Cover crops and zone tillage for reduced risk weed management in field vegetables in eastern Canada

Project Code PRR11-030

Project Lead

Diane Lyse Benoit  Agriculture and Agri-Food Canada

Objective

To evaluate the efficacy and cost benefit of various zone tillage and cover cropping techniques for weed control in cucurbits, cole crops and sweet corn in Nova Scotia, Prince Edward Island, and Quebec

Summary of results

Background

Optimal weed management is essential for viable vegetable production in Canada and it relies mainly on considerable use of synthetic herbicides. Non-chemical weed control options were needed however, to help growers transition away from full reliance on herbicides and minimize the risk of weeds developing resistance to chemicals.

Some weed suppression approaches using cover crops were successfully tested elsewhere; however these needed to be tested under Canadian vegetable production conditions before recommending for use by growers. This 3-year project aimed to identify the best cover crop management techniques with greatest weed control efficacy, highest potential to reduce herbicide use and potential for grower adoption.

Approach

A total of 10 field trials were conducted across Quebec, Nova Scotia, and Prince Edward Island over three growing seasons in 2011-2013. Approaches assessed included: a) the use of fall rye as cover crop; b) spring band tillage, oat banding, or deep zone tillage as techniques to create a clear band with no vegetation for allowing seeding of cash crop within the rye cover crop in the following spring; and c) roller-crimping, with or without application of half rate glyphosate (450 grams of active ingredient per hectare) sprays as means to destroy the cover crops. Cover crop treatments were compared to: i) standard conventional weeding practices; ii) hand weeding; and iii) a weedy control.

In all treatments, rye was used as dead plant-based mulch and was seeded in the fall prior to the trial and assessment year. The following spring, when rye was at half anthesis stage (# 61 in the BBCH scale of phenological identification key for cereals), typically 105-125 centimeters (cm) tall, it was mechanically destroyed by using a rolling crimper to lay the plants flat over the soil surface. In some cases, prior to mechanical destruction the rye canopy was sprayed with glyphosate to accelerate with the kill. Then the cash crop was direct seeded (no-till) or transplanted into the rye residue. Trials with spaghetti squash and sweet corn were conducted at Agriculture and Agri-Food Canada's (AAFC) research farm in Saint-Jean-sur-Richelieu, Quebec, trials with transplanted broccoli were conducted at AAFC research farm in Charlottetown, Prince Edward Island, whereas trials with butternut and buttercup squash at two growers’ fields in Lakeville and Canning, Nova Scotia. The combination of treatment approaches varied among the crops tested in various locations. 

Oat banding, a newly introduced technique for creating a clear seeding zone, was used in some of the treatments. This technique consists of simultaneously seeding a 30 cm wide band of oats within the rye plot in the fall, spaced to coincide with the rows where the cash crop will be planted the following year. The oats germinate in the fall at the same time as rye, but will not survive the winter, thus creating a zone with no vegetation the following spring. This technique was adopted to facilitate direct no-till seeding of spaghetti squash within the rye cover crop in the spring.

In other trials, mechanical banding techniques was achieved by: a) cultivating a 30 cm wide strip using goose type shanks equipped with residue removers or vertical rototiller (for spaghetti squash trials); or b) deep zone tillage obtained by using a Zone Builder machinery equipped with subsoilling tooth, coulder disk and debris remover unit to create a 15 cm clear band tilled to a depth of 30-35 cm (for butternut and buttercup squash trials).  

Assessments included comparisons of cover crop biomass prior to rolling, weed cover during the growing season, herbicide use, economics and crop yield for each treatment.

Results

Rye cover crop was not effective as a weed management method for sweet corn and transplanted broccoli in this study and data resulting from these trials are not included.

In contrast, rye appears promising as an alternative weed management approach in squash crops. Obtaining a sufficient amount of cover crop biomass that results in heavy residue completely covering the soil surface (greater than 7 metric tons per hectare) in spring was found to be critical for optimal efficacy of this practice. Such biomass was achieved by using high seeding rates (150-190 kilograms per hectare) in the fall and a good fertilisation regime in early spring. Cover crops prevent weed germination by physically preventing light and small seed weeds from reaching the soil. Rye was especially efficacious against annual broad-leaf weeds.

Spaghetti squash: Overall, the use of a rye was an effective weed management approach in spaghetti squash production, leading to less than 10% weed cover, and proving more effective than the conventional method which resulted in 12 to 25% weed cover. This represents a 65 to 90% reduction in weed cover compared to the weedy control when using rye as cover crop. Spraying rye with half rate glyphosate prior to crimper rolling resulted in additional reduction of weed cover. Generally, rye cover crop treatments increased marketable yield of spaghetti squash by up to 27% compared to controls in a dry year such as 2012 but decreased marketable yield by 21% in a wet year such as 2013. The use of glyphosate on rye prior to rolling crimper resulted in significantly greater marketable squash yield by as much as 28 to 56%. While the use of glyphosate increased weed control cost on per hectare basis, it reduced the cost on per marketable yield basis since greater yields were obtained. The use of glyphosate is not essential for the success of this technique but it can help with faster and consistent kill of rye and given the other benefits, it may increase the attractiveness of this practice to growers.

Butternut and buttercup squash: Rye cover crop combined with deep zone tillage and glyphosate treatments may also offer an acceptable alternative for weed management in butternut and buttercup squash production. This combination reduced weed cover in some years and resulted in yields equivalent to the commercial standard for both butternut and buttercup squash crops. Application of clomazone as a banded pre-emergence weed control spray over the deep zone tilled rows may also be beneficial to improve weed control or increase squash yield. The use of deep zone tillage in rye cover crop, with or without herbicide is recommended for squash production in Nova Scotia.

Overall, all squash production can benefit from rye cover crop since squash grown on rye mulch are generally cleaner at harvest and have reduced disease symptoms.

Recommendations which flow from the project include a number of equipment modifications (e.g. adapting a cereal seeder), as well as a new cover crop management technique (oat banding) necessary for optimal use of this practice in the field. The adapted seeder allows simultaneous seeding of oat in bands within the rye plots and oat banding technique eliminates the need of pre-emergence herbicide in spaghetti squash production.

This project was an example of a successful collaboration of AAFC scientists with academia and provincial specialists. Through numerous field days and presentations, the project team has informed and educated growers about the benefits of using cover crops as part of an integrated weed management program.

For more details please contact Dr. Diane Lyse Benoit or Dr. Vicky Toussaint   

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