Weeding manually is very costly and labor-intensive. But with herbicides, weeding becomes easier. Below are herbicides you can use without killing your soybean crops.
Post Emergence Herbicides:
These are herbicides that kill weeds that have grown out from the soil. You can apply it to kill weeds before you start land preparation. See manufacturer’s label for dosage. Below are 2 post emergence herbicides you can use.
1. Glyphosphate: This is a systemic herbicides – meaning that it enters the weeds’ system and kill them completely. It kills both broadleaf and grass weeds. It will kill soybean but because it has no residual activity in the soil, you can use it before you plant soybean but not after. It acts slowly and takes about 2 weeks to kill weeds.
2. Paraquat: This is a contact herbicide because it kills the part of weed it comes in contact with. It does not kill the weeds completely and so they’ll still grow back. It kills both broadleaf and grass weeds. It is best to use this after planting the soybeans. Use it to control weeds that grow between rows. But you must make sure it doesn’t come in contact with the soybeans as it will kill any leaf it comes in contact with. You can use 2 plywood boards to shield the soybeans as you spray.
Preemergence Herbicides:
These are herbicides that kill weeds before they emerge from the soil. You apply them before weeds appear – immediately after making ridges. Some are not effective on emerged weeds while some can still control young weeds.
After applying any preemergence herbicide, they need to be activated by mixing them with the soil to a depth of about 5cm. This can be achieved by cultivation, irrigation or rainfall (at least 0.5in rain). Check product label for recommended method of activation.
As the weed grow through this treated zone, they get killed. Incorporating into the soil also prevents sunlight from destroying the herbicide.
Note: a.i = active ingredient
Below are preemergence herbicides you can use:
1. Alachlor: 469g a.i/ha.
2. Clomazone: 1.08kg a.i/ha
3. Metribuzin: 525g a.i/ha. This provides satisfactory full-season control of several weed species and gave the highest crop yield.
4. Pendimethalin: 1.03125kg/ha. Weed control also effective like Metribuzin: 525g a.i/ha.
5. Tank-mixed Clomazone (960g a.i/ha) + Pendimethalin (928g a.i/ha)
6. Tank-mixed metribizin (350g a.i/ha) + Pendimethalin (928g a.i/ha). Weed control also effective like Metribuzin: 525g a.i/ha.
The above herbicides applied at those concentrations shows no visible crop injury and no herbicide residue was detected in vegetable soybean (i.e soybean harvested at 80% maturity) after harvest.
One thing you must keep in mind with regard to preemergence herbicide is that some can last a long time in the soil. So if you decide to plant soybean this season and rotate to a different crop next season, the preemergence herbicide you applied for soybean may badly affect the growth and yield of the next crop. But with the above mentioned herbicides, their residue will not affect baby corn and cucumber.
Other herbicides like Acetochlor (1874g a.i/ha), Isoxaflutolen (75g a.i/ha) and Oxadiazone (1kg a.i/ha) badly affected soybeans. So don’t use them.
Disclaimer: Try this on a small portion of land before you scale up. I got this information from a scientific papers: Weed control with preemergence herbicides in vegetable soybean and have not tried them before. So you are responsible for whatever happens if you apply this. Thanks.
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