A Comparison of Weed Control Strategies in Christmas Tree Plantations Using Mechanical and Chemical Methods or Shropshire Sheep

View the project final report

Commodities

• Agronomic: clovers, grass (misc. perennial)
• Additional Plants: trees
• Animals: sheep

Practices

• Animal Production: grazing - rotational, stocking rate
• Crop Production: silvopasture
• Pest Management: Weed Management
• Production Systems: integrated crop and livestock systems

Allocating time, space, and labor on our farm is a constant challenge, as each is limited. Land dedicated to one enterprise limits the second enterprise. For example, reserving land for sheep pasture eliminates the ability to plant more Christmas trees, while a field exclusively growing trees limits sheep numbers by removing grazing area. This dilemma applies for time, as well. Time spent maintaining trees could be spent providing for the flock, and vice versa. Labor is spent both removing weeds in trees and manually providing food for sheep.

Incorporating sheep into our Christmas tree operation maximizes efficient use of these finite resources. Combining the two operations as a solution seems evident, but little comprehensive data exists describing the successful integration of sheep and Christmas trees. This study provides information on infrastructure, methods, and material and labor costs of grazing sheep compared with conventional methods for suppressing weeds on Christmas tree farms.

The focus on suppressing weeds was chosen because of the constant challenge Christmas tree growers face with various grasses, legumes, or forbs competing with pines, firs, and other conifers. Research into Shropshires, one of the sheep breeds we raise, revealed the breed is used in Europe to graze in orchards, vineyards, and Christmas tree plantations. The potential to reduce labor and input costs for weed management was high. Therefore, we designed our study to analyze if Shropshires grazing in Christmas trees could be beneficial in the United States, as well.

This study divided one acre of Christmas trees into two half-acre patches. One patch served as the control with conventional weed control practices of mowing, mulching, and spraying herbicide. In the second patch, Shropshires grazed within the trees to eat weeds. Material and labor costs for both methods were measured. Material costs included equipment and inputs. Labor costs were calculated at $25 per hour and were measured for tasks related to either sheep or Christmas trees.

Combining sheep and Christmas tree operations is indeed possible, but actively managing the correct breed of sheep in the correct tree species is essential. 

Combining these operations is financially advantageous. Overall cost savings for sheep grazing for weed mitigation in Christmas trees become apparent after only a few seasons. Although upfront expenditures for the sheep grazing system were comparatively high, the equipment can be used indefinitely. Costs for fuel, herbicide, and other items needed for conventional weed control are recurring and nonrecoverable, thus negating the initial savings over time.

During the first year of the study, sheep labor costs were higher than labor costs for conventional weed control due to the learning curve for netting placement, rotation durations, and sheep behaviors in the trees. However, during the second year, sheep labor costs decreased because patterns for grazing and paddock lay-outs had already been established.

Findings also showed tree species matters when grazing sheep, with fir species undisturbed as long as there was plenty to eat. Eastern white pines attracted the sheep, who consumed the needles. Sheep enrichment activities were also needed. Ewes could rub their heads against larger trees, causing damage that could limit tree marketability. To mitigate this, we placed scratch brushes on the water wagons.

Study results were shared through conference presentations, a podcast recording, and media interviews. A guidebook, Grazing Sheep in Christmas Trees: A Guide for Shepherd and Tree Grower Success, was created to help both sheep producers and Christmas tree growers succeed in intercropping.

Results also were shared through one-on-one conversations with other Christmas tree growers, with some showing interest in grazing sheep in their own operations. Shropshire breeders who heard about our study became interested in promoting the breed for the purpose of grazing in an intercropping system.

Grazing sheep in Christmas trees is rewarding, cutting down on the amount of time spent on the mower. When sheep producers or Christmas tree growers face limited time or land access, intercropping with sheep and trees can be a good solution to solving those two obstacles. There are some challenges and a learning curve, but with patience and careful observation, grazing Shropshire sheep in Christmas trees while still growing a marketable Christmas tree is possible and enjoyable.

Solution: 

As a solution to our limited time, labor, and land, we combined elements of our Shropshire sheep and Christmas tree (Canaan fir, Abies balsamea var. phanerolepis; and Concolor fir, Abies concolor) operations and examined how they could each benefit the other. We grazed sheep in a section of our Christmas tree stand so they could eat weeds.

Within Christmas tree plantations, weed control is an ongoing challenge throughout the growing season. Dense, tall vegetation can stunt, if not kill, the trees by robbing nutrients and moisture that the trees need. However, this vegetation is an unused resource that could feed livestock. Grazing sheep within the trees could potentially reduce time and labor for controlling weeds and feeding sheep. Our research trial examined the labor and material costs of sheep grazing versus the labor and material costs of mechanical and chemical weed control in a Christmas tree plantation.

Sheep can provide fertilizer, as well, and potentially reduce the labor and costs of mechanically and chemically controlling weeds. The symbiotic relationship saves on sourcing other forage and minimizes, if not eliminates, chemical and mechanical weed removal.

For our trial, we designated two areas in our acre of 800 second-year trees. In our control area, we managed weeds with the traditional control methods of mechanically mowing, spraying herbicide, and spreading mulch or compost around the base of the trees. In our experimental area, Shropshire sheep graze amongst the trees in a rotational grazing system.

Our methods measured the amount of time that we spend with each weed control method. For conventional weed control, we will measure the amount of time used to mow, apply chemicals, and mulch the trees. We will also analyze the cost of materials for mechanical and chemical methods.

For sheep grazing, we analyzed the cost of materials and measured how much time is used to set up paddocks with solar-powered temporary netting, move the sheep, and provide daily care and feeding. While we used Shropshire sheep, which have a good reputation for working among tree plantations, the sheep needed to be moved as soon as they exhausted their forage to mitigate the possibility of damage to the trees. 

The following materials were needed:

For the sheep grazing area:

1. Shropshire sheep
2. Netting
3. Solar charger
4. Trail cam
5. Water wagon and tanks
6. Supplemental feed
7. Feed/mineral feeders
8. Shade
9. Fly control
10. Portable corral gates
11. Scratch brushes

For the chemical and mechanical control:

1. Herbicide
2. Chemical sprayer
3. Mulch or compost
4. Mower

The sustainable agriculture practices used included rotational grazing and intercropping.

Objectives: 

Our objectives centered on discovering what symbiotic relationship can exist between sheep and Christmas trees and sharing the results of our research trials with other Christmas tree growers who will benefit.

• Determine how many days sheep can graze within a Christmas tree plantation without disturbing the trees
• Evaluate two systems of weed control in Christmas trees
• Share findings through presentations and a guidebook for grazing sheep in Christmas trees