Key Technical Points for Integrated Pest and Disease Control of Flowers in Protected Cultivation
The large-scale development of protected cultivation has provided convenient conditions for year-round production of ornamental flowers. However, its special environment of high temperature and high humidity has also provided opportunities for the mass reproduction and spread of pests and diseases. The occurrence and development of flower pests and diseases in protected cultivation have their own characteristics, different from those in open fields. As an ornamental product, once a flower is infected by pests or diseases, its ornamental value is partially or entirely lost, causing relatively large economic losses. Adopting a single control method makes it difficult to achieve satisfactory results. Therefore, pest and disease control of flowers in protected cultivation must adhere to the principle of "prevention being more important than cure," give play to the effectiveness of integrated control, and keep pests and diseases below the level permitted by the ornamental value of the flowers. Based on sufficient investigation and combined with several years of production experience, this article discusses the occurrence patterns and integrated control countermeasures of the main infectious pests and diseases of flowers in protected cultivation, in order to provide a scientific basis for integrated pest and disease control in protected cultivation.
1 Main Pests and Diseases of Flowers in Protected Cultivation and Their Occurrence Conditions
1.1 Main Diseases and Their Occurrence Conditions
(1) Gray mold is the most common and most damaging fungal disease on flowers in protected cultivation. It occurs extremely easily under humid and low-temperature conditions. The symptoms are complex, including blight, canker, rot of organs such as corms, bulbs and seeds, and damping-off of seedlings. It often occurs at leaf tips and leaf margins. In the early stage of the disease, the diseased parts are mostly water-soaked spots, and in the later stage they are often covered with a gray mold layer. The host range is very broad, mainly damaging cyclamen, begonia, etc.
(2) Powdery mildew: It mostly damages leaves, branches, floral organs and tender shoots. In the early stage of the disease, a layer of powdery mildew grows on the diseased parts, and later turns gray. In the vigorous growth season, high temperature and rainy conditions, excessive nitrogen fertilizer, high planting density, insufficient light or poor ventilation are conducive to the occurrence of the disease. It mainly damages Chinese rose, cineraria, etc.
(3) Anthracnose: It mainly damages leaves and stems. When the leaves are first affected, the diseased parts are mostly round or oval reddish-brown small spots, which later expand into dark brown lesions. In the center of the lesions, small streaked black dots appear, and the edges are dark green. When the stems are affected, round or nearly round light brown lesions often appear. It is mainly caused by pots and flowers being placed too densely, leaves overlapping and infecting each other, and high temperature, stuffiness and poor ventilation. It mainly damages foliage plants such as orchids, jasmine, and Rohdea japonica.
(4) Leaf spot disease includes black spot, brown spot, ring spot, etc. It is caused by local infection, with local necrosis of leaves and the production of lesions or perforations of various colors and shapes. Various dots or mold layers grow on the lesions. It mostly occurs under conditions of low temperature and heavy fog, poor ventilation and light transmission, and extensive management. It mainly damages Chinese rose, clivia, camellia and foliage plants, etc.
(5) Mosaic virus disease is a worldwide disease, mainly damaging leaves and floral organs, etc. In the early stage of the disease, the leaves begin to lose green and gradually turn brown; diseased leaves become yellowed and distorted. It is mainly caused by virus carried in seed bulbs and seedlings. It mainly damages gladiolus, cyclamen, carnation, etc.
(6) Bacterial soft rot mostly occurs on succulent tissues, namely bulbs, corms and tubers. The diseased parts show tissue disintegration and exude foul-smelling liquid. An environment with high temperature, high humidity and excessive nitrogen fertilizer is conducive to its occurrence and prevalence. It mainly damages cyclamen, iris, clivia, etc.
1.2 Main Insect Pests and Their Occurrence Conditions
Aphids, whiteflies, red spiders and scale insects are the four major insect pests in protected cultivation.
(1) Aphids: Adults and nymphs gather on branch tips and the backs of tender leaves to pierce and suck sap. Affected leaves often curl, flower buds are difficult to open, and the honeydew they secrete can also easily lead to sooty mold and virus diseases. It occurs easily when the climate is dry and the temperature is suitable. It mainly damages lilies, cineraria, tulips, etc.
(2) Whitefly, also called small white moth, is one of the important pests damaging flowers. Adults or nymphs gather on the backs of young host leaves to pierce and suck sap. Affected leaves fade, turn yellow, wilt, and even die. In addition, the honeydew secreted by adults and larvae easily induces sooty mold and virus diseases. In greenhouses, it breeds and causes damage all year round. It mainly damages rhododendron, Chinese rose, jasmine, etc.
