Control Measures for Deformed Strawberry Fruits Such as Too-Thin, Too-Plump, Cockscomb-Shaped and Flat Fruits in Greenhouses

    Greenhouse strawberries often produce deformed fruits that are too plump or too thin, cockscomb-shaped or flat. Such strawberries not only affect quality but also reduce value. To reduce or even avoid deformed fruits, the causes and control methods of deformed strawberry fruits are introduced below:

Deformed Strawberries

    I. Causes of Deformed Strawberries:

    1. Variety differences. Among strawberry varieties, most produce normal complete flowers, while a few tend to produce flowers with short stamens and long pistils, and with few pollen grains that mostly lack germination ability, which easily leads to deformed fruits. Generally, varieties with shallow dormancy, strong cold resistance and abundant, sound pollen, such as Fengxiang, Chunxiang and Baojiao Zaosheng, have fewer deformed fruits. In addition, after 3-4 years of plant age, strawberries degenerate and age, leading to an increase in deformed fruits.

    2. Flower grade. Low-grade flowers are prone to male sterility; high-grade flowers are prone to female sterility. However, as long as the former have good pollen, they can set fruit normally, while the latter set fruit poorly or even fail to set fruit, and are prone to deformed fruits.

    3. Temperature and humidity. Low temperature, high temperature or high humidity easily cause deformed fruits. High humidity affects anther dehiscence and causes water droplets to wash over the stigma. The suitable growth temperature for strawberries is 20°C-25°C; during the flowering and fruiting period, the minimum must not be lower than 5°C. Too low or too high a temperature will affect strawberry growth and pollination, and deformed fruits easily appear.

    4. Spraying pesticides during the flowering period. Spraying pesticides during the flowering period can wash over the stigma and cause deformed fruits, especially in strawberry flowers that open on the same day. In some greenhouses, the abuse of pesticides during the flowering period not only directly hinders pollination and fertilization but also kills bees and flower flies, causing an outbreak of deformed fruits.

    5. Light conditions. Pollen formation begins about 2 weeks before flowering. If light is insufficient during this period, or if there are cloudy and rainy days, the accumulation of starch needed for pollen germination is inhibited, thereby reducing the pollen germination rate, which is unfavorable for fertilization and causes deformed fruits.

    6. Cultivation management. During the flower bud differentiation period of strawberries, if fertilizer is insufficient or excessive, or if the nitrogen level in the seedlings is too low or too high, it will affect the quality of flower bud differentiation and is unfavorable for normal pollination. During the flower bud differentiation, flowering and enlargement periods of strawberries, if water is insufficient, it will cause poor flower organ development, incomplete pollination and fertilization, and hindered strawberry enlargement, easily forming deformed fruits.

    II. Control Methods:

    To control deformed strawberry fruits, in addition to selecting good varieties and interplanting some varieties with abundant pollen among the main cultivated varieties, several points should also be done well:

    1. Promote full flower bud differentiation. Whether strawberry flower buds differentiate fully affects strawberry yield and quality. With good flower bud differentiation, there are more flowers, larger fruits and fewer deformed fruits. Generally, starting 2 weeks before strawberry planting, root cutting, shading, nitrogen control and removal of old leaves are carried out to promote full flower bud differentiation.

    2. Reasonably regulate temperature and humidity. Strawberry flower organs are sensitive to low temperature; if exposed to -2°C for 1 hour, the pistils will turn black. Therefore, the insulation performance of the greenhouse should be improved, with daytime greenhouse temperature at 20°C-25°C, nighttime at 8°C-10°C, and soil temperature at 18°C-20°C. The relative humidity for strawberry anther dehiscence is 30%-50%, and the relative humidity for stigma fertilization and pollen germination is 50%-60%. The greenhouse environment is closed, and if ventilation is not carried out in time, humidity will become too high and deformed fruits will occur. In production, drip-free film and high-ridge plastic film mulching can be used to reduce soil moisture evaporation, and ventilation can be carried out for a short time at noon to regulate temperature and humidity.

Releasing Bees During the Strawberry Flowering Period

    3. Release bees during the flowering period. When the first batch of strawberry flower buds forms, keep honeybees in the greenhouse, placing 2-3 boxes of bees per standard greenhouse, evenly placed, which can achieve a pollination rate of 95%. Bee release times: 8-9 a.m. and 3-4 p.m. Using bees to assist pollination can reduce deformed fruits.

    4. Strictly prohibit pesticide application during the flowering period. During the strawberry flowering period, pesticide use is strictly prohibited to prevent reducing the pollen germination rate and producing deformed fruits. Therefore, before strawberry flowering, diseases should be thoroughly controlled; after flowering, diseased plants should be pulled out in time, and diseased leaves and inflorescences should be removed to control the spread of diseases.

    5. Timely thin flowers and fruits. Promptly thin out secondary flowers, small deformed fruits, diseased leaves, old leaves and yellow leaves, which helps increase light exposure, can reduce the rate of deformed fruits, helps concentrate nutrient supply, and improves strawberry fruit weight and quality.

    6. Strengthen fertilizer and water management. If the soil in the greenhouse is too dry, too wet, lacking fertilizer or improperly fertilized, it will cause an imbalance in water and nutrient supply and demand, leading to poor strawberry development and deformed fruits. If soil moisture is insufficient, water lightly in time; if fertilizer is lacking, topdress with watering, increase phosphate and potassium fertilizer, applying about 15 kg per mu. After dissolving in water, apply by punching holes for better results. After fertilizing, if soil moisture is insufficient, water in time to meet the needs of normal strawberry flowering and fruiting and prevent deformed fruits.