What are the latest control measures for wheat fusarium head blight?

Wheat fusarium head blight is also known as wheat ear blight, rotten wheat head, and red wheat head. It mainly causes seedling blight, ear rot, stem base rot, and stalk rot, and can damage the plant from the seedling stage to heading. Among these, ear rot has the most serious impact.

Symptom classification

1. Seedling rot

Is caused by seed-borne bacteria or infection by diseased residues in the soil. First the sprout turns brown, then the root crown rots along with it. In mild cases the diseased seedlings are yellow and thin; in severe cases they die. On dead seedlings, when humidity is high, pink mold-like material is produced (fungal conidia and stroma).

2. Ear rot

When wheat is flowering, water-soaked light brown spots appear on the spikelets and glumes, gradually expanding to the entire spikelet, and the spikelet turns withered yellow. When humidity is high, pink gelatinous mold layers form at the diseased spots. Later, dense small blue-black granules form on them (fungal perithecia). When touched by hand, they feel raised and cannot be wiped off. The grains are shriveled and accompanied by white to pink mold. After the spikelet becomes diseased, it spreads to the rachis; the diseased part turns withered brown, causing the spikelets above the damaged part to form withered white heads.

3. Stem base rot

Can occur from seedling emergence to maturity. After the base tissue of the wheat plant is damaged, it turns brown and rots, causing the whole plant to die.

4. Stalk rot

Mostly occurs at the first and second nodes below the ear. At first, water-soaked chlorotic spots appear on the leaf sheath, then expand into light brown to reddish-brown irregular spots or extend into the stem. When the disease is severe, the part above the diseased area turns withered yellow, and sometimes the plant cannot head or produces withered yellow heads. When the climate is humid, pink mold layers can be seen on the diseased part.

Causal pathogens

The disease is caused by a variety of Fusarium species, mainly Fusarium graminearum, Fusarium avenaceum, Fusarium culmorum, Fusarium moniliforme, and Fusarium acuminatum, all of which belong to the fungi of the Deuteromycotina. The dominant species is Fusarium graminearum, whose macroconidia are sickle-shaped, with 3—7 septa, bluntly rounded at the tip, with a distinct foot cell at the base; individual spores are colorless, and when gathered together they appear pink and viscous. Microconidia are rarely produced. The sexual state is Gibberella zeae, belonging to the fungi of the Ascomycotina. Perithecia are scattered or clustered on the surface of host tissue, slightly embedded in the stroma, pear-shaped, with an ostiole, and the top is wart-like protruding, purple-red or purple-blue to purple-black. Asci are colorless, club-shaped, size 100—250×15—150(μm), containing 8 ascospores. Ascospores are colorless, spindle-shaped, bluntly rounded at both ends, mostly with 3 septa, size 16—33×3—6(μm).

Transmission routes and disease conditions

In the rice-wheat double-cropping areas of central and southern China, the pathogen not only oversummers on diseased residues, but also overwinters as a saprophyte in the diseased residues of various crops such as rice, corn, and cotton. The perithecia formed on these diseased residues the following year are the main source of infection. The maturation of ascospores coincides with the wheat flowering stage. They are spread by airflow, wind, and rain, splash onto the wilted anthers of the floral organs, germinate, first live saprophytically, then infect the spikelets, and after a few days produce large amounts of pink mold layers (fungal conidia). The infection rate is highest from flowering to full bloom. The conidia formed by ear rot have little effect on reinfection of the current field, but have a greater effect on infection of nearby late wheat. The fungus can also oversummer and overwinter as mycelium inside diseased seeds.

In the wheat areas of northern and northeastern China, the pathogen can overwinter as mycelium or perithecia on wheat plant residues, diseased seeds, and the residues of other plants such as barnyardgrass, corn, and soybean red knotweed. In the northern winter wheat areas, it oversummers and overwinters as mycelium on wheat and corn ears; when conditions are suitable the following year, it produces perithecia that release ascospores for infection. Fusarium head blight is mainly spread by wind and rain, with rainwater playing a greater role. When the spring temperature is above 7°C and the soil moisture content is greater than 50%, perithecia form; when the temperature is above 12°C, ascospores form. Under rainfall or humid air conditions, the ascospores mature and fall onto the anthers, infecting the spikelets through the filaments and causing disease. Late-maturing varieties with thicker glumes and poor fertilizer tolerance are more severely affected; a large amount of pathogen in field residues leads to more severe disease; low-lying fields, poor drainage, heavy soil, excessive nitrogen fertilizer, high density, and a closed field canopy lead to more severe disease.

Control methods

1. Select disease-resistant (tolerant) varieties

Although immune varieties have not yet been found, there are some disease-tolerant varieties with good agronomic traits, such as Sumai No. 3, Sumai No. 2, Xiangmai No. 1, Yangmai No. 4, Wanya No. 2, Yangmai No. 5, No. 158, Liaochun No. 4, Zaomai No. 5, Xingmai 17, Xinong 88, Xinong 881, Zhoumai No. 9—Aiyou 688 series, Xinbaofeng (7228), Mianmai No. 26, Wanmai No. 27, Wannian No. 2, Zhengyin No. 1, 2133, Ning 8026, Ning 8017, etc. Spring wheat includes Dingfeng No. 3 and Ningchun No. 24. Each region can select according to local conditions.

2. Agricultural control

Rational irrigation and drainage; ditches should be opened for drainage in wet fields. After harvest, deep plowing should be carried out to destroy stubble and reduce the source of the pathogen. Sow at the appropriate time to avoid rain during the flowering stage. It is recommended to apply compost fermented with enzyme bacteria, adopt formula fertilization technology, fertilize at the right time, avoid excessive nitrogen fertilizer, and improve plant disease resistance.

3. Before sowing, soak seeds in lime water; for the method, see wheat loose smut.

4. Chemical control

① Dress seeds with yield-increasing bacteria. For every 6672, use 100—150 g of solid bacterial agent or 50 ml of liquid bacterial agent, dilute with water, spray on the seeds and mix evenly, dry them, and then sow.

② The key to control is to prevent ear rot during the wheat flowering stage. At the beginning of flowering, spray 50% carbendazim wettable powder at 800 times dilution, or 60% carbendazim hydrochloride (Fangmeibao) wettable powder at 1000 times dilution, 505 thiophanate-methyl wettable powder at 1000 times dilution, 50% carbendazim · procymidone wettable powder at 800—1000 times dilution, or 605 dimefol wettable powder at 1000 times dilution; one application every 5—7 days is sufficient. A motorized mist sprayer can also be used for applying the pesticide. In addition, in areas where fusarium head blight, wheat aphids, and armyworms occur together in the middle and late stages of wheat growth, use per 667 m2 30 ml of 40% chlorpyrifos or 10 g of 10% pirimicarb plus 100 g of 40% Hekuling, or 70 g of 60% Fangmeibao plus 150 g of potassium dihydrogen phosphate, or urea, yield-increasing agents, etc.; the control effect is excellent.