The Latest Types of Post-Emergence Herbicides for Corn and How to Use Them

Summers are rainy, and weeds occur commonly in corn fields. The main weeds include crabgrass, barnyardgrass, foxtail, goosegrass, redroot pigweed, purslane, copperleaf, and purple nutsedge. Corn is most severely harmed by weeds during the seedling stage. Chemical control saves time and labor, but the corn field herbicides on the market are a bewildering variety, and farmers often do not know how to choose. Quite a few farmers mistakenly choose or misuse herbicides, causing unnecessary damage to corn growth. Therefore, understanding the types of herbicides and their correct use is the key to weed control in summer corn.

Types of Post-Emergence Herbicides for Corn

1. Single-agent types

① Amide herbicides: This category of products is currently the most important type of herbicide for corn fields. It can be absorbed by weed buds and applied as a soil-sealing treatment before weeds germinate, effectively controlling annual grass weeds and some annual broadleaf weeds. There are many varieties in this herbicide category, such as acetochlor, alachlor, butachlor, metolachlor, and pretilachlor.

② Triazine herbicides: They can effectively control annual broadleaf weeds and annual grass weeds. They are mainly absorbed by weed roots and can also be absorbed in small amounts by weed stems and leaves. Representative varieties include atrazine, cyanazine, simazine, and prometryn. Among them, atrazine is used more widely, is relatively safe for corn, and has the highest activity, but atrazine is best mixed with acetochlor and the like to reduce the dosage, improve the weed control effect, and increase safety to subsequent crops.

③ Phenoxycarboxylic acid herbicides: They are mainly used for post-emergence control of broadleaf weeds and purple nutsedge in corn. Representative varieties include MCPA sodium salt and 2,4-D butyl ester. Among them, MCPA sodium salt is widely used in corn fields to control purple nutsedge, but improper timing of use can easily cause phytotoxicity.

④ Sulfonylurea herbicides: Nicosulfuron and rimsulfuron can be used in corn fields to control grass weeds, cyperaceae weeds, and some broadleaf weeds, while thifensulfuron can be used in corn fields to control annual broadleaf weeds.

⑤ Other herbicides: Paraquat and glyphosate are non-selective herbicides and can be used for directed spraying after corn reaches 40 cm in height, effectively controlling many kinds of weeds. Fluroxypyr, dicamba, bromoxynil, bentazone, and other varieties can also be used to control broadleaf weeds in corn fields.

2. Mixture types

① 1:1 mixture of acetochlor and atrazine: The earliest produced herbicide mixtures of this type were acetochlor-atrazine mixture and acetochlor-atrazine suspension concentrate, which can be used after corn sowing and before emergence, and in the early post-emergence stage of corn, to control annual grass weeds and broadleaf weeds, and are safe for corn and subsequent crops. Similar products include butachlor + acetochlor + atrazine, butachlor + atrazine, alachlor + acetochlor + atrazine, metolachlor + atrazine, and pretilachlor + atrazine.

② 2:3 mixture of acetochlor and atrazine: This herbicide mixture can be used after corn sowing and before emergence, and in the early post-emergence stage of corn, to control annual grass weeds and broadleaf weeds in corn fields. It is safe for corn, but in especially dry years it may reduce safety to subsequent wheat. A product with similar performance is the mixture of chlorotoluron + acetochlor + atrazine, which can greatly improve safety to subsequent wheat, but it must not be used post-emergence in corn.

③ Mixture of prometryn and atrazine: It can effectively control annual grass weeds and broadleaf weeds in corn fields. When applied after corn sowing and before emergence, the weed control effect is stable and less affected by soil moisture, but when rainfall is heavy, more leaching will reduce the weed control effect. When applied during the corn growing period, adverse environmental conditions such as high temperature and drought can induce phytotoxicity in corn.

