Analysis of Garlic Diseases in Jinxiang and Detailed Explanation of Prevention and Control Methods

Editor's Note: Jinxiang in Shandong is the most important garlic-producing area in China, and in recent years several diseases have been plaguing garlic farmers. Although some newspapers have also reported analyses by many people, many of them are ambiguous and leave readers confused. Recently, this newspaper specially invited Mr. Song Yuanlin, a vegetable expert from the Shandong Academy of Agricultural Sciences, to conduct a survey and gather information among garlic farmers. The findings and preliminary conclusions are now made public as follows.

The phenomenon of secondary growth of garlic and hollow garlic

In spring, when garlic grows to a certain stage, the scale buds begin to differentiate, the leaves degenerate, and the scale buds gradually form garlic cloves. The scales outside the degenerated scale buds form the outer skin of the garlic cloves. This is the general pattern of normal garlic growth. In March, before the garlic scape emerges, 5-6 small garlic leaves grow around the garlic axis, growing around the axis. These small leaves are a long new leaf that grows along the garlic scape as the outer skin of the new garlic cloves, while the growing point of the new garlic cloves has not sprouted. This is called the regrowth phenomenon of degenerated leaves of garlic cloves, sometimes called secondary growth, also known as horsetail garlic, and garlic farmers in Jinxiang call it garlic branching. This phenomenon is the regrowth of degenerated garlic leaves when external conditions are suitable. This leafing phenomenon has a relatively large impact on garlic scape yield, generally reducing it by 30%-40%; it has a relatively small impact on garlic bulb yield.

Hollow garlic is garlic whose bulb appearance is no different from ordinary garlic, only lighter in weight. After it matures and dries in the sun, when squeezed by hand, it is as hollow as bread and has no edible value. This phenomenon is sometimes called air-filled garlic or onion-like garlic, and it has an extremely large impact on yield.

Secondary growth of garlic and hollow garlic already show symptoms in December in winter, generally appearing as thick, short growth. Secondary growth can begin in March. In March, all hollow garlic plants grow vigorously, with thick and large plants, and at harvest the plants are unusually tall. The years in which these two abnormal growth phenomena occur are basically the same, and it is estimated that the causes and prevention and control measures are basically the same.

I. Factors related to the occurrence of secondary growth and hollow garlic. In 2003, most were sown at the end of September and the beginning of October, all using plastic film mulching. From the end of February to the first ten days of March 2004, the climate was relatively warm, and in the last ten days of March garlic began secondary growth. That year, secondary growth and hollow garlic were extremely severe, and those sown relatively earlier were more severely affected. In 2004, because there was a lot of rainfall in autumn, sowing was generally delayed, with most sown in the last ten days of October. In March 2005, the late spring cold was severe, and that year the occurrence of secondary growth and hollow garlic was not very severe. In the winter of 2005, the temperature was not high, and in 2006 the secondary growth phenomenon was not obvious. In the autumn and winter of 2006, the temperature was extremely high, and the warm winter phenomenon was extremely obvious. Garlic grew excessively vigorously in winter. In the first ten days of March 2007, the temperature was relatively low, with an intrusion of cold air at -7°C. In 2007, the occurrence of garlic secondary growth and hollow garlic was extremely. In years when garlic secondary growth was severe, plots where the mulching film was severely damaged had lighter occurrence of secondary growth and hollow garlic. At field edges and bed edges, wherever the plastic film mulching was poor, the occurrence of secondary growth and hollow garlic was lighter. Where urea fertilizer alone was applied, secondary growth was more severe than where compound fertilizer was applied.

II. Causes of the emergence of secondary growth and hollow garlic. The generally recognized physiological factor for the occurrence of garlic secondary growth and hollow garlic is that in February-March, aboveground vegetative growth is excessive, and excessive nutrition promotes the regrowth of degenerated leaves, leading to the emergence of secondary growth and hollow garlic. Therefore, factors such as a warm winter, a relatively warm spring, excessive application of chemical fertilizers, especially excessive application of nitrogen fertilizer, sowing too early causing excessive vegetative growth, sowing too late causing the nutrition in the seed garlic to be released concentrated in early spring, and plastic film mulching causing excessive vegetative growth can all cause garlic secondary growth and hollow garlic. In any year when garlic secondary growth and hollow garlic are severe, there must have been relatively high temperatures from the end of February to the first ten days of March, relatively rapid garlic green-up, and relatively vigorous vegetative growth. Without this condition, even if all other conditions are present, it will not cause a large occurrence of secondary growth and hollow garlic. Therefore, a warm spring is the main cause of garlic secondary growth. A warm winter is one of the causes of secondary growth and hollow garlic. The winter of 2006 was especially warm, but in 2007 the garlic secondary growth phenomenon was not severe. It can thus be seen that a warm winter is not the leading cause of garlic secondary growth and hollow garlic. Sowing too late is one of the causes of secondary growth, but in 2004 sowing was generally too late, yet it did not lead to severe secondary growth and a large occurrence of hollow garlic in 2005. It can thus be seen that sowing too late is not the leading factor in secondary growth. Plastic film mulching is one of the causes of garlic secondary growth and hollow garlic, but the advantages of plastic film mulching outweigh the disadvantages, so mulching cannot be abandoned. Excessive application of chemical fertilizers, especially an excessive amount of nitrogen fertilizer, is one of the causes of garlic secondary growth and hollow garlic. It is related to variety: red-skinned garlic has a high leafing rate, while white-skinned garlic has a low leafing rate. Some individuals believe it is caused by relatively low temperatures and excessive humidity during the storage period of seed garlic. In garlic-producing areas such as Jinxiang, seed garlic is all stored indoors at natural temperature, and the temperature during the storage period is above 20°C, so there is no phenomenon of relatively low temperature and excessive humidity at all. It seems that this understanding has not been proven in most production practices. Some also believe it is caused by a deficiency of the boron element. However, in the same plot, without applying the boron element, it occurred severely in some years and did not occur in others. This understanding also needs further verification.