Prevention of brown leaf disease in fruits: (3) The middle leaves of potassium deficiency produce dark brown gangrene spots gradually spreading to the veins. (4) The new leaves of calcium deficiency tops are distorted, and browning and desiccation of the mesophyll occur. The growth is inhibited. (5) Deficiency of magnesium between veins, but the tissue near the main vein remains green. Severe gangrene spots appear between veins. (6) The iron deficiency of the new leaf is white and the color of the lower leaves is normal. (7) Boron growth stops growing, and the new leaves have irregular brown gangrene spots and dwarf plants. Severe necrosis of buds. (8) The new leaves of the copper-free proximal buds were brown and distorted, but the tip tissues did not stop growing or necrosis. Other zinc- and zinc-deficient plants did not show obvious symptoms during the observation period and their growth was not affected. Guava Orchards are often caused by continuous cropping of the same kind of fruit trees, which can easily lead to insufficient elements, especially the lack of boron in trace elements, which has a very serious impact on the production of guava. In the first and second years of fruit trees, the lack of fruit production has little effect on the lack of boron, but when the fruit tree enters the third year, the productivity suddenly increases greatly. Therefore, the effect of deficiency is more obvious and serious. If the winter temperature is low, the soil temperature When the guava root absorption capacity decreases, the boron deficiency becomes more serious. In the absence of boron, guava twigs and fruits are affected. The first shoot sprouts are poorly grown or stalled, and the whole plant is sexual. This can be differentiated from the emergence of sprouts only on the affected shoots. The distance between the nodes and the sections where the leaves are growing is reduced, and more serious old branches or branches will have a rough surface, the epidermis will thus be broken into grooves, and the epidermis will be broken and the inner layer will be black and dry. As for the fruit, it ripens about 1/2-1/3 of the weight of the normal fruit, yellows ahead of time, touches the surface of the fruit and shows a soft sensation, and the internal seed of the fruit is unable to grow and is black. The vascular bundles from the white fruit stem to the seed cavity also showed a transverse cracking. Boron deficiency can use borax to dilute the water 1000 times and spray the leaves directly. After 20 days of spraying, the leaves are quickly and directly absorbed to reduce the sequelae of insufficient boron. In addition, borax can be applied on the surface of the orchard, about 1-2 grams per plant, and once a year. Orchard application of organic fertilizer, boron is less likely to lack, such as chemical fertilizer should pay attention to the growth of leaf buds, pay attention to add borax at any time. 2. Fruit sunburn disease guava fruit Thailand strains and their offspring have two layers of bagging protection, namely the inner layer of styrofoam and outer plastic bags. Occurrence of fruit burns can occur occasionally. Irregularly brown lesions appear on the skin of the fruit, appearing only in upward and forward parts of the skin, but not under the fruit. In the orchard, if the nitrogen fertilizer application is high, the fruit enlargement effect can be enhanced, but the skin of the fruit is prone to sunburn due to the high temperature of the sun. When the fruit is near mature, if it is pruned, the bagged fruit is directly exposed to strong light and high temperature. It is more vulnerable. To prevent sunburn, it is necessary to reduce the amount of nitrogen fertilizer in the result period and apply more calcium fertilizer. In this way, in addition to preventing sunburn, it can also improve fruit quality. In addition, the fruit can be pasted on top of the outer plastic bag in the near ripening period to prevent direct sunlight and reduce the temperature. 3. Physiological rust of fruits In late summer and early autumn, the monsoon began to change from southwest to northeast, and the air quality became poor due to monsoon, resulting in high frequency of photochemical pollutant ozone and acetylacetate. Although these actinic pollutants have no obvious symptoms on the surface of guava, they will affect the evapotranspiration of mesophyll stomata, reduce the absorption of water and fertilizer components, and cause a lack of fertilizer in fruits, such as the deficiency of boron and calcium in the fruit. Surfaces. Fruit rust often appears in small fruit to medium fruit. There are dark green vesicles on the fruit surface. In severe cases, the vesicles turn reddish-brown and all parts of the whole fruit surface are present. The early appearance of reddish brown appears at the top of protruding vesicles. At the later stage, all diseased parts turn reddish-brown, and it will appear whether it is bagging or not. Prevention of water rust can use 1000 times ascorbic acid spray foliar, and spray boron and calcium chemical fertilizers, supplement nutrition.