Detailed Explanation of Flower Disease Identification and Prevention Methods

I. Physiological Diseases

The main causes of physiological diseases include: unsuitable temperature, unsuitable light, water imbalance, unsuitable nutritional conditions, excessive soil salinity, harm from harmful gases and substances, unsuitable soil pH, etc., all of which can affect the normal growth and development of flowers and lead to disease occurrence. Therefore, this type of disease is also called non-infectious disease. It cannot be effectively controlled by spraying chemicals. It occurs relatively commonly in the field, has no disease center, and the time and location of onset are relatively consistent, with no infectivity. Physiological diseases share a common characteristic: they often first appear on young leaves and new shoots, such as leaf yellowing, withering, and dropping, root rot, and the appearance of soft, slender, easily broken stems and leaves, lodging, and other poor growth phenomena.

II. Bacterial Diseases

Flower diseases caused by bacteria: if not controlled promptly, they can often cause devastating disasters. Bacterial diseases mainly include types such as streak, spot, blotch, wilt, and rot. Bacterial leaf spot disease generally manifests as acute necrotic spots, appearing water-soaked, with a yellow halo around the lesion, such as bacterial leaf spot of chrysanthemum and begonia. Bacterial rot disease has a fishy odor, and the rotting tissue carries yellow bacterial ooze, such as soft rot of lily, and rot and soft rot of calla lily. Bacterial wilt disease often causes green wilt (while fungal wilt is often accompanied by yellowing), such as green wilt of chrysanthemum and dahlia, bacterial wilt of carnation, bacterial wilt of chrysanthemum, and bacterial wilt of primrose.

III. Fungal Diseases

The vast majority of flower diseases are caused by fungi: such as downy mildew of chrysanthemum, gray mold of geranium, anthracnose of rubber tree, anthracnose of osmanthus, black spot of calla lily, downy mildew of rose, brown spot of cockscomb, tulip blight, and damping-off and seedling blight of various flower seedlings. The mycelium of fungi is the vegetative body, and asexual and sexual spores are the reproductive bodies. They spread through wind, rain, insects, seeds and seedlings, or weeds, and can also be transmitted through soil from generation to generation. They invade plant tissues through natural openings such as stomata, hydathodes, and lenticels on the epidermis of flower plants, as well as various wounds. Fungal diseases often cause symptoms such as plant rot, wilt, and discoloration. The symptoms are particularly obvious, and the pathogen or its modified forms can be observed with the naked eye, such as powdery mildew, gray mold, black mold, downy mildew, black spots, sclerotia, and other symptoms. Fungal necrosis is one of the most important symptoms of fungal diseases.

IV. Viral Diseases

Mainly caused by viruses: Viral diseases of flowers are mostly chronic diseases affecting the whole plant. External symptoms often include flower or leaf margin fading, ring spots, blistering, yellowing, necrotic spots, clustered spots, or leaf thinning, shrinking, and malformation of branches, leaves, flowers, and fruits. Viral diseases only have symptoms but no signs, which differs from fungal and bacterial diseases. The symptoms of some viral diseases are easily confused with non-infectious diseases. The difference lies in that the occurrence of viral diseases has an obvious spreading nature of gradual expansion from point to area, and the symptoms appearing on diseased plants often start from the top and then spread to other parts of the plant. Such as viral diseases of Asteraceae flowers, viral disease of Daphne odora 'Aureomarginata', viral disease of carnation, etc. Viral diseases are mainly transmitted by pests with piercing-sucking mouthparts such as aphids, leafhoppers, planthoppers, psyllids, and thrips, and can also be transmitted through nematodes and fungi in the soil, seeds and seedlings, and pollen; at the same time, during grafting and management of flower seedlings, contact between diseased plants and healthy plants, and asexual propagation materials such as cuttings, tubers, corms, and bulbs can all be opportunities for the spread of viral diseases. Even when pruning branches and cutting flowers, human hands and tools are conditions for transmission.

V. Nematode Diseases

Root-knot nematode disease can harm many kinds of flowers: such as root-knot nematode disease of various ornamental tomatoes and ornamental peppers, and root-knot nematode disease of cockscomb and Asteraceae flowers. This disease only infects the roots of plants, with lateral roots being more severely affected. Many root knots form on the lateral roots, interconnected into a rosary shape. The root knots are often spherical or conical, varying in size, with many fibrous roots growing on the surface, forming clustered fibrous roots. When a root knot is cut open, many translucent white, pinhead-sized, pear-shaped nematodes can be seen. The root knots are light in color initially, with a smooth and relatively firm surface, and gradually become light brown, brown, and dark brown and rot. The nematodes feed on sap inside the galls. Affected plants show malnutrition, stunting, small and wrinkled leaves, clustering, and then gradually wither, with root necrosis, resulting in leaf blight, flower drop, and other consequences.

