Final report for GS18-181

Integrated Weed Management for Long-Term Nutsedge Control and Its Economic Impact in Florida Vegetable Production

Project Type: Graduate Student
Funds awarded in 2018: $15,361.00
Projected End Date: 02/28/2021
Grant Recipient: University of Florida
Region: Southern
State: Florida
Graduate Student:
Major Professor:
Peter Dittmar
University of Florida
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Project Information

Summary:

This project is aimed to develop sustainable methods for nutsedge control under Florida vegetable production systems and its economic impacts. Nutsedge is rated one of the most troublesome weeds for vegetable production systems not only in Florida but rather across the globe. Previously, growers used Methyl bromide as a primary tool for nutsedge management, but since its phaseout nutsedge management has been a challenge. Nutsedge is a problematic weed mainly due to its ability to propagate through tubers, and most of the currently available management strategies are not very effective on tuber control.

The project focuses on the mechanical option for nutsedge tuber removal from the field using a peanut digger. Following the tuber removal, other weed management tools can be used such as cover crops, herbicides, fumigants, etc. based on the type of cropping system the grower has adopted.

The project basically includes a greenhouse study and a 2-year long field study followed by partial budget analysis to assess the cost to benefit ratio.

 

Project Objectives:

The objectives of the research are as follows:

1. To evaluate the herbicides and growth regulators for artificially breaking nutsedge tuber dormancy.

2. To evaluate the long-term nutsedge control feasibility through tuber removal using peanut digger and cover crops.

3. To assess the cost to benefit ratio for physical tuber removal technique for nutsedge control.

Research

Materials and methods:

This project began in April 2019 and field selection was been made for it. The field sites were selected at UF Plant science research and education Unit, Citra, FL and Live Oak, FL. The selected has a known history of nutsedge infestation. 

The materials and methods listed in the original proposal were applied to conduct the research and for data collection and analysis.

Objective 1: Weed control methods could be improved if foliage could be captured by the machinery. Treatments were selected to break the apical dominance in the nutsedge tubers and induce foliar growth on more tubers. This experiment was a greenhouse trial; yellow and purple nutsedge tubers were planted into pots containing field soil (Hague sand). The treatment design was a 4 x 2 factorial design. The four chemical treatments included glyphosate, paraquat, s-metolachlor, and cytokinin.  The two application times were 2 or 6 weeks after planting. All treatments were applied with a backpack CO2 sprayer. Visual nutsedge control and sprout emergence data were collected at 4, 6, 8, and 10 WAP. Visual control was evaluated on a scale of 0%=no necrosis and 100%= complete plant necrosis. At 10 WAP, the study was terminated above-ground plant biomass, total tuber count, and tuber viability were collected. Data were analyzed with ANOVA and means were separated with Fisher’s protected LSD.

Objective 2: The long term impact of mechanical tuber removal was evaluated with plots being maintained for 2 years. The studies were conducted at the Plant Science Research and Education Unit, Citra, FL and North Florida Research and Education Center, Live Oak, FL. In 2019, the entire field received an initial cultivation to cause an equal emergence of nutsedge across the field [0 weeks after initial cultivation (WAIC)]. The treatments included MTR at 4 WAIC, glyphosate at 4 WAIC, MTR at 4 and 8 WAIC, glyphosate at 4 and 8 WAIC, MTR at 4 WAIC f.b. glyphosate at 8 WAIC, glyphosate at 4 WAIC f.b. MTR at 8 WAIC, and MTR at 4 WAIC f.b. MTR at 8 WAIC f.b. glyphosate at 12 WAIC. All treatments had a cowpea cover crop planted 2 weeks after the final MTR or glyphosate treatment in that plot. The cover crop was terminated at 18 WAIC and bell pepper were transplanted at 20 WAIC.

In 2020, the entire field was planted with cowpea and then terminated at 8 weeks after planting the cover crop. Then bell pepper were planted at 10 weeks after planting the cover crop. 

Mechanical tuber removal was completed with a peanut digger 8 inches deep, nutsedge tubers and foliage were dropped onto the soil surface, raked by hand, and then removed from the field.  Glyphosate at 1.5 lb ae/A was applied with a backpack CO2 sprayer. Cowpea was drill seeded at 40 lb/A. 

