YELLOW NUTSEDGE TUBER VIABILITY IN RESPONSE TO FUMIGATION

Joel Felix and Joey Ishida

Malheur Experiment Station

Oregon State University

Ontario, OR, 2007

Introduction

Yellow nutsedge has become a major problem weed in agricultural land in the Treasure Valley, especially in fields planted to onion. Control of yellow nutsedge presents a major challenge because of its ability to reproduce by rhizomes and tubers. Yellow nutsedge can produce millions of tubers per acre in a single season if not properly controlled. Successful control of yellow nutsedge will partly rely on tuber destruction by effective fumigation procedures. Some growers and other weed managers have suggested that use of Telone^® C-17 soil fumigant could enhance the control of yellow nutsedge if applied prior to application of Vapam^®. Some researchers have also suggested that supplementing the fumigants with fall application of Dual Magnum^® herbicide could provide synergistic effects and enhance nutsedge control. Consequently, this study was established to study the effectiveness of Telone C-17, Vapam, and Dual Magnum applied alone and in combinations to test their synergistic effects in reducing tuber viability.

Materials and Methods

The trial was conducted in a field severely infested with yellow nutsedge along Oregon Hwy 201, approximately 2 miles from the Malheur Experiment Station. The field was furrow irrigated on September 1, 2006 and disked on September 7 to create a smooth seedbed to enhance fumigant penetration into the soil and sealing after application. The experiment was laid out in a randomized complete block design with four replications. The seven treatments evaluated were individual fumigant or fumigant combinations and an untreated check (Table 1). It is important to recognize that these treatment combinations are for experimental purposes only and are not endorsed by respective product labels or manufacturers. Individual plots were 16 ft wide and 60 ft long. Soil sampling for tuber quantification was done immediately after fumigation by taking 5 cores each measuring 4.25 inches in diameter and 12 inches deep from each plot. The soil cores were processed to recover yellow nutsedge tubers using the washing and sieving procedure. The recovered tubers were placed in ziplock plastic bags and stored in a dark cooler at 40°F until counted and weighed.

In order to further degrade the tubers, the study area was fallowed in 2007, and the integrity of individual plots was maintained by corner triangulation and working the soil in one direction to avoid cross contamination of different treatments. Plots were monitored for yellow nutsedge emergence and counts done on May 3 when seedlings were small to enable identification of individual plants. Additionally, five soil cores from each plot were taken on March 27 to characterize tuber population density and were processed using the methodology described above. The plots were treated with Roundup Original^® at 32 fl oz/acre plus ammonium sulfate (AMS) at 3.2 pt/acre beginning May 25, 2007 and repeated on June 13, 2007. The study area was disked on July 20, bedded, and irrigated to encourage yellow nutsedge emergence. The final Roundup plus AMS was applied on August 20, 2007 for a total of three applications during the summer. Outlook^® at 21 fl oz/acre was applied on June 12, 2007 to enhance yellow nutsedge control.

The study area was disked, roller harrowed twice, bedded and irrigated during the fall of 2007, and will be planted to onions in 2008. Five soil samples, each measuring 4.25 inches in diameter and 12 inches deep, were taken from each plot on November 19, 2007 and processed for tuber recovery by washing and sieving. The tubers were counted and weighed for each plot and placed in ziplock plastic bags and stored in a dark cooler at 40°F for use in emergence studies.

Results and Discussion

Since the 2006 results indicated substantially more tubers were produced in the 0- to 12-inch depth than at the 12- to 16-inch depth (Shock et al. 2006), all soil samples for tuber characterization in 2007 were taken to the 12-inch depth. The data for yellow nutsedge tubers before and after fumigation in 2006 are presented in Table 1 to indicate changes over time. Yellow nutsedge seedling counts during spring 2007 indicated a significantly lower density in plots treated with Telone C-17, followed by Vapam and Dual Magnum (Table 1), compared to other treatments. Similarly, the synergistic effect of Telone, Vapam, and Dual Magnum resulted in a pronounced reduction in the number of tubers produced. Telone in combination with Vapam or Dual Magnum resulted in significantly fewer tubers than each product used alone. Similar results were observed when Vapam was used in combination with Dual Magnum. Soil samples taken during fall 2007 indicated similar trends, with a combination of Telone, Vapam, and Dual Magnum having the lowest number of tubers.

The plot integrity has been maintained and the study area will be planted to onions during 2008. We expect the treatment effects will show more pronounced differences in yellow nutsedge infestation during the 2008 cropping season. Plots will be sampled again for tuber population density during spring 2008 and onions will be grown to maturity. Herbicides recommended for use in onions including Outlook, Nortron^®, and Dual Magnum will be used in 2008.

This study will be repeated at a different site using the same fumigant treatments during fall 2007 and evaluation of yellow nutsedge control will begin in the spring of 2008. The study site will be fallowed in 2008 and planted to onions in 2009.

Currently, Dual Magnum is not a registered treatment for plow down preceding onion in Oregon. However, it received a label for fall plow down in Idaho and Syngenta is still working on the label for Oregon. The use of this treatment does not constitute a recommendation to use this product in Oregon until a label is received.

References

Shock, C.C., J. Ishida, and E. Feibert. 2006. Yellow nutsedge nutlet production in response to nutlet planting depth. Oregon State University Agricultural Experiment Station Special Report 1075:160-162.