Mechanical Weeding in the Field - Star Hoe
1. Presentation
Characterization of the technique
Description of the technique:
The principle:
The star harrow is a mechanical weeding tool used in the open field. It has a mechanical action on weeds during germination – white filament stage – or at the cotyledon stage, and acts by uprooting or covering the weeds due to the friction and vibration of the teeth on the soil. It is used blindly in pre-emergence at 1 or 2 cm above the seedbed as soon as weed emergence is observed or on low-height crops (varies according to crops so that they can withstand the tool's action). It is effective on annual dicotyledons up to stage 2F and grasses up to stage 1F (see page 2 The star harrow, AgroTransfert) but ineffective on perennials and more developed weeds. It is an alternative to the use of pre- and post-emergence herbicides in crops. It can also be used to destroy false seedbeds and in this case represents an alternative to glyphosate use.
Conditions for success:
To succeed in weeding with the harrow star harrow, the seedbed must be flat, without large clods. Effectiveness is also maximized by dry soil conditions, avoiding heavy crusting (surface crusting) (the teeth do not penetrate the soil) and heavy soils. It is less effective in the presence of too many crop residues and in wheel tracks and tramlines. The presence of stones slightly reduces the tool's effectiveness, unlike the rotary hoe. The intervention must be followed by one or two days of dry and sunny weather to ensure desiccation of uprooted plants. To be effective, it is necessary to intervene on weeds from germination to stage 2-3 F at the latest. In pre-emergence, plan a maximum of two passes, as soon as a peak in weed emergence is observed. In post-emergence, count a maximum of four passes, depending on the number of days available (example: map for mechanical weeding of wheat in autumn). Seeding density should be increased by 10 to 15% to compensate for possible plant losses during harrowing. Also beware of the raking effect of crop residues, which if accumulated in front of the star harrow teeth may damage the crop.
Equipment:
The star harrow is equipped with long teeth (400 to 550 mm) and flexible (6 to 8 mm) mounted on articulated panels to follow the terrain. Its width varies from 6 to 24 m. The adjustment of aggressiveness aims to find the best compromise between weeding effectiveness and risk of plant loss. Aggressiveness is related to:
- Tooth inclination: the more vertical they are, the more aggressive they are towards weeds and crops. This must be considered according to soil condition, crop stage, and weed stage. Curved teeth, more aggressive, are less suitable for very stony soils.
- Working speed: the higher it is, the greater the aggressiveness. In pre-emergence, it is possible to go up to 15 km/h. In post-emergence, speed should be more moderate (4-12 km/h), especially if the crop is young to avoid damage.
- Working depth: by adjusting the position of the gauge wheels, from 1 to 2 cm in pre-emergence passes, 2 to 3 cm in post-emergence. Be careful not to set too deep to avoid promoting weed emergence.
There are harrows ranging from 6 to 24 m wide. A 12 m wide harrow allows a work rate close to that of a sprayer. Three tooth diameters are offered by manufacturers: 6-7-8 mm. Tooth length can vary between 400 and 550 mm (long teeth used in fragile soils or on delicate crops).
Details on the technique:
The star harrow complements other mechanical weeding techniques (rotary hoe, hoeing) or chemical methods which can be used in addition or as catch-up if intervention is difficult due to weather (example: see page 2 The star harrow, AgroTransfert).
The star harrow can be used post-sowing pre-emergence of crops, while weeds are at the "filament" stage.
Its use is generally discouraged between the emergence and one leaf (or hook) stage of all crops.
Used post-emergence, the star harrow must be used at precise stages depending on the crop:
Source: Mechanical weeding: the star harrow, Chambre d'agriculture Seine-et-Marne
It can also be used on oilseed rape (from 3 F to 6F / 1 cm ear), peas (from emergence to 6 F), soybean (from 1F to 4F/tillering), (sunflower 1F to 3-4F), on vegetable species or for maintenance of grasslands (but low penetration: use 8 mm diameter teeth, more aggressive).
For an example of implementation in a "fully mechanical" weeding itinerary on maize, follow the link to the trajectory sheet DEPHY-Ecophyto. For an example of implementation and its limits in "mechanical + chemical" itineraries, follow the link to the trajectory sheet DEPHY Ecophyto.
