What to Do About Soybean Flower and Pod Drop? A Full Guide to Prevention and Control Measures

Soybean flower and pod drop is a major factor affecting yield. Under ordinary cultivation conditions, the number of dropped flowers and pods can account for more than 50% of the total number of flowers, and in severe cases up to 70%. Soybean flower and pod drop is mainly caused by internal physiological imbalance in the plant and adverse external environmental conditions. Based on practical experience in our area, the following measures can be taken to prevent soybean flower and pod drop:

1. Apply more phosphorus and potassium fertilizer, and appropriately top-dress with nitrogen fertilizer and micronutrient fertilizer. Applying more phosphorus and potassium fertilizer to soybeans can reduce flower and pod drop and promote full grains. Therefore, on the basis of applying sufficient base fertilizer, at sowing time use 25-30 kg of calcium magnesium phosphate fertilizer and 500 kg of burnt soil ash per 667 sq m (1 mu), mix them thoroughly and cover the seeds as seed fertilizer, which can make the plants grow vigorously, branch early, and set more pods. When soybeans have just begun to flower, for plots with poor soil fertility and slow-growing soybean seedlings, top-dress 5-6 kg of urea and 7.5-10 kg of potassium chloride per 667 sq m to meet the nutrient needs of the plants during the flowering and podding stage, which can reduce flower and pod drop. During the flowering stage, an appropriate amount of micronutrient fertilizer should also be top-dressed, that is, use 1 g of ammonium molybdate per 667 sq m, first dissolve it in a small amount of warm water, then add 150-200 g of potassium dihydrogen phosphate, dilute with 50-60 kg of water, and spray it on the leaves as foliar fertilizer, which has a clear effect on increasing the pod-setting rate and increasing grain weight.

2. Adjust measures to local conditions and plant at a reasonable density. If soybeans are sown too densely, the lower part of the plants will be shaded, which can also cause flower and pod drop. Therefore, the planting density should be reasonably determined according to variety characteristics, soil fertility, sowing time, and other conditions. Varieties with strong luxuriance should be planted slightly sparsely, while varieties with weaker luxuriance can be planted slightly densely; fertile land should be planted slightly sparsely, while lean land should be planted slightly densely; early sowing gives a longer growth period and more luxuriant vegetative growth, so the planting density should be slightly sparse, while late sowing should have an appropriately increased planting density. At present, the general field density is 15,000-20,000 plants per 667 sq m, and it is advisable to keep 15,000 plants on fertile land and 20,000 plants on lean land.

3. Pinch off the growing tip at the right time. For varieties with an indeterminate growth habit, from the beginning to the full flowering stage of soybeans, choose a sunny day after the dew has dried and pinch off 2-3 cm of the top of the main stem, which can effectively control the apical dominance of soybeans. Under conditions of relatively sufficient fertilizer, timely pinching can also control excessive vegetative growth, promote seed maturity, and increase yield.

4. Prevent and combat drought in a timely manner. The flowering and podding stage of soybeans is a period with a relatively high water requirement; if continuous drought occurs at this time, it will cause a large amount of flower and pod drop. Therefore, drought prevention and resistance work should be done early, with frequent and light irrigation, watering once every 5-7 days. When waterlogging occurs, drain the field water in a timely manner to prevent damage from waterlogging.

5. Prevent and control diseases and pests. Doing a good job in disease and pest control is also an effective measure to prevent soybean flower and pod drop. To control aphids, spray with 1500-2000 times dilution of 40% omethoate emulsifiable concentrate; to control bean pod borers, use 100 g of 50% malathion emulsifiable concentrate and dilute with 100 kg of water for spraying; for purple spot disease, spray with 500 times dilution of zineb or spray with Bordeaux mixture 1-2 times, which can suppress its damage.