Symptom Identification and Control Methods of Bacterial Blight in Lablab Bean

Lablab bean, Lablab purpureus (Linn.) Sweet, commonly known as hyacinth bean, also known as huolian lablab bean, vine bean, hedge bean, magpie bean, cha bean, moon vegetable, belongs to the Dicotyledoneae class. There are also many varieties, such as: white lablab bean, purple lablab bean, oil bean, snake bean, pig's ear bean (shaped like a pig's ear). It is a perennial, twining vine plant of the genus Lablab in the Fabaceae family. It is a type of legume plant.

Plant morphology of lablab bean

Annual twining herb. Leaflets 3; terminal leaflet rhombic-broadly ovate, lateral leaflets obliquely rhombic-broadly ovate, 6—10 cm long, 4.5—10.5 cm wide, apex shortly acute or acuminate, base broadly cuneate or nearly truncate, both surfaces with white short pubescence along the veins. Racemes axillary; flowers 2—4, clustered on the nodes of the rachis; upper 2 teeth of the calyx almost completely connate, the remaining 3 teeth nearly equal; corolla white or purplish red, the standard petal with 2 appendages on both sides at the base; ovary sericeous, with glands at the base, style with white beard hairs near the apex. Pods flat, sickle-shaped or semi-elliptic, 5—7 cm long; seeds 3—5, flat, oblong, white or purplish black. Flowering and fruiting period July—September.

Growth habits of lablab bean

Perennial, twining vine. The whole plant is almost hairless, stems up to 6 m long, often pale purple. Pinnately compound leaves with 3 leaflets; stipules basifixed, lanceolate; stipels linear, 3-4 mm long; leaflets broadly triangular-ovate, 6-10 cm long, width approximately equal to length, lateral leaflets unequal on both sides, oblique, apex acute or acuminate, base nearly truncate. The suitable germination temperature for seeds is 22-23°C. The plant can tolerate high temperatures of around 35°C, has a well-developed and strong root system, strong drought tolerance, and good adaptability to various soils. Planting in well-drained and fertile sandy soil or loam can significantly increase yield. Annual herbaceous plant, stems trailing, leaflets lanceolate, flowers white or purple, pods oblong, flat, slightly curved. Seeds white or purplish black. Prefers warm and moist conditions, tolerant of heat. Generally sown in spring and harvested in autumn. Young pods are an ordinary vegetable, and the seeds can be used as medicine.

Symptoms of bacterial blight in lablab bean:

Green oil-soaked spots appear at the leaf margins, later developing into reddish brown, surrounded by a yellow halo; as the disease progresses, the lesions merge into patches. After the stems and vines are infected, sunken reddish-brown elongated spots appear; in severe cases, the lesions encircle the stem, and the leaves above the lesions wither. After the pods are infected, slightly sunken circular or irregular brown spots appear. When humid, colorless transparent bacterial ooze exudes from the diseased parts. The pathogenic bacteria can overwinter inside the seeds and adhering to the seed coat, and are spread by wind, rain, and insects, invading through the stomata, hydathodes, and insect wounds of the host. The disease is severe under high temperature and high humidity, leaf dew, and heavy fog; improper field management, poor drainage, insufficient fertility, excessive application of nitrogen fertilizer, and weak plant vigor also lead to severe incidence.

Control methods for bacterial blight in lablab bean:

① Seed disinfection: Select disease-free seeds; when it cannot be determined whether the seeds carry bacteria, seed disinfection should be carried out. Soak seeds in warm water at 55°C for 15 minutes, then remove and cool in cold water, air-dry and sow. Alternatively, soak seeds in 500-fold streptomycin sulfate solution for 12 hours.

② Agricultural measures: Strengthen cultivation management, rational close planting, increase plant ventilation and light penetration, avoid water accumulation in the field, and do not use flood irrigation.

③ Chemical control: In the early stage of the disease, spray with 14% copper ammonia complex aqueous solution at 300-fold dilution, or 72% agricultural streptomycin sulfate soluble powder at 3000-4000-fold dilution, or 78% mancozeb•zinc wettable powder at 500-fold dilution, or 40% bacterial quick-kill wettable powder at 600-fold dilution, or 50% xiaojunling soluble powder at 1200-fold dilution, or 60% copper succinate•diethyl aluminum•zinc wettable powder at 500-fold dilution, or the antibacterial agent “401” at 800-fold dilution, and other agents for spray control, once every 7 days, spraying 2-3 times consecutively.