How to keep pesticide residues from exceeding the standard in greenhouse vegetable planting?

In the process of greenhouse vegetable cultivation, it is an unavoidable topic to use pesticides to control pests and diseases. However, pesticides are a double-edged sword, which cannot be controlled properly when used. Residues on vegetables will not only do harm to our health, but also directly or indirectly harm the surrounding environment. Then, in the process of growing vegetables in greenhouses, how to ensure that pesticide residues do not exceed the standard? Can you improve quality and efficiency to ensure a bumper harvest?

Understand pesticide residues in vegetables

Pesticide residue in vegetables refers to the general name of toxic substances left in vegetables and the environment after pesticide use. These toxic substances include pesticides themselves and their toxic metabolites, degradation products and impurities. Pesticide residues can be gradually digested by sunlight, hydrolysis and microbial degradation. The speed of digestion is related to the physical and chemical properties of each pesticide. Complete digestion needs 1 ~ 2 days, more than ten days, dozens of days or even longer.

If the pesticide residue in vegetables does not dissolve to the maximum limit standard stipulated by the state food safety before sale, it means that the pesticide residue exceeds the standard. Pesticide residue is the inevitable result of using pesticides, but we need to look at this problem objectively. In fact, according to modern toxicology theory, whether any substance is toxic to human body depends on its intake. If it exceeds a certain limit, it should be said to be toxic.

For example, nicotine, the main component of cigarettes, is actually a highly toxic substance. Rats will die if they ingest 1 mg per kilogram of body weight. Its toxicity is 20 times that of methamidophos, 450 times that of imidacloprid, 4640 times that of diflubenzuron and more than 15000 times that of carbendazim. Caffeine, the main component of coffee, is also moderately toxic, which is much more toxic than some pesticides and fungicides. Even salt has low toxicity, which is higher than the pesticide diflubenzuron and much higher than the fungicide carbendazim.

Therefore, pesticide residue is not as terrible as the legend, but we should not take it lightly. We should pay full attention to its harm and control its usage and residue not to exceed the standard and excessive, which will not cause harm to our health.

Causes of pesticide exceeding the standard in greenhouse vegetables

Greenhouse provides a suitable environment for vegetable growth, but also provides more opportunities for many pests and germs. In the process of vegetable cultivation in greenhouse, the main pests are aphids, whiteflies, tetranychus urticae, thrips and so on. The easily occurring diseases include fungal diseases such as powdery mildew, downy mildew, gray mold and leaf mold, as well as soil-borne diseases such as melon blight and pepper blight and bacterial diseases such as angular leaf spot.

It is precisely because of the frequent occurrence of pests and diseases in greenhouse vegetables, which seriously affects the healthy growth of vegetables, that pesticides are used. As mentioned earlier, pesticides are a double-edged sword, which can not only control pests and diseases, but also endanger the quality of vegetables. This is the result of excessive pesticide residues. So, what caused the pesticide residue to exceed the standard?

1, over-reliance on chemical pesticides

If our improper management in the process of vegetable planting leads to the frequent and rampant occurrence of these pests and diseases, we usually do not attach importance to the application of green pest control technology in planting management. Excessive dependence on chemical pesticides after the occurrence of pests and diseases is likely to lead to excessive pesticide residues.

2. Use high-residue pesticides

If pesticides with high toxicity and residues are used, it is more likely to cause pesticide residues to exceed the standard. Highly toxic pesticides have obvious harm because of their high inherent toxicity. High residue pesticides are not necessarily highly toxic, but they remain in the environment and vegetables for a long time and may have cumulative toxicity.

3, drug use is not standardized and scientific.

In addition to the above reasons, the most common reason for pesticide residues exceeding the standard is that we do not pay attention to the standardized and scientific use of chemical pesticides in production. The most common is the use of chemical pesticides in excessive concentration, dosage and scope. For example, when dispensing medicine, you don't need accurate metering equipment to dispense medicine, you can increase the dosage at will, increase the spraying times at will when preventing and controlling, and require spraying three times, or directly use high-concentration field crops and garden plants on vegetables; Poor atomization degree of sprayer or serious dripping phenomenon of nozzle will lead to excessive liquid medicine falling on vegetables, eventually forming pesticide residues.

In addition, repeated use of the same pesticide in a production season will make bacteria and pests resistant, so the dosage must be increased. Furthermore, medication is random and there is no symptomatic medication, which leads to poor prevention and control effect and requires more prevention and control times. The last point is that the application site of the drug is not accurate. Many diseases and insect pests, such as aphids and botrytis cinerea, mainly occur on the back of leaves. If we spray most of the liquid medicine on the front of vegetable leaves, the control effect will be very poor, so it is necessary to increase the control frequency or dosage. Many vegetable farmers think that the drug effect is not good and will increase the concentration of the drug. Not paying attention to the safe interval when picking vegetables is also an unscientific and irregular performance of drug use, and it is also one of the main reasons for the excessive pesticide residues.

How to prevent pesticide residues from exceeding the standard in greenhouse vegetable planting

In the process of greenhouse vegetable production, in order to ensure that the pesticide residues in the vegetables produced do not exceed the standard, the following aspects must be done well:

The first is agricultural measures to reduce pesticide residues exceeding the standard.

