What are the control methods for root rot in flowering plants?
Root rot in flowering plants often occurs on varieties such as wax begonia, African impatiens, and petunia. Since root rot often occurs in summer, preventive work for flowers needs to be done before early summer. The editor will introduce to you the causes and control methods of flower root rot.
Wax begonia
I. Causes
The pathogens that cause root rot mainly include Pythium, Phytophthora, Rhizoctonia, and Thielaviopsis basicola, among others. These pathogens can infect the roots of plants and cause the roots to rot. When 10% of the roots are rotted, the aboveground part can still appear healthy, but at this time if the environmental conditions are not improved, the rot will spread further; when the rotted roots reach 20% to 30%, the aboveground part begins to show symptoms, such as chlorosis (similar to nutrient deficiency), leaf drop, or leaf necrosis; when the infection spreads to the top of the plant, the plant will die quickly.
II. Control methods
1. Avoid excessive moisture in the substrate, maintain a well-drained environment in the substrate, and disinfect the medium and cultivation environment.
2. Carry out chemical control. Spray Yongning or Shaduvet (oxadixyl + mancozeb) at 600 to 800 times dilution, drench roots at 1000 times dilution; Suzhining (metalaxyl + mancozeb) at 600 to 800 times dilution for spraying, 800 to 1000 times dilution for root drenching; Minjia (fosetyl-aluminum) at 600 times dilution for spraying, 200 to 500 times dilution for root drenching; Previcur (propamocarb) at 800 to 1000 times dilution for spraying, 1000 times dilution for root drenching.
The above several chemicals all have protective and therapeutic effects and can be used before onset or in the early stage of the disease, with regular application every 7 to 10 days; root drenching gives better results.
Control methods for root rot in succulents
It really is true that "for pests there is root mealybug, for diseases there is Fusarium oxysporum." The ability of "black rot" to cause panic is no less than that of "root mealybug," right? Master succulent growers abroad sent samples of diseased plants for testing, and among the results one fungus was mentioned: Fusarium oxysporum.Fusarium oxysporum (F. oxysporum) is a soil-borne pathogenic fungus with a worldwide distribution and a wide host range. It can cause wilt disease in more than 100 species of plants, including cucurbits, Solanaceae, banana, cotton, legumes, and flowers. Fusarium oxysporum belongs to the Imperfecti fungi, Moniliales, Tuberculariaceae, Fusarium. Cultured on PDA plates, the colony is raised and floccose, with white and dense mycelium. The colony is pinkish white, light pink to flesh-colored, slightly purplish, and appears powdery due to the production of large numbers of spores. The colony height is 3-5 mm. Microconidia are borne on single phialides, often gathering into balls at the tips of the phialides, single-celled, oval; macroconidia are sickle-shaped, slightly curved, mostly with 3 septa. Chlamydospores are apical or terminal, spherical. The Fusarium wilt pathogen can produce three types of spores under natural or artificial culture conditions: microconidia, macroconidia, and chlamydospores. Microconidia are colorless, single-celled, oval, kidney-shaped, etc., borne on long false heads, 5-12 um x 2-3.5 um in size. Macroconidia are colorless, multicellular, sickle-shaped, slightly curved, with slightly pointed cells at both ends, 19.6-39.4 um x 3.5-5.0 um in size. Chlamydospores are pale yellow, nearly spherical, with smooth surfaces and thick walls, intercalary or terminal, single or in chains, and highly resistant to adverse environments.
Fusarium wilt
Fusarium wilt is one of the important diseases of ornamental flowers and can infect many flowers such as lilies, Cymbidium orchids, Phalaenopsis orchids, cyclamen, poinsettia, gerbera, chrysanthemum, lisianthus, and carnation. Once a plant is infected, if control measures are not taken in time, the disease will spread rapidly. Fusarium often causes plants to show multiple disease symptoms such as root rot, stem rot, stem base rot, and flower rot, and the host plants infected number more than 100 species. Fusarium often infects the vascular bundle system of host plants, destroys the plant's conductive tissues, and produces toxins during the plant's growth, development, and metabolism to harm the crop, causing plant wilting and death and affecting yield and quality. This disease is currently one of the important diseases that are relatively difficult to control in ornamental flower production.
