Occurrence of Tulip Diseases and Integrated Control Methods

Tulip is a perennial bulbous herbaceous plant of the genus Tulipa in the family Liliaceae, also known as foreign lotus, grass musk, peony lily, etc., and is one of the most popular cut flowers in the world. With the adjustment of industrial structure, many places in Jiangsu Province have formed tulip fresh cut flower bases. However, in the production process, we found that every stage may be harmed by fungal, bacterial and viral diseases, thereby affecting the normal growth of plants, reducing the quality and ornamental value of cut flowers, and in severe cases causing devastating damage. Therefore, preventing the occurrence and development of tulip diseases is the first issue that cut flower producers must consider. The common diseases in tulip production and their control methods are described below.

1 Symptoms and Occurrence Patterns of Fungal Diseases

1.1 Brown Spot

1.1.1 Symptoms It mainly harms leaves, flowers and bulbs. Leaf lesions are initially light yellow, round or oblong, slightly sunken, with dark water-soaked margins; later the lesions expand and turn grayish brown. When lesions occur at the leaf margin, the leaf curls and wrinkles to one side. When air humidity is high, the diseased parts are covered with a large amount of gray mold. After the perianth is infected, light brown lesions appear, which then gradually expand and turn dark brown, and finally wither. Severely infected flower buds fail to open. Lesions on the stem are relatively long and sunken rather deeply; when they extend around the entire circumference of the stem, the upper part collapses and rots. The outer skin of infected bulbs often fades, cracks, and bears many dark brown small bodies (small sclerotia). After peeling off the outer skin, dark brown nearly round lesions can be seen. Plants growing from infected bulbs are dwarfed, yellow-green, and their flowers wither.

1.1.2 Occurrence pattern The pathogen overwinters as sclerotia in diseased plant residues or in the soil, becoming the infection source for the following year. The pathogen spreads through rain and airflow. Rainy, foggy and dewy high-humidity weather favors the occurrence and spread of the disease. When plants are planted too densely, ventilation is poor, or weeds grow around them, the disease is more severe. Plants that grow poorly or are injured are also prone to the disease.

1.2 Root Rot

1.2.1 Symptoms At the initial stage, the roots show translucent water-soaked spots, which after expansion cause the vascular bundle tissue to turn brown, resulting in root rot. When bulbs are infected, gray spots appear around the base of the bulb with brown margins, and in severe cases the bulb becomes soft and rotted. After diseased bulbs are planted, some fail to emerge, and although some can emerge, they grow poorly, causing gaps and missing plants in the rows.

1.2.2 Occurrence pattern The pathogen is a fungus of the genus Pythium. The pathogen can survive in the soil and begins infecting as soon as it contacts the host. Watery and humid environments favor the spread, infection and occurrence of the pathogen.

1.3 Fusarium Wilt

1.3.1 Symptoms On the outer scales of the bulb, dark brown and gray sunken spots appear, which later expand into yellowish brown or dark brown lesions. If diseased bulbs are placed in a warm and humid place, white or pink mycelium and conidia grow on them, causing the diseased tissue to shrink and harden. After the base of the bulb is affected, rapidly developing lesions can spread over all scales. Ethylene produced by infected scales can cause healthy bulbs to exude gum, affecting growth. Leaves on the bulb show premature senescence, and some leaves appear upright and gradually turn a characteristic purple. The flowers produced are thin, small, deformed, and even withered.

1.3.2 Occurrence pattern The pathogen overwinters as mycelium and chlamydospores in infected bulbs and in the soil. Planting diseased bulbs often causes the disease. In cultivation, shady, wet andheavy soil, application of undecomposed organic fertilizer and excessive application of nitrogen fertilizer make the disease more likely. When black cutworms, wireworms and bulb mites occur abundantly, bulb damage is greater and the disease is more severe.

1.4 Penicillium Rot

1.4.1 Symptoms It mainly damages bulbs, and also often shows symptoms on aboveground parts. Infected bulbs initially develop dark brown sunken spots, the inner bulb gradually rots, and finally the bulb becomes dry-rotted like rotten wood. Water-soaked lesions appear on the tips of young shoots and tender leaves, and the lesions are often covered with blue mold, which is the fruiting body of the pathogen. Plants growing from infected bulbs are short, chlorotic, fail to flower or produce deformed flowers, and die prematurely.

1.4.2 Occurrence pattern The pathogen is Penicillium corymbiferum, a fungus of the genus Penicillium in the Deuteromycotina, mainly saprophytic, and most infections form through mechanical wounds, burns, or wounds caused by mite damage. Cool environments favor infection by the pathogen, and the disease develops rapidly when the storage site has poor ventilation and is stuffy and hot. Bulbs are easily damaged during storage and transport, and bruised bulbs are most susceptible.

2 Bacterial Diseases

2.1 Black Rot

2.1.1 Symptoms It mainly damages bulbs. On the basal plate and the stem surface, and sometimes on the 2nd and 3rd scales, irregular lesions initially yellowish brown and later dark brown are produced, with a rough surface.

2.1.2 Occurrence pattern The pathogen is a Pseudomonas bacterium. The bacterial cells are rod-shaped with 1 to 3 polar flagella. The optimum temperature for disease occurrence is 20 to 25°C, and the minimum temperature is 5°C. The pathogen survives in infected bulbs and soil, and diseased residues are the source of infection.

