With the goal of investigating the implementation of sheep as an alternative to conventional weed management techniques, we conducted an experiment that addressed three primary questions: 1) Did sheep reduce labor costs associated with weed management, 2) Did sheep reduce material costs associated with weed management, 3) How was the crops yield and quality affected by the sheep’s presence.
The experiment was conducted over the course of 10 days on a mature hop yard located in Gorham, Maine. Prior to our experiment that yard had been receiving uniform weed management controls. Five Scottish Blackface and one Katahdin sheep were utilized in an experimental plot that was broken into four different rotational grazing bays. A control plot surrounded the sheep’s pen, which continued to receive conventional weed management techniques.
It was observed that the sheep gravitated quickly towards a eating the basal foliage of the hop plants, and they then consumed the 17 different varieties of mid season weeds surrounding the plants quite effectively. Disregarding the upfront establishment costs associated with infrastructure for the sheep, and implements required for conventional weed control, the relative annual input costs of the labor and materials associated for utilizing sheep as opposed to conventional methods proved to be higher at the one acre scale. However, when projected onto a 10 acre scale we have estimated that the non-linear costs associated with sheep management will alter the value proposition, where sheep become a less expensive weed management solution than conventional methods. The numbers on a one acre scale we mapped to $539 for conventional and $1,000 for experimental control. On a 10 acre scale, those numbers adjusted to and an estimated $5,390 for conventional and $2,875 for experimental control. These numbers for experimental control could be further adjusted if the sheep acquisition model shifted from rental to ownership. Rental facilitated our experiment, but it is likely that ownership would be a less expensive model.
Unfortunately, the experimental plots crop yield and quality went unmeasured against the control due to late season crop loss associated with a spider mite infestation. This infestation went uncontrolled across both the experimental and control plot, and prevented the planned end of season measurements.
The Hop Yard, LLC is a Maine farm growing hops for use in the beer brewing process. Ryan Houghton, Geoff Keating, Peter Busque & Charlie Hamblen are the owners of The Hop Yard. Since starting in 2011 the farm has grown to 10 acres and 9,000 plants in production between our two properties in Gorham and Fort Fairfield. In 2014 our harvest was sold 15 different breweries across Maine.
One of the primary challenges of a young small-scale hop farm is managing the input costs year-over-year. Specifically, one of the major constraints to growing hops at scale in fields that have been converted from long term hay production is the impact of perennial grasses and weeds on the health of the overall yard. Finding alternatives to conventional sprays, and manual input, could relieve a pain point that acts as a barrier to entry for potential growers and a bottleneck to expansion for established farms.
We have done a thorough investigation of existing research and both conventional and unconventional approaches to weed management in hop yards.
FNE12-742 conducted by another hop farm in Maine showed limited effectiveness of using cover crops or straw for weed management but observed effectiveness in mechanical tilling as would be expected.
Several previous SARE projects have observed the effectiveness of sheep for weed control. FNE07-607 from 2007 proved the effectiveness of this approach with Christmas Trees. FNE02-431 from 2002 saw limited success with early growth blueberry fields. FNC14-980 from 2014 is investigating a similar approach but during the early growing season for hops (prior to July) due to the organic requirement of removing sheep from the field 90 days before harvest.
Commercial hop growers in the pacific northwest rely on cover crops, tilling and extensive herbicide use for weed management. We have visited several farms and observed their approaches as well as talked to farm managers to understand what works and what does not.
Our approach for this study is innovative because it leverages the natural grazing ability of sheep to reduce reliance on potentially harmful tilling, costly herbicide procurement and application, and labor intensive manual processes for weed control.
Our technical advisor for this project is Professor Donna Coffin, of The University of Maine Cooperative Extensive.
The goal of our research was to analyze the effectiveness of grazing sheep on mature hop plants during the latter parts of the growing season (July to early September) to reduce reliance on conventional weed control methods. We planned to use the cost of labor, materials, and health of the soil and hop bines to quantify our results. To limit our scope, we focused on residual/annual costs associated with the implementation of both conventional and our experimental methods and did not include infrastructure and equipment costs.
This experiment utilized a three year old hop yard located in Gorham, Maine. The chosen field was planted on top of a long standing hay field in the Spring of 2012, and each subsequent year the perennial weeds and grasses have persistently returned. Before initial planting in 2012, the ground was tilled multiple times, but no herbicides had been applied. In the years since, the field had received uniform application of several applications of herbicides targeted at both the broadleaf weeds and perennial grasses. In addition, manual weeding and defoliating of the lower hop leaves took place during the summer months. During 2015, the year of our experiment, no herbicides or manual weeding was applied to the experimental plot, but standard applications were continued in the control plot.
