Summer is humid and plants at home are prone to disease; how do you treat them according to the symptoms?

The hot and humid summer is a period of high incidence of plant diseases. If you are not careful, the potted flowers at home may fall victim to various diseases. Let's look at the common disease identification methods summarized by flower growers for the following 3 kinds of flowers. If your "treasure" unfortunately falls victim, then quickly treat it according to the symptoms!

Orchid soft rot and black rot

For orchid growers, the harm of rot disease is a thorny problem: not only are the symptoms difficult to identify, but once the disease occurs, prevention and control are also rather difficult. Below is a brief explanation of soft rot and black rot, which cause orchid rot.

Soft rot

Disease symptoms: This disease mainly infects orchid varieties with thicker leaf flesh. On foreign orchids such as Phalaenopsis and Cattleya, it mainly harms new leaves, showing water-soaked spots on the leaves that gradually change from dark green to brown to black-brown; on Chinese orchids such as Cymbidium goeringii and Four Seasons Orchid, it mainly shows small yellow-brown water-soaked spots first appearing on the upper and lower parts of new shoots, after which the lesions rapidly expand, and the water-soaked or wounded parts quickly rot. After rotting, they can be pulled up with a gentle lift, or break off and fall over, which is where the name soft rot comes from. When the disease is severe, the whole leaf turns brown and droops in a soft-rotten state. When the leaf flesh tissue rots, yellow-brown mucus flows from the diseased part, and the mucus has a foul odor.

Conditions for onset: Orchid soft rot is caused by bacterial infection. The bacteria mainly overwinter on the remains of diseased plant tissues, spread by wind and rain, and invade through various tiny wounds on the orchid plant. Direct use of unclean culture soil, garden soil, etc.; excessive application of nitrogen fertilizer during the new shoot growth period easily leads to thin cell walls and induces bacterial invasion; long-term excessive moisture in the potting soil causes massive reproduction of anaerobic bacteria and harmful microorganisms in the soil, affecting orchid root growth and lowering resistance, making the plant susceptible to disease; in open-air cultivation, poor ventilation, extensive management, watering with bacteria-laden water, or accumulation of water in the heart leaves of the orchid plant after summer rain turns clear and the temperature rises sharply, all easily trigger soft rot.

Prevention and control methods:

1. Choose clean culture soil. Alpine humus soil is the most ideal orchid-growing medium. If garden soil, pond mud, etc. are used, they must be exposed to high temperature in the sun and mixed with fungicide before use.

2. Fertilize and water reasonably. If conditions permit, choose clean mountain spring water or river water to water orchids. If the water source is not clean, it must be settled to remove residue, then treated with a disinfectant before use. During high-temperature periods, watering must be done in the early morning when the temperature is lower, avoiding heavy flooding, and especially not using coarse spray or directly pouring water into new leaves or new shoots. Apply more phosphorus and potassium fertilizer; choose liquid nitrogen fertilizer from before the new shoots sprout until the new shoots have grown but the leaves have not yet unfolded.

3. Chemical control. After potting the orchid, do not water for 3 to 4 days, and spray once with 50% thiram 500 times solution to disinfect and sterilize. Diseased plants rescued after onset should temporarily be isolated from other orchids to avoid infection, and only after returning to normal may they be placed together with other orchids. In the disease season, especially after heavy rain, you can use neophytomycin or agricultural streptomycin sulfate 4000 times solution for prevention, generally once every 5 to 7 days, spraying 2 to 3 times continuously, using a fine spray method to spray the new shoots and lower leaves or pseudobulbs.

Black rot

Disease symptoms: Black rot mostly occurs on leaves, the base of roots and growing points. Small translucent spots appear on the leaves of affected plants, almost all over the whole leaf. After the lesions expand, they affect the whole plant (including the roots). After adult plants are affected, within 2 to 5 days dark and slightly water-soaked spots appear on the leaves or pseudobulbs, and the lesions later turn purple-black and glossy. In a warm, humid environment the diseased part becomes soft, and water sometimes seeps from the diseased leaves. When the environment is dry, the diseased part dries accordingly.

Prevention and control methods: Cut off diseased leaves and affected pseudobulbs and destroy them centrally. Used knives and scissors can be immersed in 75% alcohol to disinfect and sterilize. Avoid splashing when watering, and maintain ventilation and light transmission.