Fusarium wilt is one of the important diseases of ornamental flowers and can infect many flowers such as lilies, Cymbidium orchids, Phalaenopsis orchids, cyclamen, poinsettia, gerbera, chrysanthemum, lisianthus, and carnation. Once a plant is infected, if control measures are not taken in time, the disease will spread rapidly. Fusarium often causes plants to show multiple disease symptoms such as root rot, stem rot, stem base rot, and flower rot, and the host plants infected number more than 100 species. Fusarium often infects the vascular bundle system of host plants, destroys the plant's conductive tissues, and produces toxins during the plant's growth, development, and metabolism to harm the crop, causing plant wilting and death and affecting yield and quality. This disease is currently one of the important diseases that are relatively difficult to control in ornamental flower production.
Symptom identification
Different ornamental flowers show different symptoms after being infected by Fusarium. For example, after annual and biennial herbaceous flowers and cut flowers are infected, the lower leaves first lose green color and turn yellow. Sometimes when one side of the plant or half of an individual leaf is infected, one side of the branches and leaves or half of the leaf clearly wilts and loses luster; then the symptoms spread upward, and the upper leaves also begin to wilt and droop, turning brown; at this time the lower leaves begin to fall off and shrink, and finally the whole plant yellows and wilts. When the plant first shows symptoms, it appears normal in the morning and evening but wilts at noon, resembling water deficiency. Careful observation of the stem base shows that the epidermis becomes rough, occasionally with cracks, and when humidity is high, white mold-like material can be seen, sometimes pink. For some high-grade potted flowers, such as Phalaenopsis orchids, Cymbidium orchids, and anthurium, after infection by Fusarium, in addition to leaf yellowing, red-purple discoloration, and falling off, water-soaked lesions can also be seen at the stem base, gradually turning black; after the lesions dry up, the stem base of the plant becomes constricted. Another obvious feature of plants infected by Fusarium is that when the stem base is cut transversely or longitudinally, brown or dark brown ring discoloration of the vascular bundles can be seen. The wilt symptoms caused by Fusarium develop most rapidly and severely during high summer temperatures.
Pathogen
The pathogen of wilt disease is Fusarium oxysporum (Fusarium spp.), belonging to the Deuteromycotina fungi. It is a pathogen that specifically causes vascular bundle diseases in ornamental plants; it is also a type of fungus with a worldwide distribution, extremely widespread, commonly present in soil and on animal and plant organic matter, and even existing in the severe cold Arctic and arid hot deserts, living as a facultative parasite or saprophyte. It can not only overwinter and oversummer in the soil, but also show different specialized forms on different ornamental plants.
The pathogen generally produces sporodochia. There are two types of conidia, namely macroconidia and microconidia. Macroconidia are relatively stout, scattered on aerial mycelium or borne on sporodochia, in slime masses, and in slime layers. Macroconidia have diverse shapes, slightly curved, including sickle-shaped, orange-segment-shaped, spindle-shaped, club-shaped, etc., with slightly pointed tips and relatively thin spore walls. The number of septa in macroconidia is mostly 3 to 10, and some have more septa. The septa also differ; some are obvious, while others are not obvious. Spores produced on sporodochia are more typical and stable in morphology than those on aerial mycelium. Microconidia are smaller, mostly single-celled, a few with 1 to 3 septa, and include oval, kidney-shaped to oblong forms.
When the environment is unfavorable, dying plant tissues and diseased residues in the soil can produce large numbers of chlamydospores, which are a smaller, round, thick-walled spore.
Disease patterns and transmission routes
The pathogen of Fusarium wilt overwinters as mycelium or chlamydospores in soil, cultivation substrate, or attached to seeds, and can live saprophytically. The rotting parts of diseased plant roots or stems produce fruiting bodies in humid environments. Spores spread by airflow, rain, and splashing irrigation water, and invade through young roots and the stem base or wounds on cuttings. The pathogen may sometimes reside in the vascular bundle system without showing symptoms, and sometimes after entering the vascular bundle system it can immediately block the vessels and produce toxic substances that spread and gradually extend upward, causing the diseased plant's leaves to wither and yellow and then die.
