The action principle of herbicide is more complex, different action principles need to be fully used through certain use methods. The scientific use of pesticides is particularly prominent in the application of herbicides. As the object of control, weeds and crops belong to higher plants, and their physiological and biochemical characteristics are basically similar. The use of herbicides to control weeds, on the one hand, to kill weeds, on the other hand, must avoid damage to the same field crops and even subsequent crops, which puts forward high requirements for the scientific use of herbicides.

1. Weeding mechanism of pre seedling herbicides

Most of the pre seedling herbicides play a role through the absorption of weeds' young buds (generally, monocotyledon weeds are absorbed by the coleoptile, dicotyledonous weeds are absorbed by hypocotyls), and the roots are rarely absorbed. In order to achieve the weeding effect, the collected pesticides should reach 0-5cm "weed germination circle".

2. Problems in spring application of pre seedling herbicides in North China

During the spring spraying period (from late April to mid May) in northern China, strong wind and drought are often encountered. After application, herbicides are easy to be blown by the wind or stay on the ground surface, and can not contact with weed sprouts, so it is difficult to exert weed control effect. If there is no rainfall or irrigation after application, mechanical measures should be taken to ensure the efficacy.

3. Technical points of using herbicide before seedling

1) The quality of soil preparation should be good: the soil should be broken and there should be no plant residues on the surface to ensure the even distribution of pesticides.

2) Select the pesticide varieties officially registered by the state

3) use standardized spraying machinery and accurate spray technology:

The diameter of spray droplets is 300-400 microns, 30-40 droplets per square centimeter.

The artificial backpack sprayer should be equipped with fan-shaped sprinkler, equipped with 11003 fan shaped nozzles and 50 sieve filters. The spray pressure is 2 atmospheres, and the spraying volume is 225~300 liters / ha (15~20 litres per mu). When spraying, a spray can be sprayed at one time, and the spray can not be left and right.

The tractor sprayer is equipped with fan-shaped sprinkler, equipped with 11003, 11004 fan shaped nozzles and 50 sieve filters. The spray pressure is 2~3 atmospheres, the spray volume is 180-200 liters / ha, the height of the spray rod is 40 to 60cm from the ground level, and the speed of the vehicle is 6-8 km / h.