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Precautions for Corn Herbicides

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Precautions for Corn Herbicides

1. The best application time of post-emergence herbicides:

It takes 2-6 hours for the herbicides to be absorbed by the corn after spraying. Whether the weeding effect during this period is ideal is closely related to the temperature and air humidity.


When applied in the weather with high temperature and low humidity, due to high temperature and strong light, the herbicide evaporates quickly, which results in a significant insufficient absorption of it by the weeds, which affects the weeding effect and is also likely to cause phytotoxicity to the corn seedlings.


The best application time is after 6 pm, because the temperature is low and the humidity is high at this time, the herbicide stays on the weed leaf surface for a long time, the weed can fully absorb the herbicide, which can improve the control effect and it is not easy to cause phytotoxicity.


2. When can corn seedlings be sprayed with post-emergence herbicides?

Corn grows 3 to 5 leaves, and 2 to 4 leaf stage of weeds is the best, especially nicosulfuron mixed with 2,4-D butyl ester can not be applied after the 5 leaf stage of corn.


Spraying when weeds in the field are basically neat and most weeds are in 2~4 leaf stage. If the herbicide is sprayed too late, the weeding effect will be affected due to the enhanced weed resistance. When spraying, the air temperature should be 15~25℃, the air relative humidity should be above 65%, and the wind speed should be below 4m/s. Choose spraying equipment and nozzles according to requirements and apply drugs according to operation specifications.



One method summed up in practice is that, on the premise of sufficient dosage, relatively speaking,the more water the better. For example, it is recommended to mix 1 barrel of water with 1 bottle of herbicide to change it into2 barrels of water. This can make the land fully soaked and improve the effect.


Be sure to spray evenly.


The size of weeds

Many people think that the smaller the weeds, the less resistance, the better the weeding effect. In fact, it is not, because the weeds are too small and there is no area where the herbicide is applied. The best weed age is between 2 leaves and 1 heart stage to 4 leaves and 1 heart stage. At this time, the weeds have a certain area of application and the resistance is not strong, the weeding effect is better.


Since most of the post-emergence herbicide ingredients of corn are nicosulfuron, some corn varieties are sensitive to this ingredient and are prone to phytotoxicity. Therefore, corn fields that grow sweet corn, waxy corn, and Denghai series cannot be sprayed to prevent the occurrence of phytotoxicity. For new corn varieties, please test before promoting.


7 days before and after spraying herbicide, it is forbidden to spray organophosphorus pesticides, otherwise it is easy to cause phytotoxicity. However, it can be mixed with pyrethroid insecticides, and attention should be paid to avoid heart leaves when spraying, so as to prevent herbicides from pouring into them.


Matters needing attention in using post-emergence herbicides

1. Use according to the prescribed dosage, do not increase the dosage at will;

2. Using the "secondary dilution method", the mother solution is first prepared, and then mixed with water and sprayed evenly;

3. The suitable period for using post-emergence herbicides in corn is between the 2-5 leaf stage of corn. If sprayed at the 5-7 leaf stage, it should be used between rows of corn to avoid spraying it into the heart leaves;

4. Some post-emergence herbicides are sensitive to sweet corn, seed fields and inbred lines, so don’t use them. It should be used in strict accordance with the instructions or the use methods recommended by technicians;

5. Corn treated with organophosphorus pesticides is sensitive to post-emergence herbicide. The interval between the two is at least 7 days;

6. Use a motorized sprayer to spray, do not increase the dosage without authorization, and prohibit repeated spraying;

7. The sprayer used to spray organophosphorus pesticides should be cleaned;

8. Spraying after 4 pm will have a higher control effect. Avoid spraying in continuous high temperature weather (temperature over 35℃).


It rained after the corn was sprayed with the herbicide. Do I need to spray again the next day?

First of all, we do not recommend to use post-emergence herbicide twice.


But some users are afraid that the weeds have not been killed and want to spray again. What should we do?

1. It rains immediately after applying the herbicide;

2. Heavy rain or heavy rain lasts a long time;

3. There is no weed poisoning for a period of time after spraying the herbicide (3-5 days for broad-leaved weeds and 5-7 days for sharp-leaved weeds), and corn also grows normally.

When the above three conditions are met, the herbicide can be sprayed again.



1. The rain is not heavy and the duration is short;

2. It rains 6 hours after spraying the herbicide;

3. Weeds have been poisoned.

If the above 3 points are met, it is not recommended to respray the herbicide to avoid phytotoxicity.


Principles of mixing pesticides

1. No adverse chemical reactions (such as hydrolysis, alkali hydrolysis, acid hydrolysis or oxidation-reduction reactions) occur between the mixed varieties, and can maintain the efficacy or synergy, and will not affect the physical properties of the pesticides (such as emulsification, suspension rate) reduce);

For example, most organophosphorus pesticides cannot be mixed with Bordeaux mixture, lime sulfur mixture; powders cannot be mixed with wettable powders and soluble powders.


2. The mixed use of different varieties of pesticides can cause phytotoxicity to crops. For example, the mixed use of organophosphorus insecticides and propanil will cause phytotoxicity to rice, and the mixed use of Bordeaux mixture and lime sulphur mixture will easily cause phytotoxicity to crops;


3. After the pesticide is mixed, its toxicity cannot be increased to ensure the safety to humans and animals;


4. The mixing should be reasonable. For example, to control gramineous weeds in soybean fields, it is enough to use the sethoxydim and haloxyfop alone. If the two are mixed, it will neither increase the efficiency nor expand the control spectrum, which is considered unreasonable mixing;

The mixed use of pesticides is to improve efficiency and economic benefits, and should not increase costs.


5. Pay attention to the antagonism between different varieties of pesticides. For example, the mixture of bentazon and sethoxydim will reduce the control effect on gramineous weeds due to antagonism.