④ Mixture of nicosulfuron and atrazine: It is an ideal herbicide mixture. It can not only effectively control many annual weeds, but also control perennial grass weeds and cyperaceae weeds. It is convenient to apply and safe for corn and subsequent crops. However, before and after use, it must not be mixed with organophosphate insecticides, but it can be mixed with pyrethroid insecticides.

⑤ Mixture of acetochlor, atrazine, and paraquat: It has both non-selective and soil-sealing weed control effects. When applied during the corn growing period, it can effectively control many weeds in corn fields. There are many similar products, and there are also herbicide mixtures in which glyphosate replaces paraquat.

How to Use Post-Emergence Herbicides for Corn

In chemical weed control in corn fields, paying attention to selecting suitable herbicides, mastering the optimal application period, strictly following safe and effective dosages, and adopting correct application methods are the keys to ensuring chemical weed control efficacy and safety to corn.

1. Correctly choose herbicides

① Choose herbicides according to the target of control. Look at which weed population is dominant in the field and choose a herbicide with a corresponding weed control spectrum.

② Choose suitable herbicides according to the field crop. For corn fields, choose herbicides specifically for corn fields.

③ Choose herbicides according to the application period. Those used after sowing and before emergence must not be used post-emergence, and those for soil treatment must not be used for stem and leaf treatment.

④ Consider safety to adjacent crops and subsequent crops.

2. Strictly follow the dosage

Herbicide dosage must strictly follow the standards specified in the instructions, and the dosage must not be increased at will. When 2 or more herbicides are mixed, the dosage of each herbicide should be 1/3 to 1/2 of its conventional dosage. For the amount of spray liquid per mu (after diluting the original liquid with water), for soil treatment it should be no less than 30 kg when straw is not returned to the field, and no less than 45 kg when straw is returned to the field. For stem and leaf treatment, it should be no less than 30 kg when weeds are small, and no less than 45 kg when weeds are large.

3. Scientific mixing and matching

When using a single herbicide, attention should be paid to calculating the dosage according to the safe and effective dosage of the herbicide and the actual area of the corn field. When mixing 2 or more herbicides at the same time, herbicides with different weed control spectra must be selected, but the applicable crops, periods, and methods of use must match and be basically consistent. When mixing wettable powder with emulsifiable concentrate, first dissolve the wettable powder in a small amount of water to make a mother liquor, then add the emulsifiable concentrate. When preparing the spray liquid, first put half a sprayer of water, then add the pesticide mother liquor that has been diluted twice, finally add enough water, shake well, and then spray.

4. Apply at the right time and choose the right moment

The right time means strictly following the period specified in the instructions and choosing to apply the herbicide during the growth stage when weeds are most sensitive to the herbicide and corn has the strongest tolerance to the herbicide. Only in this way can the control effect be improved and the safety of seedlings be ensured. For those suitable for soil treatment before sowing, use them before sowing. For those suitable for use after sowing and before emergence, use them after sowing and before emergence. For those suitable for stem and leaf treatment, avoid the crop's sensitive period. Choosing the right moment means avoiding high temperature, high humidity, strong wind, or cooling weather, so as to prevent phytotoxicity or reduced efficacy. Generally, it is safer to choose clear and windless weather and apply the herbicide after 5 p.m. Corn is most sensitive to herbicides during the bud stage and before the 4-leaf stage and is prone to phytotoxicity. When applying herbicides during these growth stages, attention should be paid to the concentration of the formulation.

5. Scientific operation and use

When spraying herbicides, be careful and operate scientifically. When working in the field, walk at a uniform and appropriate speed, keep the sprayer working pressure stable and moderate, and ensure accurate overlapping of passes back and forth in the field, without missing or overlapping sprays, so that spraying is uniform and consistent. After application, carry out corresponding field management according to the requirements in the instructions.

6. Clean the spray equipment in time

After spraying with a sprayer and other tools that have been used for herbicides, soak them in alkaline water or a dedicated cleaning agent in time and wash them multiple times to prevent phytotoxicity when they are used on other crops. It is best to use a dedicated sprayer.