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Funded Project

Funding Program: IPM Enhancement Grants

Project Title: Developing IPM Practices for Bermudagrass Stem Maggot in Forage Production.

Project Directors (PDs): Allen Knutson [1] Forrest Mitchell [2] Vanessa Corriher-Olson [3] Jim Muir [4]

Lead State: TX Lead Organization: Texas A&M University AgriLife Extension

Undesignated Funding: $27,980

Start Date: Mar-01-2016 End Date: Feb-28-2017

No-Cost Extension Date: Jun-30-2017

Pests Involved: Bermudagrass stem maggot

Site/Commodity: Bermudagrass hay

Area of Emphasis: Invasive pests, develop economic injury level and sampling methods

Summary: The bermudagrass stem maggot (BSM) is a new pest of bermudagrass forage in the southeastern US. BSM was first reported in TX in 2013 and during 2015, infestations were reported throughout Texas and many fields were treated with insecticide for BSM control. Although BSM damage has created grower alarm and initiated insecticide treatments, the effect of BSM injury on forage yield and quality is unknown and economic thresholds and sampling methods necessary to guide management decisions have not been developed. We propose to investigate the impact of BSM on bermudagrass forage yield and quality, develop initial economic thresholds and evaluate sampling methods for BSM. The outcomes should provide the foundation for expanded studies to develop an IPM program growers can use to make informed management decisions regarding control of bermudagrass stem maggot. Bermudagrass is the most important warm-season grass forage in the southern US. In Texas, bermudagrass hay is harvested from 2.6 million acres and valued at over $1 billion. BSM is native to south Asia and was first reported in the southern US in Georgia in 2010. The BSM larva feeds inside the stem just below the top node and this feeding damage results in the death of the top 2-3 leaves which turn brown or white and can be easily pulled from the stem. The damaged shoot stops elongating as a result of the maggots feeding injury, plant growth is stunted and forage yield is reduced. Current management recommendations, developed in Georgia, suggest that if damage is found, the crop is unlikely to add a significant amount of yield and therefor the crop should be harvested as soon as possible and the field treated with an insecticide. While these guidelines have been useful to-date, research is needed to more clearly define how much damage can be tolerated before economic loss occurs and the parameters needed to make that assessment. The Economic Injury Level EIL is a critical component in many IPM programs and is used by growers and consultants to decide when control practices should be implemented to prevent an increasing pest population from exceeding a pest density that results in economic loss that is greater than the cost of control. We propose to develop an EIL that will consider the value of the potential yield loss due to BSM relative to the value of lost production due to early harvest and the cost of insecticide treatment. Also, there are no recommended methods to monitor BSM infestations that growers can use in conjunction with an EIL. The objectives of this proposal are: 1. Determine the relationship between BSM infestation and loss in forage value (yield and quality), 2. Evaluate methods for monitoring BSM density and injury, 3. Disseminate project results to growers and consultants via Extension educational programs, and 4. Train students in field plot experimentation, IPM and agricultural production and IPM. We will conduct replicated field plot trials in bermudagrass fields at the Texas A&M AgriLife Research and Extension Centers in Stephenville and Overton and in 2 grower fields. The relationship between BSM infestation and yield will be determined for each of 3 harvests from four fields (12 trials) and used to calculate an EIL. We will monitor BSM abundance and activity throughout the growing season using sweep net counts and percent stem injury. Traps and attractants will be evaluated for monitoring adult flies. Results will be disseminated via regional and county based Extension educational programs and through Extension outlets. Project outcome will be evaluated based on grower knowledge and adoption of practices using pre- and post-program surveys. Objectives: Outputes: 1.Determine relationship between Bermudagrass Stem Maggot BSM injury and hay yield and quality in small plot, replicated field trials. BSM injury (percent infested tillers measured weekly) and hay yield and quality will be compared in a treatment with extant BSM infestations and in a treatment that excludes BSM using insecticide. The trial will be repeated for each of 3 hay harvests in 2 irrigated fields at TAMU Research and Extension Centers at Stephenville and Overton and in 2 grower fields (12 trials). Data will be used to calculate the Economic Injury Level EIL. 2.Evaluate methods for monitoring presence of BSM adults that could be used by growers to anticipate BSM infestations. The number of BSM adults captured on sticky cards and in baited traps will be compared to the number captured in sweep net samples and percent of stems with BSM injury. Sampling will be conducted throughout the growing season to determine seasonal activity of BSM adults. 3.Write Extension publications detailing guidelines for managing BSM based upon research results. Disseminate management guidelines through regional and county based Extension educational programs (presentations at grower meetings, workshops, etc) and through Extension outlets (web sites, electronic newsletters, on-line). 4.Evaluate program impact and outcome and generate base-line data through surveys of growers attending Extension educational programs. Anticipate presentations at 6 grower meetings attended by a total of 250 hay producers. 5. Employ and train two summer student interns from nearby Tarleton State University and University of Texas at Tyler to assist in project activities. Outcomes 1.Hay producers and consultants will increase their understanding of the potential economic impact of BSM and when an insecticide treatment is necessary to prevent economic loss. Treatment decisions will no longer be based upon the presence of BSM damage or visual appearance of injury but on research relating percent infested tillers to potential yield loss at harvest. 2.Hay producers and consultants will monitor BSM adult activity with simple but efficient methods that can be used to calculate the economic injury level. Season long sampling will identify seasonal activity of BSM and identify times when hay is at greatest risk to infestation. 3.Growers and consultants increase their knowledge of the damage potential of BSM in Texas and how using the EIL and sampling methods can be used to manage BSM. 4.Change in grower knowledge will be documented and provide benchmark to measure future adoption of IPM practices for BSM. 5.Students increase their knowledge of field experiments, IPM practices forage production practices.

