Improving Nutsedge and Grass Control in Organic Production Systems Using Sequential Mowing and Organic Herbicide Application

Progress report for GS21-252

Project Type: Graduate Student
Funds awarded in 2021: $15,654.00
Projected End Date: 08/31/2023
Grant Recipient: North Carolina State University
Region: Southern
State: North Carolina
Graduate Student:
Major Professor:
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Project Information

Summary:

Yellow (Cyperus esculentus) and purple nutsedge (Cyperus rotundus)] are ranked the 6th most troublesome weeds in vegetable and fruit crops and soybean, and cotton in the U.S. (VanWychen 2019).  These nutsedge species and annual grasses including large crabgrass (Digitaria sanguinalis) and goosegrass (Eleucine indica) are difficult to control in organic systems including plasticulture, and no-till systems. In organic systems, no organic herbicide options are registered for controlling nutsedge species, and organic herbicides provide little to no control of annual grasses.   These weeds are primarily controlled by hand weeding and cultivation in organic systems. Continuous cultivation is detrimental to soil health, promotes soil erosion, and reduces organic content in the soil. In turfgrass, mowing is commonly used as a means of controlling perennial nutsedge by depleting their tubers with repeated mowing (Summerlin and Coble 2000).   Preliminary evaluations suggest an application of an organic herbicide applied immediately after mowing may improve weed control, as well as reduce the number of mowings required to inhibit nutsedge tuber production (Ippolito, unpublished data). To reduce tillage and improve weed control, studies will be conducted to determine the effect of subsequent mowing in conjunction with organic herbicide applications on nutsedge (yellow and purple), large crabgrass and goosegrass control.   Additionally, the impact of these treatments on the weed seedbank will be determined.

Project Objectives:

 

  1. Develop a nutsedge and annual grass management program utilizing subsequent mowing and organic herbicide application.
  2. Determine the optimum program of sequential mowing and organic herbicides to reduce weed seedbank composition and seed density.
  3. Determine the effects of organic herbicide rate in combination with mowing to identify optimal herbicide rate for perennial nutsedge and annual grass control.
  4. Disseminate information, knowledge and recommendations through grower meetings, extension articles, and refereed journal publications.

Research

Materials and methods:

Objective 1. Develop a perennial nutsedge and annual grass weed management program utilizing mowing followed by organic herbicide application. Studies will be conducted with nutsedge (yellow and purple), large crabgrass, and goosegrass. Plot size will be 1.5 wide by 3 m long with a nontreated 1.5 m border on all sides. Studies will be conducted utilizing a 4 (organic herbicide) x 3 (mowing height) x 2 (weed growth stage) factorial design with at least four replications each year (Table 1). Organic herbicide treatments will include d-limonene, pelargonic acid, ammonium nonanoate, and a nontreated check. Mowing height treatments will include low, (approximately 2.54 cm), high (7.62 cm), and no mowing control treatment. Weed growth stage treatments will include seedling (< 10 cm) and mature (> 10 cm but < 15 cm). Each treatment will be applied as needed to maintain weed suppression. Treatments that include mowing will be mowed just before herbicide application.

 

Table 1.  Treatment list for Objective 1. 

Treatment no.

Organic herbicide

Mowing height

Mowing timing

1

None

None

None

2

d-limonene

No mowing

None

3

d-limonene

Low

Seedling

4

d-limonene

Low

Mature

5

d-limonene

High

Seedling

6

d-limonene

High

Mature

7

Pelargonic acid

No mowing

None

8

Pelargonic acid

Low

Seedling

9

Pelargonic acid

Low

Mature

10

Pelargonic acid

High

Seedling

11

Pelargonic acid

High

Mature

12

Ammonium nonanoate

No mowing

None

13

Ammonium nonanoate

Low

Seedling

14

Ammonium nonanoate

Low

Mature

15

Ammonium nonanoate

High

Seedling

16

Ammonium nonanoate

High

Mature

           

For each study, visual weed control will be collected weekly for 8 weeks after initial treatment (WAIT). Aboveground weed biomass will be collected at 8 WAIT. Studies will be replicated in two locations. Data will be subjected to analysis of variance using PROC MIXED (SAS 9.4, SAS Institute, Inc. Cary, NC).

 

An additional study will be conducted to determine the effect of herbicide application frequency on weed control. The same weed species will be utilized in this study.  The study design will be a 3 (organic herbicide) x 3 (herbicide frequency) x 2 (weed growth stage) factorial design replicated at least 4 times. Herbicide treatments (d-limonene or pelargonic acid or ammonium nonanoate) will be applied 7, 10, and 14 days after initial mowing treatment to seedling weeds (< 10 cm) or mature (> 10 cm ≤ 20 cm).   Following the initial treatment, applications will continue as needed for the following 6 weeks. The studies will be replicated in two locations. Data collection will be the same as the prior study with the exception of weed biomass being collected 6 WAIT. Data will be subjected to analysis of variance using PROC MIXED (SAS 9.4, SAS Institute, Inc. Cary, NC).

 

Objective 2.  Determine the effect of sequential mowing and organic herbicides on seedbank composition and density. In spring 2022 field studies will be conducted in a  bareground area.  A known quantity of each weed seed will be spread and incorporated into the soil and allowed to germinate. A minimum of 10 treatments identified from objective 1 as those  providing optimal weed control will be utilitzed in this study.  Weed counts within a representative 0.5 m2 quadrat of each species will be collected beginning at the initial treatment then bi-weekly for 8 WAIT. In spring 2023, weed counts will be collected upon emergence. Studies will be replicated in two locations. Data will be subjected to analysis of variance using PROC MIXED (SAS 9.4, SAS Institute, Inc. Cary, NC).

 

Objective 3. Determine the effects of organic herbicide rate in combination with mowing to identify optimal herbicide rate for perennial nutsedge and annual grass control. Studies will be conducted with yellow nutsedge, purple nutsedge, large crabgrass, and goosegrass. In spring 2023, a known quantity of seeds will be spread and incorporated into the soil at the study locations. The study design will be a 3 x 3 factorial design replicated 4 times. The first factor will be herbicide and will include d-limonene, pelargonic acid, and ammonium nonanoate.  The second factor will be herbicide rate with a 1x, 1.5x, and 2x rate (A 1x rate being the labeled rate). The last factor will be mowing with mowed and non-mowed treatments. The height of the mowed treatment and growth stage will be selected from data collected in objective 1. Data to be collected will be the same as the mow height studies. Data will be subjected to analysis of variance using PROC MIXED (SAS 9.4, SAS Institute, Inc. Cary, NC).

 

Objective 4. Disseminate information, knowledge and recommendations through grower meetings, extension articles, and refereed journal publications. Data collected will be presented at grower field days, local and regional commodity meetings, and scientific conferences. Extension and peer-review articles will be published to disseminate results to the broader agronomic and scientific community.

Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.