Symptoms and Control Methods of Common Pests and Diseases in Horticultural Plants

During cultivation, horticultural plants may encounter downy mildew, powdery mildew, viral diseases, tomato leafminer, melon aphids, and so on, which not only affect the beauty of horticultural plants but also affect the planting benefits of horticultural plants. Therefore, horticulturists should master the symptoms and control methods of common pests and diseases.

1. Common Pests and Diseases of Horticultural Plants

1.1 Downy Mildew

Generally, melons, fruits, and vegetables are susceptible to downy mildew. Downy mildew strikes swiftly and spreads extremely fast; once one vegetable is infected, other vegetables are easily infected as well. Downy mildew mainly infects and spreads through plant leaves. Generally, after a plant is infected with this disease, small light yellow spots appear on the leaves in the early stage. As time goes on, the spots gradually spread and become irregular in shape, and the color gradually changes from the initial green to yellow, and in severe cases becomes dark brown.

1.2 Powdery Mildew

Powdery mildew is a disease with a long duration and an uncertain onset time. Generally, powdery mildew can appear at any stage of melon, fruit, and vegetable production, and is most severe in the middle and late stages of vegetable production. Powdery mildew also occurs on the leaves of fruits and vegetables. Initially, irregular small spots form on the front or back of the leaves. As they gradually spread, white patches form and in severe cases cover the entire leaf. In plants infected with this disease, the leaf color changes from green to yellow in the early stage, and in the later stage many small brown spots appear, the leaves gradually die, and in severe cases this leads to reduced yield or even death of melons, fruits, and vegetables.

1.3 Viral Diseases

Viral diseases are also a type of disease that occurs on vegetables, melons, and fruits, but viral diseases are caused by multiple viruses occurring together. Melons, fruits, and vegetables infected with viral diseases initially grow slowly, and the yield of the plants is severely affected. Once melons, fruits, and vegetables are infected with this disease, the symptoms are mainly reflected in the mosaic pattern on the leaves, where green spots of varying colors appear on the leaves. As the infection progresses, the leaves gradually become smaller, turn yellow, and even wither, thereby causing the plant to wither and die.

1.4 Tomato Leafminer

The tomato leafminer is a pest that has an extremely serious impact on plant growth. In severe cases, damage by the tomato leafminer can lead to large-scale leaf death, thereby causing reduced yield or even death of the plant. The tomato leafminer is a small fly that burrows into plant leaves to cause damage during plant growth, and lurks on the plant until the larvae grow up, then pierces the leaves, sucks the leaf sap, and lays eggs on the leaves, thereby causing secondary damage to the plant. The tomato leafminer has an extremely strong reproductive capacity, so it can affect plants year-round, and the impact is even more serious during the rainy season.

1.5 Melon Aphid

The melon aphid, also known as the cotton aphid, is a relatively common and highly damaging type of pest in melons, fruits, and vegetables. Melon aphids basically occur in clusters on the back of leaves and on stems and leaves, using their needle-like small mouthparts to pierce into the stems and leaves and suck sap, causing leaf curling and even withering, and in severe cases leading to plant death. Melon aphids have a strong reproductive capacity, so they can reproduce one generation after another at intervals and spread extremely quickly. In northern regions, melon aphids overwinter on plants in the form of eggs, and when plants revive in spring, the pest also begins to reproduce. In the warm southern regions, however, melon aphids reproduce and damage plants all year round.

2. Effective Methods for Controlling Pests and Diseases in Horticultural Plants

2.1 Selecting and Breeding Excellent Varieties with Strong Resistance from a Genetic Perspective

At present, plants are genetically modified for hereditary variation by using new technologies and means such as sexual hybridization, artificial mutation, and bioengineering. Prevention should be carried out from the root so as to enhance the disease resistance of the variety. For example, the leaves of some trees contain resin components that can prevent pests. Even if pests hide eggs or larvae in the leaves of such plants, they will be blocked and killed by the resin components secreted by the plant. In addition, the trunks, leaves, and fruits of the chinaberry tree all contain toosendanin, so pests do not like to eat them. In some countries such as India, this component has been fully utilized to make insecticides.

2.2 Planting According to the Site and Reasonable Cultivation

Some plants like a dry environment, so placing them in a humid environment is not conducive to plant growth and makes them more susceptible to pest infestation. Conversely, placing moisture-loving plants in a dry environment also makes them susceptible to pest infestation. Therefore, first, reasonable planting and arrangement should be carried out according to the growth habits of the plants; second, reasonable crop rotation should be carried out: because plant pests and diseases all parasitize in shallow soil, growing the same species in one plot for a long time also provides a habitat and overwintering environment for pests and diseases. In addition, long-term cultivation of the same plants on one piece of land will also destroy the structure of the land and lead to a decline in soil fertility, which will also affect plant growth and promote the reproduction of pests and diseases. Reasonable crop rotation can change the soil texture and structure of the land, improve fertility, enhance plant growth, and leave pests and diseases without a suitable host, thereby reducing the occurrence of pests and diseases.