Implementation period
During intercrop
On established crop
Spatial scale of implementation
Plot
Application of the technique to...
All crops:
Easily generalizable
Technique adapted to many species, mainly arable crops and open-field vegetable crops. However, be careful not to intervene during sensitive crop stages (very young stages).
All soil types:
Generalization sometimes difficult
The effectiveness of the star harrow is limited in heavy, clayey or crusting soils and in plots with large amounts of plant residues which it tends to rake. Its use is much more appropriate on light or stony soils (alluvial, white soils, sandy soils, shallow soils).
All climatic contexts:
Easily generalizable
One to two dry days must follow the intervention to ensure weed desiccation.
Regulations
The acquisition of a star harrow for row crops is subject to a CEPP sheet (action no. 30: Weeding crops in rows using a mechanical weeding tool).
2. Services provided by the technique
see +
Weed regulation and management
The star harrow destroys weeds by mechanical action (uprooting, covering with soil). It has a selective action towards the crop thanks to the differential development between weeds and crop (the latter is better rooted) and because the rows of cultivated plants tend to spread the teeth of the star harrow. The use of a rotary hoe produces fine soil that improves the effectiveness of the star harrow. Effect level: MEDIUM if technique used alone, to be combined Confidence index: HIGH
COMPLEMENTARY TECHNIQUE(S)
Practicing mechanical weeding on inter-row - Hoeing
Practicing mechanical weeding in the open field - Rotary hoe
Performing false seedbeds during intercrop
Physical stability and soil structuring
The superficial soil work reduces runoff risk by improving soil aeration and breaks the surface crust that would have formed (formation of a new crust remains possible). The star harrow also improves precipitation infiltration into the soil and reduces capillary rise, limiting evaporation. Effect level: LOW, if technique used alone, to be combined Confidence index: MEDIUM
3. Effects on the sustainability of the cropping system
Environmental criteria
Effect on air quality:
Decreasing
pesticide emissions: DECREASE
GHG emissions: INCREASE
particulate emissions: INCREASE
Effect on water quality:
Increasing
pesticides: DECREASE
Effect on fossil resource consumption:
Variable
fossil energy consumption: VARIABLE
phosphorus consumption: NEUTRAL
Other:
No effect (neutral)
As an alternative to chemical weeding, the star harrow reduces the use of herbicides and thus their transfer to water and air.
Fossil energy consumption and GHG emissions: lien=|alt=yellow face size 10
Increasing, if multiple mechanical weeding passes and/or chemical catch-up are needed compared to a herbicide treatment. Required traction is 7 to 10 hp/m of tool width.
Agronomic criteria
Productivity:
Variable
Using a star harrow can cause plant losses of 5 to 15% if the tool is poorly adjusted and depending on crop stage and soil conditions. However, this loss can be compensated by increasing seeding density by 10-15%. Note that oilseed rape has a strong compensatory capacity and is therefore not sensitive to moderate plant loss. The same applies to winter cereals. More attention should be paid to plant loss risks for spring cereals, maize, and sunflower.
Product quality:
Variable
If the harrow pass is too late, it may affect vegetable crops whose leaves are harvested.
Soil fertility:
Increasing
Mechanical action promotes mineralization of soil organic matter and organic fertilizers, aeration, and soil warming. It improves placement of phosphate and nitrogen fertilizers. There is a reduction in runoff and erosion risk by increasing soil aeration.
Functional biodiversity:
No knowledge on impact
Mechanical tool passes may disturb surface fauna (macro/micro).
Other agronomic criteria:
Variable
New weed emergence:
The harrow pass, by stirring the soil at a shallow depth, promotes emergence of new weeds. However, these emerge later than the crop which exerts strong competition on them.
Economic criteria
Operating costs:
Variable
Impact is low, as increased fuel consumption is offset by reduced herbicide purchases. However, about 10-15% more seed is needed to compensate for plant losses.
Caution is needed in crusting silty soils as the star harrow pass can cause significant plant loss on young soybean and sunflower (four leaves) if the crust is too dry.
Mechanization costs:
Increasing
Requires an investment of about €3,500 for a 6 m wide harrow to €7,000 for a 12 m wide harrow.
