What to Do About Eggplant Flower and Fruit Drop? Cause Analysis and Countermeasures
Eggplant, also known as “qie” and by the alternative name “luosu,” is one of the few purple vegetables and a very common home-style vegetable on the dining table. In parts of Jiangsu, Zhejiang and Anhui it is called luosu, while in Guangdong and Guangxi it is called "aigua." It is an annual herbaceous plant of the genus Solanum in the nightshade family, and perennial in the tropics. Its fruit is edible, mostly purple or purplish-black in color, though there are also pale green or white varieties, and the shapes include round, oval, pear-shaped and various others. Eggplant is a typical vegetable, and depending on the variety it has many uses. Eggplant has quite high value for recovery from illness, and falls within the effective range for improving vitality.
Eggplant belongs to a member of the nightshade family and is one of the few purple vegetables, as well as a very common home-style vegetable on the dining table. The purplish-red color comes from delphinidin and its glycosides contained in the cells of the fruit skin; when mature, whether green or purplish-red, the fruit turns brownish-yellow. The edible portion includes the skin, the placenta and the “core” portion. All are composed of spongy parenchyma tissue, with relatively many intercellular spaces and a soft texture.
Eggplant originated in India and was introduced to China in the 4th-5th century AD. The eggplant cultivated during the Northern and Southern Dynasties was round, similar to the wild form. In the Yuan Dynasty, long eggplants were developed, and by the late Qing Dynasty this long eggplant had been introduced to Japan. Eggplant has a taproot, with roots reaching 50 cm deep and spreading 120 cm horizontally; for round eggplant plants, most are distributed within the 30 cm plow layer. The fruit on the main stem of the eggplant is called the “door eggplant"; the fruit on the first-order side branch is called the “paired eggplant”; the fruit on the second-order side branch is called the “four-door bucket”; the fruit on the third-order side branch is called the “eight-face wind”; and the fruit on later side branches is called the “starry sky”.
Causes of and countermeasures for eggplant flower and fruit drop
In eggplant production, flower and fruit drop is usually severe, restricting yield improvement and hindering the improvement of production efficiency; good countermeasures should be mastered in production.
The main causes of eggplant flower and fruit drop are:
1. Unsuitable temperature. The fruiting period of eggplant requires relatively high temperatures; the suitable temperature during the fruiting period is between 25-30°C, and the nighttime temperature should be between 15-20°C. When the temperature is below 15°C or above 35°C, growth is slow and flower drop is severe, showing in production as fewer fruits in the early stage and in summer.
2. Poor flower development. If eggplant flowers develop well, the flowers are large and deeply colored, and at flowering the style is longer than or equal in length to the anthers, which favors pollination and fertilization and leads to good fruit set; if development is poor, the style is shorter than the anthers, pollination is difficult to obtain, and most drop off.
3. Nutrient deficiency. With insufficient fertilizer and water, the plant grows thin and weak, and nutrients are used to maintain growth, so reproductive capacity is low and fruit set is poor.
4. Untimely topdressing or inappropriate timing is also unfavorable for fruit set. It generally shows as topdressing too early, causing excessive vegetative growth and leading to flower and fruit drop. If topdressing is untimely, the plant ages prematurely and production capacity decreases, which is also unfavorable for fruit set.
5. Improper fertilization ratio causes the plant to become leggy or weak, so the ratio of vegetative growth to reproductive growth becomes unbalanced, and fruit set is also difficult.
6. Poor light leads to low photosynthetic capacity, poor flower quality, and easy shedding; eggplant is a light-loving crop with relatively strict light duration requirements. Under weak light, plant growth and development slow, fewer flowers form, and flower bud quality is poor.
7. Damage from pests and diseases reduces the plant's photosynthetic capacity, which is unfavorable for the accumulation of photosynthetic products and also unfavorable for flower formation and fruit set. The main pests and diseases damaging eggplant include Verticillium wilt, aphids, red spider mites, and others.
Verticillium wilt generally does not occur at the seedling stage; it mostly occurs during the fruit-setting period, developing from bottom to top or from one side to the whole plant. Leaves turn yellow at the leaf edges and between veins, then develop until half the leaf or the whole leaf turns yellow; photosynthetic capacity decreases, nutrient accumulation is reduced, and the fruit-setting rate declines.
Aphids mostly gather in groups to cause damage, using needle-like sucking mouthparts to suck host sap, causing leaves to yellow, shrivel, deform and wither.
