Our project objective has been to study a promising non-chemical management tactic for fly pests management: pasture dragging to break up manure pies with a light harrow. This practice is sometimes recommended for fly management (e.g., Kaufman, 2011; Rutherford, 2015) because the larvae of horn flies and face flies (together referred to as ‘filth flies’) feed in cow pads; and thus it is conceivable that spreading the manure will reduce fly survival through desiccation. Field trials at the project farm showed apparent success in 2017. This tactic has yet to be tested scientifically—which we aim to do in the 2018 summer field study.
Cattle in pasture settings suffer a reduced quality of life due to a complex of fly pests that feed on their blood and facial secretions. Prominent among these pests are the horn flies (Haematobia irritans), which feed on cow blood 20-30 times per day while resting on backs and sides of cows (Oyarzún et al., 2008). Cows may be afflicted by hundreds or even thousands of horn flies at once and are not immune to the annoyance nor to the loss of blood. Another prominent pest species is the face flies (Musca autunma), which feeds on the mucus secretions of cow’s eyes and noses. These flies are a less directly harmful but problematic because they vector pink eye (Pickens and Miller, 1980). In response to fly pressure, cows congregate and swat their tails—behaviors that significantly reduce their feeding and growing efficiencies. This combination of irritation and defensive behaviors in cows have a significant economic cost. In the cattle industry nationwide, horn flies account for estimated losses of 730-876 million US dollars (Watson et al., 2002). Even greater losses occur when the cost of insecticides are considered. Yet insecticides are not always effective. Due to the development of insecticide resistance in horn flies (Watson et al., 2002) as well as the harmful effects of insecticides on non-target organisms, an integrated pest management (IPM) approach is needed that employs diverse tactics to reduce reliance on insecticides (Fincher, 1999; Kogan, 1998; Oyarzún et al., 2008).
Raising beef cattle on pasture is a sustainable alternative to conventional feedlot beef production with many potential benefits to farmers, including reduced energy consumption, sequestration of carbon in pasture soils, and access to high end niche markets. Improving pastured animal welfare and productivity via reduced fly pressure has potential economic value for livestock producers across the Northeast. This efforts of this project should also be of interest to pasture based dairy farms.
The Dickinson College Farm operation includes a herd of pastured beef cattle – between 25 and 35 animals are on the farm depending on the time of year. Breeds raised are black Angus and Angus-Herford crosses. The herd includes cow-calf pairs, a bull, young and finishing stock. Direct market freezer beef is the main product sold, along with some young stock sold to other local farms. The cattle are third-party certified grass fed and Animal Welfare Approved (AWA) by A Greener World. The AWA program provides guidelines for animal husbandry to ensure low stress, humane treatment. The farm practices management intensive rotational grazing, moving the cattle once or twice daily through small paddocks on about 45 acres of pasture. In the winter the cattle are fed dry hay on a covered heavy use area. The farm operation also includes 10 acres of certified organic vegetables, grass fed sheep, lambs, and a small flock of pastured laying hens.
Filth fly management has been attempted historically through a range of chemical and biological practices. Chemical management with synthetic pyrethroids, organocholorines or other nerve toxins administered through ear tags, sprays, powders and dip tanks have been employed successfully on short timescales (Oyarzún et al., 2008; Pickens and Miller, 1980). But it is well documented that filth flies develop resistance to these compounds (Oyarzún et al., 2008; Pickens and Miller, 1980). Moreover, this approach is generally contrary to the goals of sustainable agriculture for health and environmental reasons, and is somewhat limited by the stipulations of organic certification.
By contrast, biological and mechanical control methods have potential to be employed sustainably. Biological control in particular is an attractive option in some systems. In dairy barns, for example, parasitoid wasps that lay their eggs in filth fly pupae have been employed quite effectively. Unfortunately, commercially available parasitoids have low dispersal ability and do not favor the pupae of horn flies and face flies, rendering them ineffective in pasture situations (Fincher, 1999; personal communication with Spalding Labs).
Yet another biological control option is the use of dung beetles to out-compete filth flies. Scarab beetles such as the beneficial species Onthophagus taurus have been intentionally introduced into to the US because they have the potential to reduce fly larvae success by rapidly dispersing dung pads through their tunneling and burrowing behaviors. In the southern US the populations of O. taurus reach high densities and colonize dung pads by the hundreds, which effectively reduces the manure availability and quality, leaving fragments of manure pads that desiccate quickly (Roth, 1989). Our surveys at the Dickinson Farm as well as a survey from New York (Pimsler, 2007) show that O. taurus and other dung beetles are already present in the northeastern US, but their populations are much smaller: only about a dozen beetles per dung pad at the Dickinson Farm. Thus dung beetles are of limited utility for biological control of filth flies in our region.
