Which pesticide is most effective for late blight? Causes and differences from early blight

AbstractThe pesticides that can effectively control late blight include phosethyl-Al and mancozeb wettable powder, pyrimidine nucleoside antibiotics, and azoxystrobin and chlorothalonil. When the field temperature is 10°C-24°C, and the relative humidity is above 75%, or in rainy days with excessive humidity, heavy dew, and heavy fog in the morning and evening, late blight can occur. Late blight and early blight differ in nature, characteristics, and color.

I. The most effective pesticides for controlling late blight

1. Generally, at the early stage of the disease, it is necessary to promptly remove diseased leaves, diseased fruits, and severely diseased branches, then according to the concurrent diseases of the crop at that stage, use 40% phosethyl-Al and mancozeb wettable powder 300-fold solution, plus pyrimidine nucleoside antibiotics 500-fold solution, plus azoxystrobin and chlorothalonil 800-fold solution, spraying once every 5-7 days, for 2-3 consecutive applications.

2. When the disease is relatively severe, it is necessary to promptly remove the central diseased plants and diseased leaves, etc., and at the same time promptly adopt a combined control method of Chinese and Western medicine, and according to the growth period length and fruiting habits of different varieties, adopt different close-planting methods, for example, for double-stem pruning, about 2000 plants per mu is suitable, and for single-stem pruning, 2500-3500 plants per mu is suitable. Reasonable close planting can effectively improve the ventilation and light transmission conditions in the field, reduce field humidity, and reduce the occurrence of disease.

II. How late blight is caused

1. The suitable temperature for the occurrence of late blight pathogens is 18°C-22°C. Generally, for sporangia to form in large numbers, a relative humidity above 95% is required. When the field temperature is 10°C-24°C, and the relative humidity is above 75%, the disease can occur.

2. At the same time, under conditions of high humidity on rainy days, heavy dew, and heavy fog in the morning and at night, the disease is also likely to occur. Protected cultivation is more prone to the disease than open-field cultivation. Excessive planting density, for example, for mid- and late-maturing tomato varieties more than 3500 plants per mu, and for early-maturing varieties more than 4000 plants per mu, as well as poor ventilation in the plot, can all lead to the occurrence of late blight.

III. Differences between late blight and early blight

1. Different nature

Early blight is a fungal disease and can generally occur at the seedling stage and adult plant stage, while the late blight pathogen mainly overwinters as mycelium in diseased potato tubers, and can also harm and overwinter on greenhouse tomatoes.

2. Different characteristics

Early blight mainly damages the leaves, stems, fruits, and other parts of the crop, and generally occurs easily on the leaves and at the branching points of stems and leaves, while late blight mainly causes rapid disease development simultaneously on stems, leaves, and fruits.

3. Different colors

With late blight, the stems turn dark brown and become rotten in appearance, the leaves have water-soaked irregular lesions, and white mold mostly grows at the boundary between diseased and healthy tissue on the underside of the leaves, while the fruits, especially green fruits, have oily, slightly sunken lesions, whereas early blight lesions have concentric rings in the middle, and when moist, black mold grows on the diseased parts, which is one of the typical identifying symptoms of the disease.