CCM Discusses 5 Problems in Disease and Pest Control of Minor Crops in China

Guangzhou, China, October 24, 2016 (Newswire.com) - ​Compared to bulk crops such as rice, wheat, corn, soybean and cotton, minor crops like fruit trees, vegetables and fruits need a huge amount of pesticide even if they are not widely grown. Various kinds of diseases with serious harm on minor crops are not the only reason why minor crops need a huge dosage of pesticides. Great values coming from minor crops also encourage farmers to invest on and pay attention to the control of diseases and pests.

However, lacking of the knowledge on occurrence rules of diseases and pests of minor crops, "over-control" became a norm among farmers in China. "Over-control" speeds up the drug-resistance problems of minor crops, increases the cost in controlling and brings more serious pollution on farm products and environment.

Different from that in developed countries, in China, the pesticide is not applied on the crops by professional and licensed staff but farmers who receive less education, and lack knowledge of controlling diseases and pests. Thus, the problems on pesticide application are on an immediate need to be solved. Moreover, most of the vegetables are directly eaten without being processed, which makes rational use of pesticide more important in China.

The irrational uses of pesticides are as follows:

1.       Wrong pesticide on wrong diseases or pests

Every control on diseases and pests should be based on correct diagnosis on the diseases and pests occur on crops. However, farmers in China are quite "blind" in choosing certain pesticides due to their lack of knowledge and poor disease and pest forecast from plant protection departments in different provinces.

For example, the similarities between cucumber downy mildew and cucumber bacterial angular leaf spot in early symptoms often confuse farmers in China. The bacteria sources are different in cucumber downy mildew and cucumber bacterial angular leaf spot, with the former one belongs to lower fungus while the latter is bacteria. Thus, it takes different pesticides to control the different diseases. Without guidance from professional staff, it is difficult for farmers to tell the differences between two similar diseases, which leads to misuse of pesticides on controlling.

It is the same when it comes to controlling pests. For example, both maruca testulalis geyer and soybean-pod-borer are cow peas. However, pesticides should be sprayed on these two kinds of plants in two different periods of time and farmers fail to know, which leads to incorrect application on controlling pests on the plants.

Hence, it is very important for farmers to learn about the occurrence rules of diseases and pests, to correctly tell the types of diseases and pests, and to choose the right pesticides and to apply it in the right time and way.  

Farmers should apply pesticides when the pests are still in their larval phases because larva is weak in drug-resistant and does most harm to the crops. Moreover, pesticides should also be sprayed on the effective areas to kill the pests. For instance, aphis citricola van der goot and citrus aphids always do harm to tip part of apple trees. Therefore, tip part is the effective area for pesticides to kill the pests and pesticides should be sprayed on the tip part.

2.       Random mix and overuse of pesticides

Random mix and overuse of pesticides are a norm among Chinese farmers in controlling diseases and pests in fruit trees and vegetables.

Many farmers want to get all the diseases and pests killed in one-time spray, so they would usually randomly mix fungicides, pesticides and acaricides to control diseases and pests at the same time, which help farmers reduce the application time and save their cost. Though it is understandable, it may be useless for the diseases and pests, and harmful for the crops and environment.

Every kind of disease or pest has its specific infesting period for control. It is very rare for various kinds of diseases and pests to have their best spraying time in the same period. If the spraying time between two diseases and pests vary a lot, the mix-use of pesticide will not be effective in controlling.

Mixing different pesticides is in high need of technique. The basic method to mix pesticides is to select single formulations with different active ingredients mechanisms, as to increase the pesticide efficacy, reduce the drug-resistance of diseases, pests and weeds.

In addition, farmers always randomly increase the dosage of pesticide to guarantee the result. In reasonable range, with the increase of the pesticides concentration, the result will get better. However, if the concentration is over the limit, the pesticide efficacy will not increase with the concentration increase.

For example, phenoxyalkanoic acid herbicides are non-selective and trans-located herbicide. If there is too much dosage when spraying, the plant conducting tissue will be killed immediately and the pesticide will not be conducted to the roots or growing points.

Some pests are very sensitive in their smell. If the pesticide sprayed on the crops is with high concentration, some pests will refuse to eat the crops and therefore, they will not be killed.

Spraying the pesticide with high concentration will encourage the pests to have drug-resistance, damage the crops, pollute farm products and environment, and poison the farmers more easily.

3.       Farmers depend too much on pesticide

Currently, many farmers depend too much on pesticides and neglect other measures on protecting the crops.

For example, root rots on fruit trees such as apple valsa canker and peach gummosis are caused by the weakening of trees. To prevent root rots, farmers need to do rational pruning to reduce the number of fruits on trees, and plough and reform the soil to apply more organic fertilizer and etc. Controlling with pesticides is only a means of supplementary.

However, many fruit farmers only depend on application of pesticides to control diseases and pests, which has quite bad results. Diseases like root-knot nematodes, cucurbits fusarium wilt and verticillium wilt of eggplant should be prevented and cured by selecting disease-resistant varieties and rotating crops.

It is normal for farmers to "over-prevent" on diseases and pests in some vegetables and fruit trees with good economic profits. In a huge orchard, farmers hurry to spray pesticides when there are two or three aphides or specks on the leaves or even no pests.

Such over preventions waste resources and destroy the ecosystem of the orchards and vegetable farms.

4.       Random use of illegal pesticide

Among all the chemical pesticides, most of the fungicides are lowly toxic, especially some newly developed fungicides with its toxicity being even lower than that of salt, while some traditional pesticides are still highly toxic.

Though the Chinese government has banned the use of highly toxic pesticide or those with high residue in the planting of vegetables, fruit trees, tea leaves and herbal medicine, some farmers are still spraying the illegal pesticides.

Many farmers still use asomate which is banned in 2005 in China, to prevent and control apple valsa canker. Some vegetable farmers in China still apply carbofuran and phorate to control chive maggots, grubs and wireworm. Carbofuran and phorate are both highly systemic pesticides, which is difficult for the crops to degrade once it goes inside the plants. If the vegetables get harvested this time, people who eat the vegetables would get poisoned easily.

Most of the farmers don't know much about what pesticide toxicity stands for and believe that higher toxicity means better pesticides. In fact, pesticide toxicity stands for the pesticide capability to poison warm-blooded animals rather than the targeted pests or diseases.

Pesticides like phorate, which has special pungent odor and is east to vaporize are often used by farmers because they mistake it for good pesticide because of the pungent odor.

5.       Pay little attention to safety interval

 Safety interval for pesticides is set by the Chinese government to make sure the safety of farm products, food products and people's health. Safety interval refers to the period during that from the last pesticide application to the time when the crops are harvested, used or consumed. Safety interval aims to ban the use of pesticide for a period of time before the crops get harvested, as to make sure the pesticide residue to be less than the maximum limit of residue. In China, the time between the last spraying and the "first" harvest should be more than that in safety interval.

According to Guideline for Safety Application of Pesticides(Ⅶ), the Chinese government has regulated the safety intervals of different pesticides which are marked on the labels of all qualified pesticides.

For example, mancozeb is a protective fungicide with low toxicity, with its safety interval on cucumber and tomato being 15 days; pimento, 14 days; and watermelon, 21 days. Azoxystrobin's safety interval is 1 day on cucumber, 3 days on tomato and chili, 14 days on broccoli and watermelon. However, the farmers usually neglect the safety intervals when applying pesticides.

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Source: CCM