Analysis on the Causes of Orchid Brown Rust

The pathogen of orchid brown rust is Uredo japonica. Symptoms: first produce light brown or orange-brown small spots on the leaves, generally mainly in the middle and lower parts of the leaves, some whole-leaf disease, and then gradually develop into black patches (irregular plaques), resulting in the whole leaf yellowing, and finally withered, dried and died. Brown rust occurs from mid-April to early June this year. The main reason for the occurrence of brown rust is the overwetness of basin soil and the influence of low temperature in spring.

From March to April this year, the temperature in southern China is lower than normal, the rainfall is more, and the rainfall is higher than normal, which is a rare spring low temperature year after the founding of the people's Republic of China. Low temperature and high humidity caused brown rust in orchids cultivated in the open air, resulting in certain losses. The main reasons are as follows.

1. Extensive cultivation in open field is the main cause of brown rust. Brown rust generally does not occur under good or dry cultivation conditions. The disease has not occurred since 1992-1995. The average temperature in our area from March to April this year is 6 degrees lower than usual. The subjective cause of brown rust was lack of protection consciousness, and objectively, it was not covered with nylon film or moved into indoor cultivation. Any kind of orchid that is sheltered or cultivated under the eaves of shelter is not infected.

Second, under uncomfortable cultivation conditions, excessive flowering aggravates the development of the disease. This year, the spring orchid blossoms late, about 10 days later than usual, some varieties do not bloom until March 5, and the flowering period is about 30 days, and there are many flowers, and the consumption of nutrients is large, which affects the disease resistance of orchid plants. The basin soil is too wet and the root system is stunted or blocked, which is extremely vulnerable to the invasion and damage of bacteria. The condition of high humidity is beneficial to the reproduction and expansion of bacteria. The investigation found that the disease of orchid plants with more flowering and long flowering period was more serious than those with less flowering and short flowering period. According to the species of orchids, the severity of the disease was Chunlan, Hanlan, Qiulan and Cymbidium. Due to the low temperature and high humidity conditions encountered during and after flowering, the flowering period consumes a lot of nutrients and the disease resistance is weak. Cold orchid gets rest after flowering, but the time is not long. Cymbidium is in the early stage of pregnant flower and flowering, full of energy. Different species of orchids have different degrees of disease, as well as differences in physiology and disease resistance.

Third, transplanting turns the pot, the tissue is damaged, the orchid plant is easy to suffer from the disease. When transplanting in spring, the brown rust of orchid plants cultivated in the open air was the most serious, and the disease of lotus petal orchid was serious during this period. The mature grass of Luoshan Cymbidium which was transplanted in October last year was also seriously affected.

Fourth, the prevention and control of brown rust is difficult, prevention is more important than treatment in order to effectively control the disease. In this paper, the control effects of copper sulfate, Shiduqing, boric acid and lice Jingjing (containing strychnine and treating shell insects) are not good. Brown rust spreads quickly and is difficult to control after the occurrence of brown rust, but the prevention and control can be achieved as long as extensive management is avoided, nylon film is placed indoors or shed, and the basin soil is kept a little dry. As long as it is cultivated in shelter from rain, the low temperature from March to April in South China will not cause frost damage to more hardy orchids such as Chunlan. Properly controlling the flowering number of Cymbidium and Cymbidium can shorten the flowering period, which is beneficial to improve the plant disease resistance and reduce the chance of pathogen invasion. During the disease period, the disease-free orchid plants were prevented by topiramate and trimethoprim. (Zhu Xiongguan)