CATDOLL : CATDOLL: What are the main agricultural diseases?

1. What are the main agricultural diseases?

The impact of pests and land pollution on crops (such as various pathogens that are infectious to crops)

2. What are the common diseases of cucumber?

Fungal diseases

Cucumber fungal diseases have a high incidence rate and cause serious damage. After the disease occurs, cucumber plants will show symptoms such as tissue necrosis and rot. They mainly include the following diseases.

① Cataplexy

It is caused by infection by Pythium deltaense, which usually occurs in the seedling stage and is prone to occur when the temperature is low and the soil humidity is high. It can cause seed rot, bud rot, and severe damage to the roots and stems of the seedlings, resulting in sudden wilting.

②Root rot

It is caused by infection by Phytophthora melonensis, Fusarium oxysporum, and Fusarium solani, and can occur in both the cucumber seedling and adult stages. It can cause the cucumber roots and stems to turn light brown and rot, thus hindering the normal growth of the cucumber.

③ Downy mildew

It is caused by infection with Pseudocona cubaniensis, which can occur at any stage of the cucumber's growth period. It mainly harms cucumber leaves, causing irregular yellow spots to appear and gradually dry up. When the humidity is high, a black mold layer will form on the spots. In severe cases, all the spots will be connected and the entire leaf will wither, commonly known as "running dry".

④ Powdery mildew

The pathogens are Erysiphe bisporus and Sphaerotheca spp. It can occur from the seedling stage to the fruiting stage, but it is more likely to be infected in the late growth stage or when the plant is weak. The disease mainly harms the cucumber leaves, causing yellowing and tissue senescence, but this symptom also appears on the stems and fruits.

⑤Fusarium wilt

The disease is caused by the cucumber-specific form of Fusarium oxysporum, and can occur from the cucumber seedling stage to the fruiting stage. Under high temperature conditions, the seedlings will fall over in the early stages of the disease, and the temperature will drop in the evening and return to normal. If the disease worsens, the seedlings will completely wither and wilt, and the stems will rot and fall off suddenly.

Bacterial diseases

The greenhouse cucumber planting environment is relatively closed, and the high internal temperature provides suitable conditions for bacterial diseases to occur, mainly harming the leaves, easily leading to cucumber tissue necrosis, rot and even bacterial pus. The main diseases include the following.

① Bacterial blight

It is easy to occur in low temperature and high humidity environment, and the disease is caused by direct invasion through the stomata and wounds on the leaf margins, mainly harming leaves, fruits and stems. Leaves are most susceptible to the disease, first producing irregular brown water-soaked spots and then developing into brown spot-like lesions, which may eventually spread to the middle of the leaves to form large water-soaked lesions, causing the leaves to die due to blocked nutrient absorption.

② Bacterial angular spot disease

It is easy to occur under low temperature and high humidity conditions. Water droplets on the top gather and fall down, which can spread repeatedly and infect leaves, fruits, and stems. In the early stage of infection, a light brown polygonal water-soaked spot will appear on the front of the leaves. After that, the spot area gradually increases and becomes grayish white, and falls off to form holes. The pathogen invades the fruit, which may cause the fruit to dry and rot at the mildest, or spread to the inside of the fruit and cause the seeds to be infected.

③ Bacterial leaf blight

The disease is more serious when the temperature is high and the humidity is high. It spreads by infecting the stomata and wounds of the leaves, and mainly occurs in the lower and middle functional leaves of the cucumber plants. In the early stage of infection, water-soaked spots appear on the back of the leaves and the edges of the leaves begin to fade. As the disease worsens, the color of the spots gradually turns brown, and eventually the leaves dry up and die.

④ Bacterial round spot disease

It is a high temperature and high humidity disease that infects the stomata or wounds of leaves. The difference from leaf blight is that after infecting cucumber leaves, the lesions first turn yellow and then become transparent and thin, and the pus is not obvious when the humidity is high.

