DEVELOPING INTEGRATED MANAGEMENT PRACTICES FOR SMUTGRASS CONTROL USING FIRE, GRAZING, AND HERBICIDE

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: AFRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 1006034
• Grant No.: 2015-67028-23963
• Cumulative Award Amt.: $149,399.00
• Proposal No.: 2014-09685
• Project Start Date: Aug 15, 2015
• Project End Date: Aug 14, 2018
• Grant Year: 2015
• Program Code: [A1701]- Critical Agricultural Research and Extension: CARE

Recipient Organization
UNIVERSITY OF FLORIDA
G022 MCCARTY HALL
GAINESVILLE,FL 32611

Performing Department
AG-RCREC-ONA

Non Technical Summary
Smutgrass species are a critical problem in the southeastern U.S. to the extent that the Florida Cattlemen's Association has formally requested research and education efforts focusing on long-term smutgrass management. The recommended chemical control for this species, hexazinone, is expensive and prone to failure due to insufficient or excessive rainfall. Recent research suggests that smutgrass can be controlled by sequential applications of reduced rates of hexazinone under optimum environmental conditions. Furthermore, prescribed burning followed by intensive grazing reduces smutgrass cover, but not density. Therefore, our hypothesis is that smutgrass will be effectively controlled using reduced rates of hexazinone following prescribed burning and intensive grazing. To test this hypothesis we plan to burn bahiagrass and intensively graze bahiagrass pastures until hexazinone can be applied during the rainy season in south Florida. During this field experiment, we will measure smutgrass and bahiagrass response to these practices and compare them to standard practices of no burning and rotational grazing. This information will provide initial metabolism-based data to ensure that cattle are receiving adequate nutrition while grazing smutgrass. The results of this research will ultimately lead to the development of an integrated smutgrass management plan. The short-term goal of this project is to develop such a plan, while our long-term goal is implementation of this plan by land managers as well as sustainable beef production.

Animal Health Component

100%

Research Effort Categories

Basic

0%

Applied

100%

Developmental

0%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	1610	1140	60%
307	1610	1010	40%

Knowledge Area
213 - Weeds Affecting Plants; 307 - Animal Management Systems;

Subject Of Investigation
1610 - Pasture;

Field Of Science
1010 - Nutrition and metabolism; 1140 - Weed science;

Keywords

bahiagrass

beef cattle

fire

herbicide rate

smutgrass

stocking rate

Goals / Objectives
The short-term goal of our project is to develop an integrated management plan for smutgrass control in bahiagrass pastures, while our long-term goal is implementation of this management plan by land managers as well as sustainable beef production.