1, plant protection measures without chemical pesticides

For plant protection measures that do not use chemical pesticides, agricultural measures bear the brunt, such as crop rotation, selection of insect-resistant varieties, use of insect-free seedlings, fitness cultivation, and control of cultivation environment. In addition, there are some physical measures, such as hanging yellow and blue boards, applying insect nets, and solar high-temperature disinfection. And some biological measures, such as using natural enemies insects and biological pesticides. Using these measures well can help us greatly reduce the incidence of vegetable diseases and insect pests in all aspects of greenhouse vegetable production, reduce the degree of occurrence, and make many diseases and insect pests not occur, rarely occur or lightly occur.

(1) crop rotation

By changing the host vegetables, germs and pests can't adapt to the new host, so many diseases and pests can be avoided and alleviated.

(2) Selecting insect-resistant varieties

On the basis of crop rotation, if insect-resistant varieties are re-selected, the probability and degree of some pests and diseases will be further reduced;

(3) selecting healthy and disease-free seedlings

Vegetable production in greenhouse basically needs seedling transplanting, and the transplanting process is often the process of some pests and diseases entering the greenhouse, such as aphids, whiteflies, stem borers and so on. Therefore, it is very important to ensure good quality when raising seedlings. In addition to strong seedlings, seedlings should be disease-free and insect-free, which has a very obvious effect on reducing the occurrence of pests and diseases in the early stage of vegetables.

2. Preparations for the greenhouse

We should control the seedlings of vegetables, and we should also control the greenhouse. Greenhouse used for many years is often prone to accumulate more germs and pests, which is the initial source of infection for many vegetable diseases and insect pests. Therefore, the greenhouse must be disinfected before transplanting and planting. First of all, we should start with greenhouses and soil.

(1) high temperature stuffy shed

Vegetable production in autumn and winter can take advantage of shed break in July and August, choose sunny and hot weather, and use sunlight for high-temperature disinfection. This method is relatively simple. After the land is turned over, the greenhouse can be closed. If the environmental conditions can be maintained for more than 10 days, most pathogens and eggs on the greenhouse and soil surface can be killed.

(2) Sulfur fumigation and disinfection

The production of winter and spring crops and vegetables is not suitable for high-temperature greenhouses because the greenhouses are closed in the middle and late February, but we can carry out sulfur fumigation and disinfection. Sulfur powder melts at high temperature, releasing sulfur dioxide gas with pungent smell, which has the function of eliminating tiny pests and germs. Closed fumigation 1~2 days can also kill most pests, germs and other harmful organisms on the surface.

(3) Installation of necessary facilities

When choosing a shed film, don't be careless, you must choose a shed film without dripping; Air defense nets can isolate and block some migratory pests in space, and generally use 40~60 mesh insect nets. In addition, choosing a good cultivation form is also conducive to reducing the occurrence of pests and diseases. Plastic film mulching can prevent weeds that are easy to breed pests and diseases, and can also prevent water evaporated from the soil from evaporating into the greenhouse.

3. Reasonable close planting

After mastering the two levels of seedlings and greenhouses, the first thing to pay attention to is to arrange reasonable density when transplanting and planting. If the density is too high, the branches and leaves of vegetable plants are easy to block each other in the middle and late growth stage, which leads to the closed field environment and relatively high air humidity in some areas, and is easy to breed some high-humidity diseases such as pepper leaf mold, powdery mildew and downy mildew.

4, color swatch lure defense

Colors are very attractive to some insects, and these pests in greenhouses are no exception. Winged aphid whitefly likes yellow, thrips likes blue. In the greenhouse, a piece of 20? Is hanging in 15 cm above the plant every 20 square meters. 30 cm color board, this color board is coated with a very sticky glue, which can stick pests on it. This measure can be used to trap and kill winged aphids, whiteflies, thrips and other pests, which is helpful to control their harm to vegetables.

5. Environmental control

The occurrence of pests and diseases in the field is not only related to the number of disease sources and insect sources, but also directly related to environmental factors such as temperature and humidity. Therefore, in the daily management of greenhouse vegetable cultivation, the top air outlet should be opened in time every morning to keep the relative humidity of the air in the greenhouse below 60%. At the same time, open the waist tuyere at noon to cool down, and try to keep the temperature in the shed within the most suitable range of vegetable production stages.

6, vegetable fitness cultivation

Vegetable plants are robust, resistant to pests and diseases, and the incidence of pests and diseases is relatively low. By controlling the temperature and humidity, keeping the maximum temperature difference of 65438 05℃ every day, keeping sufficient illumination, adding reasonable fertilizer and water, providing balanced nutrition and other measures, the plants can grow healthily.

Second, reduce pesticide residues through biological control measures.

Biological control is a control method that uses beneficial bacteria or other organisms to inhibit or eliminate harmful organisms. It is a biological measure to prevent and control harmful agriculture by using the ecological phenomena and some biological characteristics of interdependence and mutual restriction among various organisms in the ecosystem. Therefore, biological measures are the best choice for early treatment if diseases and pests occur in greenhouse vegetables.

