A Detailed Introduction to Fennel Powdery Mildew and Its Control Measures

Both large fennel and small fennel are commonly used seasonings, and are essential when cooking fish, stewing meat, and making braised foods. Because they can remove the unpleasant odor from meat and restore its fragrance, they are called "fennel". Large fennel is star anise, whose scientific name is "star anise" (Illicium verum). The seed fruit of small fennel is a seasoning, and its stems and leaves also have an aroma and are often used as filling for foods such as buns and dumplings. Their main component is fennel oil, which can stimulate the nerves and blood vessels of the gastrointestinal tract, promote the secretion of digestive juices, increase gastrointestinal peristalsis, and expel accumulated gas, so it has the effects of strengthening the stomach and promoting the flow of qi; sometimes gastrointestinal peristalsis decreases after excitation, which helps relieve spasms and reduce pain. Also known as fennel seed, small fennel, fennel, huixiang, fragrant silk vegetable, and small fennel.

Nutrition and effects of fennel

Fennel greens are rich in vitamin B1, B2, C, PP, carotene, and cellulose. What gives them their special spicy aroma is fennel oil, which can stimulate the nerves and blood vessels of the stomach and intestines and has the effect of strengthening the stomach and regulating qi, so it is an excellent vegetable to pair with meat and fatty foods. Eaten cooked or steeped in wine, fennel greens can promote the flow of qi, dispel cold, and relieve pain. The seedlings and leaves of fennel, when pounded fresh to extract the juice for drinking or for external application, can treat malignant toxic swellings.

Types of fennel

Fennel is also called fennel seedlings. It is a 1- to 2-year herbaceous plant of the Apiaceae family. The whole plant has a special fragrance, and it is mainly used for fillings, though it can also be stir-fried. Fennel has different types such as small fennel, large fennel, and bulb fennel.

1) Small fennel: the plant is relatively short, with a plant height of 20-35 cm, 7-9 leaves, short petioles, small leaf spacing, slower growth, and late bolting. Small fennel includes round-seeded and flat-seeded types. The round-seeded type has a shorter growth period, bolts earlier, and has lower yield; the flat-seeded type has strong adaptability, bolts late, and has strong regeneration ability. Small fennel is mainly cultivated in various parts of Shandong Province.

2) Large fennel: plant height 30-45 cm, 5-6 leaves, longer petioles, larger leaf spacing, fast growth, and earlier bolting. Large fennel is mostly cultivated in Shanxi, Inner Mongolia, and other provinces (regions).

Introduction to fennel powdery mildew and its control measures

Diagnosis of fennel powdery mildew:

It mainly damages leaves and stems. At the beginning of the disease, white powdery spots appear on the surface of stems and leaves, then gradually expand and merge with one another, occupying most of the stem and leaf surface. In severe cases, they cover the entire stem and leaf surface, and the diseased tissue discolors, causing local necrosis and death of the whole plant.

Pathogen of fennel powdery mildew:

It is Erysiphe heraclei. The conidiophores of this fungus are upright, and the upper part gradually divides into catenate conidia. The conidia are nearly cylindrical, a few barrel-shaped, with bluntly rounded ends. The cleistothecia are generally scattered to nearly clustered on the stem and leaf surface, dark brown, flat-spherical, with 7-38 appendages, having irregular branching and dichotomous branching, a few unbranched, with 0-3 septa, nearly colorless, mostly light brown at the base. There are 2-5 asci, occasionally up to 7, nearly oval or broadly oval to nearly spherical, with a short stalk or no stalk.

Occurrence pattern of fennel powdery mildew:

In warm regions, the pathogen overwinters as conidia on overwintering hosts; in cold regions, it overwinters as mycelium and cleistothecia on diseased residues, begins activity in the following spring, and infects via ascospores or conidia; in addition, seeds can also carry the pathogen and can spread it over long distances, and in the field the pathogen spores spread through wind and rain. The pathogen prefers warm and humid conditions, and is prone to occur under conditions of dense plant growth, warm days, cool nights, and heavy dew and humidity.

Control measures for fennel powdery mildew:

1) Choose plots with higher terrain and good ventilation and drainage for planting.

2) Use seeds harvested from disease-free plants, maintain suitable density, apply sufficient organic fertilizer, and avoid excessive nitrogen fertilizer.

3) In protected cultivation, pay attention to ventilation, reduce humidity, and increase light.

4) Maintain field sanitation, and promptly pull out and deeply bury central diseased plants when found. At harvest, thoroughly collect diseased residues and burn them.

5) In the early stage of disease, promptly spray 15% triadimefon wettable powder at 1500 times dilution, or 25% diniconazole emulsifiable concentrate at 3000 times dilution, 50% sulfur suspension concentrate at 200-300 times dilution, or 30% solid lime sulfur at 150 times dilution, and be careful to spray evenly and thoroughly.

Agricultural control:

(1) Reasonable fertilization: apply sufficient decomposed organic fertilizer and increase the application of phosphorus and potassium fertilizers to improve plant disease resistance.

(2) Strengthen ventilation: maintain suitable planting density, strengthen ventilation, and reduce humidity, which can reduce disease occurrence.

(3) Clean the field: diseased leaves and diseased plants must be thoroughly removed, taken out of the field, and concentrated for deep burial or burning, which can reduce the spread of the pathogen in the field.

2. Physical control: in the early stage of disease, spray 27% higher fatty alcohol membrane emulsion at 100 times dilution, once every 6 days, for 3-4 consecutive sprays. After spraying the higher fatty alcohol membrane, a fairly thin molecular film forms on the leaf surface or stems, causing oxygen deficiency and thereby killing the powdery mildew pathogen. This molecular film cannot be seen by the human eye and can only be observed under an electron microscope.

3. Biological control: in the early stage of disease, spray 2% Wuyimycin (agricultural antibiotic BO-10) aqueous solution at 200 times dilution, or 2% antimycin (agricultural antibiotic 120) aqueous solution at 200 times dilution, once every 7 days, for 2-3 consecutive sprays.

4. Pollution-free pesticide control: when the disease has just occurred (only individual plants and 1-2 small spots), immediately spray baking soda at 500 times dilution, once every 3 days, for 5-6 consecutive sprays. When applied in protected cultivation, it not only has a good effect but can also release carbon dioxide and increase yield. The reason baking soda can control powdery mildew is that the powdery mildew pathogen prefers acidic environmental conditions, while baking soda is alkaline; after spraying, it changes the pH of the environment, causing the powdery mildew fungus to die.

Chemical pesticide control:

In the early stage of disease, spray 20% triadimefon emulsifiable concentrate at 1200-1500 times dilution, or 25% triadimefon wettable powder at 1500-2000 times dilution, or 30% triflumizole wettable powder at 1500-2000 times dilution, or 12.5% diniconazole wettable powder at 2000-2500 times dilution.

Or 70% mancozeb wettable powder at 500-600 times dilution, or 40% sulfur suspension concentrate at 500 times dilution, or 50% sulfur suspension concentrate at 300-400 times dilution, or 20% dithianon suspension concentrate at 600-800 times dilution, or 25% diniconazole emulsifiable concentrate at 3000 times dilution, once every 7 days, for 2-3 consecutive sprays.