Viral diseases

Cucumbers are widely planted and grown in many varieties, making them hosts to many plant viruses. Viruses mutate quickly and infect host plants in different ways, causing yield reduction or even death of the entire plant. The main melon viral diseases that infect cucumbers in my country are as follows.

① Cucurbit chlorosis virus

The disease is spread rapidly between host plants in a semi-persistent manner by whiteflies, causing cucumber leaves to turn green and yellow except for the veins, and the plants to shrink slightly, starting from the bottom and gradually developing upwards, with new leaves showing no symptoms.

② Zucchini green mottle mosaic virus is transmitted in a non-persistent manner by aphids, and can also be transmitted mechanically through leaf contact or human activities.

It can cause systemic damage to plants, manifested as: ring-shaped chlorotic spots on leaves, local deformity and necrosis, fruit deformity, stiff and bitter taste, reduced cucumber yield and decreased commercial value.

③ Cucumber mosaic virus can overwinter on perennial host plants and infect different host plants in the following year. It is transmitted through aphids through non-persistent transmission routes or mechanical friction.

It mainly infects cucumber leaves. The infected cotyledons will gradually wither or turn yellow. The young leaves will be small mosaics of dark green and light green and wrinkled and thickened. In severe cases, they will curl in reverse. The stem nodes will be deformed, elongated or shortened to varying degrees, and may wither along with the leaves. The fruits will have green spots and different degrees of protrusions on the surface.

④ Cucumber green spot mosaic virus is mainly transmitted through seeds, soil and branches and leaves of other strains. It is divided into two types: common green spot mosaic disease and yellow spot mosaic disease.

In the early stage of infection, the cotyledons are mottled with light green and dark green. The diseased areas suddenly swell and form tumors. In severe cases, the leaves of the plant will twist and shrink, causing the entire plant to become dwarfed. The fruits will also develop tumors and become deformed, resulting in reduced yield and a worse taste.

2 Integrated prevention and control of cucumber diseases

To solve the problem of cucumber diseases in actual production, prevention should be carried out first and then control should be carried out, and comprehensive prevention and control measures should be used to avoid the occurrence of diseases. Only by clarifying the causes of the diseases and accurately identifying the symptoms of the diseases can we prescribe the right medicine and control the diseases.

Agricultural control

Before planting, try to select disease-resistant and high-yield varieties and cultivate non-toxic seedlings. When planting, it is best to choose a high, sunny, and well-drained plot; during planting, weeds around the crops should be cleared in time, and the greenhouse should be cleaned to reduce the source of disease; organic fertilizer should be applied appropriately. The theoretical maximum yield of cucumber is 23.56 t/h㎡ of organic fertilizer, which should be fully mixed with the topsoil of about 20 cm thickness; control the planting distance to ensure a reasonable planting density of cucumbers, the spacing between plants can be maintained at about 25 cm, and the row spacing at about 50 cm; rotate with non-cucurbit crops to effectively reduce the number of bacteria and fungi in the soil and reduce the probability of disease.

3. What are the fungal diseases?

There are five main subphyla of fungal diseases.

1: Mastozoa: Mycorrhizal fungi, Pythium, Phytophthora, and Downy mildew.

2: Most of the Zygomycetes are saprophytic, and only a few species cause crop diseases. For example, Rhizopus causes sweet potato soft rot. 3. Ascomycetes: powdery mildew, sphaerotheca (sweet potato black spot, cereal fusarium, ergot), sclerotinia (sclerotinia, brown rot). 4. Basidiomycetes: smut, rust. 5. Ascomycetes: sphaerotheca (rice blast, corn blast, etc.), black disc (anthracnose, etc.), sphaerotheca (cotton brown spot, sesame stem blight, etc.), asporogenes (cotton damping-off, etc.).

4. What are the main types of agricultural diseases?

There are three main types of agricultural diseases: fungal diseases, bacterial diseases and viruses.

5. What are the main types of agricultural diseases?

1. Spot type: A considerable number of plant diseases caused by Pseudomonas infection are spotted, such as rice bacterial brown spot disease, cucumber bacterial angular spot disease, cotton bacterial angular spot disease, etc.

