What are the main herbicides used in wheat fields? Detailed guide to their application methods

Wheat is a densely planted crop, making mechanical weeding difficult. Chemical weeding, however, is highly efficient, low in cost and reduces labor intensity, so it is very popular among farmers. But improper use of herbicides can also lead to problems such as poor weed control, herbicide damage to the current and following crops, and residual contamination. Therefore, mastering the application techniques of herbicides is very important. The following introduces the types and application techniques of herbicides commonly used in wheat fields in China.

2,4-D butyl ester

[Chinese common name] 2,4-D butyl ester

[Chemical name] n-butyl 2,4-dichlorophenoxyacetate

[Mode of action] 2,4-D butyl ester is a phenoxyacetic acid hormone-type selective herbicide. It has strong systemic translocation properties. In wheat fields it is mainly used for post-emergence stem and leaf treatment. After the spray solution is applied to the surface of weed stems and leaves, it passes through the cuticle and cell membrane, and finally translocates to all parts of the plant. After the weeds are damaged, their stems and leaves become twisted and deformed, and they eventually die. Generally, broadleaf weeds show symptoms of deformed curling within 24 hours after treatment, and die within 7-15 days. Due to differences among plants in external morphology, tissue structure and physiology, they show different degrees of resistance to 2,4-D. Generally, dicotyledonous plants degrade 2,4-D slowly, so their resistance is weak and they are easily damaged, while grass family plants can rapidly metabolize 2,4-D and render it inactive. Therefore, this herbicide has good selectivity between the grass family plant wheat and dicotyledonous weeds.

[Formulation] The commonly used formulation is 72% 2,4-D butyl ester emulsifiable concentrate.

[Application technique] 72% 2,4-D butyl ester emulsifiable concentrate is used in wheat fields to control broadleaf weeds such as flixweed (Descurainia sophia), shepherd's purse (Capsella bursa-pastoris), lamb's quarters (Chenopodium album), smartweed (Polygonum spp.), cleavers (Galium aparine), hops (Humulus scandens), bitter lettuce (Ixeris denticulata), thistle (Cirsium setosum), and field bindweed (Convolvulus arvensis); it is ineffective against grass family weeds. Suitable application period and dosage: at the wheat regreening stage, use 40-50 ml of 72% 2,4-D butyl ester emulsifiable concentrate per mu, add 25-30 kg of water and spray evenly. 2,4-D butyl ester emulsifiable concentrate can be mixed with dicamba, bromoxynil and others, with each dose halved, to broaden the weed-killing spectrum.

[Precautions]

1. 2,4-D butyl ester is highly volatile, and the spray droplets can drift far in the air, damaging sensitive plants. Dicotyledonous crops such as spinach, beans, cotton, rapeseed and sunflower that grow at the same time as cereal crops are extremely sensitive to it, and this is a major cause of herbicide damage to broadleaf crops in China. Therefore, this herbicide should be applied in windless or low-wind weather, and the sprayer nozzle should preferably be fitted with a protective hood to prevent spray droplets from drifting to dicotyledonous crop fields. It must especially not be used in wheat fields intercropped with sensitive crops.

2. Strictly control the application period and dosage. Wheat is sensitive to 2,4-D butyl ester before the 3-leaf stage and after jointing; applying the herbicide at these times can easily cause damage to wheat. The symptoms of damage only appear after the wheat heading stage. In mild cases, when the wheat heads, the ears appear bent and are not easily extracted from the flag leaf, showing a “crane's head” shape. In severe cases, the wheat ears appear deformed, becoming “square-headed” ears. Therefore, this herbicide should be applied after the wheat 3-leaf stage and before jointing.

3. Equipment used for repackaging and spraying 2,4-D butyl ester must be dedicated, to avoid causing “secondary contamination”.

4. 2,4-D butyl ester emulsifiable concentrate must not come into contact with acidic or alkaline substances, to avoid reduced efficacy due to hydrolysis, and it should not be stored together with seeds and chemical fertilizers.

MCPA

[Chinese common name] MCPA-sodium

[Chemical name] sodium 2-methyl-4-chlorophenoxyacetate

[Mode of action] The mode of action and selectivity are the same as 2,4-D butyl ester. However, its volatility and speed of action are lower and slower than those of 2,4-D butyl ester emulsifiable concentrate.

