A Complete Analysis of Common Flower Diseases and Their Prevention and Control Methods
Common Diseases and Their Harm
During their growth, flowers often suffer infection by harmful organisms and the effects of adverse environments, causing a series of pathological changes in both their physiology and external morphology, which leads to a decline in flower quality and yield. This phenomenon is called flower disease. There are many causes of flower disease, mainly infection by harmful organisms such as fungi, bacteria, viruses, mycoplasma-like organisms, nematodes, algae, mites and parasitic seed plants, as well as the effects of adverse environments. Flower diseases caused by these different factors are respectively called fungal diseases, bacterial diseases, viral diseases, nematode diseases and physiological diseases (also known as non-infectious diseases).
1. Fungal diseases
Fungal diseases are caused by fungi. Fungi are a class of lower organisms that lack chlorophyll, varying in individual size, most of which can only be seen clearly under a microscope. The development of fungi is divided into two stages: nutrition and reproduction; the hyphae are the vegetative body, and asexual and sexual spores are the reproductive body. They are mainly spread by wind, rain, insects or flower seeds and seedlings, and enter the plant body through natural openings such as stomata, water pores and lenticels on the flower's epidermis, as well as various wounds; they can also directly invade an uninjured epidermis. On the diseased parts they show symptoms such as white powder, rust powder, sooty mold, spots, rot, wilting and deformity. The main ones include rose black spot, powdery mildew, chrysanthemum brown spot, peony red spot, orchid anthracnose, rose rust, and flower seedling damping-off.
2. Bacterial diseases
Bacterial diseases are caused by bacteria. Bacteria are smaller than fungi and are a class of single-celled lower organisms; their morphology can only be observed under a microscope. They are generally spread by rainwater, running water, insects, soil, flower seeds and seedlings, and diseased plant residues. They mainly invade the flower body from the plant surface through stomata, lenticels, water pores, nectaries and various wounds, causing harm. They manifest as symptoms such as spots, cankers, wilting and deformity. Common bacterial diseases include cherry bacterial crown gall, ornamental peach bacterial shot hole, and bacterial soft rot of iris and cyclamen.
3. Viral diseases
Viral diseases are caused by viruses. In recent years, viral diseases have risen to a position second only to fungal diseases. Viruses are an extremely tiny class of parasites that can harm many precious flowers, such as narcissus, orchid, carnation, lily, dahlia, tulip, tree peony, herbaceous peony, chrysanthemum, gladiolus, African chrysanthemum (Gerbera), etc. Their symptoms include mosaic yellowing, leaf curling, deformity, rosetting and necrosis. Viruses are mainly transmitted through piercing-sucking insects and through grafting, mechanical injury and other routes; even the virus sap on hands and gardening tools during pruning, cutting flowers and weeding can play a role in transmission. Common ones include tulip viral disease, cyclamen viral disease, salvia mosaic viral disease, and chrysanthemum and dahlia viral diseases.
4. Nematode diseases
Nematode diseases are caused by nematode parasitism. Nematodes are a type of lower animal with a very small body. They are generally slender and cylindrical, pointed at both ends, resembling the roundworm familiar to people; a few species have pear-shaped females. In the mouth cavity of the nematode's head there is a spear-shaped stylet, used to pierce plant cells and suck sap. Nematode diseases mainly harm flowers of the Asteraceae, Primulaceae, Rosaceae, Balsaminaceae and Begoniaceae. Their main symptom is the production of tumor-like growths of varying sizes on the host's main and lateral roots. Common ones include root-knot nematode disease of cyclamen, balsam, tree peony, rose and other flowers and shrubs.
Targeted prevention and control must be timely
Among flower diseases, fungal diseases are the most common, widely distributed and most harmful. In recent years, the harm of viral diseases and nematode diseases has become increasingly serious, and they have become one of the important reasons for the degeneration of flower varieties and deterioration of quality. There are many kinds of flower diseases; a brief introduction grouped by different prevention and control methods is given below.