Red spider mites, whether adult mites or nymphs, can feed on plant sap, causing leaves to discolor or dry up, leading to reduced leaf photosynthetic capacity and unfavorable fruit set.
Based on the above causes, corresponding countermeasures should be taken in eggplant production to promote an increase in the fruit-setting rate and improve production and management efficiency. The main measures are:
1. Pay attention to promoting the growth of long-styled flowers and reducing the proportion of short-styled flowers, so as to help raise the fruit-setting rate. The key measure to apply in production is to strengthen temperature management during the flowering and fruiting period. Within the suitable temperature range for the fruiting period, keep the temperature slightly lower, controlling it at around 25°C during the day and between 15-20°C at night, so that flower bud differentiation is slightly delayed, which favors the formation of long-styled flowers and can effectively control the proportion of short-styled flowers. In addition, production should reasonably arrange the planting crop sequence so that during the fruiting period the daytime temperature is above 25°C and the nighttime temperature is between 15-20°C. During high-temperature summer periods, attention should be paid to watering to lower the temperature. If there is continuous high-temperature weather, a shade net can be used to build a shade shelter to lower the temperature and promote an increase in the fruit-setting rate.
2. Strengthen fertilizer and water management, keep plant growth moderate, and balance the relationship between vegetative growth and reproductive growth, so as to help raise the fruit-setting rate: in particular, the first topdressing should be timely, preferably when the first layer of fruit is 3 cm in diameter, and topdressing should be applied at the appropriate time to prevent fertilization too early, which causes flower and fruit drop. After that, apply topdressing once after each fruit harvest to supplement nutrients and prevent premature aging of the plant, which leads to reduced production capacity. In addition, attention should be paid to an appropriate fertilization ratio to prevent unbalanced fertilization from causing an imbalance between vegetative growth and reproductive growth. In particular, attention should be paid to preventing excessive nitrogen fertilizer, which causes leggy growth. Generally, in eggplant production, the suitable ratio of nitrogen, phosphorus and potassium is 2:1:1.7. In production, observe plant growth and use the method of promoting weak plants and controlling vigorous ones to balance plant growth.
3. Strengthen plant shape adjustment and ensure good air permeability of the plants, so as to help fruit set: in production, attention should be paid to promptly removing old branches and old leaves. Since eggplant generally forms flowers and sets fruit at the branching points, production should pay attention to promoting branching. Generally, the fruits set at the first, second and third branching points are mostly effective flowers and can develop and set fruit well; after the fourth branching point, flower bud differentiation is poor and the fruit-setting rate is low, with mostly ineffective flowers. Therefore, in production, attention should be paid to removing branches after the fourth branching point to control the number of branches in the field, concentrate nutrient supply, and help fruit set.
4. Strengthen pest and disease control: in production, strengthen control of Verticillium wilt, red spider mites and aphids. Before sowing, soak seeds for 1 hour with 50% carbendazim wettable powder at 0.2% of seed weight, or soak seeds in 55°C warm water for 15 minutes, cool in cold water, then promote germination; in the planting field, broadcast carbendazim per mu for soil disinfection. In the early stage of Verticillium wilt occurrence, use 50% mixed sulfur suspension concentrate or 50% carbendazim wettable powder 500-fold solution for root drenching, applying 500 ml per plant.
After red spider mites occur, spray 1.8% Nongkeman emulsifiable concentrate 2000-fold solution or 2.5% Tianwangxing 3000-fold solution for control. In the early stage of aphid occurrence, spray 50% pirimicarb wettable powder 2000-3000-fold solution or 21% mieshabi 3000-4000-fold solution or 10% imidacloprid 3000-fold solution for control.
For plants damaged by pests and diseases, promptly spray foliar fertilizer such as Yemianbao, Zhibaosu, 0.5% urea + 0.5% potassium dihydrogen phosphate on the leaves to supplement nutrients, improve leaf photosynthetic capacity, increase the accumulation of photosynthetic products, and thereby raise the fruit-setting rate.
5. Spray chemical substances to preserve flowers and fruits. 1-2 days before flowering, apply 30-40 ml/kg of 2,4-D to the calyx or fruit stalk; after the first layer of fruit sets, spray 120 ml/kg or 180 ml/kg or 200 ml/kg sodium bisulfite, which can effectively increase matter accumulation and raise the fruit-setting rate.