Replacing Chemical Weed Control with Mulch in Commerical Blueberries

Final Report for FNC97-193

Project Type: Farmer/Rancher
Funds awarded in 1997: $4,980.00
Projected End Date: 12/31/1998
Region: North Central
State: Wisconsin
Project Coordinator:
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Project Information


Rush River Produce, a family run small fruit farm started in 1986, is one of the largest small fruit producers in the Upper Midwest and a major “ag-tourism” destination in the Mississippi River Valley. The main crop is 7 acres of blueberries, with one acre of fall raspberries, one acre of currants, and one acre of lingonberries. Sales of farm produce are all direct market U-picks, with a marketing area including Eau Claire, WI, Rochester and Minneapolis/St. Paul, MN. Rush River Produce also operates as a horticultural research facility – we are always looking at “new” crops with commercial potential (currants, lingonberries), at more efficient ways to grow our crops, and at other interesting horticultural projects.

We consider ourselves to be organic/sustainable agricultural producers who have made a few compromises with chemical use to be in business. Since beginning work on the farm in 1986 all our planning decisions have been made with long term sustainable production of quality fruit as a focus point. Chemical inputs have been minimized, soil quality and conservation have been emphasized, and innovative production practices have been developed as part of the Rush River Produce business plan.

The objective of this project was to eliminate or reduce the use of chemical herbicide on a commercial blueberry planting by producing and distributing wood chip mulch produced from weed trees growing on the farm. The specific goals of the project were:
1) Mulch up to two acres of blueberry plants using less than 500 man hours of labor
2) Design a system for safely producing and distributing the mulch material
3) Evaluate effectiveness of weed control
4) Evaluate the effectiveness of the mulch on growing conditions for the blueberry plants

The project was started in November, 1997, with the evaluation of available wood chipping technology and calls to several equipment suppliers. At about the same time a two acre section of unused over grown pasture was surveyed for weed trees. Quality hardwood trees such as oak, basswood, black cherry, ash, and maple were flagged for saving. Crowded trees were thinned and weed trees such as Siberian elm, poplar, box elder, and thorny ash were removed between mid November, 1997, and April 1998. The wood lot area thinned was in close proximity to the blueberry field to be mulched and cut trees were stockpiled in an area about 200 feet from the wood lot near the blueberry field. Mulch production and distribution began in February, 1998 and continued through the end of April, 1998. Project evaluation activities were conducted between May, 1998 and November 1998.

Determining the time and expense involved in producing the mulch is one of the main objectives of this project. A total of 154 hours were spent on mulch production and distribution related activities over the period of this project. This produced enough mulch to cover approximately ¾ acre of blueberry rows with mulch four feet wide and four to six inches deep, or approximately 250 cubic yards of wood chips. An additional expense in chain was and tractor equipment rental of $1,445 was used in the production of the mulch material. Cost of wood chips production and distribution was roughly $6.40 for labor (at $10/hour x 0.64 hours of labor) and $5.78 in equipment related costs per cubic yard of mulch. The cost of the chipper was in the $3,000 range - $6,000 per year if amortized over five years, for cost of $2.40 per cubic yard of wood chips attributable to the chipper. Total cost of farm produced wood chip mulch distributed on the blueberry plants is $14.58 per cubic yard.

A larger capacity chipper, something with a 9” to 12” maximum diameter, should have greatly reduced the cost per cubic yard of mulch. Using the largest capacity (5” maximum) chipper available in the $3,000 range, much of the wood removed from the wood lot was too large for the chipper. The volume of chips available from the larger diameter wood is much greater than what is available from small diameter wood. I would estimate that the project could have produced 600 to 800 cubic yards of wood chips for the same amount of effort and expense using a 9” capacity chipper as opposed to a 5” capacity chipper. A larger chipper might have produced mulch as 0.2 to 0.26 hours of labor and $1.80 to $2.40 in equipment expense per cubic yard. A larger chipper would have cost about $7,000 or $1,400 per year if amortized over five years, for a cost of between $1.75 to $2.30 per cubic yard of chips. Total cost of the mulching process would have then been in the range of $5.55 to $7.30 per cubic yard.

Wood based organic mulch material is available in our area for a cost of $4.00 to $9.00 per cubic yard delivered to the farm. It appears that purchasing delivered mulch is more cost effective than on farm production of wood chips under current market conditions, unless a larger capacity chipper is used.

Work area safety and efficiency are a major concern in on farm production of wood chips. The work involves extensive use of chainsaw and tractors in the woods. Tree cutting and removal is very arduous and inherently risky labor. Operating the chipper includes its own set of risks, even with adequate safety equipment. While no significant injuries occurred during the performance of this project there were a significant number of near misses as well as a number of minor scrapes and bruises. It is certainly labor intensive and one can easily underestimate the actual physical labor involved.

Perhaps one of the main safety issues was the result of timing project operations. Late winter/early spring is a slow time in our operation and seemed to be the best time to complete the project. However, the ice and mud that are common at that time of the year made the largest negative impact on safety of operations.

