Summer seedling corn is grown during a hot and rainy season, when weeds in the fields are widespread and diverse. According to the National Weed Census, there are 22 families, 38 genera, and 43 species of weeds found in corn fields. The most common weeds include crabgrass, madder, green foxtail, goosegrass, amaranth, purslane, iron amaranth, and fragrant grass, among others. These weeds pose a serious threat to young corn plants, making it essential to focus on chemical weed control during the critical periods before and after the emergence of seedlings.
There are several main types of herbicides used for weed control in corn fields. First, **amide herbicides** are widely used and considered one of the most important classes. They are absorbed by weed seeds and can effectively control annual grasses and some broadleaf weeds before they germinate. Common examples include acetochlor, alachlor, butachlor, metolachlor, and propisochlor. Studies show that their effectiveness varies, with acetochlor being the most active, followed by metolachlor, propisochlor, butachlor, and alachlor. The effectiveness also depends on soil moisture levels, as dry conditions can significantly reduce their performance.
Another key group is **triazine herbicides**, such as atrazine and simazine. These are effective against both grassy and broadleaf weeds. Atrazine is the most commonly used, known for its high efficacy and safety in corn. It is often combined with acetochlor to reduce the dosage and improve crop safety after application.
**Phenoxycarboxylic acid herbicides**, like 2,4-D and 2A4 sodium chloride, are mainly used for post-emergence control of broadleaf weeds and Cyperus species. They are particularly useful for controlling aconite without causing phytotoxicity if applied at the right time.
**Sulfonylurea herbicides**, such as nicosulfuron and rimsulfuron, are effective against grassy weeds, sedges, and some broadleaves. They offer good selectivity and are safe for corn when used properly.
Other herbicides like **paraquat** and **glyphosate** are non-selective and are typically applied after the corn has reached about 40 cm in height. They are useful for controlling a wide range of weeds. Additionally, **bromoxynil** and **bentazon** are used to manage broadleaf weeds in corn fields.
In terms of **herbicide mixtures**, several combinations are commonly used. For example, a 1:1 mixture of acetochlor and atrazine is effective for pre-emergence weed control and is safe for both corn and subsequent crops. A 2:3 mixture of acetochlor and atrazine is also popular, especially in drier conditions, though it may affect wheat safety in certain cases.
The **prometryn and atrazine complex** is another effective option, providing stable pre-emergence control of grassy and broadleaf weeds. However, heavy rainfall can cause leaching and reduce its effectiveness. High temperatures and drought can also increase the risk of crop damage.
The **nicosulfuron and atrazine mixture** is highly effective against both annual and perennial weeds, offering good safety for corn and future crops. However, it tends to be more expensive than other options.
Finally, a **triple mixture** of acetochlor, atrazine, and paraquat is often used for both pre- and post-emergence weed control. Some formulations replace paraquat with glyphosate for similar results.
When applying herbicides, the recommended dosages vary depending on the stage of corn growth. At sowing, a mixture of E-A (acetochlor + atrazine) is typically used at 150–200 ml per mu. At the early post-emergence stage (1–4 leaf), 38% atrazine suspension (75–100 ml/mu) plus 4% nicosulfuron suspension (75–100 ml/mu) is effective. During mid-growth, 10% glyphosate (200–300 ml/mu) or 20% paraquat (100–150 ml/mu) can be applied. Always ensure spraying is done under calm conditions to avoid drift and maximize effectiveness.
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