Final Report:

Outcomes 1. Field studies documented a declining forage yield with increasing stem maggot damage as measured by the number of stems with the top 2 leaves dead or dying due to stem maggot feeding. An economic analysis of the cost of insecticide treatment and hay value found that in fields with good to high quality forage (hay value of $100-80/ton), an insecticide treatment should be considered to control stem maggot when 22% ($100/ton hay) or 27% ($80/ton hay) or more of the stems are damaged by stem maggot. This relationship appears to be valid for either Coastal or Tifton-85 and irrigated or dryland, making it an easy guide for growers to use. 2. Methods to monitor adult flies, including sweep net sampling and sticky cards, are unlikely to be adopted by growers due to do the time required for sampling and cost. The most practical method to-date is sampling for stem maggot damage which is easy identified by the death of the top 2 leaves on the stem (or death of leaves initiated at lower nodes). To determine percent stem damage, all of the stems are cut from an area of about one square foot. From this sample, 50 stems, selected without bias, are examined for stem maggot damage and the percent damaged stems is recorded. This is repeated at several locations in the field to calculate an average percent damage for the field. The estimated stem damage can then be used to calculate the Economic Threshold to determine when an insecticide application can be considered. Baited traps appear to have potential for monitoring adults and could be useful in research studies and improved IPM practices but more research is needed. 3. Clientele gained information on BSM identification, life cycle, damage, labeled insecticides and management guidelines, including insecticide treatment or early harvest, via Extension publications and electronic media. 4. Bermudagrass hay producers, county Extension agents, and consultants gained knowledge of BSM identification and IPM methods through presentations at Extension entomology meetings and statewide crop production meetings. Hay producers (85% of 144 surveys) attending these meeting responded that they would use the new economic threshold guidelines (stem damage greater than 20%) in making decisions to apply an insecticide for BSM control. 5. Student works gained skills in identifying BSM and other insects commonly found in Bermudagrass, the use of methods to monitor insect activity and the collection of scientific data.

Outputs 1. The relationship between Bermudagrass stem maggot BSM damage and forage yield was evaluated in five commercial Bermudagrass fields and two fields each at the Texas A&M AgriLife Research and Extension Centers in Stephenville, TX and Overton, TX. Data from five fields could not be used due to the lack of significant stem maggot infestations or insecticide applications for fall armyworm control. Data from four fields showed a consistent relationship (same slope) between increasing stem maggot damage and decreasing yield. The relationship was the same regardless of variety (Coastal and Tifton-85) or irrigated vs. non-irrigated. These data were used to calculate an Economic Injury Level EIL and Economic Thresholds (80% of the EIL) for a range of control costs and hay value. As an example, an insecticide application for BSM is about $10.00 per acre, including the cost of insecticide, surfactant and buffer, and application cost. If the value of the hay is $100/ton (high quality forage), the Economic Threshold was calculated to be 22% of the stems with stem maggot damage. If the value of the hay was $80/ton, the EIL increased to 27% of the tillers with BSM damage. 2. Sweep net sampling, sticky cards and baited traps were evaluated as methods to monitor adult fly activity evaluated in the field. Sweep net sampling was deemed impractical due to the time to separate stem maggot flies from other captured insects. Sticky cards captured flies but were tedious and costly. Baited traps showed promise in capturing adults and further studies on trap design and bait evaluation are needed. 3. Information on BSM identification and management was distributed to forage producers and county extension agents via the “Forage FAX” electronic newsletter and the Texas AgriLife Extension Publication “Managing Insect Pests of Texas Forage Crops”, available as a free download from agrilifebookstore.org. 4. Information on managing BSM was presented at six county and regional Extension educational programs attended by 424 hay producers from more than 34 counties in central and north Texas. Presentations were also made at the statewide Texas Plant Protection Conference in College Station, TX and at the annual meeting of the Texas Pest Management Association in San Angelo, TX. 5. Student workers were employed to assist with collecting BSM data from sweep net, sticky card and counts of stem damage at the Texas A&M AgriLife Research Centers in Stephenville and Overton.

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