2. Leaf blight: Most of them are caused by Xanthomonas aeruginosa infection, and the leaves of plants will eventually wilt after being infected, such as rice bacterial leaf blight, cucumber bacterial leaf blight, konjac bacterial leaf blight, etc.

3. Bacterial wilt: Generally caused by Pseudomonas infecting the plant vascular bundle, blocking the transport pathway, causing the plant stems and leaves to wilt. Such as tomato bacterial wilt, potato blight, strawberry bacterial wilt, etc.

4. Ulcerative type: generally caused by Xanthomonas aeruginosa infecting plants, the lesions become corky in the later stage, with raised edges and sunken centers, forming an ulcer-like shape. Examples include citrus canker, bacterial spot disease of edible soybeans, and bacterial spot disease of tomato fruits.

5. Rot type: Most of them are caused by Erwinia infecting plants, such as bacterial soft rot of cabbage, bacterial soft rot of Solanaceae and Cucurbitaceae crops, and basal rot of rice.

6. Deformity: caused by infection with Bacillus thuringiensis, which causes the roots, root collars, lateral roots and branches of plants to become deformed and tumor-like, such as chrysanthemum root cancer.

6. What are the main types of agricultural diseases?

1. Spot type: A considerable number of plant diseases caused by Pseudomonas infection are spotted, such as rice bacterial brown spot disease, cucumber bacterial angular spot disease, cotton bacterial angular spot disease, etc.

2. Leaf blight: Most of them are caused by Xanthomonas aeruginosa infection, and the leaves of plants will eventually wilt after being infected, such as rice bacterial leaf blight, cucumber bacterial leaf blight, konjac bacterial leaf blight, etc.

7. What are the main types of agricultural diseases?

Agricultural diseases are divided into fungal diseases, bacterial diseases, viral diseases, and nematode diseases, among which fungal diseases account for about 80% of diseases.

Pest and disease classification:

Category I crop pests and diseases refer to crop pests and diseases that occur over a particularly large area year after year or that may cause particularly heavy losses to agricultural production;

Category II crop diseases and insect pests refer to crop diseases and insect pests that occur in a large area throughout the year or may cause significant losses to agricultural production.

The main types of agricultural diseases are:

1. Fungal diseases

(1) Fungal diseases account for about 80% of diseases.

(2) Trichoderma and Powdery Fungi mainly cause cell enlargement and division.

(3) Fungi of the genera Peronospora and Chlorella mainly cause downy mildew.

(4) Ascomycota fungi, mainly causing powdery mildew.

(5) Ustilago and rust fungi in the Basidiomycetes mainly cause smut and rust diseases.

(6) Fungi of the subphylum Ascomycota, which mainly cause tissue necrosis in the host.

(7) Bacillus pathogenic fungi, mainly causing wilt and verticillium wilt.

(8) The genus Melanosporium of the class Anospora mainly causes anthrax.

(9) Fungi of the order Glomerales. They cause a variety of diseases: spot-type, which harms leaves; canker-type, which harms stems and branches.

2. Bacterial diseases

(1) Bacterial infection destroys thin cells and cell wall tissues, causing plant necrosis, rot, wilting, deformity and other symptoms.

(2) Bacterial diseases do not have hyphae or spores, and there is no mold on the surface of the lesions, but there is bacterial pus overflowing and the surface of the lesions is smooth.

3. Viral diseases

Most of the time, they harm crops through systemic infection, causing symptoms such as dwarfing, bushy branches, deformities, and ulcers.

4. Nematode disease

Nematodes parasitize on the roots, stems, leaves, flower buds, seeds, and fruits of plants, absorbing nutrients from the plants, destroying plant tissues, and causing mechanical damage.