This project was conducted with safety in mind and was completed safely. The physical exertion, while extreme at times, was generally beneficial.

Distribution of the mulch material in a safe and efficient manner was of primary concern. Initially we planned to purchase a used silage wagon with bunker unloader to distribute the wood chips. Further research indicated that our farming operation lacked sufficient tractor horsepower to operate a silage unloader. That approach to wood chip distribution was abandoned and other mulch distribution options were investigated.

Initially the trees and branches were processed through the chipper directly onto the blueberry rows. This resulted in fairly good coverage with a minimum of hand spreading required. However, it did result in the wasting of a large quantity of wood chips that landed out of the target area. We decided, at that time, to get a larger tractor (35 HP) with a large capacity front end loader to move the wood chips with the loader and drove them to the appropriate area to dump and spread. This worked fairly well but left a lot of waste chips on the ground at the chipping stockpile site. Eventually we worked out a system of chipping the wood directly into the ladder bucket, after covering the bucket and chipper discharge with a section of snow fence to stop from flying out. This system worked pretty well with only slight waste of chips.

Weed control was the primary objective of this project. The wood chip mulch was distributed on the blueberry rows about four feet wide and four to six inches thick. Evaluations of weed suppression were made at approximately monthly intervals over the growing season. Early weed suppression in May and June was very good on all weeds except dandelions. Later in the season thistle and quack grass got though the mulch. The common annual weeds, including Foxtail, lambs quarters, and to a lesser extent, red root pigweed appeared to be effectively suppressed by the mulch. Over all weed population density was significantly reduced in the mulched areas. There appeared to be significant benefits to the blueberry plants from the mulch. Some random measurements of plants in the mulched area vs. the unmulched areas indicated that the blueberry plants were mulched had 10% to 15% more stem growth then blueberry plants in the unmulched areas at the end of the season.

Early suppression of break through perennial weeds, using directed systemic herbicide sprays, would have further reduced weed populations but the press of seasonal work on the farm did not allow us to implement that operation.

The effect of the mulch on blueberry plant growing conditions was very evident. In general, as stated before, blueberry plant growth was increased 10% to 15% in mulched rows. More specifically, soil erosion was nearly eliminated. Unmulched rows showed significant soil erosion due to several high intensity rain events in late May through early July. Mulched rows showed very limited erosion, and then only in areas of concentrated run off. Several mulched areas had significant runoff flowing over the mulch, but rather than washing the mulch away, the mulch filtered the soil from the runoff and the mulch ended up covered with soil.

Average soil moisture was increased in mulched areas vs. unmulched areas. While we did not make quantitative measurements sensory testing indicated that not only was the mulched soil damper than unmulched soil in the upper four inches, but that it was also less “sticky”. Our soil is a fairly heavy silt loam with a moderate clay and low organic content. Exposed soil crusts readily and balls tightly when squeezed. The mulches soils, in the four inches below the mulch player, were more friable, darker, and moister then untreated soils. We also noted that irrigation water, supplied from low flow drip line, spread much less over the soil surface in mulched rows as opposed to the unmulched rows. This indicates an fairly immediate increase in soil permeability from mulching, which should result in a significant reduction in irrigation requirements over the long term. Soil temperatures in the first four inches were also reduced significantly in mulched rows vs. unmulched rows. This benefits the blueberry plants both from reduced heat stress on the plants and from reduced irrigation requirements over the long term.

We were unable to directly measure soil organism populations other than earth worms. Earth worm populations were very low in unmulched areas, averaging zero to two worms per shovel full of dirt. Mulched areas sampled averaged zero to five worms per shovel of dirt. There was also significant fungal growth apparent in the mulch, both as fine hyphae in the mulch and as mushrooms emerging from the rotting wood chips. None of this fungal growth was noted in unmulched areas.

There was some initial concern that nitrogen requirements of mulch decomposition would reduce nitrogen available to the blueberry plants and limit growth of the plants. The mulched rows were supplied with the same nitrogen application as the rest of the field, approximately 60 lbs. actual N per acres banded on the blueberry rows.

Current plans are to continue the application of wood based mulch materials to commercial blueberries at this site, at higher rates than applied in this project, and to rely on spot application of systemic herbicides to for more effective weed control in mulched plots. The improvement in plant growth and reduction of soil erosion, due to improved soil condition, alone make the cost and labor of mulch application a good investment.

A field day, 5/23/98, was held in conjunction with River Country Resource Conservation and Development Council Farm Tour and about a dozen area farmers toured the project. A presentation about the project was given at Farm Progress Days, Menomonie, WI, 9/22/98. Several other individual project tours were given during the summer of 1998. We expect continued interest in the project and will continue to show interested parties the results for the foreseeable future.

Information gained from our participation in this project will be used in the next revision of the book “Growing Blueberries: a Guide for the Small Commercial Grower”. The book was written and published by the Cuddy’s in 1986. The next version is scheduled for late 1999.


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.