Data collection included nutsedge density at 2 week intervals through the fallow period and nutsedge biomass and tuber counts at the end of the fallow period. Data in the bell pepper included nutsedge density at a 2 week interval and nutsedge tuber counts and biomass after the final bell pepper harvest. Bell pepper fruit were harvested according to grower practices. 

Objective 3: During the Objective 2 experiment, equipment type, operation time, and material information were collected to complete a partial budget analysis of each treatment.

Research results and discussion:

Objective 1: The greatest nutsedge control was from glyphosate and paraquat at 2 or 6 WAP. S-metolachlor and cytokinin did not result in nutsedge necrosis. Cytokinin at 2 WAP had the greatest nutsedge sprout emergence, however, the no sprout emergence between the nontreated and cytokinin at 6 WAP. Paraquat would burn the foliage and regrowth would occur from that tuber, however, new shoot growth was not greater than the nontreated. Whereas the glyphosate translocated to the parent tuber prevent regrowth of that tuber. The translocation of glyphosate caused a reduction in tuber viability at the experiment termination.

  Yellow nutsedge emergence Yellow nutsedge emergence Purple nutsedge emergence 2019 Purple nutsedge emergence 2019 Purple nutsedge emergence 2020 Purple nutsedge emergence 2020 Tuber viability Tuber viability
  Num./pot Num./pot Num./pot Num./pot Num./pot Num./pot % %
  4 WAP 8 WAP 4 WAP 8 WAP 4 WAP 8 WAP 2019 0 c
Glyphosate 2 WAP 0.13 b 0 d 2.75 0 d 0 c 0 c 13 c 100 a
Paraquat 2 WAP 0.13 b 0 d 0.75 1.25 bcd 0 c 0 c 50 bc 50 b
S-metolachlor 2 WAP 0.13 b 0.38 cd 1.25 2.25 abc 0 c 0 c 100 a 100 a
Cytokinin 2 WAP 2.00 a 3.13 a 1.25 2.25 abc 4.75 a 6.00 a 71 ab 94 a
Glyphosate 6 WAP 0.63 b 0.13 d 2.75 1.75 bcd 3.00 b 0 c 63 ab 100 a
Paraquat 6 WAP 0.38 b 0 d 3.00 0.25 cd 1.00 c 0 c 100 a 100 a
S-metolachlor 6 WAP 0.63 b 1.75 b 2.75 3.00 ab 1.25 c 1.75 b 92 ab 100 a
Cytokinin 6 WAP 0.38 b 0.88 bcd 1.75 1.75 bcd 3.00 b 4.25 ab 92 ab 100 a
Nontreated 0.25 b 1.5 bc 0.25 4.00 a 0.50 c 1.5 c 100 a 100 a

Objective 2: The field at Live Oak had a very low nutsedge population and no differences were measured. In Citra at the end of the 2019 fallow period in all the fallow programs had a lower nutsedge density than the nontreated (115 plants/0.5 m2). Although the fallow period management was limited to only cover crop; all of the fallow programs still had a lower nutsedge density than the nontreated. In the bell pepper, the most intense program, MTR f.b. MTR f.b. GLY had the lowest nutsedge density, however, this difference was not measured in 2020. Bell pepper yield was the lowest in the nontreated in 2019 and no yield differences were measured in 2020.

  Nutsedge density Nutsedge density Nutsedge density Nutsedge density    
  End of fallow period 2019 End of fallow period 2020 End of bell pepper 2019 End of bell pepper 2020 Bell pepper yield 2019 Bell pepper yield 2020
  Plants/0.5 m2 Plants/0.5 m2 Plants/0.5 m2 Plants/0.5 m2 kg/ha kg/ha
MTR 1 b 4 b 27 bc 12 b 30,963 ab 10,000
GLY 2 b 7 b 31 b 13 b 26,159 cd 8,114
MTR f.b. MTR fb GLY 16 b 7 b 10 d 12 b 29,139 abc

8.691

MTR f.b. MTR 13 b 5 b 28 bc 12 b 27,321 bc 8,874
GLY f.b. GLY 28 b 8 b 20 c 9 b 31,631 a 8,813
MTR f.b. GLY 26 b 7 b 24 bc 13 b 30,444 ab 7,130
GLY f.b. MTR 21 b 5 b 29 bc 12 b 32,069 a 9,294
Nontreated 115 a 54 a 66 a 66 a 22,696 d 9,444

Objective 3: The largest expense treatment expense was the unskilled labor to remove the nutsedge using the MTR fallow programs. This put the MTR at a huge disadvantage compared to the glyphosate and nontreated. However, the weed pressure in the nontreated caused the yield to be very low resulting in high net returns using MTR during the fallow.