8. How to distinguish bacterial diseases from fungal diseases?

As the saying goes, the railway police are in charge of different sections. The same is true for pesticides. Different agents prevent and treat different diseases and pests. In general, most pesticides cannot cure diseases, and most fungicides cannot kill insects. Lime sulfur can cure rust, powdery mildew, spider mites, and rust mites of many crops, but it is a minority after all. Agents that belong to fungicides cannot kill both fungi and bacteria. For example, carbendazim, methyl thiophanate, mancozeb, triadimenol, etc., which are used in large quantities, only kill fungi but not bacteria. There are only a few agents that can kill bacteria specifically, including 72% agricultural streptomycin sulfate, 88% oxytetracycline hydrochloride soluble powder, chlorothalonil (Sichuan Chemical-018), and chlorfenapyr. Agents that can cure fungal and bacterial diseases are mainly copper-containing fungicides, including copper hydroxide, copper oxychloride, copper chloramine, copper succinate, thiophanate-copper, etc., as well as sinoprolin, seed soaking spirit (dithiocyanate methane), etc. Drugs that can treat multiple fungal, bacterial, and viral diseases, such as dichloroisocyanuric acid, chlorobromoisocyanuric acid, and oligomeric D-glucosamine, are even rarer. Therefore, farmers should be reminded to first understand what drugs can treat what diseases, and second, to accurately distinguish the types of diseases.

In the field, fungal diseases and bacterial diseases can be distinguished based on the following points:

Since the two pathogens cause disease in different ways, the symptoms they present are very different. After the bacteria invade the plant, they live only between cells, destroying the cell wall, causing the intracellular substances to seep out and fill the intercellular space, so the edge of the lesion will appear oily or water-soaked, and translucent when facing away from the sun. Although both are rotten, the rotten caused by bacteria is humid, soft, and often smells bad; the rotten caused by fungi can be dry or wet, and has the smell of moldy clothes or fermentation.

Since the two pathogens have different structures and propagators, the symptoms they manifest are also different. The fungal body is filamentous. After developing to a certain extent in the body, most of them will form some special structures on the surface of the diseased part and produce some propagators, thus forming the mold layer, powder, rust, small black spots, small black particles, etc. that are unique to fungal diseases; bacteria are some single-celled organisms. Under moist conditions, the lesions can produce bright yellow beads, which are bacterial pus, and form colloid particles or bacterial films after drying. Bacterial wilt and wilt caused by Fusarium both cause the vascular bundles of plants to turn brown, but dirty white pus can overflow from the cross section of the diseased stems of bacterial wilt.

Since the two pathogens have different transmission pathways or infection methods, their field distribution characteristics are also different. Bacteria cannot directly invade the plant epidermis, so wounds and water are important conditions for the spread of diseases. Rice bacterial blight often breaks out after a storm, and the distribution of Chinese cabbage soft rot is closely related to irrigation water. Fungal diseases often show the characteristics of air flow transmission, seed transmission, and diseased body transmission. (Xiao Yueyan, senior consultant of Sinofert Corporation and professor of China Agricultural University)

9. How to distinguish fungal diseases from bacterial diseases?

Different methods to distinguish fungal diseases from bacterial diseases are different. Fungal diseases usually manifest as brown spots, white spots, pits and other symptoms on the surface and inside of plants, which will cause plants to wilt, wither and die. Bacterial diseases generally manifest as fading and withering of leaves, branches and other parts, and may have symptoms such as rot and ulceration. In actual operation, we can make a preliminary identification by observing the surface morphology of the diseased part, the morphology of the diseased leaves, the color of the fungal hyphae and other characteristics, and then further identify by measuring the chemical composition and disease resistance of the diseased tissue to confirm the type of disease and take corresponding control measures.

10. What animal doesn’t look like a fish but is a fish?

The lancelet is known as the least fish-like fish.

Amphioxus, also known as Bai's lancelet, slug fish, double-pointed fish or sea hair, is a precious marine animal. Due to its extremely special morphological structure, it has the characteristics of both invertebrates and vertebrates. It is a typical representative of the transitional type from invertebrates to vertebrates. Therefore, it is highly valued by the biological community at home and abroad.

The appearance of lancelet is very strange and interesting. It has a very small body, flattened on the left and right sides, pointed and thin ends, and a spindle-shaped body. It is generally only 4 to 5 cm long.