2.2 Canker

2.2.1 Symptoms It mainly damages leaves, flower stalks and bulbs. After sprouting, the disease occurs when the first leaf unfolds, initially producing water-soaked silvery white lesions on the leaves; later the lesions continue to expand, causing the epidermis and internal tissue to separate. Infected bulb tissue cracks, the scales turn brown, white spots appear on the outer scales, and diseased scales fall off piece by piece. In the later storage period, the lesions bulge and turn yellow. Infected flower stalks develop light yellow to brown canker spots, and diseased plants are dwarfed.

2.2.2 Occurrence pattern The pathogenic bacteria overwinter in diseased tissue, and in the following year when young shoots emerge they become infected through contact with diseased parts. In open-field cultivation, bacteria oozing from diseased tissue are splashed by wind and rain to neighboring plants for expansion. The optimum temperature for disease occurrence is 10°C, and the disease is severe in springs with many rainy days.

3 Viral Diseases

3.1 Color Breaking

3.1.1 Symptoms The disease can show symptoms on both leaves and petals. Light green or grayish white streaks appear on the leaves, sometimes producing mosaic and mottling. Petal symptoms often vary slightly among cultivars. In cultivars with red or purple flowers, the petals show light yellow or white stripes of varying sizes, which actually adds a bright landscape compared with the original healthy flower, making the diseased flower even more beautiful. In the past some people mistakenly regarded this as a new cultivar, causing the disease to spread widely. In cultivars with light-colored or white flowers, because the petals themselves have little pigment, the symptoms are not very obvious. At the same time, varietal quality rapidly degenerates.

3.1.2 Occurrence pattern Tulip breaking virus can be transmitted by sap, aphids and seed bulbs. The tulip bulb aphid mainly transmits the virus during the bulb storage period, but not during the growing period. In Shanghai and other places, most cultivars of seed bulbs imported from the Netherlands can only be planted for 2 to 3 years, after which they gradually degenerate and become smaller, and may even fail to flower; this virus is the main cause of degeneration.

3.2 Necrosis

3.2.1 Symptoms Spindle-shaped necrotic spots with purple margins or slightly white are produced on leaves, stems and petals, causing leaves and flowers to become deformed. Diseased plants die prematurely, and the number of bulbs decreases.

3.2.2 Occurrence pattern The virus was originally tobacco necrosis virus and can be transmitted by sap inoculation.

4 Integrated Control

4.1 Seed Bulbs and Seed Bulb Treatment

Select disease-free bulbs with large diameter and high specific gravity, and remove diseased bulbs. For bulb disinfection, use carbendazim 800-fold solution plus propargite 1000-fold solution, soak for 20 to 30 minutes, then dry in the shade and sow the next day. If conditions permit, hot water seed soaking can also be used, which is more effective in killing pathogenic organisms, but the temperature must be well controlled.

4.2 Strengthen Soil Treatment

Generally, crop rotation once every 2 to 3 years is needed. In fields with severe disease, carrying out rotation for more than 3 years is an effective measure for disease control; avoid planting tulips in soil contaminated by pathogens. For soil disinfection, irrigate with a mixture of 50-fold formalin and 1000-fold phoxim, cover with plastic film for 7 days, then uncover it and let it air-dry naturally (to avoid phytotoxicity to seed bulbs), and plant again after 14 days.

4.3 Careful Management

Provide careful maintenance to ensure ventilation and light penetration. In greenhouses, attention should be paid to reducing humidity, avoiding large-scale sprinkler irrigation, preventing water droplet splashing, and rain-shelter cultivation is recommended. If the climate is dry, replenish water in time to favor root and bud development. Control the use of nitrogen fertilizer to avoid excessive application that promotes disease occurrence, and choose compound fertilizers of nitrogen, phosphorus and potassium. Apply fertilizer in time during the leaf expansion stage. At the bud stage, to ensure flowering quality, potassium dihydrogen phosphate can be sprayed on the leaves 1 to 2 times while fertilizing. When fertilizing, avoid fertilizer entering the flower center and causing heart rot. During the growing period, promptly prune diseased leaves and flowers and bury them deeply or burn them in a centralized manner.

4.4 Chemical Control

For any disease, early detection and early control must be achieved. For fungal diseases, during the disease period spray 70% chlorothalonil wettable powder or 50% procymidone wettable powder or 70% thiophanate-methyl wettable powder 800 to 1000-fold solution, 64% oxadixyl mancozeb wettable powder 500-fold solution, or 50% carbendazim wettable powder 500-fold solution, etc., spraying once about every 7 days for 2 to 3 consecutive times, with good control effects. To prevent fungicides from developing resistance, please alternate the use of the above pesticides. For bacterial diseases, before onset or at the initial stage, spray 68% agricultural streptomycin powder 3000-fold solution, 47% kasugamycin-copper wettable powder 700-fold solution, or 30% copper hydroxide glufosinate 500 to 600-fold solution, spraying once every 7 to 10 days. For viral diseases, control aphids as early as possible to reduce opportunities for virus transmission, using 2.5% lambda-cyhalothrin emulsifiable concentrate 3000 to 4000-fold solution or 10% imidacloprid wettable powder at 1.5 g per mu. When necessary, spray 20% virus A wettable powder 500-fold solution or 5% Jun Du Qing 400-fold solution, or use 1.5% Zhi Bing Ling 1000-fold solution for spraying, once every 7 days for 3 to 4 consecutive times.