The Pathogenesis and Control Methods of Lettuce Soft Rot

Lettuce is the common name for leaf lettuce, belonging to the genus Lactuca in the Asteraceae family. It is an annual or biennial herbaceous crop, and is also a popular vegetable in European and American countries, deeply loved by people. In recent years, the cultivation area has expanded rapidly, and lettuce has also moved from hotels and restaurants onto the dining tables of ordinary people.

Growth Habits of Lettuce

Lettuce prefers a cool environment; it is neither cold-tolerant nor heat-tolerant. The suitable growth temperature is 15°C-20°C, and the growth period is 90-100 days. The seeds are relatively tolerant to low temperatures and can germinate at 4°C. The optimum germination temperature is 18-22°C, and they hardly germinate above 30°C. During plant growth, it prefers a cool climate, with 15-20°C being the most suitable for growth, yielding high output and excellent quality; when continuously above 25°C, growth is poorer, the leaves become coarse and tough, and slightly bitter. However, it is also quite cold-tolerant, and 0°C or even short-term subzero low temperatures do not greatly hinder growth. Lettuce has a well-developed root system and a waxy leaf surface, giving it strong drought tolerance, but when cultivated in fertile, moist soil, the yield is high and the quality is good. The suitable soil pH is 5.8-6.6.

The Principles and Control of Lettuce Soft Rot

Symptoms of lettuce soft rot:

This disease often begins to occur in the mid-to-late growth stage or the head-forming stage of lettuce, mostly starting from wounds at the base of the plant. The diseased area initially becomes soaked and semi-transparent, then expands into an irregular, water-soaked shape, filled with light grayish-brown sticky matter, and releases a foul odor. As the disease progresses, the damage rapidly spreads upward from the base, causing the lettuce to rot. Sometimes, the pathogen also begins to rot from the leaf margins of the outer leaves and the top of the head.

Occurrence pattern of lettuce soft rot:

The pathogen mainly overwinters on diseased plants and diseased residues in soil and fertilizer, or continues to cause damage on other vegetables through the winter. It spreads through watering, fertilization, or insects, and invades through wounds and physiological cracks in the plant. The growth temperature of the pathogen is 4-39°C, with the optimum temperature being 25-30°C. When field water and fertilizer management is improper, when there are many pests, or when wounds caused by farming operations are frequent, the disease occurs severely.

Control methods for lettuce soft rot:

1. Agricultural control: Clear the stubble as early as possible, and even if replowing and preparing the soil, allow the residues of the previous crop to fully rot and decompose before planting; for severely diseased plots, use high ridges or high beds for planting; apply fully decomposed farmyard manure; plant at the appropriate time so that the susceptible period avoids high temperatures and the rainy season; when planting in high-temperature seasons, use shade nets or non-woven fabric for sun and rain protection; after watering or rainfall, pay attention to drainage at all times to avoid water accumulation in the field; promptly remove diseased plants when found.

2. Chemical control: In the early stage of the disease, use 50% Keshade wettable powder at 500 times dilution, or Xinzhiromycin or agricultural streptomycin at 5000 times dilution for control, spraying once every 7-10 days, for 2-3 consecutive times.