What should be noted when using chemical herbicides in corn fields?
What should be noted when using chemical herbicides in corn fields? Please advise on the following issues to note when using chemical herbicides in corn fields: 1. Improper selection of variety. Different herbicide varieties have different control effects on weeds. Some farmers do not understand chemical herbicides and mistakenly believe some casual claims, thinking that any herbicide can control weeds, result...
What should be noted when using chemical herbicides in corn fields? Please advise
The following issues should be noted when using chemical herbicides in corn fields:
1. Improper selection of variety
Different herbicide varieties have different control effects on weeds. Some farmers do not understand chemical herbicides and mistakenly believe some casual claims, thinking that any herbicide can control weeds. As a result, the phenomenon of corn seedlings dying while weeds survive often occurs in corn fields. Most of the corn field herbicides currently used rely on differences in plant conduction of the agent for selective weed control. If the weed species in the field differ, using the same agent for control will naturally give different results. Farmers, hating that the weeds do not die, blindly increase the dosage, resulting in corn phytotoxicity. For example, 50% acetochlor EC is a widely used herbicide and is also safe for corn. Used before weeds emerge, it has a very good effect on grass weeds such as crabgrass and barnyardgrass, but its control effect on weeds such as knotgrass, amaranth, and velvetleaf is very poor.
2. Improper timing of use
(1) Causing poor efficacy. Weeds at different growth stages have different sensitivity to herbicides. Most grass weeds and broadleaf weeds are generally more sensitive to herbicides at the germination stage. Considering corn safety, most chemical herbicides for corn fields are soil treatment agents. When used after corn sowing and before emergence, before weeds emerge, up to before the three-leaf stage of corn and before the two-leaf stage of weeds, they have ideal control efficacy on weeds and are safe for corn seedlings. The same soil treatment agent, if used after the five-leaf stage of corn and after the four-leaf stage of weeds, will not only have poor control efficacy on weeds, but corn will also suffer phytotoxicity. For example, 40% acetochlor atrazine SC (acetochlor atrazine) was a commonly promoted corn field herbicide in previous years. If used according to technical rules, it has a broad weed-killing spectrum and ideal efficacy. However, some farmers do not apply the agent until they see weeds, and then use it when the weeds are large, so the effect is still poor.
(2) Causing severe phytotoxicity. The same herbicide, especially a soil treatment agent, generally must be used before corn emergence. The younger the corn seedling age, the stronger its resistance to the herbicide. For example, 40% propisochlor atrazine SE is a relatively safe corn herbicide currently on the market. Used for soil treatment from before corn emergence to the 3-leaf stage after emergence, it is not only safe for corn, but corn seedlings are also robust with dark, thick leaves. However, if used after the 5-7 leaf stage of corn, it often causes yellow spots to yellow withering of corn leaves and inhibits growth.
(3) Causing a lot of residue in subsequent crops. Some corn herbicides have a long residual effect period. For example, 38% atrazine SC has a residual effect period in soil of more than 3 months. If applied too late and at too high a dosage, it will directly affect subsequent crops (wheat, etc.).
3. Improper application method
Herbicide application methods are relatively complex and technically strict. A slight negligence not only affects the weed control effect, but also often causes crop phytotoxicity. For example, when some farmers use non-selective herbicides such as 20% paraquat AS (Gramoxone) and 41% Roundup AS (glyphosate) for weed control in corn fields without carefully protecting the corn, both weeds and seedlings die. Some use soil treatment agents as foliar treatment agents, often causing severe corn phytotoxicity while having basically no effect on weeds. Conversely, when foliar treatment agents are used for soil treatment, they also have no effect.
4. Improper dosage
(1) Not understanding the normal dosage. Every corn field herbicide has its correct dosage under certain conditions, mainly obtained through experiments and application. For example, 40% propisochlor atrazine SE, in light loam corn fields under non-drought conditions, at 180-220 milliliters per mu, has ideal weed control effect. Below 180 milliliters, the effect is often very poor, while above 250 milliliters, phytotoxicity often occurs. In current corn fields with high wheat stubble, for wheat-interplanted corn, herbicide dosage after wheat harvest should generally be increased by 10%-20%.
(2) Dosage should differ for different soil types. Sandy soil has poor adsorption capacity for herbicides and is prone to leaching with water, while clay soil has strong adsorption capacity for herbicides. The dosage of soil treatment agents should increase in the order of sandy soil, loam soil, and clay soil. Soil organic matter has adsorption and decomposition effects on herbicides. Plots with high organic matter content should appropriately increase the herbicide dosage.
