What causes fruit abortion in cucurbit vegetables?
Fruit abortion means that newly set fruit buds and developing fruit stop growing, gradually turning yellow from the tip to the whole fruit, shriveling, and finally drying up. Fruit abortion is a common problem in cucurbit vegetable production and directly affects yield and output value. Especially in greenhouse cultivation, if management is improper, the fruit abortion rate can reach as high as 30%-60%. The causes of fruit abortion are many-sided; overall, it is because the young fruit does not receive sufficient nutrient supply during growth and stops developing. The specific causes are as follows:
1. Unsuitable temperature
Daytime temperature too high (above 35°C) or too low (below 20°C). If the daytime temperature in the greenhouse is above 32°C and the nighttime temperature is below 18°C, photosynthesis will be hindered, assimilation products will decrease, respiration consumption will increase, and nutrient accumulation will be low, thus leading to malnutrition and fruit abortion.
If cucurbit vegetables encounter low-temperature chilling injury during the growth period, especially excessively low soil temperature, root development will be poor and absorption capacity will decrease, so the nutrient supply to the fruit is insufficient and fruit abortion occurs.
2. Low carbon dioxide concentration
Cucurbit vegetables are generally very sensitive to changes in carbon dioxide concentration. If the carbon dioxide concentration in the greenhouse is too low, fruit abortion is likely to occur.
3. Excessive planting density and unreasonable fertilizer and water supply
Excessive planting density, continuous cloudy days with little light, poor ventilation, causing a closed canopy, and an unreasonable trellis shape are not conducive to photosynthesis, result in few assimilation products, and easily cause fruit abortion. Lack of water and fertilizer, or lack of trace elements caused by improper fertilization, also affects photosynthesis.
4. Parthenocarpy
When seedlings are raised in a solar greenhouse and during the early growth stage, the day-night temperature difference is large, forming many female flowers and few male flowers. At this time, insects are not yet active and there is a lack of pollination vectors, and artificial pollination is not carried out, so parthenocarpy mainly occurs. Varieties with weak parthenocarpy are prone to fruit abortion.
5. Excessive stem and leaf growth
Due to factors such as excessive nitrogen and sufficient water, relatively high nighttime temperature, watering and topdressing before the first fruit is set, temporary empty vines, and still supplying sufficient water and fertilizer when there is no fruit on the plant, the stems become thick and the internodes long, the leaves thin and large, and the growth is excessively vigorous, while the fruit grows slowly. Female flowers and young fruit cannot obtain assimilation products and abort.
6. Excessive flower and fruit growth
If there are too many female flowers and young fruit on the plant, the limited assimilation products can only be distributed to the large fruit or to some female flowers and young fruit, causing most female flowers and young fruit to abort. During the peak period of plant growth and fruiting, if the lower fruit is not harvested in time, it is also easy to cause the upper fruit to abort.
7. Severe disease and pest damage
Downy mildew, bacterial angular leaf spot, anthracnose, powdery mildew, black spot, and others all directly damage leaves, causing leaf necrosis; in severe cases, the whole leaf or all leaves of the entire plant dry up, photosynthesis cannot proceed, and fruit abortion occurs. Pests such as aphids, tea yellow mites, and whiteflies suck sap from cucurbit vegetable leaves and contaminate the leaves, destroying photosynthesis and causing malnutrition and fruit abortion.
8. Phytotoxicity
Unreasonable choice of pesticides, excessively high spraying concentration, or spraying too frequently causes cucurbit vegetables to suffer phytotoxicity, age, and dry up, and leaf photosynthetic capacity declines or is even lost. In addition, mechanical damage during management may also damage young fruit.