Final report for GS21-252
Project Information
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improve weed control, as well as reduce the number of mowings required to inhibit nutsedge tuber production (Ippolito, unpublished data).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.
- Develop a nutsedge and annual grass management program utilizing subsequent mowing and organic herbicide application.
- Determine the optimum program of sequential mowing and organic herbicides to reduce weed seedbank composition and seed density.
- Determine the effects of organic herbicide rate in combination with mowing to identify optimal herbicide rate for perennial nutsedge and annual grass control.
- Disseminate information, knowledge and recommendations through grower meetings, extension articles, and refereed journal publications.
Research
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.
Effect of Herbicide
For every study, there was a herbicide by year interaction; therefore, the effect of the herbicides applied was sliced by year. In 2022, halosulfuron had a significant effect in all three trials 7 weeks after application (WAT). In the mow height trial, only halosulfuron had a significant effect compared to the nontreated check in 2022, and none of the herbicides applied had a significant effect in 2023. In the application timing trial both ammonium nanoate and halosulfuron significantly reduced PΔ compared to the nontreated check in 2022; however, none of the herbicides applied had a significant effect on PΔ in 2023. In the herbicide rate study, all of the herbicides significantly reduced PΔ compared to the nontreated check in 2022. In 2023 only halosulfuron had an effect on PΔ in the herbicide rate trial 7 WAT.
The lack of significance in 2023 was likely a result of the increase in rainfall within the year. In 2022 the period in which the trials were conducted had little rainfall, which likely helped to make the differences between treatments easier to see. With heavier rainfall in 2023, nutsedge population grew much faster making it difficult to capture any difference between treatments.
Effect of Herbicide Rate
The interaction between herbicide rate and year was significant; therefore, the effect of herbicide rate was sliced by year. In 2022 every rate significantly reduced PΔ compared to the nontreated check 7 WAT. In addition, application of a 2X rate significantly reduced PΔ more than the 1X or 1.5X rates 7 WAT. Herbicide rate did not have a significant effect on PΔ in 2023.
Effect of Mow Height
There was a significant interaction between herbicide and year, therefore the effect of herbicide was examined by year. At 7 WAT after treatment the effect of mow height did not have a significant effect on PΔ.
Effect of Application Timing
Application timing did not have a significant effect on PΔ.
Practical Implications
Options for Yellow nutsedge control are limited, especially in organic production systems. The trials in this paper examine potential methods to improve control of Yellow nutsedge through management tools.
Educational & Outreach Activities
Participation Summary:
We are in the process of writing a peer-reviewed journal article that will be published in the journal Weed Technology. Also an extension publication for growers, extension agents and other agricultural professionals will be published in 2025.
Project Outcomes
No information available.