In lieu of hoards of dung beetles, we are interested in the practice of mechanically spreading manure to promote desiccation and inhibit filth flies. This strategy is often suggested for filth fly suppression but its efficacy remains in question (Kaufman, 2011) because scientific tests of the practice have not been published. Further, since the mechanism of action is thought to hinge on desiccation, this tactic may be climate- or season-dependent. Hence, testing of the tactic in the northeast throughout the growing season is necessary determine whether farmers in this region would benefit from implementing it.
Farmers at the Dickinson College Farm have anecdotal evidence in support of this tactic. In 2017 farmers in consultation with cooperator Dr. Jason Smith trialed several methods for low input fly control on pasture. Methods trialed include feed through insect growth regulators (currently under evaluation), construction and regular use of a walk-through fly trap, application of commercial essential oil blends designed to repel flies, use of commercial hanging traps, and dragging. Pasture dragging to reduce fly breeding habitat in manure pads coincided with reduced fly densities on cows, but we do not yet have data that could show a cause-and-effect relationship. Since pasture dragging requires regular investment of farm labor and machinery use, we intend to rigorously evaluate the effectiveness of this practice before promoting it to other farmers in the region.
Use of free range laying hens to disperse manure pies is an alternative approach to this problem. Trials of this method at the Dickinson College Farm proved problematic due to chickens wandering out of the cattle pasture and into neighboring vegetable fields. Fencing chickens with portable electric mesh nets was found to be incompatible with the pace of cattle advancing across the farm. While hens did demonstrate an ability to disperse cow pies, the area covered by the chicken flock was much smaller than the area soiled by the faster moving cattle herd. Thus, we seek to evaluate mechanical pasture dragging as an alternative for diversified farms that do not have appropriately matched cattle and poultry operations.
The 2018 summer field study was completed according to plan. The following is a summary of the steps taken:
In March we (PI Matt Steiman and Cooperator Dr. Jason Smith) hired student Cecilie MacPherson to be our summer research assistant. Cecilie will graduate Dickinson College in 2020, majoring in environmental biology.
Field work began in June. After an introduction to the cattle, flies, and manure management issues, the following initial efforts proceeded simultaneously:
Steiman built a pasture drag to be used in the study. After shopping around at landscape and equipment suppliers we elected to construct our own drag from materials on the farm. The goal was to make an effective yet inexpensive tool appropriate to the scale of our equipment (for this project we used a John Deere Gator off-road utility vehicle to pull the drag). We settled on a double gang of steel bed frames oriented with the long sides parallel to the direction of travel. The bed frames were chained loosely together to permit floating over obstacles, then weighted down at each end with 6X6 lumber. The whole unit was attached to the rear of the towing vehicle with heavy rope.
Meanwhile Smith, Steiman and Macpherson worked on constructing the fly traps. The inverted cone screen emergence traps were designed to capture flies that mature from pupae on cow pies on the ground surface. Large outer cones were made from rolls of 48″ aluminum screen. A pattern was developed and traced onto flat pieces of screen with a carpenter’s crayon, then cut out using heavy scissors. Cones were formed by rolling the cut screens into a cone shape, then stapling the seam to a 3/4″ strip of wood using a staple gun. A small hole (1-2″) was left open at the top of the large cones.
Smaller cones were formed from scraps of screen left after making the large cones. These smaller cones were glued to the inside of lids for wide-mouth pint mason jars using an outdoor rated epoxy. To set the traps, large cones were supported vertically with a plastic or fiberglass fencing stake with the wide end down. Edges of the large cone were tacked to the soil surface with 6″ landscaping staples. The smaller cones with jars attached were set atop the hole at the top of each large cone. Flies emerging from the ground beneath the trap travel upwards along the screen into the jar at the top, where they are trapped and die within a few days. Collection of the flies for analysis was executed by removing jars with flies from the mason jar rings, then fitting them with a cap for transport to the lab. When necessary, flies were euthanized by inserting a cotton swap doused with acetone into the jars.
In practice the traps proved to be quite effective – we have confidence that the majority of flies emerging from cow pies on the soil below were caught in the trapping jars.
