High daytime temperatures exceeding 34°C, combined with nighttime temperatures above 20°C, or prolonged periods of 40°C heat lasting up to four hours can lead to anti-dropping and fruit-dropping issues. When the temperature is too high, the style elongates significantly compared to the anther barrel, causing the ovary to shrink. This disrupts normal pollen transfer and reduces stamen fertility, ultimately leading to flower and fruit drop.
To manage these conditions, several control measures can be implemented. First, use a shade net to lower the temperature in the growing area. Second, apply balanced fertilization techniques, avoiding excessive nitrogen application. Watering should be done in small amounts, not through flooding, to maintain proper moisture levels while managing temperature stress. If pollination is poor, auxin sprays like 2,4-D can be used. These should be applied carefully, either by spraying or wiping the flowers as directed.
It’s important to note that 2,4-D is a commonly used growth regulator, but improper concentration can cause phytotoxicity. The recommended concentration depends on the post-planting temperature: between 15°C and 20°C, use 10–15 ppm. Once temperatures rise, reduce the concentration to 6–8 ppm. Avoid direct contact with tender shoots or young leaves, and never spray directly onto them. In cases where there are many flowers in the field, a higher concentration of 25–40 ppm may be used for better resistance. Always follow the manufacturer's guidelines and test on a small area first to ensure safety and effectiveness.
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