Can corn herbicides be mixed with pesticides?

For crops, pre-germination treatment mainly refers to the spraying treatment of soil before sowing (or before transplanting), or after sowing, before emergence of crops, so as to close and kill weeds that have not emerged.


Such herbicides in corn fields include acetochlor, metolachlor, atrazine, etc., which can control a variety of annual gramineous weeds and some small seed broad-leaved weeds in the field. If it is in three provinces of Northeast China, a mixture of herbicides such as 2,4-d butyl ester will be used to expand the herbicidal spectrum or increase the efficacy.


If no herbicide is applied in this period or the soil sealing effect is not good, you can choose to spray the stems and leaves of the emerged weeds with post-emergence herbicides, including nicosulfuron such as sulfonylurea.



It must be used in strict accordance with the technical points and precautions in the herbicide manual to avoid causing phytotoxicity.


It's best not to mix them, because they have different goals, one is weeds and the other is corn. Also, pesticides may contain organic phosphorus, which is easy to cause phytotoxicity when mixed with post-emergence herbicides.


Reasons why corn herbicides and insecticides cannot be mixed?

1. The respective ingredients are not clear. For corn herbicides, the mixture of nicosulfuron-containing herbicides and organophosphorus pesticides will cause phytotoxicity, that is, organophosphorus pesticides cannot be used within 7 days after the corn herbicides are used;


2. The spraying targets are different. The corn herbicide is mainly sprayed on the weeds to absorb the liquid to kill the weeds, while the insecticide is sprayed on the corn leaves to absorb the liquid to achieve the purpose of controlling pests.


When can the pre-emergence herbicide be used? Do I have to walk backwards when applying herbicides? Under what circumstances can the best sealing effect be achieved?


Pre-seedling herbicide, that is, the soil sealing treatment agent, is treated before the emergence of weeds, and a soil layer containing herbicides is formed in the topsoil of 2-3 cm. The weed seeds are also in this soil layer, and once they germinate, they absorb the herbicide solution and die. However, corn seeds are generally in 3-5 cm soil layer, protected by coleoptiles during germination, and hardly absorb herbicide solution (even if some are absorbed, corn itself has certain drug resistance), thus ensuring the safety of corn.


Pre-emergence herbicides refer to weed seeds before germination, not corn seeds.


The corn has emerged, can we use herbicides?

The answer is yes. From seedling emergence to 3-leaf stage, corn itself absorbs limited herbicide solution and has certain drug resistance, so it is possible to spray herbicide before seedling. During the 3-5 leaf stage, corn itself secretes zeatin, which can relieve the phytotoxicity of nicosulfuron, and has certain resistance to pre-emergence herbicides, so both post-emergence herbicides and pre-emergence herbicides can be used, but attention should be paid to the dosage of pre-emergence herbicides. After the 5th leaf stage of maize, the secretion of zeatin was reduced or stopped, and the drug resistance was also greatly reduced. Therefore, pre-emergence herbicides cannot be used after the 5-leaf stage.


According to the action mechanism of pre-emergence herbicide, it is to form a layer of herbicide soil layer, not just a herbicide film, so stepping on the ground has no effect on the formation of herbicide soil layer.


The efficacy of pre-emergence herbicides is mainly affected by soil texture, soil moisture, organic matter content, soil microbes and rainfall. Considering comprehensively, a 2-3 cm soil layer containing herbicides will achieve a good sealing effect, and the soil layer is too shallow, too deep or intermittent, which will cause poor sealing effect.


What are the ingredients and precautions of herbicides in the early stage after seedling?

The main active ingredients are nicosulfuron, mesotrione, topramezone, bromoxynil octanoate, MCPA-Na, fluroxypyr, atrazine, etc.


The properties and matters needing attention of nicosulfuron, mesotrione and atrazine are mainly introduced.

Nicotinsulfuron, a systemic and conductive herbicide, generally takes effect within 5-7 days, and weeds die in about 2 weeks. It prevents most of the weeds in corn fields, but it is not effective for abutilon. It is not safe for special corn such as sweet corn, sticky corn, pop corn, and field corn, so it cannot be used. The 3-5 leaves of corn can be sprayed throughout the field, and those containing safeners can be sprayed in the whole field during the 3-10 leaf stage. Use 7 days apart from organophosphorus pesticides.


Mesotrione, a contact herbicide, takes effect in 3 days, and weeds die in 7-10 days. Controls most of the weeds in corn fields, but is not effective against setaria. It has higher safety to all varieties of corn. It can be used in the 3-10 leaf stage of corn, with high safety.


Atrazine, a systemic and conductive herbicide, can either close weeds or kill weeds (2-4 leaf grasses). There is a long residual period in the soil, which will have residual phytotoxicity on the next cruciferous crops and vegetables. Compounding with nicosulfuron or mesotrione can expand the herbicidal spectrum of the two, improve the efficacy, and increase the safety to corn,and mixed with nicosulfuron and mesotrione, it can also eliminate the antagonistic effect of nicosulfuron and mesotrione.


Cyperus rotundus, a weed in the Cyperaceae family, has roots, three-sided stems, parallel leaf veins, no petioles, and no obvious nodes. Weed control belongs to broad-leaved weeds in science. The ingredient that has a special effect on it is Halosulfuron-methyl (75%WG 5 g/bucket of water), and it is also effective with MCPA-Na and Bentazon. High content of nicosulfuron can inhibit the growth of weeds, and mesotrione can only kill the above-ground parts of weeds to a certain extent.


Commonly used products such as Nicosulfuron+Atrazine, Mesotrione +Atrazine, Nicosulfuron+Mesotrione+Atrazine, it rains 6-8 hours after the application, and the effect is less affected.

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