Weed control

Weed control involves combating the development of weeds, the presence of which is detrimental to sales crops. These plants, introduced unintentionally, can slow crop growth and cause yield losses because they compete with crops for resources (light, water, minerals, etc.) or because they produce chemical substances with allelopathic effects. The presence of weeds can also be problematic at harvest time, as they can cause impurities and alter the moisture content of the harvested crop.

Preventive weed control involves agronomic levers such as the choice of crop species, the length of rotations, sowing density, etc.

Working the soil

Ploughing: buries weeds present before sowing to a depth where they cannot germinate. Ploughing should be as shallow as possible (between 20 and 25cm deep). It is only effective if it is intermittent (between 2 and 3 years between each ploughing), as a second ploughing too early could bring the seeds to the surface and cause them to germinate.

False seeding: destroys the regrowth of annual weeds that emerge after harvesting. False seeding also makes it possible to get as many weeds as possible to emerge with several passes before destroying them (passes spaced 10 to 15 days apart). Various tools can be used, such as stubble harrows or disc harrows.

Rotation

Grassland (or alfalfa) limits the development of weeds through a "cleaning" effect, as it prevents seeds from emerging for several years.

Alternate sowing dates and diversity of species grown in the rotation: prioritise 2 spring crops followed by 2 autumn crops and not just winter or summer rotations.

Cultivation methods

Sowing density and spacing

Shifting the sowing date (later than the optimum range): effective for winter cereals, on ryegrass (Lolium perenne) and vulpine (a 10-day shift in October can reduce ryegrass, vulpine and bromegrass emergence by 50 to 75%).

Intercropping cover and sowing under cover (permanent or annual)

Mechanical weeding with a rotary hoe, a curly harrow or a curly rototiller

Keeping plots clean

Preventive" treatments (to avoid contamination of plots) :

Treating the edges of plots: prevents the infestation from spreading to the whole plot
Clean the combine harvester, which may contain weed seeds
Manual weeding of the first outbreaks, which is a more cost-effective method than tillage and herbicides on a fully contaminated plot.

Other levers

Weed control: application of a herbicide to the row and hoeing in between the rows. This technique is mainly used for sowing weed crops: maize, sunflower, soya and rapeseed.^[1]

Thermal weeding (market gardening): reduces seed germination potential ^[2]
Green manure: a soil-covering crop intended either to be ploughed in green on the spot, or left on the spot as a protective mulch for the following crop. It helps to limit weed populations and can be used in arable crops, market gardening, vineyards and vineyards.^[3]

There are many curative methods for destroying weeds, before or after sowing: weeding by hand, using mechanical farm tools or robots, using chemical products(herbicides), covering the soil or using thermal (solarisation, flames, infrared) or electrical processes. Grazing animals also helps to limit the development of weeds.

Integrated weed management, which combines several weed control methods, aims to reduce the use of synthetic herbicides.

It is also possible to optimise weed control thanks to our knowledge of weeds, which enables us to target and use control methods more judiciously.

The first step is to return to sites such as Infloweb, etc. to re-acquaint yourself with the basics of the weeds to be eliminated. Then you need to look at the properties of the weeds in order to adapt the control methods.

Annual Decline Rate (ADR)

The ADR corresponds to the percentage of seeds that will no longer be able to germinate after one year. The higher the ADR, the shorter the lifespan of the weed^[4]

TAD of several weeds

Ploughing mainly targets weeds with a high TAD. To target weeds with low TAD, it is necessary to combine several levers (rotation, ploughing, temporary grassland, etc.^[5]

Depth of emergence

Most seeds are present in the first 2 cm of soil and can germinate up to 5 cm deep.

There are a few exceptions:

Vulpine, ivy-leaved speedwell and wild buckwheat, which can germinate up to 10 cm deep.
Wild oats, which can germinate up to 30 cm deep

Period of emergence

Annual weeds are characterised by emergence periods that are specific to each species. Some emerge over a relatively short period (e.g. vulpine, which emerges in autumn and winter) or over a very long period, or even all year round (e.g. annual bluegrass).

Stubble ploughing or false seeding should be carried out according to the type of weed targeted and at times when it is not likely to germinate.^[3]