In recent years, the cultivation of summer squash has expanded significantly, and in certain regions, it has become one of the primary vegetable crops supplied during the winter and spring seasons. In the summer greenhouse production of cucurbits, the use of 2,4-D liquid to promote fruit set has become widespread. However, in many areas, 2,4-D phytotoxicity frequently occurs, sometimes leading to severe crop losses.
The symptoms of 2,4-D injury on summer squash in solar greenhouses typically appear 2-3 days after flowering. Affected plants show curled and distorted young leaves, with a degradation of the mesophyll tissue, prominent veins, and a stiff texture. These symptoms are often referred to as "chicken paw disease" by local farmers. The growing point becomes stiff and shrinks, eventually disappearing. The young fruits turn dark green, remain short, and female flowers fail to open properly, often remaining half-closed. Stems become thickened, and some even wrap around the base of the fruit. Most affected plants produce coarse, pointed melons that lose their market value. The stem sections of infected plants are shortened, and the petioles often have milky exudates, with severely damaged nodules. Lower middle leaves turn dark green, lose their luster, and show signs of early aging. The impact of 2,4-D injury on summer gourd production depends on the severity of the damage and the number of affected plants. According to a survey conducted in southern Hebei Province, some greenhouses suffered losses exceeding 70%. In many cases, 2,4-D injury was mistakenly diagnosed as a viral infection.
The causes of 2,4-D injury include: (1) using an overly concentrated solution or applying too much liquid during flowering; (2) accidentally spraying the drug onto the leaves or growing points, or using large containers that allow evaporation, leading to higher concentrations; and (3) using low-quality or counterfeit 2,4-D products.
To prevent and manage 2,4-D injury, there is currently no specific antidote, so prevention is key. Farmers should strictly follow recommended dosages when preparing the solution. During deep winter, 1 gram of 2,4-D should be mixed with 35 kg of water, while in spring, when temperatures rise, the same amount should be diluted in 40 kg of water. Too low a concentration may result in poor fruit set or misshapen fruits, while too high a concentration can cause phytotoxicity. When applying the solution with a brush, avoid excessive application and ensure the drug does not drip onto leaves or growing points. Recently, many growers in southern Taiwan have successfully used syringes to inject the solution directly onto female stigmas through fine needles. After each use, containers should be tightly sealed to prevent water evaporation and concentration increase. It is crucial to use only certified, high-quality products from reputable manufacturers and avoid counterfeit or substandard drugs. Before adopting new fruit-setting agents, farmers should conduct small-scale trials to confirm effectiveness and proper usage before large-scale application.
The recovery speed of 2,4-D injury depends on temperature and moisture levels. Under normal management, symptoms may take over 40 days to resolve in winter, while in spring, they may improve within 20–30 days if temperatures are slightly increased and watering is enhanced. For severely affected plants, it's important to promptly remove deformed fruits. In greenhouses with serious 2,4-D damage, immediate removal of the entire crop might be necessary to prevent further losses.
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