Control Methods for Anthracnose on Cotyledons of Bottle Gourd (Calabash) in Greenhouse Cultivation
Bottle gourd (Calabash; pinyin: hù zǐ), aliases: sweet gourd, sweet calabash, calabash gourd, Jingjie Chui, Longmi melon, Tian melon, long calabash, flat gourd; phylum Angiospermae, a species under the genus Lagenaria in the family Cucurbitaceae, a variety of the genus plant bottle gourd (Lagenaria siceraria), an annual climbing herb.
Morphological characteristics of bottle gourd
Annual climbing herb; stems and branches grooved, covered with viscous long soft hairs, gradually shedding when old, becoming nearly hairless. Petiole slender, 16-20 cm long, with the same hair covering as stems and branches, with 2 glands at the apex; leaf blade ovate-cordate or reniform-ovate, both length and width 10-36 cm, undivided or 3-5 lobed, with 5-7 palmate veins, apex acute, margin irregularly toothed, base cordate, sinus open, semicircular or nearly circular, 1-3 cm deep, 2-6 cm wide, both surfaces covered with fine soft hairs, denser on the leaf back and veins.
Tendrils slender, initially with fine soft hairs, gradually shedding, becoming smooth and hairless, upper part 2-forked. Monoecious, female and male flowers both solitary. Male flowers: pedicel slender, slightly longer than petiole, pedicel, calyx and corolla all covered with fine soft hairs; calyx tube funnel-shaped, about 2 cm long, lobes lanceolate, 5 mm long; corolla yellow, lobes wrinkled-wavy, 3-4 cm long, 2-3 cm wide, apex slightly notched with a small pointed tip, 5 veins; stamens 3, filaments 3-4 mm long, anthers 8-10 mm long, oblong, anther cells curved. Female flower pedicel slightly shorter than or nearly equal to petiole; calyx and corolla similar to male flowers; calyx tube 2-3 mm long; ovary constricted in the middle, densely covered with viscous long soft hairs, style thick and short, stigma 3, swollen, 2-lobed.
Fruit initially green, later turning white to yellowish, due to long-term cultivation; fruit shape varies greatly, differing by variety or variety, some are dumbbell-shaped, constricted in the middle, lower and upper parts swollen, upper part larger than lower part, several tens of cm long, some only 10 cm long (small gourd), some are oblate, rod-shaped or configuration-shaped, fruit skin becoming woody when mature. Seeds white, obovate or triangular, apex truncate or 2-toothed, rarely rounded, about 20 mm long. Flowering in summer, fruiting in autumn.
Growing environment of bottle gourd
Bottle gourd has strong growth vigor, large stem and leaf growth, many fruits, and requires a large amount of water throughout the growing period. Bottle gourd requires well-aerated soil rich in organic matter, and avoids continuous cropping. It grows well on fertile, loose sandy loam with convenient drainage and irrigation. Planting bottle gourd in heavy clay soil or low-lying land makes it susceptible to disease. During the growing period, a certain amount of nitrogen fertilizer is required, and during the fruiting period it prefers sufficient phosphorus and potassium fertilizer. In the early growth stage it prefers a moist environment, and during the flowering and fruiting period soil and air humidity should not be too high.
Control of anthracnose on cotyledons of bottle gourd in greenhouse cultivation
Symptoms of anthracnose on cotyledons of bottle gourd
Bottle gourd seeds carry the pathogen; after sowing, under conditions of low temperature and high humidity, cotyledons take a longer time to emerge from the soil, and it often occurs that just as the cotyledons emerge from the soil and have not yet unfolded, light brown to brown lesions appear on the edges of the cotyledons or on the cotyledons, slightly sunken after expansion, and pink viscous material grows on them when humidity is high. Bottle gourd anthracnose can also occur at the adult plant stage, mainly damaging the fruit. Fruit spots circular or nearly circular, 2-6 mm in size, initially light green, later turning dark brown, slightly sunken, and when humidity is high, yellow dot-like viscous material densely grows on the diseased part; the lesions often merge into large spots or may be seen individually. In late autumn, small black dots arranged in concentric rings grow on the lesions. When the neck is infected, the fruit mostly cannot mature, hanging on the plant or falling off.
Transmission routes and onset conditions of anthracnose on cotyledons of bottle gourd
The pathogen overwinters as mycelium and pseudosclerotia on seeds or on diseased residues in the soil. After sowing, the mycelium latent on the seeds can directly invade the cotyledons, causing cotyledon disease; when diseased seedlings are transplanted, the conidia produced in the diseased part spread through rain splash, forming a disease center. In greenhouses, disease can occur at 10-30°C, with severe disease at 24°C. High humidity during the seedling period is an important condition inducing this disease; at relative humidity 87%-98% and temperature 24°C, disease becomes visible after 3 days of incubation, and disease cannot occur when relative humidity is below 54%. In production, in early spring plastic greenhouses with low temperature and high humidity, gourd guttation and leaf surface condensation, with water droplets forming on the leaf surface, can satisfy the humidity conditions for disease onset, causing the occurrence of anthracnose at the seedling stage.
Control methods for anthracnose on cotyledons of bottle gourd:
1) Seed treatment. First select disease-free seeds, collect seeds from disease-free bottle gourds; for production seeds, soak in 50-51°C warm water for 20 minutes or soak in 100-fold glacial acetic acid for 30 minutes, rinse clean with clear water, then germinate.
2) The seedling-raising land should implement crop rotation of more than 3 years to prevent soil-borne pathogens; when rotation is not possible, seedbed soil must be disinfected.
3) In greenhouses or open fields, at the early stage of disease, spray 25% Tante Ling wettable powder 500-fold solution or 50% methyl thiophanate · sulfur suspension concentrate 800-fold solution, 50% Shibaogong wettable powder 1000-fold solution, 50% Duofengnong wettable powder 500-fold solution.
4) In greenhouses, spray or dust 80% Dasheng wettable powder 500-fold solution, 8% Ketang Ling dust formulation, 1 kg per 667 m2, once every 7-10 days, for 2-3 consecutive treatments.
5) Select disease-free seeds and bottle gourd and bottle gourd (calabash) varieties resistant to anthracnose.
6) Strengthen ventilation and temperature and humidity management to keep it away from the conditions for disease onset.