Causes of Herbicide Phytotoxicity in Paddy Fields and Control Countermeasures
Causes of Herbicide Phytotoxicity in Paddy Fields and Control Countermeasures
1 Causes
1.1 Problems with herbicide use
1.1.1 Wrong choice of herbicide Seedling-throwing fields should use herbicides containing the ingredients butachlor and bensulfuron-methyl. If a transplanting-field herbicide is used in a seedling-throwing field, that is, if a herbicide containing the ingredients acetochlor and bensulfuron-methyl is used in a seedling-throwing field, phytotoxicity will result. In recent years, one of the reasons for the severe herbicide phytotoxicity in paddy fields in Ji'an City is that some pesticide manufacturers mistakenly used acetochlor and bensulfuron-methyl in herbicide formulations specially designed for seedling-throwing fields. In addition, some fake and inferior herbicides have metsulfuron-methyl and other substances added to them, which also easily causes phytotoxicity.
1.1.2 Improper use of herbicides Improper use of herbicides includes the following situations: the dosage per 667 m2 exceeds the standard dosage; after application, the water kept in the field is too deep, submerging the growing points and leaves, which very easily causes phytotoxicity; the time of use is too early, and using herbicides within 4 d after transplanting (or seedling throwing) easily produces phytotoxicity; broadcasting application is uneven, and places where more is applied easily develop phytotoxicity, etc.
1.1.3 Residues and accumulation of herbicides in soil Herbicides containing metsulfuron-methyl degrade slowly in soil and can remain and accumulate in the soil. At present, in order to reduce costs, some manufacturers still partly use metsulfuron-methyl in the production process, and some farmers, lacking awareness, continue to use it. Accumulation over many years has caused phytotoxicity even in some fields where no herbicide was applied.
1.2 Weather causes Heavy rainfall leads to water accumulation in the paddy field submerging the seedlings; little rainfall causes the water in the field to evaporate continuously, the water level to be low, and the herbicide to damage the roots. When the temperature is high, water evaporates quickly, and the young seedlings just transplanted (or thrown) cannot adapt and are prone to herbicide phytotoxicity[1].
1.3 Other causes
1.3.1 Seedling-throwing fields are more susceptible to damage Because the seedlings thrown for planting are younger in seedling age and are sensitive to herbicides, and because after throwing the seedlings fall over and the growing points are submerged in water, they are more susceptible to phytotoxicity than transplanted seedlings.
1.3.2 Improper herbicide use in seedling fields manifests as phytotoxicity in the main field Some seedling fields use herbicides improperly, causing phytotoxicity to appear in the main field.
1.3.3 Uneven plowing and leveling of the main field In low-lying places, the seedlings suffer herbicide damage to the heart leaves, and in raised places, the seedlings lack water and their root systems are damaged[2].
2 Control measures
2.1 Strictly prohibit the use of high-residue herbicides It is necessary to strictly prohibit the production, sale, and use in paddy fields of herbicides containing metsulfuron-methyl and other slowly degrading, high-residue herbicides.
2.2 Correctly select and use herbicides At 5 to
7 d after rice transplanting (or seedling throwing), select herbicides of the acetochlor and bensulfuron-methyl type for transplanting fields, and select herbicides of the butachlor and bensulfuron-methyl type for seedling-throwing fields. Mix the dosage per 667 m2 with about 10 kg of dry fine soil (or a certain amount of urea), stir evenly, and then apply evenly; after application, keep a shallow water layer of 3 to 5 cm in the field for 5 to 7 d[3]. After applying herbicides, an appropriate water level should be maintained in the paddy field. For sandy-mud fields or leaky fields, the application rate should be reduced or herbicides should not be applied.
2.3 Improve the level of cultivation techniques To improve rice cultivation techniques, it is necessary to ensure that the paddy field is plowed and harrowed level; operate according to technical requirements when throwing seedlings, and try as much as possible to make the seedlings stand upright after throwing [Jishan Huayao].
3 Remedial methods
3.1 Change the field water First drain the field water, replace it with clean shallow water, keep it for one or two days and then change it again, changing it two or three times in succession.
3.2 Spray foliar fertilizer Per 667 m2, use 20 to 40 mL of Lünongsu or 40 mL of rice disease-resistant yield-increasing agent, mix with 30 kg of water, and spray evenly. If yellow leaves appear later, Lünongsu or potassium dihydrogen phosphate can also be sprayed [Jishan Huayao].
3.3 Broadcast black-and-white ash Per 667 m2, evenly broadcast 30 kg of black-and-white ash (25 kg of plant ash plus 5 kg of quicklime, mixed evenly) to replace toxic substances with more active substances[5].
3.4 Increase the application of phosphorus and potassium fertilizers At 7 to 10 d after application, appropriately increase the application of 5 to 10 kg of phosphorus and potassium fertilizers or compound fertilizer, but urea must not be applied.
After remediation, the phytotoxicity can be alleviated or eliminated after one or two weeks, and most of the seedlings can resume normal growth. For paddy fields where the phytotoxicity is too severe, the seedlings are about to wither and die, and remediation is impossible, flush the paddy field, plow it in time, and replant.