In recent years, the area of cultivated vegetables in facilities has been increasing day by day. Of course, the unique climatic conditions and ecological environment of facility cultivation, coupled with the long growing period, high yield and good benefits of monoculture, such as cucumbers, bell peppers, tomatoes, eggplants and other fruits and vegetables . It provides an annual living environment and feeding crops for whiteflies, aphids, leafminers, thrips and pest mites.
These five types of pests (mites) are called the "five small" pests (mites) because of their tiny size. It has strong fecundity and hidden damage. Its symptoms are often confused with other stresses, and it is difficult for a single prevention and control measure to achieve ideal control effects. Therefore, mastering the damage characteristics and prevention and control techniques of the "five minor" pests (mites) is of great significance to the production of facility vegetables.
1. Characteristics of hazards
(1) Bemisia tabaci
Bemisia tabaci can overwinter in the greenhouse. After the temperature rises in the following spring, it gradually migrates and spreads to the open field. The number of insects increases the fastest from July to August. After the temperature drops from October to November, it moves to the protected area to cause damage. Adult beetles like to live in groups on the underside of young leaves in the upper part of the plant to suck sap. As new leaves grow, the adults continue to move to the new leaves in the upper part, so there is a vertical distribution of damage spreading from bottom to top. The lower part of the plant contains pupae and newly emerged adults, the middle and lower parts contain nymphs, the upper middle part contains black eggs that are about to hatch, and the upper part contains adults and newly laid eggs. Adult insects like to live in groups, are not good at flying, and have a strong tendency towards yellow.
Bemisia tabaci damages plants. First, it directly sucks plant sap, causing plant nutrient deficiency. Second, if the adults secrete a large amount of honeydew, it can easily induce sooty mold disease and mold parasitism, seriously affecting the photosynthesis of leaves and reducing the economic value of vegetables. The third is the spread of viral diseases. As a vector of plant viruses, Bemisia tabaci can transmit Tomato Yellow Leaf Curl Virus (TYL-CV), which causes more serious damage to plants than the previous two.
(2) Aphids
The main aphids are melon (cotton) aphid and peach aphid. Adults and nymphs first pierce and suck plant sap on the underside of leaves, and then damage tender stems and flower buds. When the population is large, the entire host plant is almost completely covered by aphids.
Aphids damage plants by sucking plant sap, causing leaves to turn yellow, young leaves to curl, and stunted growth. Second, it excretes a large amount of honeydew that is easy to breed mold. Black mold covers the leaves, weakening the photosynthesis of the leaves, and covering the fruits reduces their commercial properties. Third, a variety of plant viruses, such as cucumber mosaic virus (CMV), are spread on crops such as cucumbers, zucchini, and bell peppers, resulting in serious economic losses.
(3) Spotted leafminer
The main species of leafminers on fruit and vegetables in solar greenhouses is American leafminers. In solar greenhouses, leafminers can occur every year. In winter, due to the low temperature and large temperature changes in the greenhouse, the insect body development is slow and the insect population number is extremely low. The ambient temperature in the greenhouse in spring and autumn is higher than the field temperature in the same period, which results in the early occurrence and rapid increase of insect population in the greenhouse, and the long-lasting occurrence and high insect population density in autumn.
The spotted leafminer likes to eat crops such as cowpeas, cucumbers, zucchini and tomatoes. Adult insects damage plants mainly by forming puncture wounds on leaves and feeding on them. The larvae use their mouth hooks to continuously scrape the palisade tissue of the leaves, leaving only the epidermis on the leaves, forming a snake-like tunnel, and photosynthesis is significantly reduced.
(4) Thrips
The main ones include western flower thrips, palm thrips, and tobacco thrips. The adults can fly and jump well, and can migrate long distances with the help of air currents. They are active on both sides of the leaves, flowers, young fruits and branches of the plants. They like the young parts of the plants most, and are more common in the upper and middle leaves of the plants. The adults have blue tendencies.
Because thrips are small, highly concealed, difficult to detect with the naked eye, reproduce quickly, and have a large population, they often cause damage to cucumber plants, causing leaf edges of young leaves to become scorched, slowing plant growth, and shortening plant height. When the leaf surface is damaged, silver stripes form along the leaf veins, causing the leaves to become hard and brittle. Damage to young melons will cause the young melons to lose their shiny color and become cork-shaped, and the melon strips will develop into deformed melons and cone-shaped melons. The yield will be reduced and the quality will be deteriorated. Damage to sweet peppers will cause flowers and buds to fall off, young leaves to curl and deform, stems to cork, young fruits to show chlorosis patches, and fruits to become smaller. Thrips also transmit a variety of plant viral diseases.
