Purple nutsedge (Cyperus rotundus) tuber production and viability is reduced by imazapic

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

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2016
Publication Date: 1/21/2017
Citation: Webster, T.M., Grey, T.L., Ferrell, J.A. 2017. Purple nutsedge (Cyperus rotundus) tuber production and viability is reduced by imazapic. Weed Science. 65:97-106.

Interpretive Summary: Weeds exploit underutilized space, causing economic losses in cropping systems. One tactic to reduce weed populations is to minimize production and/or viability of new propagules (e.g. seeds and tubers) to the soil. Purple nutsedge is a problematic weed that persists between growing seasons as tubers in the soil. We examined the effect of imazapic, a peanut herbicide often used in Georgia for control of purple nutsedge, on purple nutsedge tuber production and viability. Pre-sprouted tubers were transplanted into outdoor microplots and treated after six wk of growth with six rates of imazapic (5 to 140 g ai ha-1) POST and a nontreated control. All shoots that had emerged after six weeks were marked and tracked for: 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 imazapic application, tubers classified, quantified, and evaluated for their ability to sprout. The rate of imazapic that reduced the tuber population by 50% was 36 g per hectare, and the amount that reduced tubers sprouting shoots by 50% was 60 g per hectare. At 70 g per hectare, only 44% of tubers remained viable. Of the new tubers produced during the six weeks prior to imazapic treatment, only 18 g of imazapic per hectare were required to reduce sprouting by 50%. In summary, imazapic is a valuable tool in management of the long-term population density of purple nutsedge reducing foliage, number of new tubers produced, and overall tuber viability.

Technical Abstract: Weeds exploit underutilized space, causing economic losses in cropping systems. Weed management tactics alter that underutilized space until the crop can mature and efficiently use that space. One tactic is to reduce the weed populations that persist quiescent in the soil, including minimizing production and addition of new propagules (e.g. seeds and tubers) to the soil. Purple nutsedge is a problematic weed around the globe, persisting between growing seasons as tubers in the soil. Imazapic is a peanut herbicide often used in Georgia for control of purple nutsedge. The objective of the experiment was to evaluate the effect of various rates of imazapic on purple nutsedge tuber production. Single pre-sprouted purple nutsedge tubers were transplanted into outdoor microplots and treated after six wk of growth with six rates of imazapic (5 to 140 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 wk after application, the tubers in the microplots were exhumed, tubers classified, quantified, and ability to sprout evaluated. In the nontreated control, there were 544 total tubers, with a log-logistic regression model describing the declining tuber population with increasing imazapic rate. The rate of imazapic that reduced total tuber population 50% (I50) was 36 g ha-1. In the nontreated control, there were 161 tubers that were attached to shoots that emerged following imazapic application, with an I50 = 60 g ha-1. Viability of these tubers was 44% at the 70 g ha-1 imazapic, 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 358 tubers, and an I50 = 18 g ha-1. Imazapic controls purple nutsedge foliage, but also reduces the number of new tubers produced and overall tuber viability and is a valuable tool in management of the long-term population density of this weed.