VI. Prevention and Control Measures

To prevent and control flower diseases, the following key measures should mainly be taken:

1. Strictly implement relevant national quarantine regulations: Diseases subject to quarantine must be strictly guarded against. Seeds and seedlings must not be introduced from areas (or foreign countries) where such diseases occur; when purchasing seeds and seedlings, they should be carefully inspected. If quarantine objects are found, they should be resolutely refused acceptance and entry, and destroyed, such as by burning or deep burial.

2. Select disease-resistant varieties: For example, even for the same Asteraceae flower varieties, small-scale introduction trials should be conducted, and some should undergo inoculation identification and natural induction identification to screen out varieties with strong disease resistance.

3. Strengthen disinfection treatment of soil and seedlings: Especially for many precious flowers, whether planted locally or in pots, the soil must be disinfected, such as by spraying potassium permanganate and mixing in quicklime powder. Where conditions permit, carbendazim and quintozene should also be used for disinfection and sterilization. The former is mixed at 1.5 grams per square meter, or made into medicinal soil at a ratio of 1:20 and spread on the seedbed; the latter is used at 4 grams of quintozene and 5 grams of zineb per square meter of nursery land, mixed and then evenly mixed with 12 kg of fine soil. When sowing, placing it below and covering on top has a special effect on anthracnose, damping-off, seedling blight, and sclerotial disease. When sowing seeds and seedlings, they can be soaked in a 0.3% to 0.5% potassium permanganate solution for 0.5 to 1 hour, or soaked in a 0.5% to 1% copper sulfate solution for 1 to 2 hours, then rinsed, drained, and sown.

4. Strengthen cultivation management:

First, greenhouse flowers should be well ventilated and receive sufficient light. Even in severe cold winter, the side film should be lifted or windows opened every day at noon to reduce humidity inside the greenhouse; otherwise, it may induce major outbreaks of gray mold, leaf spot, downy mildew, and powdery mildew. Light intensity should be controlled at a level suitable for plant growth and development.

Second, use reasonable irrigation, drip irrigation, furrow irrigation, or watering the soil surface to prevent irrigation water from splashing and bringing pathogen spores or bacteria onto healthy plants, which can effectively control disease occurrence. Water must not be allowed to remain on petals or leaf surfaces, providing conditions for pathogens to germinate and invade plants. Too high soil moisture will cause harm to roots from various root rot pathogens.

Third, during transplanting, pruning, and pinching, try not to cause wounds that provide entry points for pathogens. It is best to operate on sunny days to facilitate wound healing and prevent pathogen invasion. When taking cuttings, disinfection should be carried out, and spreading pathogens through fingers and tools should be avoided as much as possible.

Fourth, fertilize reasonably. Do not apply excessive nitrogen fertilizer alone; appropriately increase phosphorus and potassium fertilizer. Excessive fertilizer application can instead cause fertilizer damage to plants and even lead to yellowing and poor growth.

Fifth, pay attention to field hygiene. Remove diseased plants, diseased leaves, and weeds, and take them away from the cultivation site for destruction. This can reduce or even completely eliminate the density of pathogens in the site and lessen disease occurrence, and is especially effective for controlling bacterial diseases, viral diseases, or systemic diseases such as wilt.

5. Carry out chemical control at the right time and to the right degree. Depending on the type and severity of the disease, protective agents, eradicant agents, or therapeutic agents can be used. For fungal diseases, generally 72.5% Previcur AS, 15% triadimefon WP, 50% procymidone WP, 64% oxadixyl mancozeb WP, 50% carbendazim WP, etc. can be selected. For bacterial diseases, generally 72% agricultural streptomycin WP, 77% copper hydroxide WP, 25% copper-ammonia complex AS, etc. can be selected. For viral diseases, generally 1.5% plant disease spirit EC, 20% virus A WP, 83 resistance inducer, etc. can be used. For root-knot nematode disease, fenamiphos EC can be selected, or after onset, 80% dichlorvos 1000-fold solution can be used to drench the soil around the flower roots to kill nematodes. Physiological diseases are not infectious. By improving the environmental conditions that cause the disease and implementing symptomatic treatment, plants generally recover relatively easily.