Demonstration of reduced use of broadleaf herbicides in carrot crops through chemical banding and mechanical cultivation in Nova Scotia

Project Code PRR10-090

Project Lead

Donna Crawford  Horticulture Nova Scotia

Objective

To transfer and promote the adoption of herbicide banding technology as part of an integrated weed management approach that reduces the use of herbicides in commercial carrot production in Nova Scotia

Summary of Results

Background

In Nova Scotia, growers usually rely on broadcast applications of broad spectrum herbicides to control weeds in carrot crops. However, the frequent use of a few major herbicides may lead to the risk of weeds developing resistance to herbicides. The herbicide banding technology is an integrated management practice in which herbicide is sprayed either pre- or post-emergence only over carrot rows to control weeds in rows, and is combined with mechanical cultivation to eliminate weeds between carrot rows. A previous study conducted in Prince Edward Island showed that herbicide banding could provide significant weed control without compromising crop quality and yield, while reducing herbicide use by about 66% in carrot fields. By lowering the pesticide load, this approach can minimize the risk of herbicide resistance in weed populations.

This project consisted of on-farm demonstrations to further assess the commercial suitability of the use of banding herbicide technology on carrot farms in comparison to the conventional, broadcast application method. The goal was to determine the effect on weed management and yield, as well as the economic impact of the banding method.

Approaches

Demonstration plots were established in 2011, but abandoned as treatments could not be applied at appropriate times due to sustained wet weather. In 2012, plots were established again on three carrot farms in the province of Nova Scotia: Oxford Frozen Foods, Bragg Lumber Company, and Ueffing Farms. One demonstration trial was set up on each of these three farms. The banded treatment was performed with herbicide sprays 30 centimetres (cm) wide over the top of carrot rows and then followed by mechanical cultivation between rows. The broadcast treatment was performed by spraying the entire field with herbicide. For the banding herbicide treatments, there were 3-4 herbicide applications from late June to early August, including pre-emergence with Gesegard (4 Litres per hectare (L/ha)) or Lorox (0.75 L/ha) and post-emergence with Lorox (1.5 L/ha), followed by Venture (1 L/ha), and again followed by Lorox (2 L/ha) at 3-4 day intervals. Cultivation was carried out 3-4 times during the season at 7-10 day intervals. Measures of weed dry weight, percent carrot plant stand, carrot marketable yield, and carrot root length were used to evaluate the efficacy of the banding herbicide technology against the broadcast treatment. A field tour was held with growers and project team members to demonstrate the approach and discuss issues identified in the trials.

Results

The combined results from all 3 demonstration trials indicated that no significant differences were observed between the banding and broadcast treatments in weed dry weight, marketable yield and quality of carrots. In the banded treatments, carrot yield ranged from 28.8 to 51.5 tonnes/hectare (ha), while broadcast treatments resulted in yields ranging from 38.2 to 49.8 tonnes/ha. Actually, numerically the highest yield of marketable carrots occurred in one of the banded treatments.

Significant differences, however, resulted between the broadcast and banded treatments in plant stand percentage and carrot root length. The broadcast treatment provided higher carrot plant stands (approximately 50%) and shorter carrots (average 23.4 cm) compared to the banded treatment (42% in plant stand and an average of 24.1 cm in carrot length). This suggested that the banded treatment resulted in a poorer plant stand and bigger carrots.

The demonstration also showed that herbicide use in banded treatments was reduced by approximately 50%, compared to the broadcast application. However, the cost benefit analysis showed that in this demonstration the banded treatment was more expensive than the broadcast application method. The cost of banded treatment was $59/ha (dollars per hectare) (including $37/ha for the spray and $22/ha for the inter-row cultivation), while the broadcast treatment cost reached only $21/ha.

Discussion

By reducing the herbicide use to half, the banded treatment can slow resistance development in weeds. Herbicide resistance is especially a concern with linuron and with an industry that relies so heavily on this product, reduction of its use would assist in prolonging the efficacy of this product. However, the application cost of the banding technology in this demonstration was higher than the broadcast application, because of the reduced efficiency of the sprayer and the multiple cultivations. In banded treatments, the sprayer was much smaller and covered less area in a pass, thus requiring more passes and increasing equipment and labour cost. In addition, 3-4 mechanical cultivations required over the season further increased the cost of weed control in the banded fields. Yields were similar between the treatments, so yields could not offset the increased cost associated with the banding technology. In addition, two issues were observed in relation to the mechanical cultivation needed to complement the effect of banding treatments in these demonstration trials: first, the cultivation between the rows appeared to reduce plant stand and, secondly, cultivation may bring new weed seeds to the surface. This may result in a need for additional herbicide sprays between rows, which would likely defeat a reduced risk herbicide strategy.

For more information details on this project, please contact Marlene Huntley in Horticulture Nova Scotia.

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