Occurrence and control of spider mites in peanut species

Tetranychus dichotomus occurred widely in Zhaoyuan City, mainly Tetranychus cinnabarinus and Tetranychus dichotomus. Tetranychus dichotomus occurred most frequently and seriously, and Tetranychus dichotomus occurred less in the area. However, Tetranychus dichotomus had an upward trend in Zhaoyuan City in recent years. In recent years, the damage of peanut spider mite is gradually aggravated, which seriously affects the normal growth of peanut and has become one of the important pests in peanut production.

1. Morphological characteristics. The female mite of Tetranychus cinnabarinus is oval in shape, 0.42~0.56mm in length and 0.26~0.36mm in width. Its body color is red or light red, commonly known as "red spider". There is a black spot on each side of the body, which is trifid on the outside and close to the middle of the body on the inside. Male mites are rhombic in dorsal view and less than female mites. Tetranychus bipunctatus is very similar to Tetranychus cinnabarinus, except that Tetranychus bipunctatus is pale yellow or yellow-green in body color, without red individual, nearly white in naked eye, commonly known as "white spider".

2. Occurrence law and harmful symptoms. Peanut spider mites occur 10~20 generations a year in Zhaoyuan City, overwintering as adult mites spinning silk under the rhizosphere or bark of weeds in soil crevices and peanut fields, and often gathering and hiding in groups. The activity begins in late March of the following year, moves into peanut field from late April to early May, and occurs in peak period between June and July, which can cause local damage to spring peanut. When the rainy season comes in mid-July, the occurrence of spider mites decreases rapidly. If the weather is dry in August, it can occur again and cause damage in the pod stage of peanuts. Peanuts move to winter parasitism after harvest in mid-late September and begin to overwinter in late October.

Peanut spider mites swarm on the back of peanut leaves to suck sap, the front of the injured leaves is gray at first, gradually turning yellow, and the seriously injured leaves dry and fall off. In the peak period of spider mite occurrence, a layer of white net can be seen on the surface of peanut leaves in the plots with high insect density, and large peanut leaves are connected together, which seriously affects the photosynthesis of peanut leaves, hinders the normal growth of peanut, makes pods shrivel and reduces production in large quantities.

3. control methods

1) Agricultural control. Reasonable rotation of crops can avoid the mutual transfer of spider mites among hosts; timely deep ploughing after peanut harvest can kill a large number of overwintering spider mites and reduce weeds and other host plants; weed at the edge of fields can be eliminated to eliminate overwintering insect sources.

2) Chemical control. When the disease center is found in the peanut field or when the pest rate reaches more than 20%, it is necessary to spray the pesticide in time for prevention and control. The spraying should be uniform and must be sprayed to the back of the leaf; in addition, the host plants such as weeds on the edge of the field should also be sprayed to prevent their spread. The specific method is as follows: uniformly spraying 2500 - 3000 times solution of 15% saomijing emulsifiable solution, 1000 times solution of 73% propargit emulsifiable solution or 20% miprochlorid emulsifiable solution on a single occurrence plot of Tetranychus cinnabarinus; spraying 3000 times solution of 1%7051 insecticide emulsifiable solution (abamectin) on a mixed occurrence plot of Tetranychus cinnabarinus and Tetranychus dichotoma.