We worked with North Star Sheep Farm in Windham, Maine to introduce six mature animals into our yard, five Scottish Blackface, and one Katahdin.
To quantify the impact the sheep would make several key performance indicators were selected. These performance indicators were recorded both before and after the sheep were present on the yard, and monitored in both the control and experimental plot.
While the weeds and soil in the experimental area was left unmanaged before the experiment, the control area received our standard management routine. That routine as it relates to weed management includes the follow tasks.
Tilling occurs between the rows of plants throughout the year. During the experiment, this task was scheduled to occur in the control plot on one occasion. This task promotes aeration of the soil, and prevents plant growth in this area. We would consider including this within our sheep program on a larger scale, but due to fencing used in our experiment it was not practical to do so.
Basal foliage herbicide application
We use a herbicidal spray to kill back the leafs below four feet on the mature hop bines. This task uses a hand sprayer that sits in the back of a small farm vehicle. The task takes about an hour per acre to complete, and cost $50 per acre per application, and the diesel cost added an additional $4 per acre.
Basal foliage manual leaf removal
After the basal foliage has been damaged by the herbicide, we hand strip the plants of these damaged leaves. This accomplishes the final goal of opening up airflow throughout the yard, and also removes a potential breeding ground for pests. This tasks takes three man hours per acre to accomplish, and no additional material costs.
Weed and sucker growth specific herbicides application
On a typical year we apply five sprays targeted towards weeds in the hop yard. These spray occur throughout the year, none of which were applied to the experimental yard. The sprays cost $50 per acre per application, and the diesel cost added an additional $4 per acre.
- Soil Observations
- Soil compaction
- Soil PH
- Available nitrogen in the soil
- Weed Population
- Weed height
- Weed density
- Weed composition
- Hop Observations
- Nitrogen present in petiole samples (hop’s plant matter)
- Basal foliage (leaves below 4 feet)
- Sucker growth (new hop shoots being put out by the plant’s crown)
- Bine health
- Harvestable bine count
- Total weight of harvested cones
- Animal Results
- General physical condition
Soil Observations Methods
Soil compaction was measured with a Humboldt Pocket Penetrometer, a tool that is pressed into the top of the soil and records the amount of force required to penetrate the surface. Our measurement goal was to determine the average force required within the experimental plot, to be used a a reference to the average force required to penetrate the surface in the control. When taking the measurements, 15 data points were accumulated to create each average. Data points taken with mixed proximity to the crowns, with the intent of creating a true average for the field. When considering the value of these measurements, it was our belief that they could contribute to the assessment of overall impact the sheep had on the soil surrounding the plants.
Soil PH is believed to be a key factor in the vitality of hop plants. We are targeting a range of 6 to 6.5, but have historically been a in a range of 5.3 to 5.8. While we continue to build up our soils to our target numbers, we wanted to understand the impact sheep could have on this effort. To do so, we worked with the University of Maine soil labs to monitor soil PH before and after our experiment. When taking samples, we would use a four foot soil probe, generating samples from 20 different soil pulls throughout the experimental and control plot. Soil was probed from areas within a three foot radius around the hop crowns, and from such areas evenly spaced around the plots.
Available soil nitrogen, much like soil PH, is key to plant vitality. Plants on our yard are fed through the combined efforts of topical pelletized nitrogen, and liquid nitrogen in the drip lines. A point of interest in this study was the effect sheep’s excrement would have on our soils nitrogen levels. Through the same sampling process described in for soil PH, we monitored the available soil nitrogen with our soil samples processed by the University of Maine.
Weed height was measured in inches as an average max height within each the experimental and control plot. To do so, 30 measurements were taken on what appeared to be the tallest plants in each plot. Our main goal with on control methods for weed management, is to stunt the growth of weeds and preserve the available nutrients for our hops. The significance of height was the belief that it could represent an indication of the weeds overall health.
Weed density was recorded as High, Medium, or Low. High represents no light penetration to soil, and multiple layers of plants occupying all heights below the tallest. Medium density represents significant plants, with occasional bare spots between clusters. Low represents relatively bare ground, with the occasional green plant between hops.
Weed health was recorded as Vibrant, Fair, or Bad. These terms were used to reduce confusion, as “Good” would typically be our healthy term, but it could be misunderstood as under control. Vibrant represents no pressured being observed, Fair represents some discoloring or stunted growth, and Bad represents that the weeds are dead or mostly dead.
