Successful weed control in soybean combining herbicides and mechanical techniques

The weeding strategy has to be effective during the first two months of growth. It is very important that certain species, such as nightshade (toxic), xanthium (stains soybean seeds), and datura (toxic and stains), are controlled for human consumption. As such, mechanical weeding can complement herbicide solutions for the most difficult weeds.

Problem weeds for soybean crop: 

• Ragweed 
• Thistle
• Hedge bindweed
• Wild buckwheat
• Summer grasses (Panic grass, foxtail, crabgrass)

Weeds highly regulated for human consumption:

• Jimson weeds
• Nightshade
• Xanthium

Agronomic context and challenges

Soybean offers valuable agronomic benefits thanks to its flexibility in crop rotations and its ability to fix atmospheric nitrogen, improving soil fertility for subsequent crops. Its planting window also aligns well with stale‑seedbed techniques, allowing multiple weed‑control operations before sowing. While soybean tolerates later planting dates, timing remains crucial to avoid water stress, especially for non‑irrigated fields, making careful management of seeding schedules an essential part of successful crop establishment.

Stale seeding, delayed seeding date

As with sunflower, the planting period for soybean is conducive to stale seeding, which should be carried out quite early, depending on the soil type.
Soybean is well adapted to a later seeding date, which means that one or more stale-seeding operations can be carried out beforehand. It should not be planted too late though, as it could suffer from a shortage of water. Non-irrigated soybean can be sown up to May 15th, whereas irrigated soybean can be sown as late as May 25th, no problem.

Comparing different weed-control strategies for soybean

Effectiveness of different cultivation methods on simple flora (annual mercury, black nightshade and white goosefoot):

Possible treatment periods depending on mechanical weeding tools

Weed-control programmes for soybean

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

Purely chemical

In general, two applications are necessary to weed soybean, combining a pre-emergence root herbicide, and a second herbicide, post-emergence. Different solutions are possible, mainly imazamox-based for post-emergence. The product should be adapted to the weeds on the plot. 

Mixed strategy, with a row-crop cultivator

For soybean, a mixed weeding strategy is at least as effective as a purely chemical one. Combining a pre-emergence weed-control product with row-crop cultivation kills the new weed shoots (summer grasses, for instance). 

Mixed strategy, with a tine weeder

If it is not possible to use a row-crop cultivator, you can use a tine weeder or rotary hoe early in the cycle, to limit the growth of grasses like ryegrass, and then apply a chemical product later, post-emergence. 

Purely mechanical

Without herbicides, it is important to sow soybean in rows so that you can pass with a row-crop cultivator at the end of the cycle. Grasses can prove difficult to manage. It is necessary to weed with the row-crop cultivator regularly during crop growth.

Recommendations

Just like sunflower, there can be a lack of chemical solutions to destroy difficult dicots in soybean. In addition, certain toxic weeds are subject to very strict controls for human food outlets, so mixed weeding methods can be a good solution for this crop.

Sources:
Blind Cultivation for Early-Season Weed Control in Organic Grains, Fact sheet series 22-2, Ograin (University of Wisconsin-Madison, 2023
Désherbage mécanique du soja, Terres Inovia, 2019
Gestion des adventices en soja, Terres Inovia, 2020
Stratégies herbicides pour désherber le soja, Terres Inovia, 2025