1. Prevention and control of fungal diseases
(1) Diseases such as powdery mildew, anthracnose, black spot, brown spot, leaf spot and gray mold: First, in early spring or late autumn, clear away dead branches and fallen leaves and promptly prune diseased branches and leaves and burn them; second, before the disease occurs, spray 65% zineb 600x dilution for protection; third, fertilize and water reasonably, and pay attention to ventilation and light transmission; fourth, in the early stage of the disease, spray 50% carbendazim or 50% thiophanate 500x-600x dilution, or 75% chlorothalonil 600x-800x dilution. (2) Rust: In addition to the methods in items 1 to 3 above, after the disease occurs, spray 97% sodium dinitro-o-cresolate 250x-300x dilution (add 0.1% washing powder), or 25% triadimefon 1500x-2500x dilution. (3) Damping-off and root rot: First, disinfect the soil by treating it with 1% formalin or placing the culture soil in a pot and steaming it for 1 hour; second, water according to the principle of drying before wetting, avoiding waterlogging; third, in the early stage of the disease, drench the root zone with 50% amobam 300x-400x dilution, using 2-4 kg of solution per sq m. (4) Southern blight and sclerotinia rot: First, use 1% formalin solution or
treat the soil with 70% quintozene, using about 5 g-8 g of quintozene per sq m, mixed with 30 times fine soil and applied into the soil; second, select disease-free seeds and seedlings or soak them in 70% thiophanate 500x dilution for 10 minutes before planting; third, implement crop rotation and avoid continuous cropping; fourth, water reasonably and drain promptly after rain. (5) Sooty mold: After the disease occurs, wipe the diseased branches and leaves with clean water and spray 50% carbendazim 500x-800x dilution.
2. Prevention and control of viral diseases
Preventing and controlling viral diseases requires even more emphasis on prevention first and integrated control. The main prevention and control measures are: selecting excellent varieties with disease tolerance and resistance is the fundamental way to prevent and control viral diseases. Strictly select virus-free propagation materials, such as tuberous roots, tubers, bulbs, seeds, seedlings, cuttings, scions and rootstocks; eradicate weeds to reduce sources of virus infection; spray 40% dimethoate emulsion 1000x-1500x dilution at the appropriate time to eliminate virus-transmitting insects such as aphids and whiteflies; promptly remove and burn diseased plants when found, and wash hands and tools that have touched diseased plants with soapy water to prevent artificial contact transmission; heat treatment, for example, ordinary seeds can be soaked in warm water at 50°C-55°C for 10 minutes-15 minutes; strengthen cultivation management, pay attention to ventilation and light transmission, fertilize and water reasonably, and promote robust flower growth, which can reduce the harm of viral diseases. 3. Prevention and control of bacterial diseases
(1) Soft rot: First, the storage site should be disinfected with 1% formalin solution and attention should be paid to ventilation and dryness; second, implement crop rotation, and for potted plants it is best to change to new culture soil once a year; third, promptly control pests, and from early spring pay attention to selecting pesticides such as phoxim to control underground pests; fourth, after the disease occurs, promptly drench the root-zone soil of diseased plants with dexon 600x-800x dilution. (2) Crown gall: First, when planting, select disease-free seedlings or implement crop rotation, or treat the soil with quintozene, using 6 g-8 g of 70% powder per sq m mixed with 0.5 kg of fine soil and turning it into the soil; second, after the disease occurs, immediately cut off the diseased tumors and disinfect with 0.1% mercury water. (3) Bacterial shot hole: First, before the disease occurs, spray 65% zineb 600x dilution for prevention; second, promptly remove and destroy the affected parts; third, in the early stage of the disease, spray 50% thiram 800x-1000x dilution.
4. Prevention and control of nematode diseases
(1) Implement crop rotation. This is a very effective control measure. (2) Improve cultivation conditions. Turning and sun-drying the soil several times during the dog days can eliminate a large number of pathogenic nematodes; remove diseased plants, diseased residues and wild hosts; fertilize and water reasonably to make the plants grow robustly. (3) Soil disinfection. Steam the culture soil in a steamer for about 2 hours. (4) Hot water treatment. Soak the diseased propagation parts in hot water (at a water temperature of 50°C, soak for 10 minutes; at a water temperature of 55°C, soak for 5 minutes), which can kill nematodes without harming the host. (5) Chemical control. Use about 25 g per sq m of 3% carbofuran granules (this pesticide is highly toxic, so safety must be paid attention to when using it), apply it evenly into the soil, cover with about 10 cm of soil, and water thoroughly; the effective period lasts about 45 days, and it can also control many other pests at the same time (aphids, red spiders, scale insects, underground pests, etc.)