Weed composition was of particular interest, as it guides our convention control efforts. Meaning, we have to chose what sprays to use based on what weeds are present. If the sheep were indiscriminate, it would prove to be a broad reach control mechanism. To record our weed composition, we walked the fields before and after the experiment and recorded all observed plants. It should be noted that due to a specific weeds potential negative health effect on sheep, we removed all Milk Weed from within the control plot by hand before the sheep arrived.
Nitrogen present in the hop plants petiole was measured both before and after the experiment. The petiole is the stalk of the leaf, and is a good indicator of the nitrogen available within the plant. To measure this, we collect 30 leaves from within a four to five foot height range above the ground, from both the control and experimental plot. To ensure freshness the stalks were then snapped from the leaves, and sent immediately to Agro-One for their Plant Tissue Testing service. Samples were collected in the morning hours.
Basal foliage are the leaves within four feet to the ground on a midsummer mature hop plant. These leaves can trap moisture closer to the ground around the plants, and lead to fungus issues. The leaves also prevent airflow throughout the fields, again leading to fungus related issues. The basal foliage was observed before and after the experiment, and the health of the leaves was recorded.
Sucker growth refers to the shoots that emerge from the hop plants crown, that are not trained onto the coir. This growth can detract from the plants yield by diverting energy away from the productive bines on the trellis. We recorded the average number of suckers per plant by recording the sucker count presents on 20 plants throughout each plot.
Bine health for this experiment is represented by a measure of either Good, Fair, or Poor. This measure is the culmination of observation of the general, and overall health of the plant. Specific points which build upon this observation include visible damage as a result of pests, fungus, disease, as well as the overall visible nutrition and hydration. Due to issues described later in the report, our post experiment measurements for this metric were in not fully representative of the impacts of the sheep’s presence.
Harvestable bine count and total weight of harvested cones were metrics intended guide our thinking regarding the impact sheep had on the yield of plants. Due to issues described later in the report, our post experiment measurements for this metric were in not representative of the impacts of the sheep’s presence.
The general physical condition and weight of the sheep were observed by their owners at Northstar Sheep Farm. Animal health for this experiment is represented by a measure of either Good, Fair, or Poor. The sheep were delivered in “Good” condition, and that set the standard for their health moving forward. Fair would represent weight loss, fatigue, and/or any visible decline in health. Poor represented the threshold for when we would plan to remove the sheep from the farm due to any a physical condition that had begun to present a long term threat to the animal. Items that were marked as a potential threat to their health and removed the from the farm included, fungicides containing copper and milkweed, both of which are commonly present in our yard, but not during this experiment.
Because of the size restrictions on the the yard we were testing, our recordings are done in square feet opposed to acres. To help make these numbers more actionable, we have extrapolated grazing numbers in the costs reporting to represent the effort in terms of acres.
A complete chart of these recordings can be seen in Figure 1 – Field Observations.
To quantify the cost implications, records were kept to document total costs associated both with conventional and experimental methods. It can be expected that the costs could fluctuate year-to-year, due to natural variance. The upfront cost of infrastructure and equipment required to execute on each of these methods was not factored. These include cost of sprayers, tractors, perimeter sheep fence, and other one-time costs. Our focus was on the the annual input costs for management, including both material and labor.
A complete chart of these recordings can be seen in Figure 2 – Cost Records.
To understand the rate of consumption by the animals, we broke our experimental plot into four distinct grazing bays of varying size. We regulated the animals time in each bay, moving them when the weeds were less than two inches in height. In each of the experimental bays, we went through prior to the introduction of the sheep to remove the milkweed that was present. This recommendation came from North Star Sheep Farm, because of the potential toxicity threat it represents to the sheep.
The breakdown of bay size, time in bay, and notes associated with each grazing can be seen in Figure 3 – Sheep Observations.
Nitrogen observed in hop petiole samples before the sheep’s arrival was identical in both the control and experimental plot, measuring at 3.48%. After the experiment, both the control and experimental plot demonstrated lower nitrogen levels, lowering to 1.94% in the experimental and 2.29% in the control. This finding contrasts that of an increase in available soil nitrogen that was witnessed in the experimental plot (Δ +25ppm Nitrate-N), and a decrease in available soil nitrogen in the control plot (Δ -11ppm Nitrate-N). When collecting samples, no visible difference in leaf color or health was observed between the control and the experimental plot at either collection time.
The leaves within the bottom four feet of a mature hop plant represent little value to the full grown hop plant, and for a variety of reasons it’s believed they can contribute to pest and disease on the yard. Therefore, it is advantageous to remove these leaves once the hop has reached it’s final growth height for the year. The conventional method for management is either via herbicide to kill of this growth, or manual stripping of the leaves from the plant.
