What Causes Empty Chestnuts in Chestnut Burrs? Detailed Control Measures

    Chestnut is one of the important economic forest tree species in China. China currently has about 700,000 hectares of chestnut, with an annual output of about 1.5 billion kg of chestnuts, an average yield of 270-300 kg per hectare, and about 2 kg per tree. Besides the long-term use of seedling propagation and extensive management, empty chestnut burrs are one of the important reasons for the low yield. Therefore, preventing or reducing empty chestnut burrs is one of the important problems urgently needing to be solved to increase China's chestnut yield. 

    Causes of Empty Chestnut Burrs 

    ①Poor pollination and fertilization during the chestnut flowering period.

    ②Nutritional deficiency. Boron deficiency and available phosphorus deficiency in the soil can both cause empty chestnut burrs.

    ③The influence of other factors. First, variety: different varieties have different numbers of female and male inflorescences and consume different amounts of nutrients, so the rate of empty burrs also differs. Second, water: in dry years, watering sufficiently or having enough    rainfall during the chestnut flowering period, the fruit filling period and the freezing period can not only make the chestnut trees grow vigorously but also significantly reduce the rate of empty burrs. Third, light: with poor light, water, nutrients and oxygen in the soil are in short supply, and the chestnut trees cannot carry out normal photosynthesis, resulting in short new shoots, yellow leaves and poor fruiting, and the rate of empty burrs also greatly increases. Fourth, wind: during the chestnut flowering period, if the wind speed is too high, the rate of empty chestnut burrs increases; if the wind speed is too low, or even there is no wind, the rate of empty chestnut burrs also increases somewhat. The most suitable wind force during the chestnut flowering period is generally level 3-4, and there is a great difference between open areas and non-open areas. 

    Control of Empty Chestnut Burrs 

    ①Select excellent chestnut varieties with a high setting rate. In chestnut production, through many years of investigation and analysis, the excellent chestnut varieties with a low rate of empty burrs include: Jiaozha, Qingzha, Chushuhong, Dahongpao, Jiujiazhong, Maobanhong, etc.

    ②Cultivate the best tree structure. From the young tree stage to the early fruiting stage, moderate close planting should be used, with the natural spindle shape being best, which can increase early yield and economic income. In the early full fruiting stage, thinning should be carried out appropriately and pruning should be reasonable, and it is best to cultivate a trunk-shaped tree body, which can use space more effectively and increase the wind and light conditions of the tree body, thereby reducing the rate of empty burrs and increasing yield.

    ③Configure pollinator trees reasonably. Supplementary pollination with a mixture of pollen from multiple varieties can significantly reduce the rate of empty chestnut burrs. It is generally considered that the number of pollinator trees configured should be 1/3 of the main planted variety trees.

    ④Properly thin male inflorescences and burrs to reduce nutrient consumption by the tree body. When the male inflorescences grow to 1-15 cm, remove them, leaving only 2-3 under the mixed inflorescences; the abortion rate of mixed inflorescences is significantly reduced compared with the control. Generally, the ratio of female to male should be maintained above 1:149, which does not affect normal pollination of the chestnut trees and can greatly reduce unnecessary nutrient consumption by the tree body.

    ⑤Strengthen fertilizer and water management to keep the tree body growing robustly. Apply topdressing and irrigation at the appropriate time, especially paying attention to fertilization during the chestnut flower primordium stage and the pollination stage: for adult trees, apply 2-3 kg of urea or 2 kg of nitrogen-phosphorus compound fertilizer in holes, and irrigate after application. For mountainous areas without irrigation conditions, during the rainy season use the method of making a basin under the crown and shallow trenching outside the basin to intercept and store rainwater; green manure can be applied in the trench to improve soil fertility. Early topdressing should be mainly nitrogen, and later nitrogen, phosphorus and potassium should be used together.

    ⑥Spray nutrient solutions such as boron and phosphorus on the leaves. Spraying 0.15%-0.25% boron fertilizer 2-3 times during the flowering period can reduce the rate of empty burrs by 23%-32%, and among these, mixing with urea and monopotassium phosphate at the full flowering stage has the best effect. The key periods for the most effective control of empty chestnut burrs are the two periods of ovule formation (late May) and double fertilization (late June). At the stage when chestnut female flowers begin to differentiate, if a solution of monopotassium phosphate or 0.3%-0.5% superphosphate + 0.3% urea is sprayed 1-2 times, combined with boron, phosphorus and urea spraying during the flowering period, it can both prevent empty chestnut burrs and promote an increase in chestnut female flowers.