedge foliage and is used in corn and several vegetable crops. Studies were conducted to evaluate the effect of various rates of halosulfuron on purple nutsedge tuber production. Single pre-sprouted purple nutsedge tubers were transplanted into outdoor microplots and treated after six weeks of growth with six rates of halosulfuron (7 to 208 g ai ha-1) POST and a nontreated control. All shoots emerged at the time of application were marked with plastic rings; this allowed for classification of tubers at exhumation of 1) tubers attached to shoots that were emerged at time of application, 2) tubers attached to shoots that emerged after application, and 3) tubers without an aerial shoot during the study. Seven weeks after application, the tubers in the microplots were exhumed, tubers classified, quantified, and ability to sprout evaluated. In the nontreated control, there were 530 total tubers, with a log-logistic regression model describing the tuber population with increasing halosulfuron dose. The rate of halosulfuron that reduced total tuber population 50% (I50) was 8 g ha-1. In the nontreated control, there were 200 tubers that were attached to shoots that emerged following halosulfuron application, and this class of tubers had an I50 = 19 g ha-1. Viability of these tubers was 28% at the 52 g ha-1 halosulfuron, suggesting the action of the herbicide may have rendered the tuber nonviable after new shoots were produced. The final classification of tubers was those that did not have an aerial shoot during the study. These were tubers in which apical dominance suppressed shoot development or were likely the most recent tubers to develop. Of the three classes, the tubers without shoots were the most numerous in the nontreated control, with 294 tubers, and an I50 = 1 g ha-1. Halosulfuron is an effective herbicide that controls purple nutsedge foliage, but also reduces the number of new tubers produced and overall tuber viability. This could be an important component used to reduce the long-term population density of this weed.