Research on the spread of the pathogen within the host shows that before symptoms appear, the spread of the pathogen within the vascular bundles is relatively slow, but when some propagation material is obtained from diseased plants, there may be hidden Fusarium pathogens. Therefore, propagation material is an important source of Fusarium wilt transmission, and contaminated soil or substrate is also one of the sources of disease transmission.
The most suitable temperature for the occurrence of Fusarium wilt is 27°C to 32°C. At 20°C the disease tends to ease, and below 15°C it no longer occurs. Ornamental plants with older seedling age are more susceptible to the disease than those with younger seedling age. In spring and summer, if the cultivation substrate temperature is relatively high and moist, and there is more root damage during repotting, transplanting, or intertillage, and the plant growth vigor is weak, then the disease is more severe. Excessive application of nitrogen fertilizer in cultivation, as well as acidic soil, also favors the growth and infection of the pathogen and promotes the occurrence and prevalence of the disease. In South China, wilt often occurs from April to June, while in Yunnan, Sichuan, and East China, wilt often occurs from May to August. [PS: Exactly... dozens of my Splendid plants were hit recently and passed away...]
Control methods for the early stage and late stage of disease onset
1. Select excellent disease-resistant varieties suitable for intensive cultivation.
2. Cut flowers and annual and biennial herbaceous flowers should be cultivated in rotation to prevent pathogen accumulation caused by continuous cropping.
3. Disinfect soil and cultivation substrate; during cultivation, diseased plants should be removed and destroyed promptly to reduce further spread of the pathogen.
4. Properly control plant cultivation density, strengthen ventilation and air permeability, reduce humidity, and control the water content of the soil or substrate; it is advisable to choose a well-drained substrate.
5. Chemical control: Amistar at 3000 to 5000 times dilution or Medallion at 4000 to 5000 times dilution, or thiabendazole or carbendazim at 500 to 600 times dilution can be used to treat the root system and stem base before planting cuttings. After planting, transplanting, or repotting, use Amistar at 3000 to 5000 times dilution or Medallion at 4000 to 5000 times dilution for one root drenching treatment. In the middle and late stages of vegetative growth, use Amistar at 3000 to 5000 times dilution and Medallion at 4000 to 5000 times dilution alternately for root drenching 2 to 3 times every 14 to 21 days, which can effectively control the harm of Fusarium wilt.
Note: Medallion is a contact protective fungicide. Its mode of action is to inhibit the transfer related to glucose phosphorylation, thereby inhibiting the growth of the pathogen's mycelium and ultimately causing the pathogen to die.
Control of root rot in flower seedlings
A variety of pathogens can cause root rot in flower crops, causing serious losses to flower production. These pathogens can cause flower seedlings in the medium to die before or after emergence, or cause chronic or acute root rot in mature plants. Unlike rust fungi and Botrytis, which have specific hosts, these root rot pathogens usually can infect a very wide range of plant species.
In greenhouse flower production, root rot is mainly caused by four types of fungi and some bacteria. These are Pythium, Phytophthora, Rhizoctonia, Thielaviopsis, and the bacterial genus Erwinia, among others. The agricultural control and chemical control methods differ for different pathogens, so determining which fungus is causing the damage is crucial.
1. Pythium
It is widely present in soil that has not been sterilized and may also exist in washed fine sand and certain peat media. Pythium is closely related to water because the zoospores it produces must spread or swim through water. Although these pathogens are not considered very strong competitors compared with other pathogens in the soil, they can survive in the soil for many years through spherical, thick-walled resting spores (oospores). These oospores are also usually present in diseased tissues, and examining these oospores can be used to identify the pathogen.
