Yellow Nutsedge Nutlet Loss of Viability with Desiccation

Under Controlled and Field Conditions

Clinton C. Shock, Joey Ishida, and Erik B.G. Feibert

Malheur Experiment Station

Oregon State University

Ontario, OR, 2006

Introduction

Yellow nutsedge has become a major problem weed in agricultural land in the Treasure Valley. Control of yellow nutsedge is difficult because reproduction is mainly by rhizomes and tubers (nutlets) and nutlet production is intense. One control method being investigated is nutlet desiccation. Yellow nutsedge is a stream edge or marsh plant, which suggests that nutlets might not be adapted to withstand drought. Allowing the nutlets to desiccate on the surface soil in the late summer after a wheat crop might result in high nutlet destruction. Soil surface layers typically become quite hot in midsummer, so a summer fallow might also dramatically reduce viable nutlet numbers. This preliminary trial tested the destruction of nutlets by desiccation under controlled conditions and in the field.

Materials and Methods

Controlled conditions
Two laboratory desiccation trials were conducted in 2006: one at 104°F in February and March and one at 86°F in April and May. Nutsedge nutlets for both trials were collected from a field severely infested with yellow nutsedge approximately 2 miles from Malheur Experiment Station. For the 104°F trial, nutsedge nutlets were collected on February 13 and 14. For the 86°F trial, nutsedge nutlets were collected from March 20 to March 28. The nutlets were washed with distilled water and patted dry with paper towels to remove free moisture. The experimental design was a randomized complete block with four replicates. The treatments were two desiccation temperatures, each with an unheated check and four heat durations. The durations of desiccation were 1, 3, 5, and 7 days at 104°F and 3, 7, 14, and 21 days at 86°F. We used 100 nutlets for each replicate of each temperature and duration combination (plot). The 100 nutlets for each plot were weighed, placed in tin cans and placed in a convection oven set at the respective temperature.

After drying, the nutlets were removed from the oven, weighed, and placed on filter paper in a petri dish. The nutlets were covered with another filter paper and 8 ml of distilled water was added. The petri dishes were sealed with plastic wrap and placed in a box in a dark walk-in cooler set to maintain air temperature at 80°F. Four days after nutlets were placed in the cooler, daily counts of the sprouted nutlets were initiated. After the sprouted nutlets were counted, they were removed from the petri dishes and discarded. The 104°F treatment was started on February 23 and the last nutlet count was made on March 20. The 86°F treatment was started on March 30 and the last nutlet count was made on May 19.

Field conditions
The trial was conducted on a field severely infested with yellow nutsedge approximately 2 miles from the Malheur Experiment Station. The field was furrow irrigated during the summer of 2006. The last irrigation was on July 7. On July 18, the field was flailed and disked. The two treatments were disking once a week for 5 weeks and no disking. The experimental design was a randomized complete block with eight replicates. On September 5, three cores (4.25 inch diameter) were taken at 0- to 4-inch and 4- to 8-inch depth in each plot center. The nutlets from each sample were separated by washing and sieving. Nutlets were placed in open plastic bags in a dark cooler at 40°F.

The field was divided into plots 16 ft wide and 50 ft long. The disking treatment plots were disked on September 7, September 13, September 20, September 27, and October 4. On October 16, core samples were taken in each plot as described previously.

On November 29, the nutlets in the core samples taken before the disking treatments were counted and weighed. On December 1, 100 nutlets sampled before the disking treatments from each plot were put in petri dishes between two layers of filter paper and 6 ml of water was added. The petri dishes were sealed with plastic wrap and placed in a dark, walk-in cooler at 80°F. On December 4, the first of four counts were made of sprouted nutlets in all petri dishes of the predisking samples. Sprouted nutlets were discarded, the petri dishes were resealed and placed in the cooler. The last count was made on December 15. On December 11, nutlets from the samples taken after disking were counted, weighed, and placed in petri dishes as described previously. On December 18, the first of three germination counts was made on the post-disking samples as described previously. The last post-disking count was made on December 22.

Results and Discussion

Controlled conditions
Nutlet weight loss increased with increasing desiccation duration up to 3 days at 104°F and up to 7 days at 86°F (Table 1).

Eighty-one percent of the undesiccated nutlets sprouted within the first 6 days after being placed in the cooler (Fig. 1). The desiccation treatments appeared to slightly delay sprouting, resulting in a prolonged sprouting interval. Nutlets that did not sprout decomposed.

With desiccation at 104°F, rotted nutlets increased with increasing duration of desiccation up to 3 days. With desiccation at 86°F, rotten nutlets increased with increasing duration of desiccation up 21 days.

With desiccation at 104°F, a maximum destruction of 89 percent of the initial nutlets was achieved after 3 days. With desiccation at 86°F, a maximum destruction of 66 percent of the initial nutlets was achieved after 21 days.

Since soil surface temperatures can exceed 120°F, some reduction in nutlet numbers should be possible with field cultivation practices.

Field conditions
There was no significant difference between treatments in nutlet viability after disking at either depth (Table 2). The weather during most of the disking treatment period was cool and wet. A total of 0.64 inch of precipitation occurred during the disking period. Nutlet desiccation earlier in the summer might be more effective in reducing nutlet viability than desiccation in September.

Table 1. Nutlet weight loss, sprouting, and decomposition in response to desiccation temperature and duration under controlled conditions. Malheur Experiment Station, Oregon State University, Ontario, OR.

Table 2. Yellow nutsedge nutlet response to desiccation in the field. Malheur Experiment Station, Oregon State University, Ontario, OR.

^aDifference in germination: germination before disking minus germination after disking.

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