2.3 Focusing on the Reasonable Configuration of Fertilizers

Scientific tree planting should reasonably select inorganic fertilizers and organic fertilizers. Generally, livestock and poultry manure is used as organic fertilizer, which can improve the soil and ensure soil quality. If inorganic fertilizer is used for a long time, it will lead to a decline in soil quality. Therefore, while achieving a reasonable combination of organic fertilizer and inorganic fertilizer, trace elements should also be used. Because if flowers and trees lack trace elements, it will lead to deformation and discoloration of flowers, leaves, stems, and vines, which will reduce the ornamental value of flowers and trees.

2.4 Timely Garden Cleaning

When cultivating green plants, branches that are currently diseased and already diseased should be pruned in a timely manner, so that pests and diseases can be reduced from the root. In addition, pests like to lurk in dead leaves and weeds in parks, so dead branches and fallen leaves should be cleaned up in a timely manner to reduce the base number of pest and disease occurrence. Particular attention should be paid to garden cleaning work in winter, and weeds, dead branches, and fallen leaves should be thoroughly and comprehensively removed.

2.5 Protecting and Introducing Natural Enemies to Effectively Control Pests and Maintain Ecological Balance

Various pests have their own natural enemies, such as ladybugs and birds, which can be used for effective control. To eliminate pests, in addition to protecting the natural enemies of pests, large numbers of natural enemies of pests can also be introduced. In large nurseries, artificial breeding can be carried out, and the species can also be introduced. In some places, due to the abuse of pesticides, although pests were poisoned and killed, other species were correspondingly harmed as well. In contemporary society, people's awareness of animal protection is weak, and some people like to hit birds and take bird nests. These practices deal a fatal blow to the natural enemies of pests, so that pests reproduce in large numbers and destroy the ecological balance of nature.

In summary, in the control of pests and diseases in horticultural plants, biological methods should be given priority. To avoid the reproduction of pests, improvements can be made from the genetic variation of plants; or the natural law can be used to artificially breed natural enemies of pests for pest control, which not only saves costs but also protects the environment, achieving two goals at once.

Common Pests and Diseases of Horticultural Flowers and Their Control Techniques

   Many people in life like to grow flowers and plants to cultivate their temperament, and many people also plant flowers in large quantities to meet market demand. Although flowers are beautiful when they bloom, many problems are encountered during the planting process, which requires the careful care of flower-growing friends. The greatest harm to flower growth is pests and diseases! So how should flower pests and diseases be controlled? Cherry Meimei teaches you a few techniques for common pests and diseases of horticultural flowers and their control! 

   One: Common Diseases of Horticultural Flowers and Their Control Techniques  

   1. Damping-off  

   After flowers in the growth period are infected with damping-off, root rot will directly occur. In the early stage of infection, these flowers show brown patch-like substances on the roots, and the epidermis also withers. The most prominent manifestation in the late stage of infection is the withering and death of the entire flower plant. Some flowers infected with damping-off even show lignification of plant tissues. The water-locking function in the tissues is gradually lost, causing the flowers to be unable to obtain nutrients or water through normal channels, directly resulting in upright withering.  

   Control Methods:When plant care personnel carry out planting treatment for flowers, the first thing to do is to soak flower seeds that are easily infected in medicine. According to the weight of the seeds, mix in Ceresan at a ratio of 1:500 before sowing. At this time, staff should note that after this treatment step is completed, water must be supplemented for the plants that have completed the sowing step, to prevent death from lack of water due to untimely water supply.

   2. Powdery Mildew  

   The flower species easily infected with powdery mildew mainly include cineraria and fuchsia. In the early stage of infection with powdery mildew, the main condition of these flower varieties is that the leaf surface appears light gray. Usually, a layer of white flocculent material appears on the infected parts. When these white flocculent materials extend to the entire leaf surface, the newly grown branches and leaves of the flowers stop growing. Ultimately, the entire flower plant withers, and the conditions allowing powdery mildew to spread widely are a stuffy, hot, and poorly ventilated environment.  

   Control Methods:In response to the causes of powdery mildew, staff need to create a dry and ventilated environment for flower growth during the flower planting process to meet the growth needs of the flowers. Some chemical control methods can be used. The use of phosphorus and potassium fertilizers can improve the disease resistance of flowers and enhance their immunity. If the flowers have already been infected with powdery mildew at this time, care personnel need to remove the infected stems and leaves to prevent the spread of the pathogen. Treating the pathogen-infected parts at the source can prevent the disease from threatening the life and health of the entire flower plant.  

   3. Black Mold  

   After flowers are infected with black mold, brown mold spots generally form on the leaves. As the degree of infection deepens, black mold layers gradually form, which to a large extent affects leaf photosynthesis and also greatly affects the ornamental appeal of the flowers, and may even cause flower death.  

   Control Methods: The control of flower black mold is generally carried out during indoor flower cultivation. For example, the light transmittance and ventilation of the indoor environment can be improved, and indoor temperature and humidity can be well controlled. In addition, Bordeaux mixture can be sprayed on already infected plants.

