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 production of summer cucurbits within solar greenhouses, the application of 2,4-D liquid to enhance fruit set has become a common practice. However, in many areas, phytotoxicity caused by 2,4-D continues to occur, often leading to severe economic losses.
The symptoms of 2,4-D phytotoxicity in summer squash are quite distinctive. Within 2-3 days after flowering, young leaves begin to curl and become distorted. The mesophyll tissue degrades, leaving prominent veins that appear stiff and rigid. This condition is commonly referred to as "chicken paw disease" by local farmers. The growing tip becomes hardened and shrinks, sometimes disappearing entirely. The young fruits turn dark green and remain short, while female flowers fail to open fully, often remaining partially closed. Stems become thickened, and in some cases, they grow over the base of the developing fruits. Most affected plants produce coarse, sharp-tipped melons, making them unsuitable for sale. The stem sections of infected plants shorten, and the petioles often show milky exudates at the stem junction, with severely damaged nodules. Lower and middle leaves turn dark green, lose their luster, and begin to age prematurely. 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%. Additionally, in many cases, 2,4-D phytotoxicity was mistakenly diagnosed as a viral infection, delaying proper response.
The causes of 2,4-D injury can be attributed to several factors. First, the concentration of the prepared solution may be too high, or an excessive amount of liquid may be applied during flowering. Second, the drug may accidentally come into contact with the leaf blades or growing points, or it may be stored in wide-mouth containers, allowing evaporation and increasing the concentration. Third, some substandard or counterfeit products containing 2,4-D have been used, contributing to the problem.
To prevent and manage 2,4-D injury, there is currently no specific antidote. Therefore, prevention is key. Farmers should strictly follow recommended dosages when preparing the solution. During the deep winter, 1 gram of 2,4-D should be mixed with 35 kg of water, while in spring, when temperatures rise, the ratio should be adjusted to 1 gram per 40 kg of water. Too low a concentration may result in poor fruit set or sharp-tipped melons, while too high a concentration increases the risk of phytotoxicity. When applying the solution manually, care must be taken to avoid overspraying and to prevent the solution from dripping onto leaves or growth points. In recent years, some growers in southern Taiwan have successfully used syringes to apply the solution directly to female stigmas through fine needles, achieving good results. After each use, containers should be tightly sealed to prevent evaporation and concentration increase. It is essential to use only approved and high-quality products from reputable manufacturers, avoiding counterfeit or substandard drugs. For new fruit-setting agents, it is advisable to conduct small-scale trials first, ensuring effectiveness and proper usage before large-scale adoption.
The recovery from 2,4-D injury in summer cucurbits depends on temperature and moisture levels. Under normal management, symptoms can be reduced within 40 days during winter, and within 20-30 days during spring. Increasing the temperature and providing adequate water can accelerate recovery and reduce losses. Affected plants should have malformed fruits removed promptly. In greenhouses where the damage is severe, it may be necessary to remove the entire crop to prevent further spread and minimize financial loss.
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