Causes and control of three diseases of lettuce caused by black spot of downy mildew

The late stage of lettuce production is the period of high incidence of diseases, common diseases: downy mildew, black spot, Sclerotinia sclerotiorum, prevention is very important. In this paper, the characteristics and control methods of three diseases of lettuce are briefly described as follows:

Lettuce downy mildew

1. Downy mildew:

The main results are as follows: 1. characteristics: the disease infected lettuce leaves. After the disease occurred, the seedlings became yellow and withered, the disease occurred in the adult plant stage, and the leaves occurred from bottom to top. In the early stage, there are yellowish polygonal or nearly round disease spots on the leaves, and when they are wet, the disease spots on the back of the leaves are white and moldy, and sometimes the mildew layer can extend to the front of the leaves. In the later stage, the disease spot withered and turned yellow and brown and connected into pieces, causing the whole leaf to dry up, and sometimes the pathogen could infect the stem, causing the stem to turn black.

2. Control methods: before ridge sealing, lettuce was ploughed for 2-3 times; after ridge closure, watering times were reduced, field humidity was reduced, field stagnant water was prevented, lettuce growth was promoted and pathogen development was inhibited. After discovering the disease, remove the diseased leaves and burn them in time, especially the lower old leaves to increase the permeability. Spraying 600-800 times liquid of Dasheng Mmur45 can have a preventive effect. In the early stage of the disease, the medicine is used once every 7-10 days, and the medicine can be sprayed with 72% DuPont Klu 800 times or gold remiers 600-800 times. Several pesticides are applied alternately, once every 7-10 days, for 2-3 times in a row.

Black spot of lettuce

2. Black spot:

1. Characteristics: black spot, also known as ring disease, leaf blight, mainly harms lettuce leaves, forming round or near-round brown spots on the leaves, 3-15 mm in diameter, with concentric wheel lines, black mildew on the back of the disease spot when it is wet. The disease is spread by wind and rain, warm and rainy, dew time is long, lack of fertility, lettuce is weak and easy to occur.

2. Control methods: strengthen cultivation management and increase the application of phosphorus and potassium fertilizer. Implement crop rotation to remove old, sick and residual leaves in time. In the early stage of the disease, choose 1500 times liquid of 50% prohydantoin wettable powder or 1000 times liquid of 10% high water dispersible granules, etc., rotate the medicine, spray once in 7 days, spray 2-3 times continuously.

Sclerotinia sclerotiorum of lettuce

Sclerotinia sclerotiorum

The main results are as follows: 1. characteristics: most of the disease occurs from the base of the stem, and gradually extends, causing epidermis rot. There were cotton-like hyphae and black mouse fecal sclerotia on the surface of the disease spot, and the upper part of the disease plant wilted and died. The pathogen is transmitted by wind and rain and invades from the senescent part of lettuce with low temperature, humidity and high density, which can promote the disease.

2. Control methods: apply fertilizer reasonably, avoid partial application of nitrogen fertilizer, and increase the application of phosphorus and potassium fertilizer. After ploughing and weeding frequently, the diseased residual plants and lower diseased leaves of lettuce were removed in time, and a deep ploughing was carried out after harvest, so that most of the sclerotia were buried under the soil layer of 6cm. At the initial stage of the disease, 70% thiophanate-methyl wettable powder was sprayed every 7-10 days for 3-4 consecutive times.