What should be done to control melon leaf spot?

Melon belongs to cucurbitaceae crops. Because its fruit is sweet and delicious, its meat is tender, crisp and juicy, and most watermelons are picked before going on the market in early summer, so it becomes an important fruit in early summer and is deeply loved by consumers. Many melon farmers in our school have achieved good economic benefits by planting melons. However, in the process of melon cultivation, various diseases often occur, which affect the yield and quality. Among them, melon leaves suffer from many diseases, such as anthracnose and leaf blight. These diseases are caused by fungi. Today we will talk about bacterial leaf spot-melon leaf spot.

Melon leaf spot, often called bacterial leaf spot of melon, is different from leaf spot caused by fungal diseases. After the pathogen infects melon, the damaged leaves often appear spots and brown, which affects the photosynthesis of leaves and reduces the yield of melon. In severe cases, the fruit appears spots and rot, which affects the yield and quality of the fruit and reduces the degree of commercialization. Then, what bacteria are causing the melon leaf spot disease, what are the regularity of the disease, how to identify the symptoms in the field and how to achieve comprehensive control?

1. The incidence of bacterial leaf spot of melon

1, pathogenic bacteria and habits. The pathogen of bacterial leaf spot of melon is Pseudomonas syringae PV. Tears (Smith and Brian) Yang. Dyes, etc. Pathogens are short rods, which can cross-grow, with the size of 0.7 ~ 0.9 μ m× 1.4 ~ 2.0 μ m and flagella 1 ~ 5. The colony is white, nearly round, flat, slightly convex at the center, opaque concentric ring, thin and transparent at the edge, and there are radial hairs on the edge of the colony. The suitable temperature for pathogen development is 25 ~ 28℃, and it can grow at 36℃ and die above 40℃. The pathogen not only harms melon, but also infects watermelon, pumpkin, zucchini, wax gourd, Solanaceae, Leguminosae and other crops.

2. Infection route and disease state of pathogens

There are two main infection routes of bacterial leaf spot of melon. One is the seed, when the pathogen on the seed meets the suitable conditions, it directly invades the cotyledons and becomes ill after growth and development. The other is that the pathogen overwinters as a sick remnant, and then invades the plant through wounds, stomata and stomata in the following spring, resulting in disease. After the bacteria propagate in the diseased parts of plants, they overflow from diseased spots and stomata, spread through wind and rain, contact between insects and people, and then re-invade the plants with water drops from stems, leaves, stomata and water holes to form re-infection. High humidity in the field is the main condition of the disease. For example, under continuous rainy weather or flood irrigation, it is easy to cause excessive humidity of soil and air, and bacteria can easily multiply rapidly in the presence of water, infecting plants and causing the occurrence, spread and epidemic of diseases. In addition, when the humidity is high, pruning and wound healing are slow, which will also accelerate the reproduction and infection of germs. Generally speaking, plots that have been planted continuously for many years have serious diseases due to the large pathogen base. It is difficult to get rid of the accumulated water in low-lying land, and the germs multiply quickly and the diseases are serious.

Second, the symptoms of bacterial leaf spot of melon

Melon leaf spot can occur in all growth stages of cultivation, which mainly harms leaves, fruits and stems. The newly emerged seedlings directly infect cotyledons due to the bacteria carried by seeds, and the cotyledons appear water-like nearly round or irregular translucent spots, and then the spots are sunken and yellow-brown. After the pathogen infects the true leaves, the surface of the leaves appears as small spots in water at first, and then the spots gradually expand into polygonal or irregular light brown spots, which are limited by the veins (see Figure 3). There are often rust-yellow oil-immersed rings at the edges of spots, and finally they look translucent, and when they dry, they will break (see figure 1 and 2). When wet, yellow-white "bacterial pus" overflows from the diseased part of the leaf back. After fruits and vines are infected by pathogenic bacteria, dark green spots appear on the surface of fruits (see Figure 4), cracks appear (see Figure 5) or ulcers are formed in severe cases, and bacterial liquid overflows.

Three. Comprehensive control measures of bacterial leaf spot of melon

1, do a good job of seed treatment and soil disinfection. If you want to choose disease-free seeds, even if you save them yourself, you should avoid the disease of plants causing the seeds to carry bacteria. Germs will die above 40℃, so soaking seeds in warm soup, soaking seeds in warm water at 50 ~ 52℃ for 20 minutes before sowing, and then accelerating germination or sowing can kill germs. You can also disinfect the seeds by soaking them with drugs. Soak seeds in 40% formalin solution 150 times/0.5 hours, then wash the solution and germinate or sow. Seeds can also be mixed with 47% Galen wettable powder, accounting for 0.3% of the seed weight. Disease-free field soil should be selected as bed soil when raising seedlings, and chloropicrin fumigant can be used for disinfection before planting in greenhouse.

2. Implement crop rotation, disinfection and sterilization. Rotation can avoid the pathogen in the field and reduce the infection rate, which is an important disease prevention measure in production. It is best to rotate with Gramineae for more than 5 years. Try to avoid continuous cropping or rotation with watermelon, pumpkin, zucchini, wax gourd, solanaceae, Leguminosae, etc. Because they have the same pathogen. When applying organic fertilizer, it must be fully decomposed and fermented at high temperature to kill bacteria. When diseases are found in the field, the diseased leaves and central diseased plants should be removed in time. After pulling out seedlings, the diseased leaves should be thoroughly removed to prevent germs from attaching to the diseased body and reinfecting in winter.

3. Strengthen field management and control humidity reasonably. According to the cultivated varieties and soil fertility, reasonably determine the density, avoid excessive growth in the field, maintain good ventilation and light transmission conditions in the field, promote the robust growth of plants and enhance the disease resistance. When pruning and pruning plants, attention should be paid to avoid the infection of germs in the wounds formed by farming operations when the weather is fine or there is no dew on the surface of plants. For high ridge plastic film mulching cultivation, drip irrigation equipment can be laid under the film if possible, and when melon water is needed, dark irrigation and drip irrigation under the film can be carried out to reduce field humidity and reduce disease occurrence. In case of rain, the accumulated water in the field should be removed in time to reduce soil moisture and bacterial infection. When chemicals are used in greenhouse, dust and aerosol can be used instead of spray to reduce indoor humidity.

4, timely prevention and treatment, reasonable choice of drugs. Disease prevention must be carried out at the early stage of the disease, so as not to delay the spread of germs after a few days, increase the difficulty of treatment, increase the dosage, lead to excessive pesticide residues and increase unnecessary prevention and control costs. There are many drugs for preventing and treating cucurbit bacteria, and effective drugs can be selected according to local successful prevention and control experience. It can spray 72% agricultural streptomycin 4000 times or neophytomycin 5000 times, 20% clothianidin copper suspension 500 times and 20% diclofenac wettable powder 600 times. In order to improve the efficacy, compound agents can be used, such as spraying 20% zinc thiazole suspension 300-500 times and spraying 12% copper terpineol emulsion 600-800 times. The community with mild illness should be sprayed every 7~ 10 days, and the community with serious illness should shorten the spraying interval. The medicine can be sprayed once every 3~5 days, and it is advisable to use it for 2~3 times continuously.