First, the occurrence of hazards
1. Symptoms: (1) Foliage symptoms. Occurred early in the leaf margin, lesions are round or irregular, water stains at the beginning, after turning into a dark brown, sometimes with a ring pattern, easy to perforate when the rain and high humidity. The late stage occurred at the base of the leaves, mostly caused by the detached petal infection, and it often spread to the onset of culms. (2) Flowering symptoms. The sclerotia of ascaris spores can easily infect the petals, causing the petals to fade and give early thanks. (3) symptoms of stem branches. The disease was pale yellow-brown in early stages, and the disease was mostly soft and rot-like when the weather was wet. When the disease was dry, the disease area was light brown. The diseased part became white or off-white. The cortex was easily separated from the xylem, and it was broken into a hemp-like shape. Hollow, later in the stem, black sclerotia such as mouse excrement were born, and the diseased part died earlier.
2. Influencing factors: (1) The number of nucleus of Sclerotinia sclerotiorum overwintering over winter is large, and the climatic conditions are conducive to the generation of ascarid discs and ascospores. The flowering period coincides with the sclerotia spore release period long, and the weather is wet and rainy. It is easy to cause S. sclerotiorum epidemic. During the flowering season of rapeseed, the monthly precipitation is more than 100mm. If the rain is more than 10 days, the relative humidity in the field is more than 85%, and the disease is heavy; if the rainfall is less than the above-mentioned indicators, but more dense fog, rapeseed bacteria The occurrence of nuclear diseases is also heavier. If there is less rain and fog during the flowering season and the relative humidity is lower than 75%, the disease will be lighter. (2) The incidence of rapeseed rape was significantly different among different rapeseeds. The incidence of rapeseed rape was the heaviest, and the difference between the rapeseed varieties was also significant. (3) The incidence of rice oil rotation in the cropping area is lighter than that in the dry oil rotation area. The incidence of large rapeseed planting density is heavier, while that of partial nitrogen fertilizer application and poor drainage is also heavier.
Second, prevention and control technology
1. Agricultural control: Select disease-resistant varieties; appropriately sparse or adopt a wide and narrow row of transplanting methods; excavate the drainage ditch so that the rain stops dry; reasonable fertilization, especially to control the amount of nitrogen fertilizer.
2. Chemical control: (1) Control measures. Since the onset period of rape sclerotia lags behind the flowering period of rapeseed, the incidence of sclerotinia is closely related to the length of rain and fog during the flowering period. Therefore, the principle of “prevention as the main, and taking the initiative to attack according to the flowering process†should be followed. (2) Control period. The optimum period for controlling Sclerotinia sclerotiorum is 100% of the main stem's flowering plant rate to 80% of the first branch's flowering plant rate. It was observed that after observation, the flowering rate of the main stem of rapeseed reached 25%, and the flowering rate of 8-9 days could reach more than 90%. In order to facilitate the control in the prevention and treatment process, the main planting rate of rapeseed can reach 80-100%, and it is the critical period for the control of rapeseed sclerotiorum when the branching and flowering rate reaches 95-100%. (3) Control methods. In the past, carbendazim was used to control Sclerotinia sclerotiorum for a long time. It was found that the mixed use of carbendazim and boron fertilizer had significant effects on disease prevention and yield increase. However, in the late 1990s, local S. sclerotiorum strains were found to be resistant to carbendazim, and the disease resistance of strains was increased by 10-20 times. Therefore, it is not suitable to use carbendazim and its compounding agent to control Sclerotinia sclerotiorum, and sclerotia net, iprodione and its compound can be used.