Margin:
Variable
Effect on margin depends on the balance between increased and reduced costs. It is more relevant to compare a strategy using the star harrow (in a mechanical or mixed weeding itinerary) to an all-chemical approach than to evaluate the effect of adopting the harrow in isolation.
Example: on summer crops, 2 passes with star harrow and 1 hoeing cost between €30 and €40 per hectare versus €51 to €86 per hectare for all chemical (costs depend on working widths and products). The cost of star harrow pass is considered low.
Social criteria
Working time:
Increasing
Increase due to sometimes delicate adjustment, narrow tool width compared to herbicide treatment, and need for multiple passes, despite a high work rate (for a 9m star harrow: 5-8 ha/h in cereals and 2-4 ha/h on sensitive crops - maize, faba bean, etc.).
Peak period:
Variable
The technique requires intervention at a very precise stage, thus very likely during peak periods. Adjustments can be delicate and possible intervention windows may be short or even nonexistent some years.
Available windows for use between sowing and emergence are very limited on maize (see available days maps in the brochure Mechanical weeding of arable crops, page 57).
Observation time:
Increasing
Slight increase as it is important to observe weed development stage, crop stage, and soil drying conditions before passing the star harrow.
4. For more information
- Mechanical weeding of arable crops
- -Hélène Sicard, Laurence Fontaine et al ITAB - CASDAR project "Optimizing and promoting mechanical weeding" 2009-2011, Technical brochure, 2012 The brochure describes the basics of mechanical weeding common to all crops then details, crop by crop, the conditions for use of different mechanical weeding tools, their optimal conditions of use and their integration into mechanical weeding technical itineraries in organic farming.
- Alternative weeding guide for vegetables in Picardie Region. "Integrated Vegetable Production" program
- -Chambers of agriculture of Somme, Aisne and Oise. Agro-transfert Resources and Territories Ministry of Agriculture, Technical brochure, 2014
- Practical guide for designing vegetable cropping systems saving phytosanitary products. Technical sheet T14.
- -Launais M., Bzdrenga L., Estorgues V., Faloya V., Jeannequin B., Lheureux S., Nivet L., Scherrer B., Sinoir N., Szilvasi S., Taussig C., Terrentroy A., Trottin-Caudal Y., Villeneuve F. Ministry in charge of agriculture, French Agency for Biodiversity, GIS PIClég., Book, 2014
- Star harrow: uproots seedlings, even in stony soils
- -ARVALIS-Plant Institute, Website, 2018
- The star harrow
- -Agro-Transfert Resources and Territories, Technical brochure, 2011
- The star harrow
- -Chapuis S. LPC Bio, Technical brochure, 2013
- Star harrow pass on cereals
- -Chamber of Agriculture of Cantal, Technical brochure, 2016
- Presentation, settings and usage windows – Star harrow
- -CA17, Multimedia, 2017
- Reduction of phytosanitary product use: strategies implemented in the DEPHY FERME network - Arable crop-livestock sector
- -I. Félix et al. DEPHY Ecophyto, Technical brochure, 2018 The brochure describes 16 families of phytosanitary product use reduction strategies observed in different production contexts among farmers in DEPHY groups. Strategies 5 ("In arable crop systems, choose organic farming"), 9 ("In crop-livestock systems in maize/wheat, progress in mastering crop interventions without disrupting rotation") and 11 ("In livestock farms in western France, systems based on multi-species grazed grasslands for conversion to organic farming") illustrate various possibilities for integrating the star harrow into purely mechanical or mechanical+chemical weeding itineraries. They also highlight the tool's usage limits.
- How to adjust your star harrow
- -GAB - FRAB, Technical brochure
- Alternative weeding in market gardening - Curative measures
- -Ferrier J-D. Chamber of Agriculture of Ain, Technical brochure, 2016 See page 12
5. Keywords
Bioaggressor control method:
Physical control
Mode of action:
Catch-up
Type of strategy regarding pesticide use:
Substitution
Annexes
Est complémentaire des leviers
- Practicing mechanical weeding in the open field - Rotary hoe
- Practicing mechanical weeding on inter-row - Hoeing
- Performing false seedbeds during intercrop
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