Our Weicheng District is a traditional agricultural county. The production of corn affects the income of farmers to a certain extent. Therefore, the cultivation technology of corn is a serious issue for us.

The two-spotted spider mites (Tetranychus urticae) and the genus Tetranychus cinnabarinus are distributed throughout the country.

[harmful symptoms]

If the sputum and the sorghum group collect the juice from the back of the leaf, the leaves are grayish white or yellowish and fine spots. When it is serious, the whole leaves are yellow and shrink, until they are dry and shed, and the corn kernels are thin, resulting in reduced yield and no harvest.

【Morphological characteristics】

Two-spotted spider mites: the females become ochre and change in color, such as dark green, brownish green, dark brown, orange red, etc.; each side of the body has a dark red long spot on each side, and sometimes the middle part of the spot is divided into two parts. The female is oval, mostly dark red, and also yellow-brown; the wintering is orange-yellow, which is larger than the summer type. The male corpus callosum is nearly oval, with a rounded front end and a sharp abdomen at the end of the abdomen. Oval, smooth, initially colorless and transparent, with a gradient of orange-red, will show red eyes when hatching. When the baby cubs hatch, it is nearly round, colorless and transparent. After feeding, it becomes dark green, red eyes and 3 pairs of feet. If the corpus callosum is nearly oval in the early stage, the color becomes darker and the pigmentation appears on the back of the body; if the corpus callosum is yellowish brown in the later stage, it is similar to the adult.

The cinnabar leaf mites: the females have an elliptical shape; the sides of the body have a three-lobed strip-shaped dark brown large spot. The male body has a rhomboid shape, generally red or rust red, and also has a thick greenish yellow color, and the foot is 4 pairs. The egg is nearly spherical, initially colorless and transparent, gradually becoming yellowish or orange-yellow, and is reddish before hatching. Cub and Ruoqiang: The eggs are aged after hatching, and only have 3 pairs of feet, called juveniles. After the baby's skin becomes 2 years old, it is also called the early stage. If the skin is in the early stage, it is 3 years old. It is called the late stage. If there are 4 pairs of feet in the last stage, the males only have 1 skin in their lifetime. Hey. The baby is yellow, round, transparent and has 3 pairs of feet. If the body appears to be a scorpion, it has 4 pairs of feet. In the early stage, the body color was light, and the body color became red in the later stage.

[occurrence law]

Two-spotted spider mites: more than 20 generations per year in the south and 12-15 generations in the north. The wintering place varies with the area. In the north of China, the female adult worms in the weeds, litter and soil joints lurking over the winter; in China, weaving in weeds and bark seams in various insect states; Adults overwinter on weeds or peas and broad bean crops. When the average temperature in February reaches 5-6 °C, the overwintering females begin to move. From March to April, they first feed on weeds or other harmful objects. From late April to mid-May, they move into melon fields. Then spread the whole field. From mid-June to mid-July, it is a period of damage. Corn fields near the villages, orchards, greenhouses and weedy Xiangyang Ditch are early and heavy, followed by perennial dry fields.

Tetranychus cinnafolia: 12-15 generations occur in the north, 18-20 generations in the Yangtze River basin, and more than 20 generations per year in southern China. In the grass roots, dead leaves and soil cracks or bark cracks, the silky nets cluster over the winter, and up to thousands of heads can be gathered together. In the middle of July, the rainy season came, and the amount of leafhoppers decreased rapidly. If the weather is dry in August, it can happen again. Drought and heavy rain occurred severely; heavy rains had a significant inhibitory effect on the occurrence of Tetranychus cinnafolia; rotation crops occurred lightly, and adjacent or intercropped melons and fruit trees were heavier.

[Control method]

Arrange the crops and intercropping and intercropping crops in a reasonable manner to avoid the transfer of leafhoppers between the hosts. It is best to use water and drought. Strengthen field management, keep the pastoral clean, timely eliminate the weeds and dead branches of the fields and burn them to reduce the source of insects. Pay attention to irrigation when it is dry, increase the humidity in the field, which is not conducive to its reproduction and development. In combination with field management, when the leaves are found, they are wiped off by hand; if the amount of wax is large, the leaves are removed. After the harvest, the field branches, fallen leaves and weeds are removed in time and burned intensively. Deep conditions and winter irrigation can be carried out in places where conditions permit.

When the amount of single insects reaches more than 200 after the jointing stage of corn, spraying chemicals is prevented. The following agents can be used: 15% scented emulsifiable concentrate 2000-2500 times solution; 73% gram emulsifiable concentrate 2000-3000 times solution; 20% fenpropathrin emulsifiable concentrate 1000-2000 times solution; 20% compound liuyangmycin emulsifiable concentrate 1000 - 2000 times liquid; 20% double nail emulsifiable concentrate 1000-1500 times liquid; 2.5% cyhalothrin emulsifiable concentrate 2000-4000 times liquid; 2.5% bifenthrin emulsifiable concentrate 3000-4000 times liquid; 5% thiabendone 2000-3000 times of emulsifiable concentrate; 3000-4000 times of avermectin emulsifiable concentrate; 600-1000 times of 20% dicofol emulsifiable concentrate, sprayed once every 7-10 days, continuously 2-3 times. The medicine should be used in rotation to avoid drug resistance. The spray should be uniform and must be sprayed on the back of the leaf. In addition, the host plants such as weeds on the field should be sprayed to prevent their spread.