Root rot caused by Pythium usually occurs in cultivation containers with high water content and poor drainage and under unsuitable temperature conditions. Excessive application of nitrogen fertilizer can cause the pathogen to reproduce and grow rapidly. Plants affected by Pythium root rot often show stunted growth and even wilting. Leaves appear dull, even yellow, resembling nitrogen deficiency. After Pythium root rot occurs, almost all crops show discoloration symptoms, usually starting from small lateral roots or root tips, with the root system producing light brown damage, causing the outer layer of the roots to begin rotting, leaving only the very thin inner pith of the roots. With further development, the root system becomes dark brown even black, and saturated with water. If the root system is gently washed, the rotted diseased roots are easily washed away.
Pythium can also be found in soilless media. Soil sterilized by heating and soilless media can both easily become infected with Pythium.
The main transmission routes are:
Use of unclean tools, flower pots, etc.; people or pets walking on mixed media; dumping mixed media on the ground of planting beds or potting areas that have not been thoroughly cleaned; certain flying insects can also cause the spread of Pythium between greenhouses.
When soil is being disinfected, if the disinfection time is too long or the temperature is too high, then once such soil is infected with Pythium, it will cause more serious root rot because at this time Pythium has almost no "natural enemies."
Once the roots begin to rot, Pythium is very difficult to control, so prevention must be the main approach. The measure is to first heat the soil to 82°C and maintain that temperature for 30 minutes; too long a time or too high a temperature will also kill beneficial organisms in the substrate. Then cover and store the disinfected soil and prevent it from contacting undisinfected soil and becoming infected. Special attention should also be paid to this point in the storage of commercial soilless media.
If pond water or flowing water is used for irrigation, note that the water intake pipe should not be placed too deep, to prevent underwater sediment from being drawn into the pipe. If the irrigation water is contaminated with Pythium, the water should be disinfected before use. The reservoir of an ebb-and-flow irrigation system should be covered to prevent plant debris from entering. In addition, the return water should be filtered to remove soil and plant debris in the water, so as to protect the reservoir from Pythium contamination.
Disinfect seedbeds, potting benches, tools, and utensils that may come into contact with the growing substrate. Also regularly carry out comprehensive and thorough disinfection of the reservoir of the ebb-and-flow irrigation system. For greenhouses with a history of Pythium, the greenhouse should be disinfected as early as possible at the beginning of cultivation. Biological agents can be added to the growing substrate before, during, or after transplanting, and can even be used directly to treat plug seedlings before transplanting. However, do not use chemical insecticides within ten days before or after using biological sterilizing agents.
To achieve the ideal control effect, it may be necessary to use biological agents and fungicidal agents multiple times. Some Pythium species may also develop resistance. When the effect of some chemical insecticides is poor, other products can be used instead.
2. Phytophthora
Phytophthora is also widely present in soil that has not been sterilized, and may also exist in washed fine sand and certain peat media. It is an amphibious fungus, facultatively parasitic or saprophytic, and the vast majority are facultatively parasitic. High-humidity environments favor the growth and reproduction of Phytophthora, and its sporangia and zoospores can spread through wind, rain, infected seedlings, soil, and irrigation water. After the pathogen invades the host plant, it can produce large numbers of sporangia and release zoospores for further secondary infection. Under suitable temperature and humidity conditions, the number of pathogens rises rapidly, causing disease prevalence in a very short time. Root rot caused by Phytophthora also usually occurs under conditions of high water content and poor drainage.
3. Rhizoctonia
Most potted flowers are susceptible to infection by Rhizoctonia and develop root rot. This pathogen is widely present in soil that has not been steam-sterilized or chemically fumigated. This pathogen is easy to identify under a microscope because its hyphae branch at typical right angles. Although it cannot produce airborne spores or zoospores, Rhizoctonia can produce a hard resting structure called sclerotia, which can survive in plant residues or soil for many years.
Rhizoctonia is easily spread from one place to another through flower pots or other equipment and tools. Rhizoctonia can damage the root system, rhizomes, and even the aboveground parts. Initially, the development of diseased roots is discontinuous, producing light brown to dark brown lesions. As the disease develops, the lesions join together, causing the root system to rot and die. Unlike root rot caused by Pythium and Phytophthora, Rhizoctonia root rot does not show the characteristic of rotted roots saturated with water. After the root system is infected, the pathogen will further infect upward, causing rhizome rot or stem rot, and longitudinal cracks often form in the diseased tissue.