Tomato late blight and leaf mold
Feature description and prevention methods
With the decrease in temperature, late autumn tomatoes in greenhouses have caused late blight and leaf mold disease, prompting farmers to promptly implement prevention and treatment.
Late blight
It is a devastating disease of tomato, and it has the characteristics of rapid spread. It can be extended to a full shed in a short time, leading to premature pull. The leaves, stems, and fruits can all be affected. The damage to leaves and green fruits is serious. The incidence of seedlings generally begins with dark green water-stained lesions on the leaves, and then spreads toward the stems. The proximal petiole is dark brown and decays. As the disease progresses, the base of the young stems is constricted with moisture, the plants are wilted and collapsed, and the diseased parts are wet. White mold layer. In the adult plant stage, the dark green water-spotted lesions (like water scalding) gradually develop from the tip and the leaf edge of the lower leaves and gradually turn brown. When the leaves are wet, the white mold layer is formed at the junction of the health; The lesions are brown or dark brown water stains, slightly sunken, and produce white mold when wet; fruit lesions are initially oily dark green, gradually turning dark brown to brown (yellow), with mottled, hardened lesions. , White mold produced when wet. Low temperature and high humidity conducive to the occurrence and spread of the disease, the most suitable temperature is 18 °C -22 °C, relative humidity of 95%.
Leaf mold
Severe disease can cause dry leaves or even reduce yield. The main damage to the leaves, in serious cases also harm stems, flowers and fruit, but the field is difficult to see. After the onset of disease, the leaves appear irregular or pale yellowish chlorotic chlorotic spots. The leaves of the lesions grow grayish-white on the back and turn into tan or dark brown velvety mildew. In severe cases, the lesions may grow on the front. The diseased leaves are dry and curly. Appropriate conditions for the onset of illness are temperatures of 20°C to 25°C and a relative humidity of 90% or more.
Identification points
(I) Confusion with other diseases
Occurrence of leaves: sometimes the lesions of leaf late blight appear V-shaped from the tip of the leaf, or when the conditions are not appropriate, the disease is dry and the mold layer cannot be seen. In the case of simple leaf disease, it is easy to be confused with gray mold, and there may be no ridges. Whether the petiole is differentiating. Late blight lesions generally have no ridges, gray mold lesions are more common with buns; late blight is prone to petiole, and gray mold is less frequent in petioles.
The incidence of fruit: easily confused with streak virus disease and M.blight disease, but the whole fruit of streak virus showed obvious irregularities, and the lesions of M.pseudophorum disease had no cloudiness markings and were softer. In addition to the differences in symptoms, the climatic conditions in which late blight occurs can be distinguished from streak virus disease and M.pneumoniae.
Similar to the symptoms of mycoticosis (also known as Cercospora leafy mildew), the difference is not obvious. It is just a deeper look at the mildew layer of the mycotic fungus. It is easy to make people feel the same disease. The microscopic examination should be used to identify the pathogen. Accurately identify.
(b) Confusion with Physiological Diseases
Leaf dryness caused by simple leaf disease is easily confused with frost damage and fertilizer damage. Late blight occurs from the lower leaves. Freezing damage starts from the upper leaves and concentrates at the tuyere. The fertilizer damage caused by improper fertilization also starts from the lower leaves, but is evenly distributed throughout the field. According to the symptoms, field distribution, whether there is spread of infection, climatic conditions and inquiries about the fertilization situation of growers.
(c) Occasionally due to special performance in environmental conditions
When the environmental conditions of tomato late blight are particularly suitable, the disease rapidly develops, and there are no obvious lesions on the leaves, but there are obvious white molds; the leaf yellowing, dryness, and back sickness spots caused by leaf mold are easily confused with low-temperature chilling injury and fertilizer damage. It should be based on symptoms. Distribution, presence or absence of mould, seasons before and after the cultivation, air temperature before and after symptoms, type and amount of fertilization, whether the fertilizer was decomposed, and temperature conditions during use were used for comprehensive analysis and judgment. Indoor microscopy was performed when necessary.
Control methods
1. Properly dense planting, using formula fertilization technology, strengthening field management, timely whole-plant burping, and improving plant disease resistance.
2. In the early stage of disease, chemical control is performed in time.
Tomatoes with late blight may use 64% antiviral WP 500 times, or 58% ledomemi Mn Zn wettable powder 500 times, or 72.2% Prokary® 800 times spray, 7-10 days, 4-5 times in a row.
In the early stage of tomato leaf mold, the lower leaves can be removed and then sprayed to protect. The agent can be used: 25% Ami-Silda suspension agent 1500 times, 10% World high water dispersible granules 1200 times, 40% DuPont Fuxing Emulsion 4,000 times, spray control, spray once every 5-7 days, even spray 2-3 times.
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