1, using natural enemy insects to control pests

Aphids, tetranychus urticae, whitefly, etc. Can be prevented and controlled by their natural enemies.

Aphids: Ladybug septempunctata and Harmonia axyridis are one of the common natural enemies to control aphids. The most convenient way to produce vegetables in greenhouse is to release the eggs of ladybugs. The method is simple. The eggs of ladybugs can be hung on plants in the field according to the ratio of 1:40. After 1~2 days, the eggs will hatch into larvae. Larvae and adults have strong predation ability on aphids. Tetranychus urticae: The most commonly used predatory mite for controlling Tetranychus urticae has strong predatory ability on Tetranychus urticae. In greenhouse vegetable production, predatory mites and feeding media are usually packed in small bags, which can be scattered on leaves or torn and placed next to plants with relatively concentrated tetranychus. Whitefly: Taiwan Province Aphid, a parasitic natural enemy, is usually selected for control. Aphid wasps can lay eggs in whitefly larvae, develop into adults and then fly out to kill whitefly. In greenhouse vegetable production, whiteflies are made into egg cards, which can be hung on plants where whiteflies are concentrated when released. 2. Use biological pesticides to reduce pesticide residues.

Among the biological measures used for early prevention and control of pests and diseases, biological pesticides have obvious curative effect. Bio-pesticide itself comes from nature, and it is easy to decompose into the natural environment with the changes of light and temperature and humidity. It has the characteristics of low toxicity, no toxicity or low residue. There are several types of biological pesticides, including microbial agents, such as Trichoderma and Pythium oligoandrosaceus. Metabolite preparations of microorganisms, such as agricultural streptomycin from ningnanmycin and polyoxin; There are also plant extract preparations such as matrine and eucalyptus oil.

Trichoderma, pythium shaoxiong: It can prevent and treat most fungal diseases. In particular, the control effect on soil-borne fungal diseases such as melon Fusarium wilt and pepper blight is more prominent. Drip irrigation of roots can prevent soil-borne fungal diseases, and foliar spraying can prevent fungal diseases on leaves. Polyoxin: The effect of controlling downy mildew of cucumber and other vegetables is obvious; Ningnanmycin: It is more effective for the prevention and treatment of viral diseases; Agricultural streptomycin: It has remarkable control effect on bacterial angular leaf spot. Matrine, eucalyptus oil essence: It is also effective in controlling pests such as aphids and whiteflies. The use of natural enemy insects and biological pesticides is greatly influenced by environmental conditions. Be sure to consult the local plant protection technicians and operate in strict accordance with the requirements of the instructions.

3. High temperature and stuffy shed in vegetable growing season

Some low-temperature diseases, such as cucumber downy mildew and gray mold, are very sensitive to high temperature. In spring, summer and autumn, the method of high temperature stuffy shed can also be used for treatment. Choose a sunny day at noon, close the greenhouse, let the temperature near the growing point of vegetables and plants reach 45 ~ 48℃ for 2 hours, and then start ventilation to cool down, from small to large, let the greenhouse temperature slowly return to the normal management temperature. This method can kill most downy mildew and gray mold in greenhouse.

Three. Requirements for the use of chemical pesticides

When diseases and insect pests in the field occur seriously or have an epidemic trend, emergency measures must be taken to control diseases and insect pests quickly with chemical pesticides. On the premise that chemical pesticides must be used, we should first choose drugs with low toxicity and low residue; Secondly, we should also pay attention to the scientific and standardized use of these low-toxicity and low-residue pesticides.

How to judge whether a pesticide has low toxicity and residue? It's actually quite simple. First, it depends on whether the pesticide packaging bag is marked with the words low toxicity and slight toxicity; In addition, it depends on whether the safety interval in the manual is very short. The shorter the time, the shorter the remaining period. Master the use of pesticides, and then standardize the use.

To achieve scientific and standardized drug use, we must first choose drugs scientifically and use drugs according to the symptoms. It is best to consult the local plant protection experts first. Secondly, when spraying medicine, you should use a measuring tool, accurately dispense the medicine according to the instructions, assemble it in a small container, dilute it evenly, and then add a sprayer for secondary dilution, so as to ensure the uniformity of the liquid medicine. Third, when pests and diseases occur seriously, it is necessary to use drugs with different mechanisms alternately to avoid drug resistance of pests and diseases.

The use of each pesticide should be carried out in strict accordance with the requirements of safe intervals, especially during harvest. And try to avoid using pesticides with long safe intervals. When spraying, choosing a sprayer with good atomization effect can greatly reduce the dosage. Finally, the samples should be sent to the testing center for testing, and a test report should be issued to create higher added value for the vegetables produced.

Preventing pesticide residues in greenhouse vegetables from exceeding the standard is a comprehensive work, and it is necessary to apply various technical measures reasonably according to the specific situation of vegetable production. In production, as long as we do it conscientiously, it is not difficult to control the excessive pesticide residues in vegetables, so as to ensure the healthy and orderly development of vegetable production activities more effectively, and let people create higher economic benefits for their own vegetable planting while eating safe and secure vegetables.