What Causes Bitter Melon Leaves to Turn Yellow?

During the growing season, bitter melon may develop yellowing and wilting leaves and a low fruit-setting rate, and yellowing leaves are the most common of these phenomena. So what's going on when bitter melon leaves turn yellow?

Cause one: waterlogging

Bitter melon's root system is fairly well developed, but it consists mainly of secondary lateral roots and has weak regenerative capacity, so bitter melon likes moisture but does not tolerate waterlogging. During the growing season it needs a relative air humidity of around 85% and a corresponding soil moisture level, but it should not be waterlogged. Waterlogging can easily cause the roots to rot and the leaves to yellow and wilt, which in mild cases affects fruiting and in severe cases causes the plant to develop disease and die.

Solution: After each watering, prevent prolonged waterlogging in the field by irrigating and draining promptly; especially after rain, be sure to clear the trenches and drain in time to prevent water from accumulating in the field.

Cause two: nitrogen deficiency

When bitter melon lacks nitrogen, it shows small leaves, with the upper leaves even smaller, gradually turning yellow from the bottom upward, noticeably shortened internodes near the growing point, yellowing between the veins, prominent veins, later spreading to the whole leaf, few fruits set, slow expansion, and deformed fruits.

Solution: For yellow leaves caused by nutrient deficiency, topdressing of bitter melon should be done well, following the principle of light application in the early stage, heavy application in the middle stage, and supplementary application in the late stage. Before flowering and fruiting, the plant's growth is small, so topdressing should be light; after flowering and fruit setting, gradually increase the amount of fertilizer and water; during the peak fruiting period, when the plant grows and sets fruit at the same time, topdressing should be heavy; in the late fruiting stage, the plant begins to age, so appropriate topdressing should be applied to prevent premature aging from affecting fruit growth. After flowering and fruit setting, apply sufficient fertilizer, topdressing 15 kg of urea and 10 kg of potassium sulfate per mu. After harvesting the first batch of fruits, topdress with about 10 kg of urea each time thereafter. In addition, on clear evenings, spray the leaves with a 0.2% urea and 0.3% potassium dihydrogen phosphate aqueous solution, which can promote stem and leaf growth, extend the harvest period, and avoid reduced yield and quality caused by premature aging of the plant.

Cause three: natural aging

Bitter melon branches strongly, with luxuriant foliage; in the later stage, because nutrients cannot be supplied adequately, the lower leaves naturally turn yellow and age.

Solution: Bitter melon mainly sets fruit on the main vine, so pruning is necessary. When tying the vines, remove the lateral vines below 50 cm on the main vine; above that, select and keep 1-2 robust lateral vines and let them grow, removing the rest promptly. In the middle and late fruiting stages, the aged yellow leaves on the middle and lower parts of the plant and the thin, weak, or fruitless lateral branches on the upper part should be removed as early as possible.

Cause four: anthracnose

It mainly occurs in the middle and late stages of bitter melon growth and is prone to occur under low-temperature and rainy conditions in July and August. When leaves are affected, the disease generally starts from the old leaves near the roots and gradually spreads upward. The lesions initially appear as water-soaked, round, pale yellow spots, then expand into brown round spots 0.1-0.5 cm in diameter, with a purple halo around the outside, sometimes showing concentric rings; they break apart easily when dry. In severe cases, the lesions merge into large patches, and the leaves dry up and die. When humidity is high, pale gray to reddish-brown sticky material forms on the leaf lesions.

Solution: You can choose 70% thiophanate-methyl wettable powder at 500 times dilution, or 80% thiram wettable powder at 800 times dilution, 50% thiram wettable powder at 500-600 times dilution, 25% azoxystrobin suspension concentrate at 1500 times dilution, 68.75% famoxadone · mancozeb water-dispersible granules at 1000 times dilution, 60% pyraclostrobin water-dispersible granules at 500 times dilution, 50% kresoxim-methyl dry suspension concentrate at 3000 times dilution, 56% azoxystrobin · chlorothalonil suspension concentrate at 800 times dilution, 10% difenoconazole water-dispersible granules at 1500 times dilution, 30% difenoconazole · propiconazole emulsifiable concentrate at 3000 times dilution, 20% flusilazole · prochloraz aqueous emulsion at 55-66 ml per mu, 40% carbendazim · thiram · bromothalonil wettable powder at 400-600 times dilution, 50% prochloraz wettable powder at 1000-2000 times dilution, and other sprays for control, spraying once every 6-7 days for 3-4 consecutive sprays.

Cause five: root-knot nematode disease

It shows as poor plant growth, stunting, leaves turning yellow from the bottom upward, wilting, and necrosis; the fruit surface has no ridges or has lumpy protrusions, or is partly without ridges or with lumpy protrusions, and the plant gradually wilts and dies. However, this disease mainly damages the roots of bitter melon. Affected plants have more lateral roots and fibrous roots than normal plants, and spherical or irregular nodular growths form on the fibrous roots. The nodules are initially white and soft in texture, later turning brown or dark brown with a rough surface. You can pull out a severely affected plant and check the roots to identify it.

Solution: First, 15 days before sowing or transplanting bitter melon, apply 4-5 kg per mu of 0.2% high-osmotic abamectin wettable powder, or 2.5-3 kg of 10% fosthiazate granules, mixed evenly with 50 kg of fine soil and spread on the soil surface, then deep-plow 25 cm for soil disinfection; either can achieve the effect of controlling nematode damage. Or use 10% cadusafos granules at 3-4 kg per mu, applied in furrows, or 3% isazofos granules at 4 kg per mu evenly applied into the planting furrows or holes. In the early stage of the disease, you can drench the roots with 1.8% abamectin emulsifiable concentrate at 1000-1200 times dilution, or 50% phoxim emulsifiable concentrate at 1000-1500 times dilution, and other agents. Apply 250-500 ml of the liquid per plant, once every 7-10 days, for a total of 2-3 applications.