Glyphosate to Control Weeds in Cotton Fields, Should Beware of Phytotoxicity
Glyphosate is an killing herbicide, which is mainly used in no-till idle fields or cotton. Field weeding is carried out 1 month before sowing and transplanting, which greatly improves the weeding efficiency and reduces the labor intensity. However, the growth of cotton in some cotton fields has been inhibited after use, and the phenomenon of phytotoxicity in many cotton areas is not uncommon, and some even cause ploughing and replanting or reduce production, which deserves attention.
According to observations, the use of glyphosate in cotton fields for weeding, causing phytotoxicity of cotton, mainly manifested in slow growth at the seedling stage, especially when the soil is wet or raining after the medicine, the phytotoxicity is more serious, and the leaves are obviously yellowed, growth stagnation, and even The heart leaves are necrotic, forming multi-head cotton. After cotton is harmed by its phytotoxicity, the root system is underdeveloped and dark brown, resulting in a decrease in white fibrous roots or no white fibrous roots, resulting in less peach and low yield in the future. If the drug damage is serious, no peach will be produced, and even the cotton plant will die 15~20 days after the drug is applied, resulting in greater losses.
There are mainly the following types of phytotoxicity:
(1) osmotic phytotoxicity. The soil is too wet during application or rainfall occurs shortly after application, which causes phytotoxicity through root absorption. This is because in May or June to July, that is, weeding before transplanting and weeding between rows. At this time, when there is a lot of rain, or when it rains after medicine, glyphosate liquid will be leached to the rhizosphere of the soil, and phytotoxicity will be formed through the absorption and transportation of roots. This type of phytotoxicity is relatively evenly distributed in the field and is more harmful. The rate of damaged plants is generally 30% ~ 50%, even as high as over 90%.
(2) drift type drug damage. Generally, there are two situations: a: glyphosate is not used in cotton fields in some places, but in the vicinity of cotton fields, aircraft spraying drugs to control reed weeds, or motorized sprayer spraying glyphosate to control other field weeds, which often causes drift and phytotoxicity to the surrounding cotton fields; B: In the process of weeding in cotton fields, due to improper operation or excessive wind speed, although directional spraying was adopted, but it is still difficult to control and make glyphosate liquid drift to cotton leaves and young stems, through the leaf, young stem absorption and produce phytotoxicity. In the field, it is not uniform, linear and banded, which is easily distinguished from healthy plants.
(3) residual drug damage. In some places, due to the long-term use of glyphosate for weeding in cotton fields, sodium-salt glyphosate is easy to settle and accumulate in the soil, which causes soil salinization, and it is easy to cause toxicity to cotton plants. This kind of phytotoxicity occurs early, and some occur on the seedling bed. The cotton seedlings have obvious symptoms shortly after being transplanted to the field. They can appear on the same plot for many years and can be transmitted to the entire cotton plant, thereby inhibiting growth, severe can cause cotton growth point necrosis. This kind of harm is highly concealed and is difficult to reverse once it occurs. In some cotton areas, glyphosate is used as an insecticide by mistake due to a very small number of farmers, or the sprayer is not thoroughly cleaned after glyphosate is used, and glyphosate residue damage occurs from time to time.
Measures to avoid glyphosate phytotoxicity. To avoid glyphosate causing phytotoxicity to cotton, the following points should be emphasized:
(1) Select high-content glyphosate amine salt preparations, eliminate the use of sodium salt preparations and other inferior glyphosate, and minimize residual phytotoxicity.
(2) to ensure the safety interval. When glyphosate herbicide is used in no-tillage cotton fields, cotton must be transplanted 7~10 days after the medicine is applied. If cotton is to be transplanted in the season, glyphosate is best not used, otherwise it is easy to cause rigid seedlings in the early stage of cotton growth. In rainy seasons, glyphosate should not be used in cotton weeding between rows to prevent the liquid medicine from penetrating into the rhizosphere to form osmotic phytotoxicity. If there are no strict protective measures in weeding between rows, it is best not to use glyphosate and other systemic herbicides, and never let the liquid medicine contact cotton plants, so as not to cause cotton plants to die.
(3) It is safer to use the herbicide "gram without trace" without internal absorption and conduction to weed between cotton rows. "No trace" is also an extinct herbicide, but it loses its activity when it enters the soil. The main effect is contact killing, which can quickly kill the green tissue of the plant, but it is ineffective for non-green tissues, and ineffective for plant roots, perennial underground stems and perennial roots. Therefore, there will be perennial weeds regeneration after application. When there are large weeds in the cotton row, other opposite herbicides should be used for spraying weeding. Although it may cause some local phytotoxicity to the cotton plant, it will not cause large areas of phytotoxicity to the cotton plant and cause the cotton plant to die. This is the biggest difference from glyphosate.
(4) Take remedial measures as soon as possible. After cotton is exposed to glyphosate, it usually takes 3~6 days to show phytotoxicity symptoms. If remedial measures are taken as soon as possible, the absorption amount and action time of cotton plants to the drug can be effectively reduced. Within 6 hours after the drug is not fully absorbed and utilized, moderately turbid water can be sprayed to rinse, then 5,000 times of 0.15% brassinolide liquid can be sprayed, and 4~5kg/mu of urea can be applied appropriately, or spray 0.2% potassium dihydrogen phosphate solution to promote the vegetative growth of cotton plants and minimize the impact on the growth of cotton plants.
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