What to Do When Asparagus Lettuce Gets Sclerotinia Rot? A Detailed Guide to Integrated Control Techniques
Asparagus lettuce, also known as celtuce, is a variety of the lettuce species in the Asteraceae (Compositae) genus Lactuca that forms a fleshy tender stem; it is an annual or biennial herbaceous plant. Also known as stem lettuce, lettuce shoot, green shoot, and lettuce vegetable. Harvest period: January to April. It originated in Central or North China. Asparagus lettuce has strong adaptability and can be cultivated in spring and autumn or overwintered, mainly in spring cultivation, with harvest in summer.
Introduction to Asparagus Lettuce Varieties
1. Pointed-leaf Purple Shoot. Plant height about 40 cm, spread about 55 cm. Leaves are lanceolate, about 42 cm long, about 55 cm wide. Leaves are lanceolate, about 42 cm long, about 14 cm wide, with a wrinkled leaf surface. The shoot is long club-shaped, 51 cm long, 6 cm in transverse diameter; the outer skin and flesh are both greenish-white, the flesh is crisp, with relatively little water, and of good quality. A single shoot weighs about 1000 g, and it is relatively resistant to downy mildew. Suitable for autumn-sown overwintering cultivation; it is a mid-maturing variety.
2. Willow-leaf Shoot. Plant height 40-60 cm, spread 45 cm, with strong growth vigor. Leaves are upright, light green, lanceolate, resembling willow leaves. The leaf surface has shallow wrinkles, with wax powder, and the leaf margin is slightly wavy. The shoot is long club-shaped, 30-35 cm long, 5 cm in transverse diameter; the outer skin is greenish-white, the flesh is light green, crisp and tender in texture, and of good quality. A single shoot weighs about 500 g, with a yield of 2000-3000 kg per mu. It is both cold-tolerant and heat-tolerant, bolts late, and is a mid-to-late maturing variety. Suitable for open-field autumn cultivation.
3. Yanling Shoot. Plant height about 60 cm, spread 40 cm, with strong growth vigor. Leaves are lanceolate, light green, with a wrinkled leaf surface. The shoot is long club-shaped, 24 cm long, 5.5 cm in transverse diameter; the outer skin is greenish-white, the flesh is light green, the skin is thin, the texture is crisp, the taste is sweet, and it has plenty of water. A single shoot weighs about 500 g, with a yield of 3000-3500 kg per mu. It is both cold-tolerant and heat-tolerant, with strong disease resistance. It is a mid-maturing variety. Suitable for cultivation in both spring and autumn.
Sclerotinia rot of asparagus lettuce is one of the main diseases of asparagus lettuce, seriously affecting the planting benefits of asparagus lettuce. So how should integrated control of asparagus lettuce sclerotinia rot be carried out?
Symptoms of Asparagus Lettuce Sclerotinia Rot
Plants can be harmed by sclerotinia rot throughout the entire growth period. In the middle and late stages, with more shading, poor ventilation and air permeability, and high humidity, the damage is more severe. The stem, petiole, or leaves at the lower part of the plant generally become diseased first. After the stem is damaged, the aboveground part wilts and finally dies. When the petiole and leaves are damaged, the symptoms are the same as those on the stem. The diseased site initially appears water-soaked and light brown, gradually expands, causing the tissue to soften and rot, but without a foul odor. Under humid conditions, the diseased part produces dense white cottony mycelium. In the later stage, the mycelium interweaves and aggregates into white granules, and produces yellow water droplets. As the white granules grow, they become blackish-brown, mouse-dropping-shaped sclerotia.
Pathogen of Asparagus Lettuce Sclerotinia Rot
Asparagus lettuce sclerotinia rot is caused by infection by a pathogenic fungus of the genus Sclerotinia in the Ascomycotina subdivision, and its vegetative body is septate mycelium. The sclerotium germinates and grows an apothecium, with a stalk at the base, about 2-8 mm in diameter. The ascus is club-shaped, colorless, 91-125 × 6-9 micrometers in size, and contains 8 ascospores. The ascospores are elliptical, single-celled, colorless, 9-14 × 3-6 micrometers in size, neatly arranged within the ascus; the ascospore is its sexual reproductive organ.
