The prevention and control of whitefly has always been a headache for everyone. Recently, some farmers have reported that the whitefly in the greenhouse and the open field has become a disaster. The medicine is not easy to use, the insects are not dead, what is it? Look at this article, can you give me some answers?
Whitefly, also known as the white moth, is a worldwide pest that was introduced to China in the 1970s. Whitefly is harmful to many plants such as vegetables, fruit trees, herbs, pastures, and tobacco. Generally, it can cause losses of 10% to 30%, and severe cases can be as high as 70% or more. In vegetables, eggplant, pepper, cucumber, tomato, etc. are particularly seriously affected.
At present, whitefly has become a major pest in greenhouses, greenhouses and open field vegetables, and the degree of damage is increasing year by year, making it difficult to control.
2 Law of occurrence
The activity temperature of adult whitefly is 22 Â°C ~ 30 Â°C, and the temperature of reproduction is 18 Â°C ~ 21 Â°C. It has the characteristics of tenderness, yellowing and lightening.
Due to the close connection and alternating between the greenhouse and the open field vegetables in recent years, the hazard of the insect has occurred. The northern greenhouse has more than 10 generations of years, overlapping generations.
Whitefly has two key periods throughout the year:
(1) In the spring, it occurs in the greenhouse, and the time is from mid-April to late May;
(2) Autumn, occurs in greenhouses, cold sheds, open fields, etc., from the end of July to the end of September, the greenhouse will continue until the end of November.
Generally, adults and nymphs like to cluster on the back of plant leaves, so that the sucking mouth can absorb the plant juice, so that the damaged leaves are chlorotic, yellow, wilting, and even the whole plant is dead. Adults will be excreted, and excrement will seriously affect the fruit surface or leaf surface of the fruit, causing diseases such as soot disease. And it also spreads a lot of viruses, causing other diseases to occur.
4 Causes of difficulty in controlling whitefly
(1) There are many breeding places. With the continuous expansion of greenhouses, greenhouses, and open field vegetables, whitefly has enough food and breeding sites throughout the year.
(2) The amount of reproduction is large and the breeding is fast. More than 10 generations can occur each year in the greenhouse. The developmental time of each generation is shortened with increasing temperature. It takes 31.5 days to breed at 18 Â°C; 24.7 days at 24 Â°C; 22.8 days at 27 Â°C. The developmental stages of each insect state at 24 Â°C were: 7 days in egg stage, 5 days in 1st instar, 2 days in 2nd instar, 3rd in 3rd instar, and 8d in pseudoprine.
When the average temperature of the greenhouse is 19 Â°C, the first generation is about 30 days, and the number of eggs laid per female is as high as 3,000 to 4,000. After 1 generation, the population can be increased by 140 to 150 times. The number of reproductions has grown exponentially and is rare among agricultural pests.
(3) There are many types of vegetables. There are more than 200 host plants of whitefly. Vegetable crops mainly include cucumber crops, zucchini, pumpkin, melon and other melon crops, eggplants such as eggplant, tomato and pepper, cruciferous crops such as cabbage, white raisins and radishes, legumes such as kidney beans and lentils, and lettuce. Other crops such as Jerusalem artichoke, potato, and leek.
(4) Four insect states are simultaneously distributed. Adult whitefly can fly short distances, distributed on the back of the young leaves of the plant, and lay eggs on young leaves.
As the plants grow, the adults continue to transfer to the upper leaves. The insects form a certain pattern on the plants: the uppermost leaves, mostly adult and primiparous yellowish eggs, and the lower leaves are mostly black eggs. Most of the lower part is the nymph of the first age, then the nymph of the middle age, and the lower part is the sputum. The insects on the plants are more complicated and difficult to control. General medicine can only kill adult worms, it is difficult to kill eggs and larvae, the number of medications can not keep up with the speed of reproduction, resulting in more difficult to treat.
