In recent years, with the popularization of tomato varieties resistant to yellow leaf curl virus (TY) all over the country, tomato gray leaf spot has been widely spread In order to reduce the impact of the disease on tomato production and reduce the loss to vegetable farmers, this paper briefly introduces the symptoms, occurrence law and control methods of gray leaf spot.

1. Disease symptoms

The disease mainly damages leaves, and there are two main symptoms.

Small spots: relatively common, the spots are small brown spots, which gradually expand later, but the spots remain between 0.5-5.0mm. It is initially round or nearly round, with gray white to yellowish brown in the center and dark brown at the edge, with yellow halo. Some disease spots have concentric wheel patterns, and the color of disease spots on the back of the leaf is lighter than that on the front of the leaf.

Large plaque: this symptom is relatively few, and the plaque is large, round or near round, with a diameter of 5-10mm. The center of the lesion is brown, the color of the lesion on the back of the leaf is dark brown, and there is a yellow halo around the lesion. Sometimes large lesions are also formed at the leaf margin, and the lesions develop irregularly along the leaf margin. The above two lesions are prone to perforation and rupture in the late stage of onset. In case of serious disease, the disease spots cover the whole leaf, causing the leaf to dry and fall off, and even the whole branch to turn yellow and dry. When it is more serious, it can spread to petioles, stems and vines, even sepals and fruits, resulting in yield reduction.

2. Pathogen

The disease is caused by fungi. There are mainly two kinds of pathogenic bacteria: Pythium solanacearum and Pythium tomato, but Pythium solanacearum is the main pathogen at present.

3. Occurrence law

The pathogen can overwinter on the diseased remains and seeds in the soil of the protected area. After the disease, the diseased part produces bacteria for infection. The disease mainly occurs in spring and summer in warm and humid areas, and is conducive to the spread of the disease when the relative humidity is high. It is worth noting that tomato varieties resistant to yellow leaf curl virus will have a large area of tomato gray leaf spot in spring and autumn.

4. Integrated control technology

Because tomato gray leaf spot is a disease occurring and prevalent in China in recent years, the research on the disease is not deep enough, and there are very few disease resistant varieties. Therefore, prevention and treatment should be given priority to the disease at present.

(1) Agricultural control.

① Remove the sick and disabled bodies, timely remove the old and weak diseased leaves in the field during the planting period, and timely clean and burn the sick and disabled bodies in the field after seedling pulling, so as to reduce the initial bacterial source.

② Rational rotation: non host plants such as Cruciferae and melon vegetables should be used in the fields with heavy disease.

③ Control the temperature, strictly control the temperature and humidity in the shed at the initial stage of the disease, control the temperature below 20 ℃ and the relative humidity below 60%, release air for dehumidification in time, and prevent dripping in the shed in the morning.

④ Isolation cultivation: plant non host plants or set isolation belt around the heavily diseased fields to prevent disease-free fields from getting sick.

(2) Chemical prevention and treatment. Because of the rapid epidemic of the disease, it is very important to use drugs in time after the initial detection of disease spots. You can choose 900-1500 times of 10% Difenoconazole aqueous granules, 2500 times of 12.5% nitrile azole emulsion, 600 times of 70% thiophanate wettable powder, and 4000 times of Methoxyacrylate bactericides such as 50% ether ester aqueous granules. The use of the agents is limited The interval should be determined according to the severity of the disease and weather conditions. Because the high humid weather is conducive to the spread and spread of the disease, the interval of medication can be shortened in cloudy and rainy days.

Xi'an Jinpeng seedling Co., Ltd