5. Uneven spraying and insufficient water
Any pesticide spraying requires good atomization. Only when it is uniform and thorough can there be good efficacy. When using soil treatment agents for chemical weed control in corn fields, only with fine droplets, sufficient water, and uniform spraying can a chemical film form on the soil surface and achieve the effect of inhibiting weed buds from emerging. If spraying is uneven, when weed buds emerge and do not encounter the chemical film, there is no effect. If the water amount is insufficient, most of the spray solution falls on wheat stubble and also cannot achieve the proper effect.
6. Serious droplet drift
Because land is currently managed by households, plots are relatively small, and crops differ, this is a typical small but complete mixed planting pattern. During spraying, if operated carelessly, it often causes phytotoxicity to sensitive crops in adjacent plots such as cotton, melons, and vegetables. In particular, when motorized mist sprayers are used to spray corn herbicides, the drift phenomenon is even more serious. In windy weather, it often causes severe phytotoxicity to sensitive crops downwind.
7. Causing changes in weed species in corn fields
Most corn field herbicides are selective, and at the same time different types of weeds have different levels of tolerance to a certain herbicide. If one herbicide is used for a long time, some weeds are controlled, while other weeds become dominant species, causing changes in the weed species in corn fields, thus also increasing the difficulty of chemical weed control.
II. Countermeasures
1. Strengthen training and guidance in chemical weed control technology
Agricultural departments should increase training and guidance for pesticide operators and users so that they understand more about chemical weed control knowledge and avoid various risks borne because of this.
2. Correctly select chemical herbicides
Chemical herbicides are divided into non-selective herbicides and selective herbicides. Selective herbicides are further divided into soil treatment agents and foliar treatment agents, and also into contact type and systemic type. Herbicides with different ingredients and different varieties differ in weed-killing spectrum, adaptability, and sensitivity to crops. Before use, one should fully understand the performance of various herbicides and master their applicable dosage, applicable period, appropriate method, precautions, etc., and correctly select herbicide varieties according to factors such as soil quality, climate, corn growth stage, weed species, and weed size.
3. Master the appropriate application period
Soil treatment agents should be applied to the soil after corn sowing and before emergence, up to before the 3-leaf stage of corn and before the 2-leaf stage of weeds, making full use of the period before the 3-leaf stage of corn when corn has strong tolerance to herbicides and weed buds are most sensitive to herbicides. Foliar treatment agents, however, need to be used after the 5-leaf stage of corn, with protective spraying, avoiding corn plants as much as possible, to achieve the best effect.
4. Choose an appropriate dosage
First, establish the dosage of that variety for a certain growth stage of local corn based on guidance from agricultural technicians and pesticide instructions. Second, when using soil treatment agents, sandy soil should appropriately reduce the dosage compared with clay soil, and when organic matter content is greater than 3%, the dosage should be appropriately increased.
5. Master the application method well
For weed control in corn fields, after corn sowing and before emergence, soil treatment agents can be selected for ground spraying. After the 5-leaf stage of corn, foliar treatment agents must be selected and sprayed directly on weed stems and leaves, and attention must be paid to using inter-row directed spraying technology, placing a protective hood at the sprayer nozzle, lowering the nozzle and spraying along the rows onto the weeds, trying not to let the spray solution splash onto corn plants. When spraying corn herbicides, the water amount should be sufficient, generally more than 40-50 kilograms per mu. Spraying must be safe and thorough, without repeated spraying, without missing spraying, and without arbitrarily increasing the dosage. Manual sprayers such as the Gongnong-16 type are used for spraying, and motorized sprayers are generally not recommended.
6. Pay attention to weather conditions
Most chemical herbicides for corn fields are soil treatment agents. They should be sprayed on cloudy and rainy days or after watering, that is, when the soil is moist, which is conducive to the formation of the chemical film and improves control efficacy. To avoid phytotoxicity to other crops outside the corn field, choose windless weather for application and lower the nozzle to prevent long-distance droplet drift.
In short, chemical weed control in corn fields has become widespread, but there are many technical problems. In order to continuously improve and sustainably apply this technology, it is necessary to quickly improve the application technology of the vast number of farmers so as to achieve the proper effect.
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