Late blight is a fungal disease. Both seedlings and adults can suffer from it, which can damage leaves, stems and fruits, but leaves and green fruits at the adult stage are seriously affected.
The infection of leaves mostly starts from the lower leaves, forming dark green water stains with indistinct edges, which will become brown after expansion. When the humidity is high, white mold will appear at the junction of disease keys on the back of leaves. When the disease is dry, the diseased part will be dry, brittle and easy to break.
The disease can occur during the whole growth period, mainly harming leaves and fruits, and also infecting stems.The seedlings are damaged, and the black brown rot near the petiole spreads to the stem, causing the seedlings to wither and fall.The disease spots on the leaves mostly start from the tip or edge of the leaves, with irregular shape, dark green water stains, and then gradually become brown, the edges are not obvious, and there are no whorls on the disease spots.The disease spot on the stem is dark brown, irregular in shape, slightly sunken, with obvious white mildew on the edge.The disease spots on the fruit mostly occur on one side of the green fruit, the edge is not obvious, and they often extend outward in the form of moire. At first, the disease spots are dark brown oil stains, and then gradually become dark brown to brown. The disease spots account for one third of the fruit surface. The damaged part reaches deep into the pulp of the fruit. The fruit texture is hard without soft rot. When it is wet, the diseased part can grow white mold like substances
Occurrence characteristics
Announce
edit
Low temperature and humidity are the main conditions for the occurrence of the disease. When the temperature is 18~22 ℃ and the relative humidity is 95~100%, the disease is easy to spread.The mycelium grows fastest at 20~23 ℃, spreads by air flow and rain, deviates from nitrogen, lacks basal fertilizer, continuous rain, insufficient light, poor ventilation, excessive watering and high density are conducive to disease.It is an epidemic disease repeatedly infected.
infection route
Announce
edit
The pathogen overwinters in the diseased potato tuber with mycelium, and can also harm and overwinter on greenhouse tomato.The diseased residue could not survive in the soil, and the first infection came from the field potato or greenhouse tomato.The diseased plants produce a large number of sporangia on the diseased spots, which can be re infected by airflow, rain and running water.
Prevention and control methods
Announce
edit
1、 Agricultural control[1]
1. Crop rotation: to prevent continuous cropping, rotation with cruciferous vegetables should be carried out for more than 3 years, and adjacent planting with potatoes should be avoided;
2. Cultivate disease-free and strong seedlings: the pathogen mainly overwinters in the soil or diseased residue. Therefore, the soil for seedling must be strictly selected from the soil that has not planted solanaceous cropsNutrition bowl, nutrition bags, plug plates, etcStrong seedling；
3. Strengthening field management: sufficient applicationBase fertilizer, apply formulated fertilizer, avoid partial application of nitrogen fertilizer, and increase applicationphosphorus、potash fertilizer。After planting, weeds shall be controlled in time, and pruning, pinching and forking shall be carried out reasonably according to the bearing habits of different varieties to reduce nutrient consumption and promoteMain stemGrowth;
4. Reasonable close planting: according to the length of growth period and fruiting habits of different varieties, different close planting methods are adopted, such as: about 2000 plants per mu for double stem pruning, 2500~3500 plants per mu for single stem pruning. Reasonable close planting can improve the ventilation and light transmission conditions in the field, reduce the field humidity, and reduce the occurrence of diseases;
2、 Chemical control
Preventive medication:
When the disease is expected to occur, usePyrimidine nucleoside antibioticsSpray 800 times of Azoxystrobin chlorothalonil with 500 times of solution every 7-10 days.
Therapeutic medication:
1. At the initial stage of the disease, the diseased leaves, fruits and seriously diseased branches should be removed in time. Then, according to the concurrent diseases of the crops at this stage, 40%Ethylphosphate manganese zinc300 times liquid addition of wettable powderPyrimidine nucleosideAntibiotic like 500 times liquid sprayingAzoxystrobin chlorothalonil800 times liquid, once every 5-7 days, 2-3 times continuously.
2. When the disease is serious, remove the central diseased plants, diseased leaves, etc., and timely adopt the prevention and treatment method of integrated traditional Chinese and western medicine.
Morbid condition
Announce
edit
The optimum temperature for the occurrence of bacteria is 18 ℃~22 ℃. A large number of sporangia are formed, and the relative humidity is above 95%.When the field temperature is 10 ℃~24 ℃ and the relative humidity is above 75%, the disease can occur.It is easy to get sick in rainy days with high humidity, heavy dew and foggy morning and night.Protected cultivation is more prone to disease than open cultivation.Excessive planting density (such as more than 3500 tomato varieties with medium and late maturity per mu, and more than 4000 tomato varieties with early maturity per mu) and poor ventilation are conducive to the occurrence of the disease.
