In Xinyi City, the area of ​​summer corn planting is 200,000 mu. In recent years, due to the variety and density of weeds, the growth and development of summer corn are affected. Through the promotion of the use of chemical herbicides, the effect was significant, but because some farmers (households) used drugs improperly, resulting in crop injury in the season or the next crop, resulting in reduced production. The symptoms of phytotoxicity in corn are mostly dry rot in the roots, but the seed roots are dead. When the seed roots die, they gradually develop upward to the aerial roots. The lower leaves die and the corn seedlings grow thin and some of the whole plants die. In the fields where the seedlings are used, the yellow leaves shrink, the plants dwarf, and the growth stops, and some leaves have medicine damage. The main causes of damage caused by summer corn are as follows: (1) The use of a large amount of medicine causes a phytotoxicity to a small amount of water. 50% acetochlor EC is the main herbicide used by our farmers to control weeds in corn fields. According to the instructions for use, the amount of mu is 100--150ml, and 50kg of water is sprayed. The control effect can reach about 95%. However, peasant households arbitrarily increase the amount of medication during use and reduce the amount of water. In general, the amount of mu is sprayed in 200--400ml water to 20--25kg, and individual farmers can use more than 500ml per mu. (b) After the application of pesticides, high temperatures cause phytotoxicity. In 2002, after the wheat harvest in our city was reduced to a rain, the summer maize was sown in time, and it also provided conditions for the use of herbicides immediately after sowing. The whole city sowed and eliminated almost 7 days. However, after the sowing, it dropped 2 consecutive rains within 2 to 6 days after the sowing. The rainfall was over 30mm. The acetochlor on the soil surface penetrated into the soil through rainwater. First, contact with the roots of corn seed, so that the seed roots will die. After a few days of continuous high temperature, the water evaporates a large amount of water, and the ability of the root system to absorb water and nutrients is reduced. This results in the impediment to the growth of young seedlings. (3) The phytotoxicity was caused by the use of superstars, tribenuron-methyl, and large doses in the wheat fields of Shangyu. Due to the high density of weeds in the wheat fields and the low temperature in early spring, the chemical weeding time should be in the middle or late March. Some farmers only sprayed herbs on or around April 10, due to the large grass age, using superstars and tribenuron-methyl per acre. The dosages were 1.5--2g and 15-20g, respectively, 0.5- to 1 -fold more than the conventional dosage. In combination with the spring drought, the wheat was ripened by drought and high temperature, and the harvest period was about 7 days earlier than usual. Most summer corn sowing dates are June 3--8. The use period of superstars and tribenuron-methyl is a safe period 60 days after the sowing of the next crop, so that part of the crops produced by the farmer and the planting period of the lower jaw have not reached the safe period, plus the amount of wheat in the field has increased. Large soil pesticide residues also cause corn phytotoxicity. (d) The use of formazan and chlorsulfuron in wheat fields and their compounding agents cause phytotoxicity. Because my soil in the corn field is neutral alkali, A and chlorsulfuron are difficult to be decomposed in alkaline soil, and they are easy to produce phytotoxicity on the crop. The use of wheat in the wheat field can cause the emergence of a weak seedling. The reduction is even more serious for drought-sown crops in summer, but weaker and weaker for seedlings, and it is impossible to establish seedlings when they are heavy, so that the output can only reach 1/5 of the normal field mass. Although the use of such pesticides has been banned, phytotoxicity caused by pesticides has repeatedly occurred due to the sale of pesticides. (e) drug abuse caused by phytotoxicity. In general, herbicides should be selected according to the type of crops in order to achieve the desired control effect, otherwise it will cause phytotoxicity. Some farmers mistakenly use 50% butachlor as a 50% acetochlor to control weeds in corn fields, and some use high-efficiency herbicides to control weeds in corn fields after corn emergence, or to control broad-leaved weeds in corn fields with Huwei. All cause damage to corn. (6) The prevention and control of the time is not suitable to cause injury. All kinds of herbicides have safe application time. For example, acetochlor and drought can only be used after the seedlings of the crops are sown. They cannot be used after the emergence of corn. Yufeng can be used in corn fields before and after seeding. It can also be used after emergence of corn, but corn is safer within the 3-leaf period when applied, and the greater the corn leaf age is, the heavier the injury is. (7) The harm of geographical adaptability of pesticides causes phytotoxicity. The use of pesticides by the pesticide manufacturer should be repeated and tested in multiple places and at multiple points to confirm that they can be used and then introduced to the market. In particular, herbicides are greatly affected by the weather (temperature, humidity, light), and the climate difference between the South and the North is different. The effect of different medication time in the region is inconsistent. For example, in recent years, the demonstration has promoted the combination of acetochlor and thiflusulfuron --- 39% of drought-resistance, which is a "completed three certificates" product. The control effect of weeds used before seedlings after corn planting can reach above 95%. However, some farmers bought medicines to return home because of the rain, which delayed the use of pre-emergence medicines, and because the product specification stated that they could be used before the 4th leaf stage of corn emergence, resulting in some cemetery damage and some Very poor efficiency. (8) Injury caused by improper use. During the planting of summer corn, winds of grades of 5 to 6 can easily occur. Some farmers use mist sprayers to spray medicine on windy days. Since the fog is fine, it is easy to move with the wind. In addition, when pesticides are poured into the sprayer, water is added. Easy to pour the medicament into the nozzle, causing the spray to start spraying on the ground due to the large concentration of the liquid and causing phytotoxicity. Even some farmers want to reduce the labor intensity and time, and spread the medicament into poisonous soil in the corn field for weeding. The method can still achieve better control effect under the condition of good soil moisture, but it must increase the dosage, such as in the case of uneven mixing and uneven application, it is also easy to cause injury.