A Detailed Explanation of the Causes of Empty Chestnuts and Their Prevention and Control Methods
Chestnut, also known as li, chestnut, chestnut seed, fengla, is a plant of the genus Castanea in the family Fagaceae, native to China, distributed in Vietnam, Taiwan, China and mainland China, growing in areas at an altitude of 370-2800 m, mostly found in mountainous areas, and has been widely cultivated artificially. Chestnuts are rich in nutrients; their vitamin C content is even higher than that of tomatoes, and more than ten times that of apples. Chestnut has a relatively wide range of adaptability to climate and soil conditions. Its suitable annual average temperature is 10.5—21.7℃. If the temperature is too high and dormancy is insufficient, it will lead to poor growth and development; if the temperature is too low, chestnut is prone to freezing damage. Chestnut likes moist soil, but it also fears the effects of waterlogging. If rainfall is excessive and the soil is waterlogged for a long time, it can easily affect root growth, especially mycorrhizal growth. Therefore, chestnut orchards should not be developed in low-lying, easily waterlogged areas.
Empty chestnut bur, also called empty bur or empty shell, is called “mute chestnut” by fruit growers. The rate of empty chestnut bur is generally about 15%, and can be as high as 80%, with some trees almost entirely empty. Therefore, preventing empty bur is the key to increasing chestnut yield and quality.
Reasonably select and arrange pollinator trees. Chestnut has a high fruit set rate under cross-pollination, while self-pollination often does not set fruit easily. Therefore, when planting, excellent varieties with a high fruit set rate should be selected, and attention should also be paid to selecting and arranging pollinator trees. There are many chestnut varieties in different regions, and pollination combinations also differ. For example, if the main cultivated variety is Gannong 77-01, the best pollination combinations are Gannong 77-02 and Gannong 77-04. The number of pollinator trees arranged should account for about 1/3 of the total number of trees. Practice has shown that reasonably selecting and arranging pollination combinations can greatly increase the fruit set rate and increase chestnut yield.
Properly thin out male flowers. The chestnut tree is monoecious with unisexual flowers; male flower catkins open first, and female inflorescences open later. When the male catkins grow to 2-3 cm, removing 90% of the male flowers not only does not affect normal pollination of the tree, but also results in fresh green leaves, a high fruit set rate, and increased single fruit weight. It can also advance maturity by 7-10 days, allowing early harvest and early marketing. Properly removing male flowers from chestnut is indeed a measure to increase production and income, and its effect is especially prominent on young trees.
Increase boron fertilizer application. Chestnut is very sensitive to boron. Especially in boron-deficient soil, increasing boron fertilizer application can effectively reduce the empty bur rate and increase yield per tree. Specific application methods: First, apply boron during the bud break stage. In early spring, together with the application of bud break fertilizer, apply borax to the soil, generally 100-150 g of borax per tree; in boron-deficient soil, more can be applied appropriately. Second, spray boron during the flowering stage. Use 100 g of borax per 1/15 hectare, mix with 50 kg of water, and spray evenly on female flowers; for those with a high empty bur rate, the boron spray concentration can be appropriately increased. After boron application and boron spraying, the empty bur rate of chestnut can be reduced by 20%-30%, and the yield can be increased by 3-4 times.