(5) People's awareness of prevention and control is weak, and they are re-evaluated. After the vegetables are planted, the young leaves are the best food for the whitefly pests. Some farmers have a weak sense of using insect nets, there is no hole to make up, there is a gap, and even after planting, vegetables start to grow. After using the whitefly, the insect net is used, which is very bad for controlling the whitefly.
(6) The problem of drug selection. Some medicines only kill adult insects and do not kill eggs, which leads to the continuous growth of eggs after hatching; some medicines only kill eggs without killing adults, causing adults to continue to lay eggs, and the eggs continue to hatch after hatching.
For example, the imidacloprid, acetamiprid, nitenpyram, pymetrozine, thiamethoxam and other agents that we usually use are all adult worms, but they have no good effect on the other three insect states.
5 Prevention and control measures
(1) Rotation. In areas where whitefly mites occur, the open-season vegetables in the sheds for autumn and winter rafts or sheds should be selected from amaranth, celery, tube stalks, spinach, rapeseed, garlic, and other white glutinous vegetables that are not suitable for food and low temperature. Harmful can prevent it from spreading to the shed.
(2) eradication of insect sources. Before planting, the residual leaves and weeds of the former crops were cleared to the field, buried or burned; the pruning was strengthened during the growth of the vegetables, and the dead yellow leaves and diseased leaves were removed and burned outside the shed. During the summer off-season period, high temperature suffocation can effectively eliminate the whitefly in the shed.
After sowing, 25% of the vegetables can be simmered and smouldering with wood chips, and ventilated for 8 to 10 hours. An insect net is installed on the seedbed or in the greenhouse vent to prevent foreign insects from moving in. The insect-proof net is preferably 40 to 60 mesh.
(3) trapping and avoiding. Whitefly has a strong tendency to yellow. In the early stage, yellow sticky insect boards can be set in the greenhouse to trap adults. In winter and spring, a yellow plate is placed in combination with a reflective curtain in the greenhouse to repel the whitefly and increase the light on the plant.
(4) Biological control. When the adult whitefly of the whitefly in the greenhouse has an average of 0.5 to 1 head per plant, the artificially propagated Lizard wasps are released, and each plant releases 3 to 5 heads of the adult beetle or black cockroach, and is placed once every 10 days. Released a total of 3 to 4 times. The control of whitefly is good. It is also possible to artificially release the grasshopper, and the average of one grasshopper can prey on 172.6 heads of whitefly larvae. In the conditioned areas, it can also be used to control whitefly.
(5) Chemical control. In the early stage of the occurrence of whitefly, the drug is administered in time, that is, when the average number of adults per plant is 2 to 3, especially in the stage of "spotting". The spraying time is best when the morning dew is not dry. In the middle and afternoon, the white powder is dry and easy to fly, and it is not easy to spray onto the body. At present, there seems to be no particularly good product for a single dose. For some time, the mixture of nitenpyram and pymetrozine worked well, but the resistance is not small. Now, there is a small method of using thiamethoxam water-dispersible granules to put a little bit on the root of each vegetable, which can basically prevent the sucking mouthparts pests such as whitefly, thrips and aphids throughout the growth period.
It is also recommended to follow two principles when spraying:
(1) Select insecticides with different mechanisms of action. For example, imidacloprid, acetamiprid, nitenpyram and other nicotine insecticides and pyridylamide flonicamid, or pyridine pyridone. It can also be controlled by the combination of ethyl spinosyn + acetamiprid; spirotetramat + imidacloprid; bifenthrin + thiamethoxam.
(2) Adult and nymphs are simultaneously controlled. It is recommended that the above insecticides be used in combination with spirotetramat or pyriproxyfen, and the adult nymphs are simultaneously controlled.
At the same time, in the case of serious resistance to pests, try mineral oil. The test results show that some mineral oils have high activity against whitefly.
(Source: Tianbao Agricultural Technology Service Platform)
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