The most notable outcome from our experiment is the sheep’s affinity for hop leaves. It was a hope that they would defoliate the bottom several feet of the plant, however, it was unexpected that they would so strongly seek out the leaves. It was observed that the animals would at times step onto each other to access leaves higher up on the plants after the bottom leaves had been consumed. It was also observed that the animals would step onto the wire fence to access hop leaves in the control plot. This ultimately led to an issue where the weight of the animals stepping on the fence would collapse the structure. During these times, the animals would leave the pen to access more hop leaves.
Hops continue to put out new growth heads throughout the year, which are commonly referred to as suckers. Their growth represents no value to our farm, but can act as distraction to the plant as it diverts energy away from the primary bines. Prior to the sheep’s arrival, the experimental plot had four to eight sucker bines per plant. These sucker bines had largely been stunted in the control plot through the use of herbicides.
The sheep acted as an effective control mechanism for sucker bines, as none were present in the experimental plot after the experiment.
Our evaluation of bine health encompassed all visible observations of the plant.
Downy mildew represented our largest pressure in years past, and it was expected to see it contribute to overall bine health observations in 2015. Notably, fungicides containing Copper are one of the major controls for Downy Mildew, but Copper’s toxicity to sheep did prevent the use of these products across the entire yard. Both the control and experimental plot were managed through the use of other fungicides, with only a brief lapse in their use in the experimental plot directly before and during the sheep being present. At year end, Downy Mildews effect on the control and the experimental plot did not differ, and it’s believed it did not strongly deviate from years prior.
Spider mites represented the biggest pressure to our bines health this year. Ultimately, spider mites led to a crop loss we estimated at 95% in this particular field This was a new pressure to our farm, and one that was improperly managed. It was recognized late and also sprayed very conservatively due to the presence of the sheep. The point where the spider mites were identified aligned with the first half of the sheep’s time on the farm. Our spraying routine that resulted was perhaps overly cautious due to our deep concern about doing anything that could harm the rented sheep. Even though the miticide that was sprayed was not listed with restrictions to animals such as sheep, application around the animals was not something we were comfortable with. To manage spray drift during application, we only applied pesticide to parts of the control plot that were well outside the range deemed safe for the sheep. This operational challenge was a product of having the sheep on the farm, and likely contributed to the significant loss of crop our farm experienced. When considering the involvement of sheep, or any animal in our management plans moving forward, we realized risks associated with our inability to react to diseases and pests the way we may be able to without animals on the farm.
Bine damage did directly result from the sheep’s presence as well. This occurred in two distinct ways. The first came from sheep chewing on the bines. While defoliating the plants the sheep would sometimes chew on the bine as well. It is also believed that when the sheep were left in a space that had sparse vegetation left, they would resort to chewing on the bines. Both behaviors were observed and later manifested in the death of a plant. The second way we observed the sheep damage hop bines was through their indiscretion when moving. Generally moving as a herd, the animals would walk into and often through the hop bines. This resulted in snapped bines, which ended the viable life of the bine for that season. Between these two contributors, roughly 8% of the bines in the test plot died prior to harvest, seemingly independent of other factors. It is believed that with unlimited vegetation and more space for the animals to move, both of these contributors would be reduced, and the loss of plants could be in a more tolerable single digit range.
The report we received from Ground Research reported 17 different broadleaf weeds in addition to the grasses present in the experimental plot. The sheep as a group consumed the all varieties of the weeds and grasses within each bay at a varying rate, ranging between 10 square feet per hour to 40 square feet per hour. This rate represents the cumulative effort of the six animals, and is derived from the amount of time they spent in each bay, and the total square feet the bay contained. This number is perhaps misleading though, as it is derived from the total square feet of the bay because the entire area was filled with grasses and weeds, while in a typical hop yard environment the high concentration of etables is really isolated to the three foot wide rows where the hops exists. The 12 foot spaces between rows would have a very loose density of weeds due to soil cultivation. When considering the consumption rate outside of our experimental environment, we would assume the the total square feet per acre eatable acreage would be 25% that of a typical pasture. This is quite valuable, as it could represent a 75% total reduction of time required of the sheep.
In our experiment, the sheep were removed from a bay after the weeds averaged two inches or less in height, as we wanted to ensure the animals had a continued food supply. The weeds that remained were heavily damaged by their continued contact with the animals. Most did not regrow for the remainder of the year.
Using the high end of the consumption range, 40sqft/hour or 960sqft/day, we are left with a consumption rate of .022 acres per day. This effort is from the 6 sheep, who averaged 45lb each, or a total live weight of 270lbs.
During the sheep’s time in the last two of the four bays, they learned that they could step onto the fence to get out and access the hop leaves of plants in the control area. The time they spent out of the fenced in bays is expected to be skewing the recorded rate of consumption lower in some cases.