  MTR GLY MTR f.b. MTR f.b. GLY MTR f.b. MTR GLY f.b. GLY MTR f.b. GLY GLY f.b. MTR Nontreated
Equipment cost 261.90 199.06 189.78 339.51 269.45 302.29 300.83 0.00
Herbicide cost 0 12.97 12.97 0 25.94 12.97 12.97 0.00
Unskilled labor cost 773.95 0 1547.91 1547.91 0 773.95 773.95 0.00
Skilled labor cost 47.93 30.58 80.63 80.63 45.87 63.25 63.25 0.00
   Total treatment cost 1083.81 242.61 1831.29 1968.05 341.26 1152.46 1151.00 0.00
Production cost 43,815.40 43,815.40 43,815.40 43,815.40 43,815.40 43,815.40 43,815.40 43,815.40
     Total cost 44,899.21 44,088.01 45,646.69 45783.46 44,156.66 44,967.87 44,966.40 43,815.40
Net revenue 46,035.30 38,892.79 43,323.40 40,620.43 47,038.47 45,263.66 47,679.68 33,744.05
Net profit 1,136.08 -5,195.23 -2,323.29 -5,163.03 2,871.80 295.79 2,713.28 -10,071.35
Net % return relative to nontrt 36.4 15.3 28.4 20.4 39.4 34.1 41.3 0
Participation Summary

Educational & Outreach Activities

1 Curricula, factsheets or educational tools
2 Journal articles
1 Webinars / talks / presentations

Participation Summary

32 Farmers
58 Ag professionals participated
Education/outreach description:

Objective 1: Results were shared as a poster at the Southern Weed Science Society Annual Meeting. The results have been for a journal article.

Objective 2 and 3: Results were shared at the Southern Sustainable Agriculture Working Group meeting and the Weed Science Society of American national meeting. Results were discussed at the online Vegetable growers meeting. The results have been prepared for a journal article and an Extension factsheet. 

Project Outcomes

Project outcomes:

Weeds make a prominent pest encountered by the growers across the world as they compete with the crop for resources and result in yield loss. Sustainable weed control methods are very eminent for ensuring global food security. In today’s world the chemical weed control methods are the most favored weed control technique used by growers, however the excessive and exclusive use of pesticides and synthetic fertilizers has led to a greater threat to environmental sustainability. The impact of chemicals on the environment and the backlash of natural species in terms of herbicide, fungicide and insecticide resistance is pushing us to adopt sustainable agricultural techniques. This project is intended to develop a non-chemical method for long-term control of nutsedge. The positive results from this study would reduce the growers’ dependence on chemical methods for nutsedge, which will contribute to avoiding depletion of the environment and other natural resources.

The cover crop (cowpea) is a legume and known to fix nitrogen. Alongside suppressing tuber growth through its shading effect, cowpea would act as a source of organic matter. This project is intended to develop a long-term weed control strategy through mechanical and cultural methods which could be used for multiple crops, unlike herbicides. By the completion of this project, growers will have not only chemical-free alternatives for nutsedge control rather they will also simultaneously be able to attain green manuring to their fields through cover crop termination. This project will enable growers to sustainably increase their productivity.

Knowledge Gained:

The project is still in the beginning phase however by reading through literature while preparing for this project has significantly added to our knowledge about nutsedge spp. behavior under field conditions. We have learned that usually, none of the single weed management strategies is sufficient nutsedge management. There is a strong need for growers to adopt integrated weed management strategies for effective and long term nutsedge control. We are very optimistic about further expanding our knowledge about sustainable nutsedge management during the course of this project.

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.