The action mechanism and use technology of biopesticide on vegetables
With long term heavy use of chemical pesticide on crops, especially on vegetables, pesticide residue problem has attracted the public attention day by day. The demand of pollution-free vegetables is increasing rapidly, which can help to completely eradicate the pesticide residue from source and develop green agriculture. Therefore, it has become an inevitable trend in improving the control efficiency of biopesticide.
The action mechanism of biopesticide
Biopesticide, a kind of pesticide that derives from biology (animals, plants and micro-organisms), which has control effects on specific pests and extremely high security. Biopesticide has high efficiency, low toxic, no residue (has no accumulation in the environment), slow drug resistance and other advantages. It mainly includes below three categories:
a. B.t. (bacillus thuringiensis microbial pesticides), is a kind of bacillus, of which the insecticidal active ingredients are parasporal crystal and spore toxin. B.t. can kill the pests, which mainly relies on stomach action. Pests will stop feeding after eating the pesticide due to the bacterial toxin effect. Meanwhile, spores will germinate in the polypide and breed in large quantity, which will lead to the death of pests.
b. Abamectin, a new kind of antibiotics insecticide and acaricide, has stomach action and contact action, but almost has no systemic action and fumigation action. It can enter the insect body through the spiracle and palmula of insetcs, besides, it has good conduction in the cortical flow. It can influence the pests’ lives by hindering the nervous system of pests, in which the pests will have paralysis symptom after eating the drug, afterwards, their activity and feeding behavior will slow down until stop and will die eventually.
c. Nicotine + Matrine, a kind of botanical insecticide, its main compositions are nicotine and oxymatrine. It has stomach action, contact action and fumigation action on the pests, of which the toxicity mechanism to the pests is nerve paralysis. As the vapor of Nicotine + Matrine can enter the insect body from any part of insect, it will have toxic action on the pests.
Confirm appropriate drug delivery time
As biopesticide usually has slower drug effect than chemical insecticide, it should be sprayed ahead of time. Take abamectin miticide as an example, it will have best effect when it is sprayed in the period from the eclosion peak stage to second instar larvae stage of diamondback moth and other pests, however, it has low control effect on high instar larvae and pupa. B.t. and Nicotine + Matrine both have higher control effect on the low instar larvae than high instar larvae.
Reasonably control the drug concentration according to different prevention object
Different kinds of pests and insects that have different insect state will have different sensitivity to the biological pesticides. Therefore, in order to achieve good control effect, different kinds of pesticides should be selected and different drug concentrations should be used according to the pests’ sensitivity. For example, as the cabbage caterpillar is sensitive to abamectin insecticide and B.t., 3500-4500 times liquid of abamectin and 500~1000 times liquid of B.t. can be used.
Choose the suitable weather conditions
The biological activity of abamectin is related to temperature. Under same concentration, when the temperature is higher, the biological activity will also become higher, which can be called positive temperature effect. Therefore, abamectin is more suitable for being used in the pest control of vegetables in summer and autumn when the temperature is rather high. Spores in the B.t. insecticide will have highest activity and good effect when the air temperature is in the range of 20 degrees Celsius to 25 degrees Celsius and the relative humidity is more than 85 percents. Although it has strong activity under the conditions of less than 20 degrees Celsius of air temperature, long time solar radiation and strong storms, it will have poor effect. When the light is strong and the air temperature is more than 25 degrees Celsius, it can only be sprayed at 5 PM in case that the spores may be damaged by the ultraviolet ray. Besides, it can be sprayed throughout the cloudy day.
Pay attention to the spraying method of biopesticide
As the biological pesticide mainly has stomach action, it should be sprayed evenly and should be sprayed over the front and back of the blade so as to improve the pesticide effect. In order to improve the adhesiveness of abamectin pesticide, a small amount of vegetable oil can be added in the dilution process. Powder and granules of B.t. should be sprayed in the morning and evening or after slight rain, thus the drug will adhere to the stem leaves of crops and have toxin effect on the pests. Regarding the vegetable variety that has thick wax coat, a small amount of washing powder can be added in the process when the insecticide is diluted so as to enhance the adhesive ability of the pesticide.