Major Pests and Diseases of Lilies and Their Control Methods
After sowing, lilies must undergo several years of cultivation and management before commercial bulbs suitable for harvest can be obtained. Generally, asexual propagation is used first to obtain seed bulbs, or seed propagation may be used first to obtain seed bulbs; the seed bulbs are then planted in the field and, through field management, grow into commercial lilies. Seed bulbs are various propagation materials first cultivated into 50-100 g small...
Lilies originated in East Asia. In Europe and America they are cultivated as ornamental flowers, while in China the bulbs are harvested and cultivated as a food crop. There are not many types of lily pests and diseases, but the damage is severe, with losses reaching 30%-60% in bad years. To improve the control of lily pests and diseases, from 1993 to 1998 we carried out preliminary surveys of the main pest and disease species in the Shaodong area, pesticide control trials, and investigations of integrated control measures, laying the foundation for large-scale control of lily pests and diseases. 1. Main types of lily pests and diseases
1.1 Lily gray mold (Botrytis elliptica Cooke)
Commonly known as lily leaf blight. It mainly damages leaves, and also infects stems, flowers, buds and bulbs. Leaf lesions are round or oval, yellow-brown or red-brown, with the center of the lesion light yellow or light brown and the edge purplish red or pale red. When the weather is humid, a gray mold layer forms on the diseased part; when dry, the lesion becomes thin and brittle, semi-transparent, and light gray. After the lesions expand, the leaves wither and die. When buds and flowers are affected, they look as if scalded by boiling water, turn brown, and rot. When the stem is affected, light brown canker spots form, and it breaks easily in the wind. Infection of young plants mostly causes the growing point to die. It sometimes also infects bulbs, causing bulb rot.
The lily gray mold pathogen mainly survives unfavorable conditions as sclerotia. In spring, conidia are produced from the sclerotia and spread rapidly in the field by wind, rain and air currents. The disease begins in early May, and peaks from late May to late June. During this period temperatures are high, and if there is prolonged cloudy and rainy weather, the disease spreads even faster. Long rain followed by clearing and thunderstorms can promote an epidemic. Applying undecomposed organic fertilizer; excessive or too late nitrogen fertilizer; and low-lying, waterlogged conditions all favor the disease.
1.2 Lily phytophthora blight [Phytophthora cactorum (Leb. et Cohn) Schrot]
Commonly known as foot rot. When the stem near the ground is affected, water-soaked lesions appear on the diseased part, which turns brown and constricts; the upper part of the plant dies, often lodging and dying. When affected during bulb sprouting, the tip of the young stem dies. When bulbs are infected, small oily spots first appear and gradually expand into gray-brown soft rot. When leaves and flowers are infected, small oily spots form on them and gradually expand, turning gray-green. When humid, a white mold layer forms on the lesions.
The lily phytophthora blight pathogen mainly overwinters as oospores in diseased plant residues in the soil. The disease begins at emergence, and a large number of aboveground symptoms appear in mid-to-late May. Applying undecomposed organic fertilizer, low-lying waterlogged conditions, humid and rainy weather, and wounds on bulbs caused by pest damage all favor the disease. Continuous cropping results in severe disease.
1.3 Lily anthracnose (Colletotrichum liliacearum Ferr.) It mainly damages bulbs, and also infects leaves and flowers. After bulb infection, irregular light brown spots first appear, then become light black-brown and slightly sunken, and finally the lesions become nearly black, with the tissue shrinking and dry-rotting. The outer bulb scales are most severely affected, gradually spreading to the inner scales. When leaves are affected, oval pale yellow lesions form, with black-brown edges, slightly sunken. The lily anthracnose pathogen overwinters as mycelium in the affected parts and produces conidia the following year, which spread by wind and rain. Heavy clay soil with high water content; plots with many lily mites; and plots with continuous planting and abundant diseased residues all have severe disease.
1.4 Lily virus disease (Lily symptomless virus)
Common lily virus diseases include the yellowing type and the mosaic type. Yellowing type: no special lesions appear on the leaves, the whole plant is yellowish, the internodes are shortened, the plant is dwarfed, and the leaves yellow and shrink. Mosaic type: irregular light green mottling appears on the leaves, then the small pale areas connect and expand, forming slender yellow streaks along the veins, later becoming slightly sunken and turning light yellow-brown to reddish brown.
The virus mainly overwinters in the bulbs, becoming the primary infection source the following year; secondary infection in the field is mainly caused by transmission by aphids. When there are many diseased bulbs, the weather is dry, and aphid populations are high, the disease occurs severely.
1.5 Lily mite [Rhizoglyphus echinopus (Fumouze et Robin)]
Also called the bulb mite. It gnaws on lily bulbs and transmits pathogens, causing lily rot. The lily mite has an oval body, is rather thick, white or pale yellow, with the gnathosoma and legs light brown, and the body surface relatively smooth and glossy. The lily mite prefers a cool, humid environment, requires about 10-14 d to complete 1 generation, and can have more than 20 generations per year. It overwinters as eggs and adult mites in the lily core or soil. Mid-to-early April is the period when overwintered mites occur in large numbers. Female mites lay eggs on lily bulbs. Adult and nymph mites gather to feed on lily bulbs, producing a sieve-like appearance, causing the aboveground parts of the affected lilies to die and the bulbs and roots to turn black-brown and rot.
2. Control measures
1) Crop rotation for 3 a. When planting lilies along a slope, plant from the bottom upward to reduce the spread of pathogens.
2) Select bulbs free of disease, mites and mechanical injury as seed to reduce sources of pathogens and mites.
3) Burn dead branches and fallen leaves in the field and diseased and pest-damaged residues to reduce sources of pests and diseases. Apply organic fertilizer to the lower soil layer only after it has been composted and fermented to maturity.
4) Deep furrows and high ridges, clear the furrows and drain water, and control soil moisture content.
5) Soak seed for disinfection and mite elimination. Before sowing, soak the bulbs for 3-5 min in a 4000-fold solution of 20% Saomanjing wettable powder plus a 1000-fold solution of 70% thiophanate-methyl wettable powder (when the temperature is above 30°C, shorten the time to 3 min) to eliminate pathogens and mites.
6) Chemical control in the field. According to trials and investigations, chemical control in the field emphasizes prevention and values early application, and only repeated applications are effective. ① At sowing, use 10% phorate granules plus 2 kg of 50% fenaminosulf wettable powder or 0.5 kg of 50% thiophanate-methyl wettable powder per 667 sq m to make medicated soil, apply it in the sowing furrow, then sow and cover with soil. ② In mid-to-early April, drench the plant base with a 3000-fold solution of 20% Saomanjing wettable powder or a 1/500-fold solution of 40% isocarbophos emulsifiable concentrate plus a 300-fold solution of 5% junshuqing aqueous solution or a 700-fold solution of 50% fenaminosulf wettable powder. Drenching the plant base must be done on a sunny or cloudy day when the soil is not waterlogged, and the surface soil must be loosened with a hoe before drenching; otherwise, the effect is poor and normal lily growth is affected. Apply 2-3 times, with an interval of 15-20 d each time. ③ Begin spraying for protection from lily emergence, applying once about every 15 d, for 6-7 consecutive times (including the applications in ②), alternating spraying and drenching. In addition to the pesticides in ②, also use a 700-fold solution of 50% mancozeb wettable powder and a 700-fold solution of 75% chlorothalonil wettable powder.