Normal pre-winter use of tribenuron-methyl has little effect on succeeding cotton

Liu Wenzhang from Hengjing Town, Gaoyou City called to say that he sprayed tribenuron-methyl in his @#@245@#@ field for chemical weed control, using the product according to the instructions, with the per-mu rate of 10% tribenuron-methyl at less than 15 grams. He heard that tribenuron-methyl, chlorsulfuron and metsulfuron-methyl belong to the same class of herbicides, and that chlorsulfuron and metsulfuron-methyl both have very long residual activity periods, often causing residual phytotoxicity to succeeding crops. He did not know how long the residual period of tribenuron-methyl is, and whether a field sprayed with tribenuron-methyl before winter would suffer from herbicide residue effects when cotton is planted as the succeeding crop.

Tribenuron-methyl is a commonly used herbicide for controlling broadleaf weeds in wheat fields. It can be applied to wheat and barley from the 2-leaf stage to the jointing stage. Generally, it is sprayed about 40 days after wheat sowing or after the wheat seedlings turn green in spring. It has a long effective duration, and a single application before winter can control weeds during both peak weed emergence periods, before winter and after spring. Tribenuron-methyl, chlorsulfuron and metsulfuron-methyl all belong to the sulfonylurea class of herbicides, but compared with herbicides with long residual activity such as chlorsulfuron and metsulfuron-methyl, tribenuron-methyl has a shorter residual period and can disappear rapidly in soil through hydrolysis, with a residual period generally of 30-60 days. Considering the impact on sensitive succeeding crops such as cotton, peanut and soybean, the application rate must not be increased at will.

When cotton seedlings are raised in fields where tribenuron-methyl was used in spring, because the interval after spraying is short and cotton seedlings are sensitive to tribenuron-methyl, phytotoxicity is likely to occur. There have been such precedents in production. A few years ago in Rudong, over a hundred mu of directly sown cotton showed severe seedling death, with cotton seedlings in heavily affected fields all withering and dying, and even in lightly affected fields more than 60% withered and died. Later analysis by relevant experts showed that the main cause of this incident was that local farmers applied tribenuron-methyl to the preceding barley crop in March, and then began direct sowing of cotton in early April. The tribenuron-methyl residue caused phytotoxicity to the cotton seedlings, leading to the cotton starting to wither and die not long after emergence in mid-May.

When tribenuron-methyl is used before winter, there are several months between application and planting the succeeding cotton crop. If it is not applied at an excessive rate, it generally will not cause phytotoxicity to the succeeding cotton, especially transplanted cotton, which is even less likely to suffer phytotoxicity because the seedlings are larger. However, it should be noted that some tribenuron-methyl products currently on the market are adulterated or of low purity, and a small number of products are mixed with herbicides such as metsulfuron-methyl and chlorsulfuron that readily cause phytotoxicity to succeeding crops. When buying tribenuron-methyl, be sure to choose products from legitimate manufacturers.

Tribenuron-methyl is a systemic conductive herbicide. The entire plant can absorb the herbicide. After sensitive plants take up the chemical, it is conducted upward and downward from the stems, leaves and roots, blocking protein synthesis, halting growth and ultimately causing death. Under suitable temperature conditions, the symptoms of injury to sensitive plants are as follows: growth stops after about 1 day, young leaves lose green color and turn yellow after 7 days, the growing point and heart leaves become necrotic after 2-3 weeks, and the whole plant withers and dies after 3-4 weeks. In fields where tribenuron-methyl has been applied, to determine whether the soil contains residual herbicide harmful to cotton seedlings, a small amount of soil can be taken in advance and sown to grow cotton seedlings to observe whether there are abnormalities.