Where do plant pests and diseases overwinter? A detailed introduction to overwintering sites

Many flower growers think that winter is a relatively safe season as far as pests and diseases are concerned. In fact, the overwintering sites of garden plant pests and diseases are relatively fixed and concentrated, and winter is also a key period for their prevention and control. The editor will now introduce the overwintering sites of pests and diseases in winter.

Cineraria (detailed introduction)

1. Seedlings and other propagation materials. Diseased seeds, seedlings, corms, bulbs, tuberous roots, scions and other propagation materials are the main sources of primary infection by pathogens such as fungi and viruses. Pathogens can attach to the surface of these materials or lie dormant inside them to overwinter, such as zinnia black spot, cineraria virus disease, and geranium mosaic virus disease. Diseased propagation materials often become the center of disease outbreaks in green spaces and flower nurseries, and during the growing season the disease spreads and expands through re-contamination, sometimes even causing an epidemic.

2. Soil. Soil is an important source of infection for soil-borne diseases or root diseases. Pathogens lie dormant in the soil to overwinter; some can survive for several years, such as chlamydospores, sclerotia, and rhizomorphs. Soil-inhabiting fungi have strong saprophytic ability and can survive on host residues, and can also live saprophytically directly in the soil. The Pythium and Rhizoctonia species that cause seedling damping-off can survive in the soil saprophytically for a long time. If fertilizer is mixed with un-decomposed diseased plant residues, it often becomes a source of infection.

3. Diseased plant residues. Pathogens can overwinter on dead branches, fallen leaves and fallen fruit, and infect the host the following year.

4. Diseased plants. The presence of diseased plants is also one of the sources of primary infection. Once perennial plants are infected, the pathogens can remain inside the host body; for example, branch and trunk rust, canker, and rot can overwinter in the host as vegetative or reproductive bodies. Because of the particular living conditions of greenhouse flowers, their diseases are often the source of infection for outdoor flowers, such as virus diseases and powdery mildew of many flowers.

Prevention and control of plant pests and diseases in winter

  Dead branches and fallen leaves and weeds should be cleared away; diseased and pest-infested branches and overlapping branches should be pruned out. This can directly eliminate a large number of overwintering pests and pathogens, improve the ventilation and light conditions of the plants, and strengthen the trees' vigor for the coming year; insect cocoons, egg masses, and larval nests should be removed by hand, and overwintering scale insects scraped off; the soil should be turned over and exposed to the sun to reduce overwintering pests and diseases in the soil; at the same time, control of trunk-boring pests should be carried out promptly.

  Trunk whitewashing should be carried out after leaf fall and before the soil freezes (December). This can not only kill pests and diseases overwintering on the trunk, but also effectively reduce frost damage. The whitewash material is quicklime, sulfur (or lime-sulfur mixture), water and salt; the whitewashing height is 1.1 m.

  In winter, attention should also be paid to frost protection. Frost damage occurs because a sharp drop in temperature causes non-lipid gaps with greater permeability to appear in the plant's protoplasmic membrane, and the leakage of cell contents leads to cell death. The tender shoots that grow in early winter can be pruned off to promote lignification of the branches and accumulation of nutrients, improving cold resistance; nitrogen fertilizer should be stopped for trees, and some phosphorus and potassium fertilizer can be applied appropriately; antifreeze agents can be sprayed to enhance the plants' frost resistance and reduce the mechanical damage to the membrane system caused by the formation of ice crystals in the protoplasm at low temperatures; mounding soil around the root collar can prevent frost injury to the root collar and roots, and can also reduce evaporation of soil moisture; for valuable cold-sensitive tree species, a windbreak can also be set up on the windward side of the trees. 

Characteristics of the occurrence of pests and diseases of urban garden plants and their control strategies

With the rapid development of urban landscaping construction, a large number of flowers, grasses and trees have been planted in every corner of the city, adding beautiful landscape effects to the city. However, during the growth and development of these flowers, grasses and trees, they are often attacked by various pests and diseases, which makes them lose their ornamental value and landscaping effect, and can even cause the death of the whole plant, causing large areas of urban landscaping tree species, scenic forests and other forest trees to decline or die, thus causing major economic losses. In view of the problems currently faced by garden plants, this article proposes a number of comprehensive control strategies such as strict quarantine, strengthened management, cultivation-based prevention, natural enemy control, biological control, manual control, physical control, chemical control, and improved pesticide application techniques, for reference by peers in the industry.

The prevention and control of garden plant pests and diseases is based on plant pathology and general entomology, and is a science whose main content is the study of the occurrence of garden plant pests and diseases. Taking garden plants as its object, it is the science that studies the diagnosis, identification, occurrence patterns, investigation and forecasting, and integrated control theories and techniques of garden plant pests and diseases. With the increasing improvement of the economy and living standards, landscaping is also becoming increasingly important in people's lives. However, during the growth and development of these flowers, grasses and trees, they are often attacked by various pests and diseases, which makes them lose their ornamental value and landscaping effect, and can even cause the death of the whole plant, causing large areas of urban landscaping tree species, scenic forests and other forest trees to decline or die, thus causing major economic losses.

