Four issues encountered in the abamectin application in china
Abamectin is a kind of biological insecticides, biological acaricide and biological nematicides that can paralysis and kill the pests as well as has main stomach toxicity and contact action on the pests. According to the report, it has more than 84 kinds of insecticidal spectrum which can effectively control the hemiptera insects and various pest mites. In 2005, its global sales amount reached US $175 million and US $215 million in 2007. For a long time, it has been widely used in effectively control the dipteral, homoptera, lepidoptera and mite pests in the agriculture and forestry. At present, china’s annual production of abamectin is about 1800t, in which 80 percents are for export. Currently, the abamectin products registered by more than 400 enterprises in china are accumulated to above 1300 kinds, of which the sales revenue of abamectin (including the export) reaches more than 1 billion Yuan.
Abamectin insecticide is the first batch of variety that can replace the high-toxic pesticide in china, which can be used to prevent rice leaf folders and two-spotted spider mites. Especially in 2009 when the rice market was opened, the sales amount of a Chinese enterprise reached 200 million Yuan by salling a series of products with abamectin-base. However, with the rapid development and wide applications of abamectin in china, some of its problems that exist in the application should be discovered and brought to the forefront.
Increasing resistance to abamectin
In recent years, due to the irrational and unscientific use of abamectin of Chinese farmers, pests are increasing their resistance to abamectin and the dosage grows almost by 1/4. When abamectin was just listed in china, the registration content of abamectin EC was only 0.2 percent, while currently some abamectin manufacturers register 5 percents of abamectin EC products. In 1995, the dilution ratio of 1.8 percents of abamectin preparations that used to prevent no-resistant pests was 15,000 times, while now the dilution ratio is 2000-3000 times.
Processing formulation problem
Currently the main dosage form of abamectin pesticide is emulsifiable concentrate. 90 percents of dimethybenzene xylene needed to be used in processing 1.8 percents of emulsifiable concentrate. Therefore, it is a kind of non-safe and non-environmental dosage form that has big pollution, high toxicity and high cost.
Currently the dosage forms which can replace abamectin EC include Emulsion in Water, microemulsions and water dispersible granules. By processing abamectin into microemulsions, the solvent dosage and cost can be both reduced. However, the dermal toxicity, safety and environmental conservation of the microemulsions made by processing abamectin will be worse than the Emulsion in Water which is made by processing abamectin because the former needs more Emulsion in Water than emulsifiable concentrate and a large number of polar solvent are used as the cosolvent. By processing it into 50 percents of water dispersible granules, its safety and environmental conservation will be both excellent, while its market prospect mainly depends on the production equipment investment cost and finished cost, in which the equipment investment cost will be very high by processing the water dispersible granules no matter in atomizing, extrusion, fluid bed drying, disk granulating method or other granulation methods. In addition, as the dilution ratio is particularly large in using abamectin water dispersible granules, it will bring many adverse factors in generalizing and applying abamectin water dispersible granules.
As 1.8 percent of abamectin Emulsion in Water has lower dermal toxicity than the emulsifiable concentrate and microemulsion and fairly pesticide effect with the emulsifiable concentrate that has same dosage as well as equivalent safety and environmental conservation with water dispersible granules, besides, it has lower production cost and sales price than emulsifiable concentrate, microemulsions and water dispersible granules, it is the best dosage form that can replace 1.8 percent of abamectin EC and has the best market prospect.
The toxicity problem of abamectin
Many biopesticide can meet the new pesticide requirements of high efficiency, low toxicity, low-residue and no pollution, however, abamectin is a kind of high toxicity variety for human beings, livestock, bees and bombyx mori. Its rat oral LD50 in female rats and male rats are both 21.5 mg/kg (13.8-33.6 mg/kg) and according to the acute oral toxicity classification standard, it belongs to the high toxic level. Therefore, abamectin has high toxicity to fish, shrimps and other aquatic organisms and there exists potential danger for the aquatic organism when it is used on the paddy. Certainly, this problem can be solved by changing its dosage form (such as Emulsion in Water, water dispersible granules and so on), using the environmentally friendly additives or mixing use it with other low toxicity pesticide (such as chlorpyrifos, monosultap, B.t. and so on). After its dosage form toxicity is being reduced, it can be also used to prevent rice stem borer, rice leaf roller and other rice pests.
The photodecomposition of abamectin
As abamectin is sensitive to ultraviolent light, it has high photodecomposition; however, a small part of its effective constituent will enter the blade after using it, which is proved in many reports. Especially under cool conditions, it will have good penetrability and has good control effect on the mites that will do harm to the plant leaves; while it has no effect on the aphid in the same blade as the aphid will penetrate the phloem to eat by using its lancet, where the abamectin dosage is too small to kill the aphid.
In order to reduce the abamectin sensibility to the ultraviolent light, the decomposition of agentia should be avoided to ensure that the content of abamectin is not reduced. Therefore, in the process of dosage form, it is necessary to add antioxidant or ultraviolet screening agent, which will not only avoid the decomposition of abamectin, but also ensure the effective content of abamectin and its effect on the pests.