How to control root-knot nematode disease in fennel? A detailed explanation of integrated control techniques

Fennel is a perennial herb, cultivated as an annual or biennial. The whole plant has a distinctive spicy aroma, with a white powdery coating on the surface. The leaves are pinnately divided, with linear segments. In summer it bears yellow flowers in compound umbels. The fruit is elliptical and yellow-green. It prefers warmth and is suited to sandy loam soil; it should not be planted in clay or overly wet land. It can be sown in spring or autumn, or propagated by division in spring. It originated in the Mediterranean region and is widely cultivated throughout our country, with strong adaptability.

What types of fennel are there?

Fennel is also known as fennel seedlings. It is a 1- to 2-year-old herbaceous plant of the Apiaceae family. The whole plant has a distinctive fragrance; it is mainly used as a filling, and 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 can be divided into 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).

Integrated control of fennel root-knot nematode disease

Symptoms of fennel root-knot nematode disease:

Fennel root-knot nematode disease occurs only in local areas, but the incidence rate is high, generally above 50 percent, and in the most severe cases can reach 100 percent. Root-knot nematode disease, in addition to harming vegetables of the Apiaceae family, can also harm many vegetables such as those of the Cucurbitaceae, Solanaceae, Brassicaceae, Asteraceae and Chenopodiaceae.

Symptom identification

On affected plants, the aboveground symptoms are not obvious, sometimes wilting or poor growth; underground, the lateral roots and fibrous roots have root knots (also called tumors) of varying sizes. When the root knots are cut open, very small milky-white nematode bodies are found inside. In severe cases, the seedlings wither and die.

Key identification points: there are many tumor-like root knots of varying sizes on the roots.

Occurrence pattern of fennel root-knot nematode disease

1. Pathogen Fennel root-knot nematode disease is caused by infection by nematodes of the genus Meloidogyne. The male and female pathogens differ in form; the larvae are slender and worm-like, the adult males are filiform, and the adult females are pear-shaped, white or colorless and transparent. Each adult female can lay 300-800 eggs, buried and living in the root-knot tissue, fixed and immobile.

2. Infection cycle Root-knot nematodes overwinter in the soil as second-stage larvae, and can also overwinter in the soil as eggs laid by older larvae or as fallen root knots (diseased residues), and can survive for 1-3 years. When the temperature rises to about 10°C the following year, the overwintering eggs hatch into larvae, which invade from the tender roots. After invading the root system, they secrete growth hormones such as indoleacetic acid, causing root cells to proliferate and form giant cells, also called root knots. After several molts, the female larvae mate with males at the fourth stage and lay eggs, while the males leave the host and enter the soil, soon dying. The eggs hatch into first-stage larvae inside the root knots, and after the second stage they leave the egg sac and enter the soil to find roots for reinfection. Nematodes are mainly spread by diseased soil, diseased roots and irrigation water; in addition, humans, livestock and farm tools can also carry and spread them, causing repeated infection.

3. Conditions for disease occurrence

(1) Relationship between disease occurrence and temperature When the soil temperature is 20°C, the nematodes begin to cause damage; when the soil temperature is 25-30°C, the damage is severe; when the soil temperature is below 10°C, the larvae stop activity; above 40°C, large numbers of larvae die, and the lethal temperature is 55°C for 10 minutes.

(2) Relationship between disease occurrence and soil humidity The soil humidity suitable for nematode reproduction is 40 percent-70 percent. If the soil humidity is too high or too low, nematode activity and reproduction are both inhibited.

(3) Relationship between disease occurrence and cultivation Continuous cropping in diseased land leads to severe disease occurrence; in addition, loose sandy loam soil with moderate soil moisture and good aeration is suitable for nematode activity; applying organic fertilizer carrying nematodes also causes severe damage.

Pollution-free control of fennel root-knot nematode disease:

1. Agricultural control

(1) Implement crop rotation In diseased land, rotate with vegetables of the Liliaceae family for 3 years, or with wheat, corn and millet for 2 years, or with aquatic vegetables or rice for 1 year.

(2) Strengthen management Choose clay for planting; apply organic fertilizer free of bacteria; collect diseased roots and diseased plants after vine removal and deeply bury or burn them outside the field; farm tools used in diseased land should be disinfected or wiped clean, and the spread by humans and livestock should be prevented.

2. Physical control In protected diseased land, control can be carried out during the high-temperature fallow period of the three summer months. Methods: first, clean the field and thoroughly remove diseased roots outside the field and burn them. Second, apply 50 kg of lime per 666.7 sq m, plus 500 kg of rice straw (cut into pieces) or wheat husks, evenly spread on the soil surface. Third, deeply plow the soil 50 cm. Fourth, form high ridges 30 cm. Fifth, irrigate the furrows, watering daily, always keeping the furrows full of water. Sixth, cover with plastic film and seal the greenhouse or tunnel for 10-15 days. Through soil sampling and separation testing, the nematode-killing effect reaches more than 90 percent.

3. Ammonia fumigation Before sowing or before planting, apply 50-60 kg of liquid ammonia per 666.7 sq m, using mechanical operation; operators should wear goggles, masks, gloves and so on. After application, cover with plastic film and seal for 7-10 days, then remove the film and deeply plow the soil, ventilate and release gas; after 3 days, plow the soil again to ventilate and release gas until there is no ammonia smell. Only after 10 days can sowing or planting be carried out, otherwise ammonia gas will poison the seedlings.

4. Pollution-free pesticide control Before sowing or before planting, in diseased fields use 18 percent avermectin emulsifiable concentrate or 1.8 percent abamectin emulsifiable concentrate, applying 1-1.5 ml per square meter into the furrow, then cover with soil; in the early stage of disease, use 1.8 percent avermectin 3000-fold solution to irrigate the roots for control.

Chemical control of fennel root-knot nematode disease:

1. Soil disinfection In diseased land, use 55 percent D-D mixture, applying 40 kg per 666.7 sq m. 15-20 days before sowing or planting, first plow the land well, then open furrows every 60 cm, 20 cm deep, evenly apply the pesticide into the furrows, then cover with soil and press firmly. Hole application is also possible: first plow the land, with hole spacing and row spacing both 30 cm, hole depth 15 cm, pour 3 ml of diluted pesticide solution into each hole, then cover with soil and press firmly, cover with plastic film for 15-20 days, then remove the film and deeply plow the soil, ventilate and release gas, and only after several days can sowing or planting be carried out. Alternatively, use 3 percent milor granular formulation, applying 5 kg per 666.7 sq m in holes before sowing or planting. Or use 33 percent metham sodium aqueous solution, 3-4 kg per 666.7 sq m, add 75 kg of water, open furrows and pour to apply, then cover with soil and tread firmly. Or use 10 percent fosthiazate granular formulation, 5 kg per 666.7 sq m, applied in holes.

2. Root irrigation with pesticide solution In the early stage of disease, you can choose 50 percent phoxim emulsifiable concentrate 1500-fold solution, or 80 percent dichlorvos emulsifiable concentrate 1000-fold solution, pouring 250 ml of pesticide solution per plant, which also has a certain effect; generally only irrigate once.