The Pathogenesis and Control Methods of Water Chestnut Stem Blight
Water chestnut, also known as Chinese water chestnut, water chestnut, shao, fuci, wuyu, puji, dili, belongs to the monocotyledonous Cyperaceae family, is a perennial root herbaceous plant, oblate, pointed at the top, smooth and glossy surface, purplish-red or dark brown, grows in ponds and marshes, with dark green stems growing in clusters above ground, and the underground corms are edible. Because it is shaped like a horse's hoof, people also call it Chinese water chestnut. Its appearance resembles a chestnut, and not only the shape, but even the nature, flavor, composition, and functions are similar to chestnuts, and because it fruits in the mud, it is also called “ground chestnut”. The water chestnut has a purplish-black skin, white flesh, sweet and juicy taste, crisp and delicious, and has the reputation of “underground snow pear”, and northerners call it “Jiangnan ginseng”. It can be eaten raw as a fruit and also cooked as a vegetable, and is a seasonal product loved by the public.
Principle of water chestnut stem blight:
Water chestnut stem blight, commonly known as “water chestnut plague”, is the main disease on water chestnut, mainly occurring in southern planting areas, causing plants to lodge and die, leading to severe yield reduction or even total crop failure.
Symptoms mainly damage stems and leaf sheaths, and flower organs can also be affected.
On the leaf sheath, initially dark green water-soaked irregular lesions appear, which can later expand to the entire leaf sheath, with many black streaks of varying lengths on the surface, and finally the diseased part turns grayish-white. Stem damage is mostly caused by the expansion of lesions from the leaf sheath, initially dark green water-soaked, generally fusiform, also elliptical or irregular, the diseased tissue becomes soft and sunken, with black twisted streaks on the surface, sometimes arranged in concentric rings, and the lesions can coalesce with each other into larger dead spots. In severe cases, the entire stem lodges and dies, and under high humidity, a large amount of light gray mold appears on the surface of the lesions.
The pathogen Cylindrosporium eleocharidis Lentz is called water chestnut Cylindrosporium fungus, belonging to the Deuteromycetes order Melanconiales genus Cylindrosporium fungi. The hyphae are aseptate, colorless to brown, the acervuli are slender, the conidiophores are clustered in several strands, colorless to pale brown, short club-shaped, unbranched, with pointed apex; conidia are colorless, linear to crescent-shaped.
Disease characteristics: The pathogen overwinters in diseased residues. Under suitable conditions, it produces conidia. Spread by wind and rain, the pathogen spores germinate and invade the host, and after disease onset, the diseased part produces conidia again for repeated infection. Temperatures of 17-29°C, rainfall, dense fog, and heavy dew favor disease development, and if accompanied by strong winds, it is even more favorable for the spread of pathogen spores, making the disease more severe. In addition, overly dense planting, poor ventilation and light transmission, early excessive application of nitrogen fertilizer, and insufficient phosphorus and potassium fertilizer also lead to more severe disease.
Control methods for water chestnut stem blight:
(1) Select resistant varieties according to local conditions. Such as Dahongpao water chestnut (Zhejiang local variety), Weili (Fujian local variety), Guilin water chestnut (Guangxi Guilin local variety), etc., which are relatively resistant to disease.
(2) Rotate with other crops for 2-3 years in severely diseased fields.
(3) Strengthen cultivation management.
Sow at the appropriate time, plant reasonably densely, prevent excessive field humidity; irrigate at the right time, avoid flooding and cross-irrigation, fertilize reasonably, apply heavy base fertilizer and organic fertilizer, apply less chemical fertilizer in the early stage, and after entering the corm formation stage, appropriately topdress with nitrogen fertilizer and phosphorus and potassium fertilizer; promptly remove diseased plants found in the field, and after harvest, clear diseased residue tissues to reduce inoculum sources for the next year.
(4) Chemical control.
① Corm treatment. Soak corms in 25% carbendazim wettable powder 250-fold solution, or 50% thiophanate wettable powder 1000-fold solution, for 18-24 hours before use.
② Apply chemicals at the early stage of field disease onset, optionally using 25% carbendazim wettable powder 250-fold solution, or 50% thiophanate wettable powder 1000-fold solution, or 45% amobam 1000-fold solution, spraying once every 7-10 days, for 2-3 consecutive treatments.
Commonly used chemicals: carbendazim, thiophanate, amobam.
Water chestnut plague is a disease in which water chestnut is infected by multiple pathogens and lodges and dies over a large area in a short period, with a very fierce onset. Often, fields planted with water chestnut last year have more severe disease this year. The main pathogens causing water chestnut plague are fungal wilt disease and anthracnose. Due to the many types of pathogens, it is difficult to control with a single method. If considered from the perspective of integrated control, starting from the beginning and linking each step closely, it can achieve the effect of controlling water chestnut plague. The focus should be on the following aspects:
First, it is strictly forbidden to plant water chestnut in continuous cropping fields; fields planted with water chestnut last year, especially those where water chestnut plague occurred last year, must absolutely not be planted with water chestnut this year.
Second, strictly control seed selection. Water chestnut from diseased fields last year cannot be used as seed. Before planting water chestnut, corms with disease spots and wounds must be removed in advance.
Third, the soil for planting water chestnut and its seedbed must be strictly disinfected, such as treatment with 0.1% thiophanate, which can kill most pathogens.
Fourth, before transplanting water chestnut, first use dexon to disinfect the field soil.
Fifth, strengthen disease observation during the peak tillering period of water chestnut; once lesions are found, immediately use broad-spectrum pesticides such as baichongqing for protective control. If anthracnose, blight, or rust occurs, it can be controlled with 10% Shigao (difenoconazole) water dispersible granules 1000-fold solution.