Rose black spot

Rose black spot is the most common and devastating disease of roses. Besides harming roses, it can also harm flowering plants such as rugosa roses and wild roses. In the later stage of occurrence, chemical control also makes it very difficult to control its spread, so early prevention and control are very important.

Disease symptoms: This disease mainly harms leaves, and can also harm tender branches and flowers. When the disease occurs, irregular black spots appear on the leaf surface or leaf margins, causing the color of nearby leaf flesh tissue to change from green to yellow, and in severe cases the entire leaf turns yellow and falls. Another symptom is the appearance on the leaves of dark brown nearly circular or irregular concentric-ring spots, on which small black dots appear. Diseased leaves fall off easily, and in severe cases only bare branches remain, affecting the ornamental effect and the number of blooms.

Conditions for onset: Rose black spot is a fungal disease. When the temperature rises to around 25°C, the air humidity is close to saturation and the weather is muggy, the disease is most severe. During the plum rain season the disease spreads fastest and infection is also severe, especially during the two peak periods from May to June and from August to September. The black spot fungus often overwinters in fallen leaves, branches or soil. In March and April of the following year, when humidity and temperature are suitable, it spreads with the help of rain, wind, or mud splashed up during watering. It spreads faster in rainy, foggy weather with heavy dew. If watering is done too late in the afternoon and the water on the leaf surface has not dried, this can also promote the disease. In addition, planting too densely or poor ventilation at the site is also a major cause of inducing this disease.

Prevention and control methods:

1. Choose disease-resistant varieties. Different varieties differ greatly in resistance to black spot; generally climbing roses have stronger disease resistance. Among cultivated varieties, varieties such as Isabella, White Knight, Apricot Village, Golden Phoenix, Star and Sunlight have stronger disease resistance; varieties such as Yellow Peace and South China Sea are easily susceptible.

2. Strengthen cultivation management. Remove fallen diseased leaves and diseased branches in the garden and destroy them centrally; prune diseased branches and leggy branches in time to create a ventilated environment. When pruning, do not casually touch diseased leaves with your hands, to prevent human transmission, and do not pour water on the leaf surface. It is best to water into the soil to prevent the pathogen from spreading with water.

3. Prepare good culture soil. The culture soil must be air-permeable, and potted roses should be repotted with new soil in time. In combination, apply trace element fertilizers such as 1% zinc sulfate or 0.2% monopotassium phosphate, 0.1% sodium tetraborate, etc., to enhance the plant's disease resistance.

4. Chemical control. In early spring, mix 1% asomate with river sand at a ratio of 1:99 evenly and spread it on the surface of the potting soil, which can isolate or kill the pathogen on fallen leaves on the ground. When budding begins, spray 75% chlorothalonil wettable powder 1000 times solution or 70% thiophanate-methyl 800 times solution, and thereafter spray once every 15 days.

Cyclamen gray mold and bacterial soft rot

Gray mold

Disease symptoms: It mainly harms leaves and flowers. When petals are affected, water-soaked small spots 1 to 2 mm in diameter appear, which soon expand and turn brown and rot; when it occurs on flower stalks, they become brown and soft-rotten, and the diseased part bends and falls over, affecting seed maturity; when leaves are affected, brown softened lesions often appear from the leaf margins, with concentric wrinkles on the surface, and later expand to the whole leaf. When humid, a gray mold layer forms, later turning earthy-yellow gray mold.

Conditions for onset: Indoor humidity is too high and ventilation is poor, plants are placed too densely, too much nitrogen fertilizer, etc.

Prevention and control methods: Avoid excessively high humidity, promptly remove diseased leaves when found, and reduce spread and infection. In the early stage of disease, spray 1:200 Bordeaux mixture, or 65% zineb wettable powder 500 times solution, which can control and reduce the harm of gray mold.

Bacterial soft rot

Disease symptoms: It mainly harms the petioles and flower stalks of the plant, and is especially prone to water-soaked softening near the culture soil, spreading upward and downward, causing the corm to rot.

Conditions for onset: It easily occurs during the growth period from July to August, mainly caused by pathogens in the soil, and is more likely to occur at high temperatures and when the potting soil temperature is high.

Prevention and control methods: Use 0.5% formalin for soil disinfection, which can inhibit the occurrence of this disease. In addition, in summer, maintain ventilation and avoid overly wet watering. When the disease occurs, spray with crude streptomycin 100 to 200 mg/L.