Problems needed to be concerned in the usage of orchard biological pesticides
Biological pesticides are used to prevent the living modified organisms and physiological activators of the agricultural plant disease, insect pests and rats, health pests and other pests, which can also be made into the listing and circulating biological source agent commodities including the microbial source (such as bacteria, virus, fungus and its secondary metabolites), plant source, animal origin, transgenic plants resistant to plant disease and insect pests and so on. The common characteristic of biological agent is mainly in its low toxicity, non-residue, slow effect and long lasting period. Its compounding concentration and dosage are lower than the exact bottom of chemical agent and it will not cause phytotoxicity to the plants when the doses are slightly larger. It is also safe for the humans and animals and will not pollute on the environment. In the production process, the prevention of biological pesticides used in the plant disease and insect pest has caused the attention of all over the world. As the using effects of biological pesticides are influenced by multi factors, it has a series of problems in the practical applications. Therefore, we should make the most of the favorable factors and overcome and avoid the negative factors in the scientific use of biological pesticides. When using the biological pesticides, the following points should be paid attention to:
a. The prevention objects differ in different biological pesticides varities
In the practical application of biological pesticides, many people do not fully understand the nature of biological pesticides. They mistakenly think that the biological insecticide and fungicide can prevent all the plant disease and insect pests and generally use it without choosing, thus will not only not receive the desired effects, but also will delay the prevention time. The selectivity of biological drug is very strong, for example, the bacillus thuringiensis (BT), is effective in preventing lepidopteran larvae, but it has no pathogenicity to homoptera leafhopper. Besides, different varieties of bacillus thuringiensis have different preventing effects on several kinds of important pests. In addition, different types of biological pesticides should be used according to the feeding characteristics of the pests. For example, BT works well on the lepidoptera pests. It will distribute on the plant surface after spraying and make the pests eat it or died by touching it. However, it has no effect on the sucking juice pests (such as the aphids and mites), while abamectin insecticide has very good killing effect on the mites. In consequence, we should specifically choose the suitable biological pesticides varieties for different kinds of insect pests. When using the biological pesticides, we advocate cooperatively using two or more of its drugs. In the prophylaxis era and under the condition of sustained medication, we can sufficiently use one of its drugs, but it should not be used alone in the plant disease and insect pest season.
b. Choose the appropriate biological pesticides formulations
The control efficiency of biological pesticides used in farming is often closely related with the formulations and using technology. When using it, we should correctly choose the appropriate formulations according to the prevention objects, weather conditions and usage time so as to achieve the best control efficiency. For example, the powders can be scattered in wide range with the help of air buoyancy and wind, thus it will have large contact with the pests; for the pests which eat large amount of leaves, we can adopt the method of adding water into the wettable powder and change it into suspension. Its spraying effect will be better than the dusting method. Capsules not only have long releasing effect, but also can protect its pathogens from the influence of environmental factors, which can be used in the greenhouses broadcasting.
c. Confirm the appropriate prevention time
As the biological pesticides work slowly, they are appropriately used in the young larva stage of the pests. Many insecticidal effects of the biological pesticides are slow and they cannot compare with the chemical pesticide which can get the effect instantly after spaying it. Therefore, the medication time of biological pesticide should be 2-5 days earlier than the chemical pesticide. Take BT emulsions and beauveria bassiana as examples, after spaying them, the pests will gradually die in 3-5 days.
d. The spraying weather conditions should be concerned as the using effect of biological pesticide is influenced a lot by the environmental factors:
The temperature of biological pesticide should be controlled in more than the ideal 20 degrees celsius when it is spraying. This is because the active ingredients of these kinds of pesticides are composed by the protein crystal and living spores. Once the biological pesticide is sprayed lower than the above temperature, the propagation speed of spores in the pest body will be very slow and the protein crystal will also be difficult to play its role, thus the control efficiency will not be came out after spraying. The experiment data shows that, in the temperature between 25-30 degrees celsius, the biological pesticide effect will be 1-2 times higher than the temperature between 10-15 degrees celsius.
Biological pesticide has very sharp requirements on the humidity. The pesticide effect of biological pesticide agent will be more outstanding if the environmental humidity is bigger which is especially obvious in the powder biological pesticide agent.
The ultraviolet light in the sunlight has deadly killing effect on the spores. The scientific experiments shows that the spores will be killed by 50 percents with the direct sunshine for 30 minutes and the death rate of the spores will reach up to 80 percents after irradiation for 1 hour. Besides, the radiation of ultraviolet light will also generate the deformation and reduction effect on the parasporal crystals. Therefore, we should use the pesticide at 4 o’clock in the afternoon or in the cloudy days to make the most use of its effect.
As spores are most afraid of being washed out by the downpour, they should be conducted according to the weather forecast. The downpour will wash out the spraying liquid which will lose its killing effect. If it rained (light rain) after the spraying (5-6 hours later), the pesticides effect will not be reduced, on the contrary, the control effect will be improved. This is because the light rain is favourable to the spore germination and will accelerate the pest death after they eat the spores.
e. The appropriate spray equipment
As most of the biological pesticide has no systemic, it should be sprayed evenly to achieve the good results. In the practical application, currently the availability factor of most of the plant protection equipments is low, which are often used to directly spray the crops from top to bottom. Thus larger amount of pesticide will be gathered in the leaves of the top crops, while less of it will be attached in the leaves of the middle and down crops and more of it will fall or be damaged in the soil surface. If the fogdrop is large, the damage will be greater. Due to the high production cost of biological pesticide, we should choose the plant protection equipment which has high spraying efficiency, good atomizing degree and also save the pesticides, such as the mist dusters, mist sprayers and so on.
f. The mixture of biological pesticide
a. Biological insecticides mixtures: Biological insecticide can be fully mixed with most of the chemical insecticides as most of them are chemical acid and physiological neutral, which have no inhibition effect and neutral reaction with bacteria and fungus. It can be seen that the biological insecticides should not be mixed with the chemical disinfectant as the active bacteria spores of the biological agent will be killed and lose its potency once the two of them are mixed. b. Mixture of bio-fungicides: Biological fungicide can be mixed with multitude chemical agent and biological agent, but it cannot be mixed with the alkaline drugs. Only a few medicines cannot be mixed with acidic reagent, for example, the trichodema agent can be mixed use with most biological insecticides and chemical insecticides at the same time.
g. Mixing and using the biological pesticide at the same time
The biological pesticide should be mixed and used at the same time. The finished pesticide should be used up in one time. For example, the finished pesticide of beauveria bassiana should be sprayed out within 2 hours in case that the spores germinate too early and lose its effect.
h. Pay attention to the storage
The storage place of biological farming pesticides should be shady and cool and dry so as to avoid the dampness and losing its effect. Take bacillus thuringiensis and validamycin as examples, their nature are non resistant to high temperature, non resistant to storage, easily hygroscopic mildew and losing its activity and effect. Besides, their shelf life cannot exceed 2 years.