Symptoms of Schisandra Leaf Blight and Its Prevention and Control Methods
Schisandra leaf blight is a common disease, widely distributed in Liaoning, Jilin, Heilongjiang and other provinces, and can cause serious consequences such as early defoliation, fruit drop, death of new shoots, weakened tree vigor, decreased fruit quality, and reduced yield.
1. Disease symptoms Leaf blight mainly damages leaves. According to the different initial sites on the leaves and the size of the lesions, it can be divided into two types. ① The disease first starts from the leaf tip or edge, then spreads to the leaf margins on both sides, and then extends toward the center, gradually forming large brown patches; as the disease further worsens, the symptoms gradually progress from the lower leaves to the upper leaves, and the color of the diseased part changes from brown to yellowish-brown; when the disease develops to a certain extent, the diseased leaves dry up, crack and fall off, and the fruit wilts and shrivels. ② Many nearly round or irregular brown small spots appear on the leaf surface. In the later stage of the disease, the small spots merge with each other into irregular large spots. The symptom characteristics often vary depending on the variety of Schisandra.
2. Occurrence pattern Preliminary studies have found that the causes of Schisandra leaf blight are complex and may be related to factors such as pathogen infection (Septoria sp.), excessive fruiting, waterlogging in the field, sudden temperature changes, improper fertilization, and the application of herbicides. Investigations have found that the disease has no obvious center of occurrence, but the closer the area is to the sprinkler irrigation site in the orchard, the more severe the disease. In addition, temperature changes are also a factor triggering leaf blight. A sudden invasion of cold air after continuous high temperatures, or continuous overcast weather suddenly turning clear, can easily cause leaf blight.
The disease mostly begins to occur in late May, and the peak incidence period is from late June to late July. High temperature and high humidity are the dominant factors for the occurrence of the disease. Plants with excessive fruiting and regions or years with abundant summer and autumn rain suffer more severe disease; within the same orchard, low-lying waterlogged areas and sprinkler irrigation sites have severe disease; in orchards where nitrogen fertilizer is applied excessively and the trellis canopy is dense, the disease is more severe. The degree of susceptibility varies among different varieties. Some varieties are extremely susceptible and severely affected, while some varieties have strong disease resistance and are less affected.
3. Prevention and control techniques ① Strengthen cultivation management, pay attention to the reasonable distribution of branches and vines, avoid a dense trellis canopy, and enhance ventilation and light transmission. Appropriately increase the proportion of phosphorus and potassium fertilizers to improve the disease resistance of the plants. For chemical control, generally in late May, spray 1:1:100 equal Bordeaux mixture for prevention. When the disease occurs, 50% mancozeb wettable powder 500-600 times liquid can be sprayed for control, once every 7-10 days, for 2-3 consecutive sprays; alternatively, 2% agricultural antibiotic 120 aqueous solution 200 times liquid, or 10% polyoxin wettable powder 1000-1500 times liquid, or 50% iprodione wettable powder 1000-1500 times liquid can be sprayed, once every 7-10 days, for 2 consecutive sprays.