Best Timing, Methods and Precautions for Post-Emergence Herbicide Spraying on Soybean (Edamame) Seedlings

Soybean, also known as edamame, is a fairly common crop in China and is widely grown because of its strong planting prospects. To achieve high soybean yields, weed control must be done well. So when is the best time to apply post-emergence herbicide on soybean seedlings? How should it be applied? What precautions should be taken?

First, let us look at the common herbicides used in soybean fields and the common weeds found there. Among grasses there are crabgrass, barnyardgrass, goosegrass, foxtail, and so on; among broadleaf weeds there are redroot pigweed, copperleaf, cocklebur, purslane, and so on. Of course, lambsquarters (white goosefoot), thistle, field bindweed and Asiatic dayflower are also unavoidable.

Post-emergence weed control timing:

After emergence, control is carried out when soybean has 1 to 3 compound leaves and weeds are at the 2 to 5 leaf stage. The best application period for post-emergence herbicide is when barnyardgrass is at the 3-5 leaf stage and broadleaf weeds are at the 2-4 leaf stage (generally around 5 cm tall). To control Asiatic dayflower, it must be treated before the 3-leaf stage; after the 3-leaf stage it becomes difficult to control. If applied too early, weeds emerge unevenly, and later-emerging weeds cannot contact the herbicide and will not be killed. If applied too late, soybean resistance weakens and weed resistance increases, making control more difficult and requiring a higher dose, which not only raises costs but also easily causes herbicide damage.

Types of herbicide:

These are generally agents such as clomazone, bentazone, fomesafen, acifluorfen, fluoroglycofen, and so on, available as single agents or in mixtures. What is sold on the market includes both safened types and conventional types, with differences in price. When controlling weeds, choose the appropriate herbicide according to the situation.

Which product is best to use?

To control grass weeds, use 60-100 ml of 5% quizalofop-p-ethyl emulsifiable concentrate per mu, or 50-65 ml of 15% fluazifop-p-butyl emulsifiable concentrate, or 30 ml of 10.8% haloxyfop-p-methyl emulsifiable concentrate, or 50-60 ml of 6.9% quizalofop-p-tefuryl concentrated emulsion, or 80-100 ml of 12.5% sethoxydim emulsifiable concentrate, and spray with 20-30 kg of water.

To control broadleaf weeds, use 4-6 ml of 25% fomesafen (Huwe, Longwei, fomesafen, etc.) aqueous solution per mu, or 8 ml of 44% bentazone aqueous solution, or 4-6 ml of 24% lactofen aqueous solution, and spray with 2 kg of water.

Precautions:

Note: What is a soybean compound leaf? One petiole with three leaflets counts as one compound leaf. When soybean reaches three such compound leaves it is called the three-compound-leaf stage. The timing of herbicide use on soybean is also very important. Do not spray herbicide after heavy rain or when there is a lot of dew.

Factors affecting herbicide efficacy:

1. Weed age: The size and age of weeds has an obvious effect on soybean herbicide results. When you buy herbicide, sales staff will also tell you to apply it when weeds are at the 2-4 leaf stage, because if it is too early, the weeds have not all emerged, and post-emergence herbicide has no residual soil-closing effect, so more weeds will continue to grow and you will find many weeds still in the field afterward. If weed control is too late, weed resistance increases and control becomes more difficult; if you increase the dose, soybean is prone to herbicide damage. Therefore, research shows that applying at the 2-4 leaf stage of weeds is the best period.

2. Temperature: Temperature plays a very important role whenever herbicide is applied to any crop. For soybean, the suitable temperature for applying herbicide is 15-25 degrees. If the temperature is too low, below 13 degrees, or too high, above 30 degrees, application is not recommended. This is because when the temperature is too low, soybean's own metabolism slows, its sensitivity to herbicide increases, its resistance is weaker, and herbicide damage easily occurs. When the temperature is too high, first, the spray solution evaporates too quickly, and second, the ability of weeds to absorb the solution decreases, both of which weaken herbicide efficacy and fail to achieve the goal of weed control. Therefore, when applying in hotter weather, it is recommended to do so before 10 a.m. or after 3 p.m.

3. Humidity: The condition of soil moisture in the field also has a very important effect on how well herbicide efficacy is expressed. If the field is too dry, weeds will close some of their stomata to prevent overly rapid water loss for their own growth. Under such conditions, if herbicide is applied, very little spray solution is absorbed by the weeds and it cannot achieve weed control. Therefore, do not apply herbicide in dry conditions. You can irrigate, or use other methods, and wait until soil moisture is better before spraying.