What to Do About Sponge Gourd Flower Rot? Cause Analysis and Countermeasures
Sponge gourd (Luffa) is an annual climbing herbaceous plant of the Cucurbitaceae family. The stems and branches are rough, with ridged grooves, covered with fine soft hairs; the branches are angular, smooth or with coarse hairs on the angles, and have tendrils. The stem tendrils are stout, covered with short soft hairs, usually 2-4 branches. The leaves are simple and alternate, with long petioles; the leaf blade is palmately cordate, 8-30 cm long, slightly wider than long, with wavy shallow teeth along the margin, and smooth and hairless on both surfaces. The petiole is rough, 10-12 cm long, with inconspicuous grooves, nearly hairless. The leaf blade is triangular or nearly round, about 10-20 cm long and wide, usually palmately 5-7 lobed; the lobes are triangular, the middle one longer, 8-12 cm long, with an acute or acuminate apex, serrate margins, and a deeply cordate base; the sinus is 2-3 cm deep and 2-2.5 cm wide; the upper surface is dark green and rough, the lower surface light green with short soft hairs; the veins are palmate with white short soft hairs. In summer, unisexual flowers are borne in the leaf axils.
Sponge gourd is monoecious; the male flowers are in racemes and open first, while the female flowers are solitary with long pedicels and a pale yellow corolla. The pepo is long and cylindrical, pendulous, generally 20-60 cm long and up to more than 1 m at most. The seeds are flat and oblong-ovate, about 1.5 cm long, black. The root system of sponge gourd is strong. The stem is vining, five-angled, green; both the main vine and lateral vines grow vigorously; the nodes bear branching tendrils and readily produce adventitious roots. The leaves are palmately or cordately shaped, covered with down. It is monoecious with unisexual flowers, and the corolla is yellow. The male flowers are in racemes, the female flowers are solitary with an inferior ovary; after the first female flower appears, most stem nodes can produce female flowers.
When sponge gourd is sold, the quality of the flowers has become an important quality indicator, but flower rot of sponge gourd is also a problem that currently occurs rather frequently.
1. Dry flower rot
Symptoms: The edges of the petals become dry and withered, which is dry rot (as distinguished from watery flower rot), and the entire petal is no longer fresh. Disease analysis: This may be a symptom of gummy stem blight (Mycosphaerella melonis) on the flowers. It occurs more severely under low-light conditions, especially after consecutive cloudy days.
Countermeasures: Spraying agents such as thiophanate-methyl, mancozeb, or prochloraz can reduce the occurrence of the disease.
2. Watery flower rot
Symptoms: Watery rot begins at the edges of the petals; in severe cases the petals show dripping water, sometimes with a foul odor, and sometimes without but with white mold.
Disease analysis: A foul odor without mold may be bacterial soft rot, while white mold may be flower rot or phytophthora fruit rot; both conditions occur more severely under high temperature and high humidity.
Countermeasures: For bacterial soft rot, streptomycin or streptomycin sulfate can be sprayed on the leaves, and copper formulations such as copper hydroxide or copper oxychloride can also be sprayed. For flower rot and phytophthora fruit rot, agents such as dimethomorph, cyazofamid, anke, or metalaxyl can be sprayed on the leaves, or some of the agent can be added to the flower-dipping solution.
3. Stigma rot
Symptoms: The stigma of the flower develops black rot, accompanied by rotting of the flower.
Disease analysis: This may be a disease caused by a deficiency of elements such as boron and calcium in the soil, and is also related to poor root absorption or uncoordinated water supply.
Countermeasures: Foliar fertilizers containing elements such as boron and calcium can be sprayed on the leaves, such as Greenfenwei No. 3 or No. 2, Gaizhonggai, or calcium nitrate; some calcium fertilizer such as Norwegian calcium nitrate can also be applied by drenching. At the same time, be sure to care for the roots and enhance the root system's absorption capacity; humic acid and microbial fertilizers can be added, quick-absorption products can also be drenched, or one of the agents such as thiophanate-methyl, hymexazol, or phosethyl-Al plus mancozeb can be selected and then mixed with a rooting agent for root irrigation, with about 0.25 kg per plant.