   Two: Common Insect Pests of Horticultural Flowers and Their Control Techniques  

   1. Aphids  

   Aphids, also called honey bugs, are a very common type of pest during flower cultivation. Generally speaking, aphid species include chrysanthemum aphids, rose long-tube aphids, peach powder aphids, and so on. Aphids have strong reproductive capacity and often gather on the back of flower leaves, inside tender buds, and in flower buds. Aphid damage causes flower leaves to dry up, and in severe cases causes flower death.  

   Control Methods: Agents such as derris extract or pyrethrum can be selected for spraying control, or a 1:1000 laundry detergent aqueous solution can be selected for spraying. In particular, the enzyme components in enzyme-added laundry detergent can cause great damage to the epidermal tissue of aphids, thereby achieving a very good killing effect. Generally speaking, the spraying cycle is 1 week.  

   2. Red Spider Mites  

   Red spider mites are also one of the common insect pests of flowers. Compared with aphids, red spider mites can harm many flowers, such as Chinese roses, jasmine, salvia, and rhododendrons. Generally speaking, summer is the stage with the highest damage rate from red spider mites. This type of pest often spins webs on the back of leaves and then uses their piercing-sucking mouthparts to suck the sap and nutrients of the plant. Flowers damaged by red spider mites grow abnormally slowly, and in severe cases even wither and die.  

   Control Methods:Select a 1500-fold dilution of dimethoate or an 800-fold dilution of 25% chlordimeform for mist spraying, and the spraying cycle is generally half a month. It should be noted that indoor ventilation must be ensured for a period of time after spraying.  

   In summary, for the control of common pests and diseases of horticultural flowers, first, control methods should be selected in a targeted manner, and control work should be carried out according to the type of agent and the type of pest or disease infection; second, the occurrence patterns of different pest and disease problems should be accurately grasped, the best control period should be selected, and the occurrence time and patterns of various common pest and disease problems should be deeply analyzed, so that the best entry point for control can be found; third, the dosage of agents should be well mastered, the sensitivity of flowers to drugs should be accurately understood, and differentiated spraying should be implemented for different types of flowers; finally, chemical agents should be used scientifically, and the types of agents should be changed regularly to prevent the development of drug resistance.

Common Plant Pests and Diseases - Control of Blight

    Blight is a soil-borne disease in horticulture, with about 224 genera and 301
species of hosts, mainly including citrus, passion fruit, roselle, guava fruit, eggplant, lily, carnation family flowers, Araceae family flowers, and other foliage plants.
    Symptoms: Because blight occurs in different parts and produces different symptoms, it can be divided into black
rot, heart rot, stem rot, damping-off, and so on. The most common symptom of black rot is that the affected part is initially
water-soaked, but later the tissue becomes black-rotted, appearing dark brown or blackish brown. Blight infection mostly starts from the middle section or side end of the leaf
blade, and some starts first from the leaf base or leaf tip. At first, the leaf color fades green or
becomes water-soaked, then gradually expands into light brown or blackish brown, until the plant dries up and dies. Some
cases involve comprehensive damage to roots, stems, leaves, and flowers. In the early stage of damage, the leaf color does not change, and the affected parts
look as if they have been bruised, wet, and dark green, and after drying turn black. Parts not directly affected
wither and turn black because the vascular tissue is destroyed.
    Disease Conditions: Blight is prone to occur under conditions such as excessive temperature, excessive watering, poor ventilation, insufficient sunlight, and poor soil
aeration. Applying undecomposed organic fertilizer carrying diseased residues
and excessive application of nitrogen fertilizer, especially excessive application of quick-acting nitrogen fertilizer, results in severe disease. Feeding and transmission by insects such as snails and slugs
can also cause severe epidemics of blight. Using unsterilized knives and scissors for pruning, etc., also easily
causes cross-infection. June to August each year is the peak period for blight occurrence. Blight spreads through
wind, rain, watering, and unsterilized tools, forming repeated infection. In years with more rainfall
and high humidity, the disease is severe.
    Control Methods: To control blight, choose a well-ventilated and well-lit place to maintain flowers;
avoid excessive application of nitrogen fertilizer, and apply more low-nitrogen, high-potassium organic matter to enhance plant disease resistance; once
an infected plant is found, immediately remove the diseased tissue, apply thiophanate-methyl or
carbendazim to the wound for disinfection, and isolate the diseased plant. When watering, avoid spraying water from top to bottom, so as to avoid the expansion of
the disease. If the damage is severe, remove the entire plant; wash hands before daily operations, and strictly disinfect operating tools such as scissors;
for chemical control, 25% metalaxyl wettable powder, 40% thiram
wettable powder 500-800 times solution, 70% dexon 400 times solution, 70% mancozeb
600-800 times solution, 70% thiophanate-methyl 1500-2000 times solution, etc. can be sprayed,
once every 7-10 days, for 3-4 consecutive treatments.