When is the best time to control excessive growth in soybeans? A detailed guide to edamame growth control methods

In a few more months, it will be time for the soybean harvest. To achieve high soybean yields, you need to control excessive growth, especially in the southwestern region, where the summer heat and abundant rain easily cause soybeans to grow excessively, leading to flower and pod drop and reduced yields. So when is the best time to control excessive growth in soybeans (edamame)? How do you control excessive growth?

Field signs of excessive soybean growth

(1) Branches and leaves are lush, ventilation and light penetration are poor, and the leaves completely close the rows.

(2) The upper leaves are thick and fleshy, dark green in color, and nearly the size of an adult palm; the lower leaves turn yellow and begin to drop.

(3) Apart from a small number of flower clusters or pods on the upper part of the main stem, there are fewer flower clusters or pods on the lower part of the main stem and on the branches, and they drop easily, with a low pod-setting rate; some plants even have no flowers or pods at all.

Timing for soybean growth control

Paclobutrazol can be sprayed from the 2-leaf stage to the full-flowering stage of soybeans, with the early flowering stage giving the best results; spraying once each at the 2-leaf stage and the early flowering stage gives even better results. Generally, use 40-50 kg per mu of a 180-250 mg/L paclobutrazol solution. For soybeans growing excessively, use a high concentration and high dosage; for soybeans growing somewhat excessively, use a low concentration and low dosage; soybeans with weak growth should not be sprayed. Spraying should be done on a sunny day between 3 and 5 p.m.; if rain falls within 2 hours after spraying, respray after the weather clears.

Chemical growth control techniques

Seed treatment

Weigh the selected seeds according to the amount needed for the field, place them in a plastic bag, add 5% uniconazole wettable powder at l6-20 mg per 1 kg of seed, shake back and forth several times, and sow immediately after the seeds are evenly coated.

Foliar spraying

From early flowering to full flowering, simply dilute 50 g of Guangqi soybean growth-control and yield-increasing foliar fertilizer with 15-30 kg of water and spray.

Manual growth control techniques

During the flowering and pod-setting stage of soybeans, for fields where chemical growth control has not been effective, manual methods such as thinning leaves, pinching out the growing tip, and removing non-productive plants can be used to improve ventilation and light penetration in the plant population. The specific techniques are as follows:

(1) Pinch the tips and thin branches and leaves. In the early stage of excessive growth, promptly pinch the tips and cut the leaves of excessively growing plants to create a reasonable population structure. When pinching, it is generally best to nip off 2—3 cm of the tender tip at the top of the main stem. When cutting leaves, cut every other leaf on the middle and upper branch leaves; for especially excessively growing fields, some fruiting branches with fewer flowers and pods can also be cut off to ensure that the main stem and fruiting branches with more flowers and pods can flower and set pods.

(2) Remove non-productive plants. For fields with severe soybean spindling, promptly pull out plants with no flowers or pods or with very few flowers and pods.