[Formulation] 20% MCPA-sodium aqueous solution and 56% MCPA-sodium wettable powder

[Application technique] The weed-killing spectrum of MCPA-sodium is basically the same as that of 2,4-D. Suitable application period: at the peak tillering stage of wheat, apply 250-300 ml of 20% MCPA-sodium aqueous solution per mu, add 25-30 kg of water and spray evenly on stems and leaves. Precautions are the same as for 2,4-D butyl ester.

Dicamba

[Chinese common name] dicamba

[Other name] Banvel

[Chemical name] 3,6-dichloro-2-methoxybenzoic acid

[Mode of action] Dicamba belongs to the benzoic acid herbicide family and has systemic translocation action. This herbicide is used for post-emergence spraying and is quickly absorbed by the leaves, stems and roots of weeds, translocating upward and downward through the phloem and xylem; the herbicide mostly concentrates in meristematic tissues and sites of vigorous metabolic activity, hindering the normal activity of plant hormones and thereby causing death. It has significant control effects on annual and perennial broadleaf weeds. Generally, broadleaf weeds show symptoms of deformed curling within 24 hours after treatment, and die within 10-20 days.
After grass family plants such as wheat absorb the herbicide, they can rapidly metabolize and decompose it to render it ineffective, thus showing strong tolerance.

[Formulation] 48% Banvel aqueous solution.

[Application technique] Dicamba is used in wheat fields to control flixweed (Descurainia sophia), shepherd's purse (Capsella bursa-pastoris), lamb's quarters (Chenopodium album), cleavers (Galium aparine), common chickweed (Stellaria media), vetch (Vicia sativa), wild buckwheat (Polygonum convolvulus), cocklebur (Xanthium sibiricum), field bindweed (Convolvulus arvensis), thistle (Cirsium setosum), horsetail (Equisetum arvense) and others; it has no control effect on grass family weeds. Suitable application period and dosage: from wheat tillering to before jointing, use 25-40 ml of 48% Banvel aqueous solution per mu, add 20-30 kg of water and spray evenly. To broaden the weed-killing spectrum, Banvel can be mixed with other herbicides with different weed-killing spectra. Like 2,4-D, dicamba must strictly not be allowed to drift onto surrounding sensitive crops during application. Before the wheat 3-leaf stage and after the jointing stage, dicamba should not be applied, to avoid causing damage.

Bromoxynil

[Chinese common name] bromoxynil.

[Other name] Buctril.

[Chemical name] 3,5-dibromo-4-hydroxy-1-cyanobenzene.

[Mode of action] Bromoxynil is a selective post-emergence stem and leaf contact herbicide. It is mainly absorbed through the leaves and undergoes extremely limited translocation within the plant, rapidly causing plant tissue necrosis by inhibiting various processes of photosynthesis. Within 24 hours of application, leaves lose their green color and necrotic spots appear. Under conditions of higher temperature and stronger light, leaf death is accelerated.

[Formulation] Buctril 22.5% emulsifiable concentrate.

[Application technique] Bromoxynil is used in wheat fields to control flixweed (Descurainia sophia), shepherd's purse (Capsella bursa-pastoris), lamb's quarters (Chenopodium album), smartweed (Polygonum spp.), knotgrass (Polygonum aviculare), wild buckwheat (Polygonum convolvulus), veronica (Veronica spp.), common chickweed (Stellaria media), vetch (Vicia sativa) and others. It has no control effect on grass family weeds. Suitable application period and dosage: at the wheat 3-5 leaf stage, during the period of vigorous growth after broadleaf weeds have basically all emerged and before the 4-leaf stage, use 100-150 ml of 22.5% bromoxynil emulsifiable concentrate per mu, add 25-30 kg of water and spray evenly. This herbicide can be mixed with 2,4-D butyl ester or MCPA-sodium, etc., to broaden the weed-killing spectrum. When mixed, the dosage is halved compared with each herbicide used alone. This herbicide is a stem and leaf treatment contact herbicide, and the application period should be advanced as much as possible. When the weed plants are relatively large, the weed control effect decreases. In addition, if there is rainfall after application, respraying should be carried out.