Identification of Crop Herbicide Injury Symptoms and Prevention Methods
Identification and Prevention of Crop Injury Symptoms Caused by Herbicides
With the rapid development of modern agriculture, chemical weed control plays an increasingly important role in production. This brings with it the serious problem of crop injury during herbicide use, because no crop can completely resist herbicide damage; it can only tolerate a certain dose of herbicide, and once its selectivity range is exceeded, the crop will be injured. The severity of phytotoxicity ranges from total crop death to slight growth inhibition that does not affect yield. Therefore, correctly identifying crop phytotoxicity symptoms helps prevent the occurrence of phytotoxicity and remedy it.
I. Causes of herbicide phytotoxicity.
Herbicides cause harm to crops through various pathways, but most cases are caused by improper application techniques. For example, when 2,4-D butyl ester, MCPA, and dicamba are used for weed control in wheat fields and corn fields, drift of spray droplets (especially spraying on windy days, high-pressure spraying, etc.) often injures nearby sensitive crops; molinate and trifluralin injure sensitive crops such as beans, cucurbits, and tobacco through volatilized gases; improper mixing of herbicides with insecticides; poor condition of spray equipment and uneven spraying; misuse, excessive use, or application at the wrong time; phytotoxicity caused by herbicide degradation products; abnormal climatic conditions, and incomplete cleaning of equipment after spraying herbicides can all cause injury to some sensitive crops.
II. Diagnosis of phytotoxicity. The phytotoxicity symptoms of herbicides in the same class are basically similar.
1. The symptoms of phytotoxicity caused by amide herbicides (alachlor, metolachlor, acetochlor, pretilachlor, etc.) are: young buds and young leaves cannot fully unfold, and corn leaf sheaths cannot properly clasp the stem; soybean leaf midribs become shortened, leaves shrink and become rough, producing heart-shaped leaves, the central leaves turn yellow, leaf margin growth is inhibited, and cup-shaped leaves appear; peanut leaves become smaller and necrotic spots appear.
2. Dinitroaniline herbicides (trifluralin, pendimethalin, etc.). The phytotoxicity symptoms are: roots short and thick, no secondary roots or sparse and short secondary roots, root tips swollen into a mallet-like shape, bud growth inhibited, and hypocotyl swollen.
3. Phenoxycarboxylic acid herbicides (2,4-D, MCPA) and benzoic acid herbicides (dicamba). The typical phytotoxicity they cause is: morphological distortion, manifested as shortened, bent, or twisted stems, tumors growing on aboveground and underground parts and producing adventitious roots; in dicotyledonous plants, leaf veins become nearly parallel, leaflets in compound leaves fuse, the leaf blade fuses along the leaf margin into a tubular shape, and the numbers of sepals, petals, stamens, and pistils increase or decrease, with abnormal shapes; gramineous plants form onion-like leaves, inflorescences are difficult to emerge, and phenomena such as double ears, opposite spikelets, repeated spikelets, and whorled spikelets appear.
4. Sulfonylurea herbicides (nicosulfuron, tribenuron-methyl, metsulfuron-methyl, etc.). The symptoms of phytotoxicity they cause are: true leaves cannot emerge, growing points necrose or become deformed, leading to growth arrest, leaves become chlorotic, necrotic, or dark green and anthocyanin coloration appears, internodes shorten, roots age, lateral roots and main roots are short, the number of lateral roots is small, and the progression from the appearance of injury symptoms to death is relatively slow.
5. Triazine herbicides (atrazine, prometryn, simetryn, etc.) and urea herbicides (chlortoluron, diuron, etc.). They cause chlorosis and drying of crop leaf margins and leaf tips, and then chlorosis and drying of the mesophyll, growth arrest, and death of the entire plant.
6. Bentazon causes brown spots on crop leaves, and glyphosate causes slow wilting, chlorosis, and necrosis of leaves.
III. Pay attention to distinguishing symptoms that are easily confused with herbicide phytotoxicity
(1) In production, the phytotoxicity symptoms caused by abnormal environmental conditions such as freezing, high temperature, drought, and hot wind are similar to the phytotoxicity symptoms of herbicides.
(2) The symptoms of leaf damage caused by topdressing chemical fertilizers are similar to the phytotoxicity symptoms of contact herbicides.
(3) Nutrient deficiency, pollution, and excessive fertilization, especially symptoms caused by deficiency disorders and pollution by SO2, O3, Cl2, etc., are easily confused with mesophyll chlorosis caused by herbicides.
(4) Soilborne diseases are similar to the phytotoxicity of some pre-emergence soil-applied herbicides.
(5) Deformed leaves caused by viral diseases and pathogen infection are similar to leaf deformation caused by phenoxycarboxylic acid herbicides and soil-applied amide and thiocarbamate herbicides. After phytotoxicity occurs, observations should be made promptly from multiple aspects to prevent misdiagnosis.
IV. Prevention and remediation of phytotoxicity
1. Preventive measures. Correctly selecting and using herbicides is the key to prevention. (1) Adjust the application rate properly and correctly grasp the application timing. (2) Adjust the spray equipment properly, spray evenly, and thoroughly clean the sprayer after spraying. (3) After applying herbicides with long residual activity, rationally arrange subsequent crops. (4) Adding a small amount of methoxyphenone or BNA-80 to benthiocarb can prevent defluorination reactions and avoid rice dwarfing.
2. Remedial measures. Herbicide phytotoxicity should be treated differently. Some phytotoxicity does not affect yield and will naturally disappear as the crop grows; for example, after applying difenzoquat, wheat leaves briefly turn yellow and then naturally recover with growth. Some phytotoxicity causes yield reduction, and remedial measures should be taken promptly.
