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Results from the Pesticide Risk Reduction Program

Carrot production on raised beds - Reduced risk weed control strategies

Carrots in many regions of Canada are produced on raised beds. Such practice requires high levels of herbicide inputs in order to achieve adequate weed control over raised beds. Weed control is primarily dependant on broadcast applications of mainly three broad spectrum soil herbicides (linuron, trifluralin and prometryn) as carrots are considered poor competitors. Resistance to linuron has been documented in Quebec and Ontario for two major weeds: green pigweed and common ragweed. This can limit the control options available to growers for effective weed management in carrots.

Introduction

Technological advances in physical weed control may allow the adaptation of practices such as stale seed­bed, shallow tillage or propane flaming as means to reduce herbicide inputs in carrot production on raised beds and delaying resistance development.

In general, cultural and physical weed control practices do not provide high levels of control individually but combinations of methods can provide economically viable weed control. Each practice has its advantage within a crop production (Table 1).

Research was conducted in 2007 and 2008 at the Harrington Research Farm, which is part of Agriculture and Agri-Food Canada's Crops and Livestock Research Centre in Prince Edward Island, with the financial support of the Pest Management Centre's Pesticide Risk Reduction Program.

Trials, conducted on mineral soils, compared weed control and crop yield under recommended broad­cast linuron applications with different combinations of banded chemical sprays and propane flaming or shallow cultivation in either stale seedbed or direct seeded situations. These combinations are summarized in Table 2. The stale seedbeds received one pass of the basket weeder just prior to planting to loosen soil which may have crusted and for weed control.

Table 1. Cultivation practice, intended use and impact
Cultivation practice Technique Target use in carrot Purpose
Stale seedbed in combination with basket weeder Cultivation practice: Stale seedbed in combination with basket weeder
  • Control weeds prior to planting crop
  • Break soil crust
Replace linuron applied pre-emergence
Banded linuron Cultivation practice: banded linuron
  • Applied pre and/or post crop emergence
  • Control weeds in a narrow band over crop row
Reduce amount of linuron applied
Banded flaming Cultivation practice: Banded flaming
  • Applied preplanting or pre-emergence to crop or both to control weeds
Replace linuron applied pre-emergence
Banded acetic acid Cultivation practice: Banded acetic acid
  • Applied post emergence to weeds and pre-emergence to crop
  • Control weeds over crop rows
Replace linuron applied pre-emergence
Tillage with side knifes Cultivation practice: Tillage with side knifes
  • Applied post-emergence to weeds
  • Control weeds on sides of raised bed
Complements cultivation
Tillage using S-tines with or without duckfoot Cultivation practice: Tillage using S-tines with or without duckfoot
  • Applied post emergence to weeds
  • Control weeds in-between carrot bed
Complements cultivation

Table 2. Treatment combinations, the number of equipment passes
associated with each technique and respective costs
No. Treatment Combination Bed
preparation[1]
No.
passes for
weed control
No.
passes for
cultivation
Cost
($/ha)[2]
Cost
($/T)[6]
[1] Planting = beds shaped just prior to planting; Stale seedbed = beds shaped 2 wks prior to planting.
[2] Estimation according to "Machinerie, Coûts d’utilisation et taux à forfait suggérés, AGDEX 740/825, Avril 2006, Corrigé Septembre 2006, section 7,2" (Centre de Référence en Agriculture et Agroalimentaire du Québec). The estimates are based on yearly use level, 15 years economic life, 300 hours of utilization per year, Tractor 14,4kW + operator (15$/h), negligible cost for weeders (small unit) width of work corrected to effective width of application, adjusted with fuel cost of 0,95$/L and adjusted with propane cost according to trial conditions and actual price (0,8414$/L, propane, March 8 2009).
[3] Linuron broadcast PRE at 600 and POST at 1185 g ai/ha when carrots were 8-15 cm tall; linuron banded PRE and POST at same rates; banded width over the rows in all cases was 30 cm. Propane consumption was 120L/ha applied at 4 km/hr.
[4] Cultivation = S-tine cultivation; tillage with side-knives was done on the sides of the hills with 1 pass at 2 km/h 2.5 cm from the carrot row followed by a second pass at 10km/h 10 cm from the carrot row.
[5] Acetic acid applied at 6.25%.
[6] Treatment cost per marketable yield.
1 Weedy Check Planting --- --- 51.87 4.46
2 Broadcast Linuron[3]
pre & post-emerge
Planting 2 --- 327.43 5.36
3 Banded Linuron
pre & post-emerge + cultivation[4]
Planting 2 2 365.81 6.53
4 Banded Linuron
pre & post-emerge + side knifes & S-tine with duckfoot
Planting 2 2 400.43 7.96
5 Flaming pre-emerge + cultivation Planting 1 1 293.56 13.29
6 Flaming pre-emerge
+ side knifes & S-tine with duckfoot
Planting 1 1 310.92 13.85
7 Weedy Check Stale seedbed --- --- 59.84 13.51
8 Broadcast Linuron
pre & post-emerge
Stale seedbed 2 --- 335.40 5.80
9 Banded Acetic acid[5]
preemerge + cult.
Stale seedbed 1 1 1179.14 51.31
10 Banded Acetic acid
pre-emerge + side knifes & S-tine with duckfoot
Stale seedbed 1 1 1196.50 40.45
11 Flaming preplant & pre-emerge + cultivation Stale seedbed 2 2 543.22 22.26
12 Flaming preplant & pre-emerge + side knifes & S-tine with duckfoot Stale seedbed 2 2 577.94 24.81

