Weeding in maize

Adapting your weed-control strategy in maize: combining herbicides and mechanical weeding to combat weeds

Maize, the classic spring crop, is particularly well suited to mechanical weeding. Being sown in wide rows (50 to 80 cm), it is highly flexible in terms of weeding strategies, whether chemical or mechanical.

In dry years, when herbicides are less effective, row-crop cultivation is very effective. In addition to controlling weeds, it provides numerous agronomic benefits, such as preserving moisture in the soil and enhancing the mineral content of nutrients.

To ensure the success of mechanical weeding, however, it is essential to control perennials before planting the crop. Otherwise, row-crop cultivation can split the rhizomes, causing them to spread.

Problem weeds in maize: 

• Ragweed
• Datura
• Bindweed
• Mercuries
• Summer grasses (panic grass, foxtail, crabgrass) 
• Resistant ryegrass
• Knotweed
• Xanthium

What agronomic levers to implement as part of the weed-control strategy in crops? 

A long intercrop period, several possibilities

The long period before planting maize gives you time to prepare the plot. Combining cover crops with successive stubble-cultivation operations before planting the crop can reduce seed stocks and perennials as well as improving the structure of the soil.

Stale seeding is a very popular technique with maize farmers. It is very effective in the right conditions. Indeed, it can reduce weeds by 60% when carried out at the end of March/beginning of April.

*Désherbage mixte, l’alliance du chimique avec le mécanique, Chambre d’agriculture des Hauts de France, 2022

Modifying the seeding date of maize can impact yield negatively. However, it is possible to delay it slightly to desynchronise weed emergence in order to kill them before seeding. With a maize crop, it is better to sow late rather than early. 

Comparison of different weeding methods carried out by Arvalis at several different sites in France:

• Acceptability threshold for effectiveness is at 7
• Pre-emergence = chemical application before maize emergence
• Post-emergence = chemical application between 2-leaves and 6-leaves stages

Possible treatment periods depending on mechanical weeding tools

Weed-control programmes for maize

🟠optional 🟢essential 💦chemical ⚙️rotary hoe or ↘ tine weeder

Purely chemical 

There are several different ways of weeding maize. Pre-emergence root herbicides are the most effective against grasses (vulpine and ryegrass). A single application of pre-emergence herbicide may suffice to control weeds until harvest.

If it is not possible to treat the plot at the pre-emergence stage, alternative post-emergence solutions exist. The treatment is less effective on mature weeds, however, so it is better to take action early on. 

In case of late weed emergence, treatment is possible up to the 8-leaf stage of the maize crop. 

Mixed strategy, against difficult dicots and grasses 

The pre-emergence / early post-emergence strategy is very effective against grasses and difficult dicots. To limit weed development before the summer, several passes with a row-crop cultivator are a good solution, even past the 6-leaf stage of the maize crop. Depending on conditions, a chemical product can be added as a complement. 

Mixed strategy, with a tine weeder and a rotary hoe 

When dealing with simple weed flora, chemical intervention can be delayed until the 3-leaf stage. Several mechanical interventions, using a tine weeder or rotary hoe, can be carried out pre-emergence, or post-emergence at the 2- to 3-leaf stage of the maize. 

Purely mechanical 

Repeated interventions with a rotary hoe, tine weeder, and row-crop cultivator make it possible to control weeds in maize without using herbicides, thereby reducing TFIs.

The organic trick for successful row-crop cultivation

Maize does not like being covered with soil, so it is necessary to go carefully with the first row-crop-cultivation interventions (reduced speed, plant protector). However, it is beneficial to create a ridge before row closure: it stimulates the roots and buries the weeds in the row. To ensure effective results, it is essential to set the row-crop cultivator accurately.
Row-crop cultivators with fingers intensify the effect thanks to the supplementary action in the row.

Sources:
Blind Cultivation for Early-Season Weed Control in Organic Grains, Fact sheet series 22-2, Ograin (University of Wisconsin-Madison, 2023
Désherbage du maïs : quelles stratégies envisager ?, Arvalis, 2024
Désherber mécaniquement les grandes cultures, ITAB, 2012