Chemical weeding at corn seedlings
Maize 3-5 leaf stage is a critical period for spraying post-emergence herbicides. Improper use of postemergence herbicides is prone to phytotoxicity. Lighter plants retard the growth of plants and form weak seedlings. In severe cases, the growth point is damaged, and the heart leaves are rotted and cannot be normally solid. The main reasons for the occurrence of phytotoxicity are the lack of medication during the corn safety period (3-5 leaf stage), blindly increasing the application amount, overlapping spraying, spraying when the heat is hot, mixing several pesticides by themselves, and mixing other crops with weeds. There is no clean, misuse of herbicides, and short application intervals of organophosphorus pesticides, and species sensitivity. Once weed herbicide damage occurs, we must promptly change the barrel to fill the affected area with a spray of clean water; at the same time, we must use enough water to reduce the relative concentration of the drug in the crop; we must apply the available fertilizer, promote the rapid growth of the crop, and increase the resistance of the plant itself. Harmful ability; spraying plant growth regulators, such as gibberellin (920), alizarin lactone, etc., to promote the normal growth of plants and reduce injury; artificial dissection of distorted leaves, help the heart to expand. If the phytotoxicity is not serious, the maize can resume normal growth after strengthening management. If the heart leaves have rotted and necrotic, or the growth is stagnant, it is necessary to replant or destroy the seed.
Postharvest herbicide injury and use precautions for corn:
Phenoxycarboxylic acids: 2,4-D butyl ester, 2 A 4 chloro, 2 A 4 chloro, 2 A 4 chloro sodium, 2,4-D isooctyl, 2,4-D dimethylamine salt. Pharmacological manifestations: dark green leaves, yellow leaves when severe, dry; stem twisted, narrowed leaves, sometimes shrinking, curly heart was "onion tube"; stalks brittle, easy to break, stem base geese head-like The support roots are short and fused, and they are easy to fall down. Precautions for use: Apply pesticides when there is no wind, and try to avoid sensitive crops such as cotton, soybeans and melons when using them. 2,4-D butyl ester should not be mixed with other pesticides. 2,4-D isooctyl ester can not be mixed with alkaline pesticides to avoid reducing the efficacy.
In light soils such as sandy loam, sandy soil, etc., and with a large amount of rainfall after application, the chemicals are leached by rain into the soil where the maize seeds are located. The seeds or germs are in direct contact with the chemicals, which can easily lead to phytotoxicity.
Sulfonylureas: Nicosulfuron, thifensulfuron, risulfuron-methyl. Pharmacological manifestations: heart leaves chlorosis, yellowing, yellowish-white or purplish red or irregular chlorotic spots on the leaves; or leaf margin shrinking heart and leaf can not be normal extraction and expansion; or plant dwarf, clustered. Residues in the soil caused by the symptoms of pesticides are mostly purple and purple at 3-4 leaf stage. Notes for use: Nicosulfuron 3-5 leaf stage of corn, thifensulfuron-methyl and rimsulfuron-methyl application before the 4th leaf stage of corn is a safe period; in case of high temperature, drought, low temperature, rain, continuous storm water, easy to produce drug harm. Within 7 days before and after application, try to avoid using organophosphorus pesticides. Corn is sensitive to chlorimuron-methyl, tribenuron-methyl, and chlorsulfuron, avoiding sowing in these herbicide-remaining plots.
Triazobenzenes: Atrazine, Cyprofloxacin, Paracetamol. Pharmacological injury performance: from the tip and edge of the leaf blade, the chlorosis is yellowed between the veins, and then it turns brown and dead, and the heart leaves are distorted and the growth is inhibited. Precautions for use: Atrazine is effective for a long period of time. Do not increase the dose blindly, so as not to cause injury to sensitive crops. Cyprofloxacin is prone to phytotoxicity in soil with low organic matter content, sandy soil or saline-alkali soil, and it is easy to produce phytotoxicity after corn four-leaf stage.
Heterocyclic compounds: mesotrione (mesotrione), methyl oxalate. The phytotoxicity manifestation: mesotrione: partial bleaching of leaves. Methyl oxalate: The tip of the corn is yellow and the leaves have burn spots. Precautions for use: The corn is safe under normal dosage; rainfall does not have to be re-ejected after 1 hour after application; low temperature affects control effect; sweet corn and popcorn should not be used.
Triones: There is sulcotrione. The phytotoxicity manifestations: yellowing streak on one side or both sides of leaf veins, and albino striations when severe. Use precautions: corn 2-3 leaf application, grass 3 weeds after the resistance to the drug increased; no wind weather; corn, soybean sets of farming should not be used.
Bipyridyl: Paraquat. The leaves of the pesticides quickly produced water-stained gray-green spots and blemishes. The size and density of spots were different. The edges were yellow-brown and the untreated leaves were normal. In severe cases, the leaves withered and the plants withered. Precautions for use: Insecticide herbicide should not be used to contaminate crops during spraying. Spraying should be conducted under no-weather conditions. Protective measures should be taken when dispensing or spraying. Wear rubber gloves, masks, and overalls.
Nitriles: Bromobenzonitrile, octanoic benzonitrile. Performance of phytotoxicity: Bromobenzonitrile: Obvious dry dead spots appeared on the leaves of the herbicides, and new leaves did not show any harm. Octanoyl bromoxynil: After application, the corn leaves had spots of water-stained spots, after which the spots were yellow and there were obvious burning shapes, but they did not expand. Precautions for use: 3-8 leaf application, do not use in high temperature weather, no rain within 6 hours after application; it should not be mixed with alkaline pesticides, can not be mixed with fertilizers, can not add additives. Do not spray directly on corn seedlings.
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