Herbicide Selection and Use in Corn and Wheat Fields, and How to Identify and Remedy Herbicide Damage
Herbicides are chemicals that can kill weeds completely or selectively; also called weedkillers, they are a class of substances used to eliminate or inhibit plant growth. So which herbicide is best for corn and wheat fields? How should it be used? What are the methods for identifying and remedying herbicide damage?
Which herbicide is best for corn and wheat fields?
How good a wheat herbicide performs depends not only on the herbicide itself, but also on factors such as application timing, temperature, weed resistance and dosage, all considered together. In addition, the best time for chemical weed control in wheat fields is from mid-to-late November to early December, when wheat has the strongest tolerance to herbicides and weeds are most sensitive to them, giving the best weed control. You can use:
1. Xiaopai - Queshijing - tribenuron-methyl (wheat field herbicide), flucarbazone-sodium
2. Nuomandi - post-emergence herbicide for wheat fields (high-end type controlling both grassy and broadleaf weeds)
3. Yitao - new-type wheat field herbicide - Maijie
4. 10% tribenuron-methyl (wheat field herbicide) - Maicaofengsha - Yuexiu
Corn is cultivated throughout our country, and corn likes high temperatures, generally maturing in summer and autumn. Therefore, in summer and autumn, with high temperatures and abundant rain, 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 at the seedling stage. Chemical control saves time and labor, but the market is flooded with all kinds of corn field herbicides, and farmers often do not know how to choose; quite a few farmers mistakenly choose or misuse herbicides, causing unnecessary damage to corn growth. So understanding the types of herbicides and their correct use is the key to controlling weeds in summer corn. For corn weed control you can use:
1. Amide herbicides: This type of product is currently the most important class of herbicide for corn fields. It can be absorbed by weed buds and applied as a pre-emergence soil treatment to effectively control annual grass weeds and some annual broadleaf weeds. There are many varieties in this class, such as acetochlor, alachlor, butachlor, metolachlor and propisochlor.
2. Triazine herbicides: They can effectively control annual broadleaf weeds and annual grass weeds, 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 which atrazine is used more widely, is relatively safe for corn and has the highest activity; however, atrazine should be mixed with acetochlor and the like to reduce the dosage, improve weed control and increase safety for succeeding crops.
3. Phenoxycarboxylic acid herbicides: Mainly used for post-emergence control of broadleaf weeds and purple nutsedge in corn. Representative varieties include MCPA-sodium and 2,4-D butyl ester. Among them, MCPA-sodium is widely used in corn fields to control purple nutsedge, but improper timing of use can easily cause herbicide damage.
4. Nicosulfuron and atrazine mixture: This 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 succeeding crops. However, it must not be mixed with organophosphorus insecticides before or after use; it can be mixed with pyrethroid insecticides.
5. Acetochlor, atrazine and paraquat mixture: It has both non-selective and residual soil-closing weed control effects, and 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 should herbicides be used?
1. Strictly control the dosage. If the dosage used is too large, herbicide damage will occur.
2. Strictly control the timing of use. If the herbicide is applied at the wrong time and coincides with a sensitive period of the crop, it will cause herbicide damage. For example, using benthiocarb, butachlor or quinclorac during the rice seed germination period can easily reduce the rice emergence rate and lower seedling quality, and in severe cases cause seedlings to wither and die. If herbicides such as 2,4-D butyl ester or dicamba are sprayed on wheat before the 3-leaf stage and from after jointing to the flowering stage, herbicide damage will occur, causing wheat ear leaves to curl and affecting heading.
3. Choose the correct application method. If the application method is improper, it can also cause herbicide damage. For example, when using triallate in wheat fields, improper soil-mixing concentration at the same depth as wheat sowing can easily cause herbicide damage. Using soil-treatment agents for post-emergence stem-and-leaf treatment, or stem-and-leaf treatment agents for soil treatment, will fail to achieve weed control. Spraying herbicides requires a sufficient spray volume; generally low-volume mist blowers are not used.
4. Application should be even and thorough. Whether herbicides are sprayed or applied as medicated soil or medicated fertilizer, every effort should be made to ensure evenness. Uneven application can easily cause herbicide damage or poor weed control.
5. Master an appropriate application interval. When two chemicals are used on the same crop, an appropriate interval should be observed; too short an interval will also cause herbicide damage. For example, if propanil is used at the same time as, or soon before, organophosphorus or carbamate insecticides, rice loses its ability to detoxify propanil, and herbicide damage occurs.
6. Pay attention to field management. The soil should be tilled as level as possible, and field operations, fertilizer and water management, etc. should be coordinated with herbicide application.
What are the methods for identifying and remedying herbicide damage?
Most herbicides are highly selective, crops are very sensitive to them, and residue levels are relatively high. Combined with some farmers' lack of knowledge about safe use, herbicide damage is a fairly common problem.
Herbicide damage can be divided into three types: acute, chronic and residual. The acute type occurs quickly with obvious symptoms, appearing a few hours or days after application. Affected leaves show symptoms such as spots, scorching, perforation, curling, deformity, wilting, yellowing, chlorosis or whitening. The chronic type has a relatively long latent period, and the symptoms of herbicide damage are not obvious, but crop growth and development are clearly hindered, and yield and quality decline. In the residual type, the crop in the season of application does not suffer herbicide damage, but the chemical remaining in the soil causes herbicide damage to sensitive succeeding crops. Once herbicide damage occurs in production, remedial measures should be taken as early as possible.
1. Rinse with clean water. When crop stems and leaves suffer herbicide damage, a clean sprayer can be used quickly to spray clean water continuously two or three times directly onto the affected plants, to remove or reduce the chemical on the crop. For herbicide damage from herbicides that readily decompose when exposed to alkaline substances, 0.2% quicklime or sodium carbonate can be added to the clean water, mixed evenly and then sprayed, which is very effective at removing and reducing herbicide damage.
2. Attack with both water and fertilizer. After the affected plants are rinsed with clean water, irrigate with ample water as early as possible, attacking with both water and fertilizer. Ample irrigation can both satisfy the roots' large water uptake and lower the concentration of the chemical in the crop, and can also effectively leach out the residual herbicide in the soil, playing a good mitigating role. Combine irrigation with topdressing to promote rapid crop growth and improve the plants' tolerance to the chemical. Foliar topdressing can be combined with water rinsing: add urea to the clean water of the final rinse to make a 0.2% solution, or spray a 0.3% monopotassium phosphate solution, with good results.
3. Spray plant growth regulators. Herbicide damage hinders crop growth, so a plant growth regulator that promotes resumed growth, such as gibberellin or Lufeng 95, can be sprayed immediately once; about 5 days after spraying, the crop resumes growth and development. Note the strict dosage, and focus spraying on the tender leaves and tender stem tips, so that they are evenly covered with the solution.
4. Carry out timely intertillage and loosening of the soil. Combined with fertilizer and water management, carry out timely intertillage and loosening of the soil. Cultivate first shallowly and then deeply, for 2 to 3 consecutive times. This enhances soil aeration, raises ground temperature, favors microbial activity, reduces herbicide damage, promotes root uptake of water and fertilizer, and helps the crop resume growth.
5. Replant or change crops. If the herbicide damage is relatively severe and the above remedial measures are expected to have little effect, replanting or changing crops is necessary. When the season allows, the original crop can be replanted immediately; if the suitable period for replanting the original crop has passed, other suitable crops that are not sensitive to that herbicide should be planted instead in good time.