(5) Harmful mites
The harmful mites include spider mites and yellow mites. Spider mites mainly include two-spotted spider mites and cinnabar spider mites. They usually damage the lower leaves first and then gradually develop and spread upward. If the mites and adult mites are concentrated on the back of the leaves, they will suck the leaf juice, causing the leaves to quickly lose green, gradually turn brown, the leaves will become hard and brittle, and finally wither and fall off. Spider mites form webs on leaves and plants and crawl along the webs to spread the damage.
Favorite plants include eggplants, bell peppers, beans and many other crops. Tea yellow mites use adult mites or nymphs to suck the juice of plant buds, leaves and young fruits, and their habit is to become tender. In solar greenhouses, the damage is more severe during the autumn seedling planting and fruiting periods. The tender branches and leaves of bell peppers that are damaged during the seedling stage are stiff and upright, and are often mistaken for physiological diseases or viral diseases. Bell peppers are injured during the fruiting period, and the undersides of the leaves turn gray-brown or yellow-brown with an oil-stained luster. The injured young stems and twigs turn yellow-brown and become twisted and deformed. In severe cases, the tops of the plants dry up and die, the severely affected buds and flowers cannot open normally, and the affected fruits are deformed, browned, and corked. The boundaries between normal leaves and tender stems and leaves at the affected site are clear, with no transitional type in between. Severely damaged plants cannot produce new branches. The fruit becomes hard and dull but does not crack. After the eggplant is damaged, the fruits will crack and take on the shape of flowering steamed buns, taste bitter and astringent, and lose their commercial value; but the growth points of the branches will not die, and the side branches can be pulled out and continue to grow.
2. Prevention and control technology
(1) Insect source control
Mainly prevent and control the initial sources and transmission routes of the "five small" pests. Specific measures include:
① Cultivate insect-free seedlings. The nursery shed can be fumigated with 300 g of 22% dichlorvos smoke agent or 250 g of 20% isoprocarb smoke agent. To detoxify the seedling substrate, you can use Metabolite combined with solar energy to disinfect it at high temperature. The ventilation openings and doors and windows of the shed are covered with 60-mesh insect-proof net; yellow and blue insect trapping boards are hung inside the shed.
② Harmless disposal of plant residues. When changing crops in summer, pull out the vegetable residues with roots and leave them out of the shed for the time being. Use high temperature + chemical fumigation to completely disinfect the remaining insects, and then transport the treated remains out of the pile and return them to the fields.
(2) Prevention and control during production period
① Planting and rooting
When planting cucumbers, tomatoes, zucchini, eggplants and bell peppers, irrigate the roots with 2000 times of 25% thiamethoxam water-dispersible granules, 50 mL per plant. It can significantly delay the onset of whitefly in the greenhouse and control aphids, thrips, leafminers and other pests.
② Insect-proof net isolation
Set up a 60-mesh insect-proof net at the ventilation openings, doors and windows of the greenhouse to prevent aphids, leafminers, whitefly and other pests from migrating into the greenhouse.
③ Color plates attract pests
After the seedlings are planted, hang 20 to 25 pieces/667m2 of 30 cm × 25 cm yellow boards above the vegetables, which can trap and kill aphids, leafminers, whiteflies and some adults of thrips; hanging blue boards can trap and kill a variety of thrips. Hanging yellow and blue boards can also be used for monitoring and early warning. According to the trapping situation on the color boards, the amount and occurrence period of pests can be predicted, thereby providing a reference for early prevention and control.
④ High temperature and stuffy shed
When the outside temperature reaches above 20°C, greenhouse cucumber production can use high-temperature stuffy shed processing. That is, the temperature of the stuffy shed is raised to 45 ℃, and the air vent is slowly opened after continuing for 2 hours, which can kill thrips, leafminers, whiteflies, and aphids, and the effect is remarkable. Water 1 day before the shed is established, and manage fertilizer and water normally after the shed is established.
⑤ Chemical control
To control aphids, whitefly, and thrips, chemicals such as buprofen, pyriproxyfen, spirotetramat, cyantraniliprole, chlorothiazide, emamectin, sulfonicamid, and spinosad can be used. Abamectin and cyromazine can be used to control Liriomyza larvae; in greenhouses where adults and larvae are mixed, Avib insecticide sheets can be used. To control aphids, thrips, whitefly and adult leafminers, 20% isoprocarb smoke can also be used for fumigation.
To prevent and control harmful mites, you can choose avermectin, etoxazole, bifenazate, spirodiclofen, pyridaben, ethofenitrile and other chemicals. Pay attention to the rotation of medication. When spraying to control spider mites, spray evenly on the front and back of the leaves; when controlling tea yellow mites, the spray should focus on young leaves, tender stems, flower organs, young fruits and other parts.
The "five small" insects are very harmful and difficult to control. It is necessary to combine prevention and control, with prevention as the priority, and a combination of various means.