Project Methods
Our project will incorporate on-farm research trials and annual efforts to extend the findings to the ranching community in Florida. Field trials will be established in bahiagrass pastures in Okeechobee County during March 2015 and repeated in southwest Florida during March 2016. The pastures will be fertilized according to the land managers' typical practices. A split-plot experimental design with a factorial treatment arrangement with the following factors and levels will be used: burning (2 levels), grazing (2 levels), and hexazinone (3 levels). A 8-ha pasture or 2 4-ha pastures adjacent to each other will be used at each location for the field trial. One half of the selected land area will be burned during early spring according to Florida regulations for prescribed burning (Long 2011). Approximately 2 weeks after burning, one half of each area (burned and unburned) will be stocked with crossbred cattle at an approximate density of 6 cows per hectare, which is a typical stocking density for bahiagrass pastures in south Florida using a 28-d grazing rotation. The remaining sections of the pasture will be stocked at a density of 12 cows per hectare. A 28 day grazing rotation (7 days grazing, 21 day rest period) will be used for both stocking densities throughout the study. The animals will be cared for by acceptable practices (FASS 1999) approved by the University of Florida, Institutional Animal Care and Use Committee. Stocking rates will be adjusted throughout the study to ensure adequate forage for all animals during the grazing periods. Hexazinone will be applied within each of the four burning/stocking rate combinations at three rates (1.12, 0.56, and 0 kg/ha) during July, which is the recommended application time for smutgrass control in south Florida. Each hexazinone treatment will be replicated 4 times for a total of 48 plots. Smutgrass response will be determined by measuring the height and diameter of 5 smutgrass clumps from each plot (burning/grazing/hexazinone combination) at the beginning and end of each grazing period. To determine the extent of smutgrass consumption by cows, a 1-m2 exclosure will be placed in each plot to prevent grazing. The height and diameter of smutgrass clumps within the exclosure will be determined at the end of each grazing period and compared to measurements obtained from grazed areas. Additionally, percent smutgrass ground cover in each plot will be visually assessed at the end of each grazing period.Bahiagrass herbage mass will be determined before and after each grazing period using double sampling. The indirect measure will be settling height of a 0.25-m2 aluminum disk at 5 sites within each plot. All sections of the pasture will be represented and each site will be chosen by walking a fixed number of steps between each drop of the disk. Direct measurements will be used to generate a regression equation to predict herbage mass using the average disk settling height from 10 measurements before and after each grazing period for each burning by grazing intensity combination. To obtain direct measurements, all herbage from 2 cm above soil level to the top of the canopy will be clipped within the 0.25-m2 aluminum disk, dried to constant moisture and weighed. Bahiagrass herbage mass accumulation during resting periods will be determined for each plot. Herbage accumulation will be calculated as the change in herbage mass during the 21 days between the end of one grazing period and the beginning of the next grazing period.Hand-plucked samples of smutgrass and bahiagrass will be collected at the initiation of each grazing period by removing the top 5 cm of herbage at 10 sites in each burning/grazing combination. Herbage will be composited for each plot, dried at 60°C to constant moisture and ground to pass a 1-mm screen. Samples will be stored at room temperature until analyzed. Herbage crude protein (CP) concentration and in vitro organic matter digestibility (IVOMD) will be measured for both smutgrass and bahiagrass to determine the nutritive value of the diet consumed by the grazing animal. Analyses will be conducted using the micro-Kjeldahl technique for N (Gallaher et al., 1975) and the two-stage technique for IVOMD (Moore and Mott, 1974). Samples of bahiagrass, burned smutgrass, and non-burned smutgrass will be composited based on grazing rotation and nutritive value (n =~ 6 per location). Composited samples will be analyzed by Dairy One Forage Laboratory (Ithaca, NY) using the Model Profile package. Results of this analysis will be used to predict cattle performance.Statistical analysis. All response variables will be analyzed by fitting mixed-effects models using the MIXED procedure of SAS (SAS Institute Inc. 1996). Plots will be experimental units. The model statement will contain the effects of treatment (burning, grazing, and hexazinone), year (2015 and 2016), and time (grazing period) and their interactions. Replicate, year and their interactions will be considered random effects. The analysis will be conducted appropriately for the split-split plot design using time as a repeated measure. Means will be presented as least square means and considered significant at P ≤ 0.05. Nutrition Modeling. The Large Ruminant Nutrition System (nutritionmodels.tamu.edu) and equations from NRC (1996) will be used to evaluate different levels of smutgrass cover in bahiagrass pastures (0, 25, 50, 75, 100%) and burning of smutgrass on animal performance. Nutritive value of smutgrass from analyses conducted by Diary One Forage Laboratory will be used as inputs to predict growth of developing replacement heifers and stocker steers, and milk production of mature beef cows. The level of smutgrass cover will be used to determine the contribution to the total diet.