Results

Overall, stale seedbed practice combined with raised beds had more weeds on the top than beds prepared at planting (Figure 1). Linuron or acetic acid banded over the top of the bed reduced weed biomass comparable to linuron applied broadcast (commercial standard). Banded linuron gave the highest weed control and carrot yield (Figure 2). Propane flaming was not as effective as the herbicides in weed biomass reduction on top of the bed primarily because it had no residual activity. Cultivation with side knifes was effective at weed removal only on the side of beds but it was less favoured over cultivation with tines because tines allowed for faster field operation. Banding treatments reduced the cost for both herbicides (linuron or acetic acid) and flaming use. The large volume of acetic acid applied makes this treatment uneconomical. Similarly, pre-emergence flaming resulted in a low carrot yield. More precise application with better crop safety is required before pre-emergence flaming or acetic acid is to be recommended.

Figure 1. Effect of reduced risk weed control practices on weed control on the top and sides of the carrot bed in July (mean of 2007 and 2008). Standard = broadcast linuron; Banded = herbicide applied in 30 cm wide band directly over the carrot row; Knives = side knives; Lin = linuron; S+Duck = S-tine + duckfoot; 2wk Stale SBed = 2 weeks old stale seedbed; AA = acetic acid.

Description of this image follows.
Description - Figure 1

Figure 1. Effect of reduced risk weed control practices on weed control on the top and sides of the carrot bed in July (mean of 2007 and 2008).

This figure is a horizontal bar graph comparing the total dry weight of weeds in g per meter squared from different practices used to control weeds in raised carrot beds. The dry weight of weeds collected from the sides of the beds, and the dry weight of weeds from the top of the beds are provided separately. The data is presented on a logarithmic scale ranging from 0 to 9537 g per meter squared.

There are twelve treatments appearing in the graph, 6 used beds shaped just prior to planting and 6 used the 2 week old stale seedbeds. For the 6 of each type the following treatments were used: a check; the standard; banding linuron and the S-tine; banding linuron, side knives and the S-tine with the duckfoot; banded flame and the S-tine; and banded flame with the side knives and the S-tine with the duckfoot. These same treatments were also used for the 2 weeks old stale seedbed technique for a total of twelve techniques.

All treatments provided similar or better levels of control for weeds on the side of the bed compared to the standard.

For beds prepared at planting the banded flame with S-tine and the banded flame with side knives and S-tine with duckfoot has similar weed yields on top to the check. Both banded linuron treatments had weeds on top comparable to the standard.

For treatment with the 2 week old stale bed technique all had similar yields of weeds on top to the check.


Figure 2. Effect of reduced risk weed control practices on carrot yield (mean of 2007 and 2008). (Marketable = carrot diameter >19 mm).
Standard = broadcast linuron; Banded = herbicide applied in 30 cm wide band directly over the carrot row; Knives = side knives; Lin = linuron; S+Duck = S-tine + duckfoot; 2wk Stale SBed = 2 weeks old stale seedbed; AA = acetic acid.

Description of this image follows.
Description - Figure 2

Figure 2. Effect of reduced risk weed control practices on carrot yield (mean of 2007 and 2008). (Marketable = carrot diameter >19 mm).

This figure is a horizontal bar figure comparing the yield of carrot by tonnes per hectare for different practices used to control weeds in raised carrot beds. The total yield and the marketable yield are presented separately. The scale ranges from 0 to 100 tonnes per hectare.

There are twelve treatments appearing in the figure, 6 used beds prepared prior to planting and 6 used 2 week old stale seedbeds. The 6 practices using beds shaped just prior to planting were: a check; the standard; banded linuron and the S-tine; banded linuron, side knives and the S-tine with the duckfoot; banded flame and the S-tine; and banded flame with side knives, and the S-tines with the duckfoot. The 6 practices used following the 2 week old stale seedbed treatment were: a check; the standard; banded acetic acid and the S-tine; banded acetic acid, side knives, and the S-tine with the duckfoot; banded flame and the S-tine; and banded flame with the side knives and S-tine with duckfoot.

The check for both had the lowest marketable yield. The standard had the highest total yield and marketable yield. All the banded linuron treatments were very close to the marketable yield for the check. The banded flame and acetic acid provided approximately half of the yields of their corresponding checks. All treatments provided higher yields than the checks.

Summary

The weed control alternative with the greatest potential in reducing the amount of herbicide used while providing acceptable control efficacy and yields is the one where banded application of linuron over the carrot bed is combined with mechanical cultivation using side knives and duckfoot cultivators between the raised beds. The cost difference between the proposed practice and the commercial standard is negligible but the environmental benefits are of major importance. Banding herbicide on top of the bed reduced herbicide use by 66%, thereby reducing environmental impact. This helps reduce the herbicide load in the environment especially on sandy loam soils, low in organic matter, on which most of the carrots are produced.

For more information, please contact:

Kevin Sanderson, P.Ag. Research Scientist
Agriculture and Agri-Food Canada
Crops and Livestock Research Centre
Charlottetown, PE
kevin.sanderson@agr.gc.ca

or

Dr. Diane Benoit, Ph.D., Research Scientist
Agriculture and Agri-Food Canada
Horticulture Research and Development Centre
Saint-Jean-sur-Richelieu, Québec
dianelyse.benoit@agr.gc.ca


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