Symptoms of Fusarium Wilt in Tulips and Its Control Methods
This disease is also called tulip basal rot. It is a fungal disease caused by Fusarium moniliforme and Fusarium oxysporum f. sp. tulipae, which has host specificity and only harms tulips. Both are caused by fungi of the Deuteromycetes class. The pathogen overwinters as mycelium and chlamydospores in infected bulbs and soil. Under suitable temperature (20°C-34°C) and high humidity conditions, it produces large numbers of spores, which spread by rain splash. Excessive application of nitrogen fertilizer can aggravate the damage, and applying compost that is not fully decomposed and contains diseased residues also increases the chance of disease occurrence. The transport of seed bulbs contributes to the long-distance spread of the disease. Planting infected bulbs often causes disease onset. Tulips are often affected during the growing period and storage period. June is the peak period for this disease. Bulb contamination is the main route of disease transmission, and wounds on the bulbs and poor ventilation during storage are the main conditions for disease occurrence and spread. Among these, severe damage by underground pests, shady, wet and heavy soil, and application of undecomposed organic fertilizer are the main conditions for field disease occurrence. Infected corms often produce ethylene, which affects neighboring corms or plants and makes them more susceptible to infection. Excessive application of nitrogen fertilizer during cultivation can aggravate the damage of this disease.
It mainly harms corms and roots. The disease mostly occurs at the base of the corm. After the bulb is infected, small sunken spots ranging from light brown to gray appear on the outer scales, and the lesions then gradually expand and turn dark brown. In humid environments, pink spore masses of conidia can be seen on the diseased tissue. The affected area eventually shrinks and hardens. If the disease occurs at the base of the bulb, the lesions rapidly spread to the outer scales of the entire bulb, and the base of the bulb rots. Leaves growing from infected bulbs tend to turn yellow and wilt; flowers tend to become deformed or soft and wilted, roots are sparse, and the entire plant prematurely declines and dies. When tulip flowers fade, scattered diseased plants appear in the field, with leaves turning yellow and wilting, stems and leaves turning red and withering prematurely, and the base of the stems rotting, appearing as loose fibrous tissue with few roots, making the plants very easy to pull out. The bulbs exude gum, and the starch tissue decomposes and rots. At harvest time, the outer scales of diseased bulbs produce bean-sized colorless blister-like protrusions; after the blisters break, gum exudes or a wet rot appears. The bulb rots from the outside inward; some show blue-gray water-soaked wet rot, while others have the basal plate as the initial infection point, with wet rot spreading outward, giving off a pungent sour mash odor; after drying, the lesions appear grayish-white and chalky. During bulb storage, the main symptom is gum exudation, followed by yellowish-brown dry rot. In a greenhouse, infected plants will wither and die prematurely.
Epidemic characteristics: This disease generally occurs easily shortly after planting or near harvest. When soil temperature is above 15°C, it favors the spread of the disease.
Control Methods
(1) When the weather is good, corms can be harvested appropriately early to prevent sunscald and bruising. The dug bulbs should be soaked within 48 hours in a 1000-fold solution of 50% benomyl wettable powder at 25-30°C for half an hour, then dried, which can disinfect them. They can also be soaked within 48 hours in a 1000-2000-fold solution of benlate for 15-30 minutes, then dried, at low humidity (<15℃）贮藏，贮藏种球时要排成薄层，注意通风。
(2) Promptly dig out and burn diseased corms. Remove diseased corms before planting, soak them in benlate, and then plant.
(3) If diseased seed bulbs are found in the field, they should be promptly dug out and burned in a centralized manner. Do not plant tulips in low-lying plots with a high contamination rate. Drain promptly after rain to prevent moisture retention, which can reduce disease occurrence.
(4) In areas with severe disease, using 70% thiophanate-methyl wettable powder or 50% carbendazim wettable powder, applying 3 jin per 667 sq m on the soil surface and raking it into the soil is effective.
(5) In severely affected areas, implement a 3-year crop rotation system.
(6) When digging bulbs, avoid damaging the bulbs to reduce opportunities for pathogens to invade through wounds.