Progress 08/15/15 to 08/14/18

Outputs
Target Audience:Target audiences for this work include academic peers, county extension faculty, USDA-NRCS personnel, state employees, and cattlemen. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A smutgrass field day was held on May 24, 2018 where over 60 clientele attended. Clientele attending this field day included USDA-NRCS personnel, county extension faculty, state extension faculty, and private ranchers and ranch managers. Presentations that were provided that day were recorded and are available for viewing at the Range Cattle Research and Education Center "Virtual Classroom" under "Smutgrass Field Day - May 24, 2018". This information has also been provided at the Southern Weed Science Society Annual Meeting that was held in Atlanta, GA in January, 2018. How have the results been disseminated to communities of interest?The data provided from this research will be implemented into our current smutgrass management fact sheet that can be found online at http://edis.ifas.ufl.edu/aa261. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Due to excessive rainfall during the 2014 and 2016 growing seasons, we were unable to determine the effects of burning and grazing on hexazinone activity. However, we were been able to determine the effects of burning followed by rotational grazing on smutgrass utilization under low-input bahiagrass systems. Burning followed by rotational grazing reduced smutgrass clump height and diameter by at least 10 and 6 percentage points, respectively. Similarly, burning resullted in a decrease of cumulative smutgrass biomass accumulation of approximately 44% compared to non-burned smutgrass. Additionally, our results revealed that cattle consumed at least 53% more smutgrass than had been burned compared to non-burned smutgrass. Additionally, burned and rotationally grazed smutgrass retained crude protein and digestibility levels, where as non-burned smutgrass crude protein and digestibility levels remained low throughout the grazing portion of the study. Although we were unable to see conclusive evidence that burning and rotational grazing would increase smutgrass control using the herbicide hexazinone, we were able to use this lack of efficacy to garner additional funding elsewhere to determine the impact of rainfall on hexazinone activity. Additionally, we were able to educate clientele on the benefits of burning and grazing cattle to increase pasture utilization. We were able to capture the change in clientele attitude toward smutgrass utilization using a pre- and post-study survey. These surveys indicate that smutgrass continues to be a problem for Florida ranchers and that it continues to increase in severity. According to our surveys the number of clientele indicating that 76 to 100% their pastures are infested with smutgrass increased from 55 to 64%, and that there is a trend for increased smutgrass pressure overall as 28% of clientele indicated that their average level of smutgrass infestation across their entire ranch was infested by as much as 50% in 2015, and this number increased to 41% by 2018. Clientele were also asked if they know if cattle consume smutgrass. In 2015, 30% said yes, 19% probably yes, 19% maybe, 15% probably not, and 17% definitely not. By 2016, 71% said yes, 12% probably yes, 6% maybe, 6% probably not, and 6% definitely not. This indicates that ranchers are now understanding that cattle consume smutgrass more so than previously thought, but this could have been due to a change in their management techniques since this project began in 2014. For example, when clientele were asked how they managed smutgrass in 2015, burning followed by grazing was not included in any response; however, burning followed by grazing was mentioned three times in the follow up survey in 2018 as well as rotational grazing. Additionally, when asked specifically concerning burning followed by grazing, 13% indicated they had used this practice in 2015, and this number increased to 21% by 2018, indicating a behavior change has started to occur. There is further evidence of behavior change provided by the two surveys; when producers were asked if they were aware of integrated weed management practices, 41% indicated that they were in 2015, and this number increased to 81% by 2018.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Dias, J., B. Sellers, J. Ferrell, S. Enloe, J. Vendramini, and P. Moriel. 2018. Giant smutgrass and bahiagrass response to burning, grazing intensity, and hexazinone rate. 71st Annual Meeting of the Southern Weed Science Society. Atlanta, GA. January 21-24, 2018.
• Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Dias, J. and B. Sellers. Impact of burning, grazing, and hexazinone application on smutgrass control in bahiagrass pastures. Smutgrass Field Day, Ona, FL. May 24, 2018
• Type: Other Status: Published Year Published: 2018 Citation: Smutgrass Field Day Booklet. May 24, 2018. Provided handouts for participants at the Smutgrass Field Day held at the Range Cattle Research and Education Center near Ona, FL.
• Type: Journal Articles Status: Awaiting Publication Year Published: 2019 Citation: Dias, J.L.C.S., B.A. Sellers, J.A. Ferrell, S.F. Enloe, J.M.B. Vendramini, and P. Moriel. Impact of burning, grazing intensity, and hexazinone on smutgrass management in Florida. Weed Sci. Under review.

Progress 08/15/16 to 08/14/17

Outputs
Target Audience:Rancher, State and Federal agency personnel, professional colleagues/peers Changes/Problems:Excessive rainfall following hexazinone application has been detrimental to one year of research as smutgrass control with this herbicide was relatively poor overall. This has led to additional research outside of this award to better understand the impacts of rainfall following hexazinone application on smutgrass management. What opportunities for training and professional development has the project provided?Information from this research will be shared this coming October with County Extension Faculty as part of a in-service training event. This training will provide extension faculty with the knowledge needed to provide ranchers with information regarding the benefits of burning and grazing smutgrass. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?We will continue to collect data from these experiments and begin to analyze the data sets that have been collected. A field day will be held this fall and early next spring to allow producers to see the experimental plots as well as other research that has been conducted regarding smutgrass management in bahiagrass pastures. This will be followed by a producer survey to begin to ascertain the potential acceptance of this management technique and implementation.

Impacts
What was accomplished under these goals? Our research has demonstrated that burning smutgrass followed by a 2-week rest period results in uniform grazing of smutgrass tussocks by cattle, while unburned smutgrass is generally avoided. Smutgrass nutritive values following burning are comparable to that of bahiagrass, the most common forage grass grown in Florida. Similarly, smutgrass plants that are grazed continue to have similar nutritive values of bahiagrass. Preliminary results of this research have been shared during one-on-one visits with clientele who have significant smutgrass infestations. Information regarding the usability of smutgrass-infested pastures through burning has resulted in ranchers utilizing this invasive plant species as a forage resource in the early spring prior to bahiagrass growth has been beneficial to their operations.

Publications

Progress 08/15/15 to 08/14/16

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?At this point in time, no producers have been trained on smutgrass management using the techniques outlined in the proposal. However, the graduate student employed through this work has gained valuable knowledge in data collection through various techniques. In addition, county extension faculty have been trained on experimental design as well as forage measurements. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?We plant to repeat the experiment in 2017 to finalize our data collection from these experiments. A field day will be held in late 2016 and a second during the summer of 2017 to highlight the results of this research. This will be followed by a producer survey to determine the potential acceptance of this management technique and implementation.

Impacts
What was accomplished under these goals? At this point in time it is too early to determine if our technique employed in these experiments will be fruitful and accepted by producers. However, preliminary evidence suggests that mob-grazing smutgrass prior to hexazinone application is slightly beneficial when burned.

Publications