(3) Red spider mites mostly feed on the backs of leaves, damaging leaf tissue, often causing leaves to lose green and become spotted or blotchy, or curled and shrunken. In severe cases, all leaves wither and scorch as if roasted by fire. It occurs easily under high temperature and dry conditions. It mainly damages Chinese rose, rhododendron, etc.
(4) Scale insects have many species. Nymphs and female adults suck sap at branch tips and the midrib on the backs of leaves, easily causing leaves and branches to dry up. In addition to piercing and sucking sap and weakening growth vigor, they also induce sooty mold and cause damage all year round in greenhouses. They mainly damage Michelia figo, Pittosporum tobira, banyan trees, camellias, etc.
2 Integrated Control Techniques
2.1 Cultivating Strong, Disease-Free and Pest-Free Seedlings
Before sowing, strictly quarantine seeds, seedlings and seed bulbs, and promptly combine chemical disinfection treatment with warm water soaking to prevent the seed source from carrying pathogens. Do a good job in the environmental sanitation of the protected area, thoroughly remove residual plants, fallen leaves and weeds, and reduce pest and disease habitats. Strengthen seedling management. When planting or placing flowers and trees, the density should not be too high, and ventilation and hardening of seedlings should be carried out in time to control excessive growth of seedlings and improve the stress resistance of seedlings. Diseased plants should be pulled out at any time. Through the above methods, the number of harmful organism species can be reduced by about 50%.
2.2 Cultivation Control
(1) The nutrient soil for cultivation should be sun-dried before planting, or the soil should be treated with chemicals such as quintozene, to prevent it from carrying pathogens and insect eggs. At the same time, applying decomposed organic fertilizer is beneficial both for improving the antagonistic effect of microorganisms around the rhizosphere and for reducing the occurrence of wilt disease and damping-off.
(2) Crop rotation. Rotating the planting of different varieties of flowers can effectively reduce the occurrence of soil-borne diseases such as wilt disease, anthracnose and sclerotinia rot.
(3) High-ridge cultivation can use sprinkler irrigation for watering, and covering the paths with crop straw can reduce the relative humidity in the greenhouse and improve ventilation and light transmission performance, thereby reducing the probability of disease occurrence.
(4) Reasonable water and fertilizer management. According to the flower species and habits of different varieties, scientifically combine fertilization, regulate the growth vigor of flowers, strengthen the ability to resist pests and diseases, and promote vigorous growth of flowers. For watering time, it is best to make the water temperature close to the soil temperature. In spring and autumn, it should be chosen around 10 a.m. and after 3 p.m.; in summer, it should be in the morning or at dusk; in winter, it should be chosen around noon. This can also alleviate the relative humidity in the protected area and reduce the frequency of pest and disease occurrence.
(5) Choosing drip-free film or antifogging polyvinyl chloride film for greenhouse covering can reduce indoor relative humidity, increase light transmittance by 15%-20% compared with ordinary film, and improve heat preservation performance by 2-3°C, reducing the occurrence of pests and diseases.
2.3 Ecological Regulation and Control
Strengthen environmental regulation, ventilate and exchange air in time, improve the temperature and humidity conditions in the protected area, and keep flower leaves from forming condensation as much as possible. Generally, a temperature of 20-25°C and an air relative humidity of 60%-70% can ensure there are no water droplets. This can reduce the occurrence of diseases such as gray mold and downy mildew. Variable temperature management should be adopted in protected cultivation. Because the temperature in protected cultivation varies relatively greatly, strengthening regulation can prevent pathogens from successfully germinating and invading. High-temperature greenhouse sealing, with the temperature above 28°C, is unfavorable for sporulation of downy mildew, gray mold, etc.; further increase can kill the pathogens, and appropriate high temperature can also activate the defensive enzyme system in the body, thereby improving plant resistance. On sunny days at noon, when the greenhouse temperature reaches 35-40°C, sealing the greenhouse for 2 h has a certain inhibitory effect on downy mildew, gray mold, etc.
2.4 Biological Control
Where conditions permit, biological control methods should be actively adopted. Encarsia formosa is an endoparasitic wasp of whiteflies. When there are 1-2 whiteflies per plant on average in the greenhouse, release Encarsia formosa at 2800 insects/667 sq m, once every 7-10 days, for 2 consecutive times. The control effect can reach 80%-90%. Penicillium can also be used to control greenhouse whiteflies. When natural enemies such as hoverflies, lacewings and ladybugs are seen, protect them, which can effectively improve the effect of biological control.