Sheep Movement – Recap
There were four bays that the sheep occupied during the experiment. Each bay varied in size, and the time spent in each bay was based on the time it took for the sheep to consume all the weeds and basil foliage.
The sheep spent 22 hours in the first bay, which occupied 480 square feet. During this time the sheep were acclimating to the farm. As a group, the six sheep consumed at a rate of 21.82sq/ft per hour. They were moved to the next bay when the weeds were at an average height of two inches.
The sheep spent 24 hours in the second bay, which occupied 960 square feet. The sheep were more relaxed during this day, which is in part demonstrated through their rate of consumption which was at 40sq/ft hour. This bay was when we first observed the sheep’s gravitation towards the hop leaves. When first let into the bay, they ate all the hop leaves before then moving onto the weeds.
The sheep spent 72 hours in the third bay, which occupied 832 square feet. The rate of consumption calculated based on these numbers is 11.56sq/ft hour, which is not entirely accurate. This is because during the sheep’s time in this bay, they realized there were hop leaves outside of the bay walls. This resulted in several sheep stepping on the fence and creating a gateway to the rest of the hop yard. Two consecutive mornings were spent putting escaped sheep back into the bay, and performing fence repair. With the weed growth averaging two to three inches, the sheep were moved to the fourth bay to encourage the sheep to remain in the pen. These escapes are not part of our calculations for square feet per hour consumption, but we believe that a more accurate number could be closer to 30-40 square feet per hour.
The sheep spent 126 hours in the fourth bay, which occupied 1280 square feet. The rate of consumption fell to an all time low of 10.16 square feet per hour during this time. As with the third bay, we have a significant amount of unaccounted for time during this window of time, as a result of the sheep once again managing to escape their pen. The reason for escape was the same, the sheep were stepping on the fence to access the hop leaves that were in the adjacent rows. Escapes were a daily routine at this point, with half the herd (3) ending up outside the fence each time. Again, we were to estimate a “real” rate of consumption, it would be within a 30-40 sq/feet per hour range.
There are many aspects that compose healthy soil for our plants. For this experiment we focused on three of them; soil compaction, PH, and available nitrogen.
Soil compaction occurs when the soil particles are pressed together. This can lead to a reduction is water absorption, and drainage. It can also prevent beneficial soil aeration, and present challenges to plant growth penetration. To measure soil density we used a Humboldt Pocket Penetrometer, which measures penetration force in the units of tons per square foot. We tested both around the hop plants and the space between. What we found was a consistent average of 1.5 Tons per Sq Ft in both the control and experimental yard prior to the introduction of sheep. After the sheep were introduced, the experimental plots average was elevated to 2.5 Tons per Sq Ft, while the control stay constant at 1.5 Tons per Sq Ft. This compaction didn’t come as a surprise, and while no immediate consequences related to this were observed, we will be monitoring in the Spring to see if there is any noticeable impact.
PH saw a one tenth uptick in the control plot, and a two tenths up tick in the experiment, going from 5.8 to 5.9, and 5.5 to 5.7 respectively. This finding indicates that the time the six sheep spent on the yard had a weak correlation to an uptick in soil PH. If we were to consider scaling up the sheep’s involvement in our farm, we would want to study the impacts of their extending stay as it relates to PH.
As reported by their handlers at North Star Sheep Farm, no notable change occurred to the sheep’s weight or general health during their time on the farm.
Education & Outreach Activities and Participation Summary
Information related to our expirement and findings will be submitted for distribution during the University of Vermont 2016 Winter Hops Conference. In additional, to reach a wider audience we have produced a video summerizing our expirence, which will be deceminated across the social media platforms we manage. That video can be found at the follow URL, https://youtu.be/JlXQXdCj7_g
Our findings lead us to conclude that sheep do not represent a option of reduced cost for weed management on a one acre scale. However, due to the non-linear cost associated with several aspects of their management, there is potential that sheep could could lead to a reduction in annual input costs versus conventional weed management when scaled to a larger acreage.
Plant and soil health during the experiment maintained in close alignment. The exceptions being the soil compaction and bine damage received in the experiment plot. The effects of the soil compaction from the sheep will remain unknown until future growing years. However, the bine damage due to chewing and the sheep walking through the plants was immediately visible. This bine damage we believe to be in part due to the conditions we presented the animals in terms of pen size and food source quantity, and when properly managed it is believed they can be reduced.
Due to a pest infestation that dramatically diminished the marketability of the hops present in both the control and experimental plot, we were unable to properly compare the yield and quality of the hops grown.