Occurrence Patterns and Control Methods of Peanut Spider Mites
Peanut spider mites occur commonly in Zhaoyuan City, mainly the carmine spider mite (Tetranychus cinnabarinus) and the two-spotted spider mite (Tetranychus urticae), among which the carmine spider mite has the highest occurrence density and causes the most severe damage, while the two-spotted spider mite affects a smaller area, but in recent years the two-spotted spider mite has shown an upward trend in Zhaoyuan City. In recent years, the damage caused by peanut spider mites has gradually intensified, seriously affecting the normal growth of peanuts, and it has become one of the important pests in peanut production.
1. Morphological characteristics. The female carmine spider mite is oval in dorsal view, with a body length of 0.42-0.56mm and a width of 0.26-0.36mm, and the body color is red or light red, commonly known as the “red spider”; there is one black spot on each side of the body, with the outer side trifid and the inner side near the middle of the body. The male mite is diamond-shaped in dorsal view and fewer in number than the female. The two-spotted spider mite is very similar to the carmine spider mite, with the difference being that the two-spotted spider mite is light yellow or yellow-green in body color, has no red individuals, appears nearly white to the naked eye, and is commonly known as the “white spider”.
2. Occurrence patterns and damage symptoms. Peanut spider mites produce 10-20 generations per year in Zhaoyuan City, overwintering as adult mites that spin silk webs in soil crevices, at the root zones of weeds along peanut field edges, or under tree bark, often gathering in groups and lying dormant. They begin activity in late March of the following year, migrate into peanut fields to cause damage from late April to early May, and reach peak occurrence in June and July, which can cause localized damage to spring peanuts. When the rainy season arrives in mid-July, the spider mite population decreases rapidly; in August, if the weather is dry, they can break out again and cause damage during the peanut pod stage. After the peanut harvest in mid-to-late September, they migrate to winter hosts, and overwintering begins in late October.
Peanut spider mites gather on the underside of peanut leaves to pierce and suck sap. The upper surface of damaged leaves is initially grayish-white and gradually turns yellow, and severely damaged leaves dry up and fall off. During the peak period of spider mite occurrence, because adult mites spin silk webs, plots with high population density may show a layer of white silk webbing on the surface of peanut leaves, and large areas of peanut leaves are bound together, which seriously affects the photosynthesis of peanut leaves, hinders the normal growth of peanuts, causes shriveled pods, and results in substantial yield loss.
3. Control methods
1) Agricultural control. Practice rational crop rotation to avoid spider mites transferring between hosts and causing damage; after the peanut harvest, plow deeply in a timely manner, which can both kill large numbers of overwintering spider mites and reduce host plants such as weeds; remove weeds along field edges to eliminate overwintering sources of the pest.
2) Chemical control. When a damage center is found in the peanut field or the damaged plant rate reaches more than 20%, spray pesticide promptly for control; spraying should be uniform and must reach the underside of the leaves; in addition, host plants such as weeds along field edges should also be sprayed to prevent their spread. The specific methods are: for plots with only carmine spider mite occurrence, uniformly spray 15% Saomangjing emulsifiable concentrate at 2500-3000 times dilution, 73% Propargite emulsifiable concentrate at 1000 times dilution, or 20% Mieshaoli emulsifiable concentrate at 2000 times dilution; for plots with mixed occurrence of carmine spider mite and two-spotted spider mite, spray 1% 7051 insecticidal substance emulsifiable concentrate (abamectin) at 3000 times dilution for control.