(1) For phytotoxicity caused by inhibition of photosynthesis after application, quick-acting fertilizers should be applied promptly through foliar feeding.
(2) For phytotoxicity caused by amide herbicides such as alachlor and acetochlor, gibberellin can be sprayed;
(3) Applying organic fertilizer, activated carbon, and plowing can eliminate or reduce the residual activity of herbicides in the soil.
I. Causes of herbicide phytotoxicity.
Herbicides cause harm to crops through various pathways, but most cases are caused by improper application techniques. For example, when 2,4-D butyl ester, MCPA, and dicamba are used for weed control in wheat fields and corn fields, drift of spray droplets (especially spraying on windy days, high-pressure spraying, etc.) often injures nearby sensitive crops; molinate and trifluralin injure sensitive crops such as beans, cucurbits, and tobacco through volatilized gases; improper mixing of herbicides with insecticides; poor condition of spray equipment and uneven spraying; misuse, excessive use, or application at the wrong time; phytotoxicity caused by herbicide degradation products; abnormal climatic conditions, and incomplete cleaning of equipment after spraying herbicides can all cause injury to some sensitive crops.
II. Diagnosis of phytotoxicity. The phytotoxicity symptoms of herbicides in the same class are basically similar.
1. The symptoms of phytotoxicity caused by amide herbicides (alachlor, metolachlor, acetochlor, pretilachlor, etc.) are: young buds and young leaves cannot fully unfold, and corn leaf sheaths cannot properly clasp the stem; soybean leaf midribs become shortened, leaves shrink and become rough, producing heart-shaped leaves, the central leaves turn yellow, leaf margin growth is inhibited, and cup-shaped leaves appear; peanut leaves become smaller and necrotic spots appear.
2. Dinitroaniline herbicides (trifluralin, pendimethalin, etc.). The phytotoxicity symptoms are: roots short and thick, no secondary roots or sparse and short secondary roots, root tips swollen into a mallet-like shape, bud growth inhibited, and hypocotyl swollen.
3. Phenoxycarboxylic acid herbicides (2,4-D, MCPA) and benzoic acid herbicides (dicamba). The typical phytotoxicity they cause is: morphological distortion, manifested as shortened, bent, or twisted stems, tumors growing on aboveground and underground parts and producing adventitious roots; in dicotyledonous plants, leaf veins become nearly parallel, leaflets in compound leaves fuse, the leaf blade fuses along the leaf margin into a tubular shape, and the numbers of sepals, petals, stamens, and pistils increase or decrease, with abnormal shapes; gramineous plants form onion-like leaves, inflorescences are difficult to emerge, and phenomena such as double ears, opposite spikelets, repeated spikelets, and whorled spikelets appear.
4. Sulfonylurea herbicides (nicosulfuron, tribenuron-methyl, metsulfuron-methyl, etc.). The symptoms of phytotoxicity they cause are: true leaves cannot emerge, growing points necrose or become deformed, leading to growth arrest, leaves become chlorotic, necrotic, or dark green and anthocyanin coloration appears, internodes shorten, roots age, lateral roots and main roots are short, the number of lateral roots is small, and the progression from the appearance of injury symptoms to death is relatively slow.
5. Triazine herbicides (atrazine, prometryn, simetryn, etc.) and urea herbicides (chlortoluron, diuron, etc.). They cause chlorosis and drying of crop leaf margins and leaf tips, and then chlorosis and drying of the mesophyll, growth arrest, and death of the entire plant.
6. Bentazon causes brown spots on crop leaves, and glyphosate causes slow wilting, chlorosis, and necrosis of leaves.
III. Pay attention to distinguishing symptoms that are easily confused with herbicide phytotoxicity
(1) In production, the phytotoxicity symptoms caused by abnormal environmental conditions such as freezing, high temperature, drought, and hot wind are similar to the phytotoxicity symptoms of herbicides.
(2) The symptoms of leaf damage caused by topdressing chemical fertilizers are similar to the phytotoxicity symptoms of contact herbicides.
(3) Nutrient deficiency, pollution, and excessive fertilization, especially symptoms caused by deficiency disorders and pollution by SO2, O3, Cl2, etc., are easily confused with mesophyll chlorosis caused by herbicides.
(4) Soilborne diseases are similar to the phytotoxicity of some pre-emergence soil-applied herbicides.
(5) Deformed leaves caused by viral diseases and pathogen infection are similar to leaf deformation caused by phenoxycarboxylic acid herbicides and soil-applied amide and thiocarbamate herbicides. After phytotoxicity occurs, observations should be made promptly from multiple aspects to prevent misdiagnosis.
IV. Prevention and remediation of phytotoxicity
1. Preventive measures. Correctly selecting and using herbicides is the key to prevention. (1) Adjust the application rate properly and correctly grasp the application timing. (2) Adjust the spray equipment properly, spray evenly, and thoroughly clean the sprayer after spraying. (3) After applying herbicides with long residual activity, rationally arrange subsequent crops. (4) Adding a small amount of methoxyphenone or BNA-80 to benthiocarb can prevent defluorination reactions and avoid rice dwarfing.
2. Remedial measures. Herbicide phytotoxicity should be treated differently. Some phytotoxicity does not affect yield and will naturally disappear as the crop grows; for example, after applying difenzoquat, wheat leaves briefly turn yellow and then naturally recover with growth. Some phytotoxicity causes yield reduction, and remedial measures should be taken promptly.
(1) For phytotoxicity caused by inhibition of photosynthesis after application, quick-acting fertilizers should be applied promptly through foliar feeding.
(2) For phytotoxicity caused by amide herbicides such as alachlor and acetochlor, gibberellin can be sprayed;
(3) Applying organic fertilizer, activated carbon, and plowing can eliminate or reduce the residual activity of herbicides in the soil.