2.5 Physical Control
Methods such as heat treatment can effectively control pests and diseases. For example, soaking gladiolus corms in hot water at 55°C for 30 min controls Fusarium dry rot and other diseases. The use of silver-gray reflective film can repel aphids. The principle of silver-white tin foil reflection can also be used to repel migrating aphids, or the yellow taxis of aphids and whiteflies can be used by setting yellow boards on one side of the greenhouse wall or 10-20 cm above the top of plants, or hanging yellow sticky strips at ventilation openings for trapping and killing, with excellent results.
2.6 Chemical Control
Chemical control of flower pests and diseases in protected cultivation should follow the principle of "prevention being more important than cure." For target pests and diseases, fungicides such as chlorothalonil, thiophanate-methyl and Yifan Junke and insecticides such as fenvalerate, dichlorvos and Manjieke should be sprayed alternately at regular intervals, generally 2-3 times per month. In protected cultivation, when the greenhouse is closed at dusk, smoke agents can also be used for fumigation and killing, which saves labor and trouble, is evenly dispersed, and overcomes defects such as uneven spraying. In winter greenhouses, disease prevention should be the main focus. A 20% chlorothalonil smoke agent can be used regularly, evenly ignited at 250 g per 667 sq m, and fumigated for sterilization, which can avoid large-scale occurrence of diseases. The following methods should be adopted for sudden pests and diseases:
2.6.1 Control of Main Diseases
(1) Gray mold, anthracnose and blight: In the early stage of the disease, use 75% chlorothalonil soluble powder at 600 times dilution or 70% thiophanate-methyl powder at 1500 times dilution for control.
(2) Powdery mildew: Use agricultural antibiotic 120 and 25% triadimefon at 2000 times dilution for 2-3 consecutive sprays. Since powdery mildew fungi are particularly sensitive to "sulfur," use 0.25 kg sulfur powder + 0.5 kg sawdust per 250-300 sq m, ignite and fumigate overnight, with good control effect.
(3) Bacterial soft rot: Continuously spray or irrigate with agricultural streptomycin 3-4 times, which can effectively prevent the occurrence of this disease.
(4) Mosaic virus disease: Do a good job in controlling aphids, scale insects, etc., and regularly spray virus inhibitor, which has a certain effect on controlling virus diseases.
(5) Leaf spot disease: Use 25% carbendazim wettable powder at 300-600 times dilution once every 10 days; or use 25% triadimefon wettable powder at 2000 times dilution once a month, with good effect.
2.6.2 Control of Main Insect Pests
(1) Aphids: Use 20% fenvalerate at 3000 times dilution or 2.5% deltamethrin at 5000 times dilution for control. A 22% dichlorvos smoke agent at 0.3 kg/667 sq m or 10% aphid-killing smoke agent can also be used for closed fumigation overnight. The method is simple and has a special effect on controlling aphids.
(2) Whiteflies: Use 10% imidacloprid (Yashijing) at 3000 times dilution for control. Use 25% buprofezin wettable powder at 1500 times dilution or 2.5% Uranus emulsifiable concentrate at 5000 times dilution in mixture. Chlorpyrifos has a special effect on controlling whiteflies. The agent should be sprayed in the morning or at dusk, for 2-3 consecutive treatments, which can both alleviate whitefly resistance to the pesticide and improve the control effect.
(3) Red spider mites and scale insects: On the basis of manual removal of infested branches and leaves, use 90% trichlorfon emulsifiable concentrate or 40% omethoate emulsifiable concentrate at 1000 times dilution, or 20% pyridaben emulsifiable concentrate at 3000-4000 times dilution, and add a small amount of washing powder to facilitate even spraying. Spray once every 7-10 days for 3-4 consecutive sprays. Dicofol at 1000 times dilution can also be used, with a control effect of more than 90%. In addition, fumigating with 10% Chongmanjing smoke agent at 250 g/667 sq m for 4-5 hours in protected cultivation has a certain control effect on whiteflies, red spider mites and scale insects.
3 Summary
The occurrence of the main pests and diseases of flowers in protected cultivation is closely related to the specific environmental conditions of high temperature and high humidity in protected cultivation. Pest and disease control work should follow the principle of "prevention being more important than cure," adopt measures based on cultivation prevention, strengthen ecological environmental regulation, actively adopt biological control, physical control and regular control with low-toxicity pesticides, and follow the principle of timely control according to different varieties of pests and diseases, so as to control the occurrence of pests and diseases, effectively improve the ornamental value of flowers, and thereby achieve high efficiency in flower production.