Transmission Routes and Onset Conditions of Asparagus Lettuce Sclerotinia Rot
The sclerotium overwinters in the soil. Under suitable conditions, it forms an apothecium and releases ascospores, which spread through wind and rain and become the primary infection source. Field infection generally occurs through contact between diseased tissue and healthy plants, with mycelium spreading directly and causing damage.
The optimum temperature for sclerotium germination is about 15°C. The temperature range for ascospore germination is 0-35°C, with the optimum at 5-10°C. Mycelium can grow at 0-30°C, with the optimum at 20°C. Sclerotia can grow in an environment with a pH value of 1.68-10. A relative humidity above 85% is favorable for spore germination and mycelial growth, while below 70% the disease is mild. Therefore, when the field temperature is about 20°C and the relative humidity is above 85%, the disease will become epidemic.
Integrated Control of Asparagus Lettuce Sclerotinia Rot
Agricultural control:
1) Practice crop rotation. In diseased fields, practice rotation with Liliaceae vegetables for more than 3 years.
2) Soil disinfection. In diseased fields where rotation cannot be practiced, after clearing the vines in spring protected cultivation, use the high temperatures of the three summer months for soil disinfection. Method: first clean the garden, take diseased residues out of the field and bury them deeply or burn them; apply 50-100 kg of lime and 500 kg of chopped rice straw or wheat straw per 666.7 sq m, evenly applied on the soil surface; deep plow 60 cm and form high ridges 30 cm high; irrigate in the furrows, requiring water to be present in the furrows throughout the treatment period, so continuous watering is needed; cover with plastic film and seal all around; close the greenhouse for 15-20 days, so that the soil temperature at 20 cm depth reaches above 50°C (at the highest temperature), which can kill the sclerotia.
3) Use disease-free seeds. Save seeds from disease-free fields. Seeds carrying sclerotia can be selected with 10% salt water, the sclerotia will be removed by washing, then repeatedly rinse clean with clear water before sowing.
4) Cultivation control. Cultivate disease-free seedlings; cover with black plastic film, which can prevent apothecia from emerging from the soil; apply sufficient organic fertilizer and increase phosphorus and potassium fertilizer; strengthen ventilation and reduce humidity; promptly clean the field, take diseased leaves and diseased plants out of the field and bury them deeply or burn them (including promptly removing apothecia that emerge from the soil).
Chemical pesticide control: For pollution-free pesticide control, after planting and before disease onset, 3.5% thiabendazole (Tecto) smoke agent can be used for fumigation, carried out in the evening, once every 7 days, for 3-4 consecutive fumigations (250 g of smoke agent each time per 666.7 sq m).
1. Spraying in the seedbed. A few days before planting, spray the seedlings in the seedbed with 20% triadimefon (Bayleton) emulsifiable concentrate at 4000-5000 times dilution.
2. Spraying in diseased fields. After planting, in the early stage of disease onset, spray 50% procymidone wettable powder at 1000-1200 times dilution, or 50% procymidone wettable powder at 1000 times dilution, or 40% dimethachlon wettable powder at 1000-1200 times dilution, or 50% iprodione (Rovral) wettable powder at 1000-1200 times dilution, or 50% duomeiling wettable powder at 600-800 times dilution, focusing on spraying the stem base and basal leaves, once every 7 days, for 3-4 consecutive sprays.
3. Fumigation control. Before disease onset or in the early stage of disease onset, 10% procymidone smoke agent or 15% procymidone smoke agent can be used, 250 g each time per 666.7 sq m, closed greenhouse fumigation in the evening, once every 7 days, for 3-4 consecutive fumigations.
4. Dust control. Before disease onset or in the early stage of disease onset, 6.5% jiameiling dust, or 5% miemeiling dust, or 5% lide dust can be used, 1000 g each time per 666.7 sq m, sprayed in the morning or evening, using a duster (without adding water), once every 7 days, for 3-4 consecutive sprays.