The Causes of Tomato Late Blight and Control Measures
Tomato late blight is a devastating virus. If it is not controlled in time, it will cause severe reduction of tomato production.
Tomatoes have symptoms of late blight: the leaves have late blight, most of them start from the tips of the leaves or leaves, in the morning, the white spots on the back of the leaves will grow white mold; straw has a late blight, there will be black and yellow lesions The diseased part is often concave, and the straw often breaks from it. The late blight of the fruit is mostly when the fruit is still green. Black and yellow spots appear. The spots begin to harden and slowly decay. In severe cases, the whole tomato pod will turn black and die.
The cause of tomato late blight is the source of late blight bacteria; the second is the relatively humid climate. Phytophthora infestans have high requirements for air humidity, generally reaching more than 75%, so the more humid the weather, the more germs it produces; while the temperature requirements are relatively low, generally between 7°C and 25°C. The most suitable temperature is 18°C ​​to 22°C. Especially when there is heavy rain, heavy rainfall, high humidity, and low temperatures, the onset is early and the disease is very serious.
How to prevent tomato late blight? There are several effective measures:
First, properly control watering. In the rainy season, do not pour, do not pour before the rain, stop pouring after the rain, and dig out the drainage ditch when the rainy season arrives. Be sure that the rain will drain and prevent the accumulation of water in the ground.
Second, the diseased plant should be removed immediately. Special attention should be paid to the source of diseases in greenhouses and greenhouses. Tomatoes that have been pulled out must not be thrown indiscriminately, and they should not be used to feed pigs and grow fat. They should be buried deep to prevent the spread of germs.
Third, strengthen the cultivation and management. Tomatoes should not be planted too deeply, pruning rights should be timely, and some old leaves should be properly removed for ventilation and lightness to reduce humidity.
In addition, it is also necessary to add some potassium fertilizer, combined with the fight drugs, you can also spray some potassium dihydrogen phosphate on the leaves, improve the resistance of tomatoes.
Fourth, the diseased strains should be removed immediately and the drugs should be used for treatment.
Commonly used agents are as follows: 1 copper ammonium mixture: that is, 250 grams of copper sulfate and 2,500 grams of ammonium bicarbonate, after grinding and mixing in a plastic bag, stuffy day and night, and then put it against 100 kilograms of water and put it Dissolve and spray. 2 Bordeaux mixture: According to the ratio of 1:1:200, that is, 500 grams of copper sulfate and 500 grams of quicklime, and 100 kilograms of water, the specific approach is: first with a small amount of water to open the lime, and then water system Lime water. In another bucket, the copper sulfate is first opened with a small amount of water and then dilute with water to make a cupric sulfate solution. Then, the cupric sulfate solution is slowly poured into the lime water, and the mixture is stirred while stirring, and it becomes sky blue. The color of Bordeaux liquid. 350% Ketandan WP 500 times, 65% dexamethasone 600 times, etc., have better control effect after spraying. These agents can be sprayed once every 3 to 5 days, or they can be sprayed alternately. When spraying, spray all parts of the tomatoes.
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