Control of Brown spot in Field cultivation of lettuce

Lettuce is the common name of leaf lettuce, which belongs to the genus lettuce of Compositae. It is an annual or biennial herbaceous crop. It is also a popular vegetable in Europe and the United States. Lettuce is native to the Euro-Mediterranean coast and is domesticated from wild species. The ancient Greeks and Romans ate it first. Lettuce has been introduced into China for a long time, and it is widely cultivated along the southeast coast, especially in the suburbs of big cities and in Guangdong and Guangzhou, especially in Taiwan. In recent years, the cultivation area has expanded rapidly, and lettuce has also entered the table of ordinary people from hotels and restaurants.

Growth habits of lettuce

Lettuce likes cold environment and is neither cold-resistant nor heat-tolerant. The suitable temperature for growth is 15 ℃-20 ℃ and the growth period is 90-100d. The seeds are tolerant to low temperature and can germinate at 4 ℃. The optimum temperature for germination was 18-22 ℃, and there was almost no germination when it was higher than 30 ℃. During the period of plant growth, it likes cool climate, and 15-20 ℃ is the most suitable for growth, with high yield and good quality, and continuously higher than 25 ℃, with poor growth, thick and old leaves and slightly bitter taste. However, the cold tolerance is also quite strong, and 0 ℃ or even short-term subzero low temperature does not hinder the growth. Lettuce has developed root system, waxy leaves and strong drought tolerance, but it has high yield and good quality when cultivated on fertile and humid soil. The suitable pH value of soil is 5.8-6.6.

The main categories of lettuce

According to the growth morphology of leaves, lettuce can be divided into heading lettuce, wrinkled lettuce and upright lettuce.

Heading lettuce: the main characteristic of heading lettuce is that its terminal leaves form leaf balls. The leaf blade is entire, serrated or parted, the leaf surface is smooth or wrinkled, and the terminal leaf forms a globule, round or rounded. The main varieties are Dahu 659, avant-garde 75, Salinas, Beishan No. 3, Mamick, Green and so on.

Wrinkled lettuce: the main feature of wrinkled lettuce is that it does not bear balls. Basal leaves, leaf blade long oval, petiole longer, leaf margin wavy notched or deeply parted, leaf surface wrinkled, clustered leaves like large flowers. The main varieties are "Hongfan" purple leaf lettuce, safflower leaf lettuce, green wave, Dongshan lettuce and so on.

Upright lettuce: the main characteristics of upright lettuce are long and narrow leaves, upright growth, entire or serrated leaves, thick leaves, thick meat and poor flavor. The variety of this variety is few, the distribution area is not wide, and it is seldom planted in China.

Control of Brown spot in Field cultivation of lettuce

Introduction to Brown spot of lettuce

Lettuce brown spot is a fungal disease caused by Cercospora brown spot of lettuce or Cercospora of banana, which is mainly harmful to leaves. The disease spot on the leaf shows two kinds of symptoms, one is water-stained at the beginning of the disease, and then gradually expands into a round to irregular shape, showing brown to dark gray disease spot, 2mm in diameter; the other is a dark brown disease spot with irregular edges and a water-stained halo on the periphery. When the environmental humidity is high, dark gray mildew occurs on the disease spot, and when the disease spot is serious, the disease spot fuses with each other, causing the leaves to turn brown and dry. The first brown spot symptom is caused by Cercospora lutescens in lettuce, while Cercospora brown spot in banana causes the second brown spot symptom. The pathogen overwintered on the residual body with mycelium and conidia, carried out primary infection and re-infection with conidia, and spread by airflow and Rain Water sputtering. In continuous rainy and snowy weather, poor plant growth or excessive growth caused by partial application of nitrogen fertilizer, the disease will be aggravated.

Control measures of brown spot in lettuce field cultivation:

1. Clean the countryside and take the sick remains out of the garden and burn them in time.

two。 adequate manuring. Adopt the technology of formula fertilization, increase the application of organic fertilizer, phosphorus and potassium fertilizer, avoid partial application of nitrogen fertilizer, make the plant grow healthily and enhance the disease resistance.

3. Chemical control. Can spray more than 40% at the initial stage of the disease? Sulfur suspension 500x liquid, or 75% chlorothalonil wettable powder 1000 times liquid plus 70% methyl topiramate wettable powder 1000 times liquid, or 50% prohydantoin wettable powder 1200-1500 times liquid, or 60% ethyl phosphine aluminum wettable powder 500x liquid, etc., spray once every 10 days or so, continuous prevention and control for 3 times. Stop using medicine 5-7 days before harvest.