What to Do About Walnut Fruit Drop and Reduced Yield? Cause Analysis and Control Methods

Everyone knows that walnuts are not very demanding when it comes to growing conditions and are relatively tolerant of poor and dry environments, but if management techniques are not mastered well, fruit drop easily occurs, leading to reduced yield and income, directly affecting growers' harvests and their enthusiasm for planting. Therefore, the causes of walnut fruit drop and the solutions are summarized as follows:

I. Causes of Walnut Fruit Drop

1. Improper variety selection. Variety selection should suit local conditions, choosing varieties that fit the local climate and soil conditions. Generally, thin-shelled varieties that grow vigorously, have strong stress resistance, good quality and high yield should be chosen. Walnut is a monoecious plant with separate male and female flowers; when establishing an orchard, it is best to select 2-4 main cultivars with similar or complementary male and female flowering periods at the same time, or to configure suitable pollinizer varieties. The ratio of main cultivars to pollinizer varieties is 4:1. Main cultivars can include Xiangling, Liaohe No. 4, Yuanfeng, Fenghui, etc.

2. Rain or low temperatures during the flowering period, leading to poor pollination. Unfertilized young fruit generally drops about 20 days after flowering, which is one of the main causes of massive walnut fruit drop.

3. Insufficient nutrients. Many people believe that walnuts can still bear fruit with little or no topdressing. Because of insufficient fertilizer, the flowering period consumes a large amount of nutrients, causing a nutrient deficit, weakening the tree vigor and leading to fruit drop.

4. Lack of trace elements. When a walnut orchard is deficient in boron, zinc or copper, fruit drop is also likely to occur.

5. Excessive use of nitrogen fertilizer or one-sided application of nitrogen fertilizer. Excessive use of nitrogen fertilizer or one-sided application of nitrogen fertilizer causes overly vigorous tree growth, leading to an imbalance between vegetative growth and physiological growth, and causing flower and fruit drop.

6. Fruit drop caused by pests and diseases. The main disease of walnut is anthracnose, which mainly damages the fruit, directly causing the fruit to rot and leading to fruit drop.

II. Control Measures for Walnut Fruit Drop

1. Timely topdressing to strengthen tree vigor. Generally, topdressing should be applied once in autumn and once in spring, with 1000-1500 kg of farmyard manure applied per mu. According to the age of the walnut trees, each tree should also be topdressed with 1-1.5 kg of no-till fertilizer or ordinary nitrogen-phosphorus-potassium fertilizer. Before and after flowering, spray the leaves 1-2 times with 4000-fold diluted Shuofeng 481 plus 1000-1500-fold diluted quick-acting boron. After using quick-acting boron, it can effectively avoid undesirable phenomena in walnut trees caused by boron deficiency, such as buds that do not flower, flowers that do not set fruit, fruit that does not develop well, flower and fruit drop, and deformed fruit.

2. Strengthen the control of anthracnose. To prevent fruit rot or fruit drop caused by anthracnose, spray once each in mid-May, early June and early July with 400-600-fold diluted Bangjiawei (80% mancozeb), while adding 4000-fold diluted Shuofeng 481 for prevention.