Chrysanthemum

Author: Guo Zhigang et al. / Country:
Publisher:
Publishing Date: 2001-01-01
Features: Sclerotinia disease not only affects chrysanthemums but also occurs on other crops. Therefore, it is necessary to avoid establishing production bases in affected areas. Once the disease occurs, immediately pull it out and burn it outside the cultivation area. The main prevention methods include soil disinfection with phosphine. Alternatively, from the early stage of occurrence, disperse a 500-fold solution of Topsin M water-based agent or a 1000-fold solution of iprodione water-based agent. It can also be sprayed with a 1000~2000-fold solution of chlorothalonil (Aliette) for control. (4) Black Rust Black rust is a chrysanthemum disease discovered in recent years. At first, pale yellow spots appear, which soon expand into dark brown spots. ater, the spots rupture and release dark brown powdery spores, which adhere to other leaves and continue the infection. The onset period of black rust is basically the same as that of white rust, but in warm regions, it still occurs from mid-October to late autumn. Its control methods are basically the same as those for white rust. (5) Black Spot and Brown Spot Black spot and brown spot are more likely to occur during outdoor cultivation. They rarely occur during facility cultivation. From a symptomatic perspective, the two are basically the same. At first, small black-brown spots appear, which soon become round or elliptical spots. In severe cases, the plant's leaves gradually wither from the bottom up. The onset period of black spot and brown spot is from mid-July to mid-August. The prevention method is to disperse a fungicide every 7 days after planting until the flowers are harvested. The main fungicides sprayed include an 800-fold solution of captan water-based agent, an 800-fold solution of mancozeb water-based agent, a 500-fold solution of maneb water-based agent, or a 2000-fold solution of carbendazim (benomyl) water-based agent, etc. (6) Gray Mold Gray mold primarily occurs on inflorescences. At first, the petals become semi-transparent brown, and then gray mycelia develop. The control method for gray mold is basically the same as that for sclerotinia disease. However, gray mold fungi are more prone to resistance, so 1000-fold solutions of iprodione water-based agent and 1000-fold captan can be alternately used. (7) Stem Rot Stem rot starts from the edges of the leaves, turning black-brown, and then spreads from the petiole to the stem. When it occurs at the lower part of the stem, the adjacent roots also turn black-brown and rot. It is easily contracted during continuous rainy and cloudy weather, and it can still occur in October and November. The optimal temperature for disease development is 15~25°C, and high humidity is the main environmental factor for disease occurrence. The control method mainly starts from the seedling stage, removing diseased leaves during planting. Since the symptoms spread from the leaves to the stem nodes, removing diseased leaves as soon as possible can prevent the nodes from being infected. It is also necessary to prevent excessive humidity in facilities and ensure proper ventilation. During infection, disperse a 500-fold solution of maneb water-based agent or a 1000-fold solution of carbendazim water-based agent. (8) Wrinkled Leaf Disease Wrinkled leaf disease is caused by spider mites infesting near the buds. It occurs all year round. The leaves first show yellow wrinkles, which are easily mistaken for viral or physiological diseases caused by a lack of trace elements. The main control method is to avoid taking cuttings from infected mother plants. During pinching, the removed leaf buds should be sent outdoors for deep burial. In the early stages of infection, a 500-fold solution of maneb water-based agent or a 2000-fold solution of Keltan EC can be dispersed on cuttage beds or cultivation areas. (9) Chronic Poor Growth Chronic poor growth appears superficially as a physiological disorder but is actually induced by Rhizoctonia. This is a common soil-borne disease. It mainly manifests as the plant failing to grow after planting, reduced branching, uneven growth, and easy wilting of lower leaves. Additionally, fine roots in the soil rot, and the plant wilts on sunny days. During outdoor cultivation, it suddenly wilts and collapses after heavy rains. It almost always occurs in facility cultivation. The main control method is integrated management, which includes improving soil conditions, adjusting soil pH, using large amounts of organic fertilizer, soil disinfection, and selecting disease-free seedlings or soil replacement and rotation for prevention. (10) Acute Wilting Acute wilting is a physiological soil-borne disease and is also related to the occurrence of root-knot nematodes. It generally manifests as chronic poor growth, with sudden wilting after heavy rains or symptoms of damping-off. After the roots rot, the plant is easily pulled out of the soil, and the xylem often changes color. It is more likely to occur during outdoor cultivation but rarely during facility cultivation. The control method is basically the same as that for chronic poor growth. Additionally, deep plowing and the installation of underground drainage pipes can be used for control. (11) Virus Disease Chrysanthemums are perennial plants, and after several years of cultivation, they are easily infected with chrysanthemum stunt virus (CVB) and chrysanthemum mottle virus (CMMV). According to surveys, the infection rate of seedlings in the current year is 0%, 10% after 2 years, 25% after 3~4 years, 30% after 5~9 years, and over 75% after 10~21 years. Since chrysanthemums are propagated asexually through vegetative parts, it is inevitable to infect viruses when selecting mother plants and taking cuttings for propagation. Plants infected with viruses show dwarf growth, fine spots on leaves, and are affected in terms of flower stem weight, stem length, and flower diameter. Currently, stem tip culture or heat treatment followed by stem tip virus-free culture is the main solution.
6.2 Pests (1) Aphids Aphids are one of the most frequent pests of chrysanthemums. Controlling them with chemicals is relatively simple. However, if control is not timely, once aphids invade the inflorescences, it becomes very difficult to treat. Additionally, it is necessary to prevent re-infestation after harvesting. Before planting, 4 kg of phorate or 3 kg of fonofos can be spread per mu on the cultivation bed. During facility cultivation, fumigation with DDVP (a mixture of dichlorvos and ethyl dimethoate) is better. During fumigation, attention must be paid to the health and safety of the operator. In the early stages of occurrence, disperse a 1000-fold solution of methyl phosphine, a 1000-fold solution of DDVP, a 1000-fold solution of dimethoate, or a 1000-fold solution of malathion and a 1000-fold solution of fenitrothion for control. (2) Spider Mites There are various types, such as false red spider mites and red spider mites, which are easily found in both outdoor and facility cultivation. Control is relatively difficult. Like aphids, if the cut flowers carry eggs during harvesting, they are easily re-infested even after being sold to consumers. Therefore, it is unfavorable for both producers and consumers. Generally, DDVP fumigation is used in the early stages of occurrence. However, attention must be paid to human health when using it.