During this phase Macpherson also constructed a cow pie measuring grid from a wooden frame with 1/2″ hardware mesh stapled on tightly. The squares of the grid were highlighted with yellow paint in a pattern that made counting covered area relatively easy. This grid was laid over the top of studied cow pies and photographed before and after the dragging treatments to assess the area of each manure pile and the spreading effect of dragging.
The experimental design and time plans were worked out and field checked in early June. Working together we settled on the following program:
Cattle were moved from pasture to pasture daily. Within 1-2 days of cattle leaving a pasture, an area with a good concentration of manure piles was chosen and staked out to protect it against trampling by animals or equipment. 30 cow pies of similar size were identified and flagged – half as controls (no dragging) and half as experimental piles to be dragged. Each pile studied was measured, photographed and flagged with an identification number. Piles were grouped by location into control or experimental treatment categories in order to facilitate practical dragging using the 7 foot wide bed frame assembly. All manure piles studied were located close to one another within an area of less than 1/2 acre. Following pile ID and measurement, the experimental half were disturbed by one pass of the bed frame drag at low speed. The pies were then left alone, uncovered, for 5 to 7 days to allow for fly egg laying, development of larvae, and any predation of larvae or eggs by naturally occurring predators.
After 5-7 days, the cone traps were installed and left in place for three weeks. This length of time was chosen to allow development and emergence of all fly species of concern. During the trapping phase, Macpherson visited the traps daily to note fly emergence and fix any problems with the traps. If any trap appeared to malfunction this was noted in a log book to accompany the fly collection data. A research grade rain gauge and temperature sensing data logger were installed on a portable stake located within the trapping area – Macpherson checked these regularly to account for weather variation in the fly collection results.
A work plan was generated by Dr. Smith that allowed a subsequent set of cow pies to be flagged, measured and dragged near the end of the first trapping period, such that the traps could be redeployed to a following site quickly. This allowed us to run through five rounds of pile dragging and fly collection over the June – September period, in an effort to account for variations caused by temperature, rainfall, daylength or time of year.
Following collection of each group of flies, they were brought to a lab on the Dickinson campus and preserved in sample jars. Dr. Smith trained Macpherson to identify flies to genus using a dissecting microscope. After the first round of flies were collected, Macpherson spent many hours categorizing and counting flies, thus forming the raw data set for the project.
As a side effort, the project team developed a behavior monitoring protocol in an effort to find possible correlation between cattle behavior and fly load. Macpherson spent enough time observing the cattle herd to allow them to become familiar and comfortable with her presence. From this close position, she took photographs of individual animals, then followed these animals for a ten minute period, counting behaviors associated with fly irritation (foot stomping, back biting, tail swishing, and ear flicking). Macpherson later counted the flies in each photo in an effort to correlate easily observable cattle behaviors with actual fly load per animal. The hope of this side project is to link countable behaviors with economic or welfare threshold values for pest flies.
Stabilized fly samples collected from the traps were tallied throughout the fall of 2018. Dr. Smith conducted statistical data analysis in January of 2019 in preparation for the PASA conference in early February. Full analysis and discussion of the research results will be provided in the upcoming final report. Initial analysis shows that while dragging did have a statistically significant effect of reducing face and horn flies in some rounds of trapping, in other cases the opposite was true. Thus on a season wide basis (all five rounds of collection) we cannot say that the dragging treatment provided statistically significant reduction of fly numbers. However there is much nuance in the data which will be discussed further in a pending report.
Our 2018 efforts were somewhat hampered by the unusually wet summer weather in Pennsylvania throughout most of July, August and September (the objective of pasture dragging is to spread cow pies so they desiccate faster and become less suitable habitat for fly pupation. In 2018 there were several weeks where drying of anything exposed to the weather was difficult). A second round of data collection is being considered for the 2019 fly season.
Conclusions will be presented upon further analysis of the data.
Education & Outreach Activities and Participation Summary
On February 7th, 2019 Dr. Smith (researcher) and Matt Steiman (Farmer PI) co-presented a 90 minute talk entitled “Pastured Beef Cattle Fly IPM” at the annual conference of the Pennsylvania Association for Sustainable Agriculture. This slideshow and talk included background on the farm’s beef operation, an overview of the different fly species and their life cycles, non-chemical control measures trialed at Dickinson, and detailed results and discussion from 2017 and 2018 field studies. Northeast SARE was credited as a supporter of the work. At least 45 people attended – the room was full.
We are currently working on contacting trade and scientific journals for public release of our findings. Dr. Smith will lead the approach to journals while Steiman leads the effort for sharing through Stockman Grass Farmer and similar publications.