1 The importance of prevention and control of garden plant pests and diseases

Landscaping is an important part of urban modernization. People use abundant flower resources to green and beautify the environment. These garden plants can not only create a beautiful environment suitable for human life, but also achieve relatively good economic benefits. However, during the growth and development of these flowers, grasses and trees, they are often attacked by various natural disasters, and garden plant pests and diseases are an extremely common natural disaster. Under normal circumstances, diseases and insect pests often cause poor growth of flowers, grasses and trees, with necrotic spots appearing on leaves, flowers, fruits, stems and roots, or deformities, wilting, rot, incomplete morphology, leaf fall and root rot, reducing the quality of the flowers and trees, making them lose their ornamental value and landscaping effect, and even causing the death of the whole plant. Some pests and diseases can cause certain flower varieties to degenerate year by year until they are completely destroyed, or cause large areas of urban landscaping tree species, scenic forests and forest trees to decline or die, thus causing major economic losses. With the development of urban modernization and the improvement of material and cultural levels, people's demand for ornamental plants has increased sharply, and coupled with the increasingly depleted existing forest resources, the shortage of flower resources and forest resources is deeply felt. Therefore, while striving to expand national garden plant and forest resources, China and many other countries have formulated specific regulations and measures for pest and disease control and invested a great deal of manpower and financial resources to reduce the major losses caused by pests and diseases to the national economy. Thus, mastering and implementing the theoretical and technical measures for pest and disease control is an important guarantee for improving the ornamental value and economic value of garden plants.

2 Problems currently faced

2.1 The single introduced plant varieties create conditions for the occurrence of pests and diseases

Since the 1990s, most of the turf plants introduced into cities have been grass species (Kentucky bluegrass, ryegrass, tall fescue) and white clover, and the street trees have mainly been ash, lacking native local plants. This kind of artificially established ecosystem is very fragile, and it is difficult to establish the relationships of interaction, mutual restraint and mutual coordination between plants and the environment, between plants and phytophagous organisms (including various organisms) and natural enemies. During this period, because newly invading pests and diseases lack the restraint of biotic and abiotic factors in the ecosystem, once they encounter suitable environmental conditions, they will rapidly grow and reproduce on these abundant and continuous plant food sources, causing major outbreaks. For example, the silver-marked noctuid moth on cool-season turf in Zhengzhou in 1998 and 1999.

2.2 Single control methods

At present, the prevention and control of garden plant pests and diseases relies to a large extent on chemical pesticides, because their use is simple, fast-acting and effective, especially when pests and diseases break out, chemical control often becomes the only effective measure. However, chemical control also has many drawbacks: improper use can cause poisoning of humans and livestock, pollute the environment, kill natural enemies, and cause phytotoxicity. The lack of an overall concept of the ecological environment often leads to neglect of integrated management, especially biological control and other pollution-free control techniques, which affects the improvement of the overall control level, causes damage to the ecological environment, weakens the natural control role of natural enemies, and leads to the development of pesticide resistance in pests and diseases and their resurgence. Long-term use of a single pesticide variety will cause certain pests and pathogens to develop varying degrees of resistance, resulting in increasingly higher application concentrations, increasingly lower safety, and increasingly difficult control. In addition, the pollution caused to the environment by outdated application methods and excessive use of pesticides has attracted widespread public concern.

2.3 The growing environment of garden plants is deteriorating day by day

The growing environment of plants is deteriorating day by day. With the acceleration of urbanization, the structure of modern urban infrastructure is becoming increasingly complex, and the problem of environmental pollution is also becoming increasingly serious. Street trees and flowers and trees in street green spaces are often affected by many underground facilities such as sewers, gas pipelines, and electric and telecommunication cables, and automobile exhaust and toxic gases or wastewater discharged by factories also constantly affect plant growth. The growing environment of garden plants is harsh, the plants grow weakly, and their disease resistance is poor, providing favorable conditions for the invasion of pests and diseases.

3 Control strategies

3.1 Carry out strict quarantine

   The primary task in the prevention and control of garden plant pests and diseases is to strengthen plant quarantine and strictly prevent the invasion of dangerous pests and diseases. With the acceleration of China's urbanization process, urban construction has entered a new stage of development, and the exchange of seedlings between domestic and foreign landscaping departments is becoming increasingly frequent. When introducing or exporting plant materials, dangerous pest and disease species that have not yet been found in the seedling-receiving area, have strong reproductive capacity, wide adaptability, great harmfulness, and can spread with plant materials should be treated as key quarantine objects, and those found to have been introduced should be blocked and eliminated on the spot. Pests and diseases such as pine bast scale, pine wood nematode, root-knot nematode, crown gall, and leaf miner are all easily spread with seedlings. Therefore, strict plant quarantine is required during the introduction and transport of seedlings.

3.2 Strengthen maintenance and management, improve the stress resistance of plants The occurrence and damage of pests and diseases are related to the growth vigor of plants to a considerable extent. For those with poor growth vigor, fertilizer should be applied, water should be given, and the soil should be loosened and weeds hoed in a timely manner to improve the plants' own ability to resist pests and diseases. Combined with autumn and winter pruning, diseased and pest-infested branches should be removed. This can not only regulate plant nutrients, but also reduce the sources of overwintering pests and diseases, improve ventilation and light penetration, strengthen tree vigor, and create environmental conditions unfavorable for the overwintering, reproduction and damage of pests and diseases.

3.3 Cultivation and management prevention method

   This is a basic measure in integrated control. According to the principle that the occurrence, damage and development of pests and diseases have certain requirements for the external environmental conditions and the host situation, the main ecological factors affecting the rise and fall of pest and disease numbers should be grasped, and through a series of technical measures such as improving cultivation and maintenance management, the suitable conditions for pests and diseases should be changed, a good growth and development environment should be created for garden plants, and their ability to resist pests and diseases should be improved, so as to suppress the occurrence of pests and diseases.

3.3.1 Select and breed pest- and disease-resistant varieties In light of the local occurrence of pests and diseases, select and breed garden plant varieties that are resistant to diseases and pests, such as ginkgo and southern magnolia, and strictly control the carrying of pests and diseases during seedling raising and emergence. This is the most economical and effective method for preventing and controlling garden pests and diseases.

3.3.2 Matching trees to the site and the diversity of garden plants Use the method of combining evergreens and deciduous plants to plant turf, ground cover plants, trees and shrubs in multiple layers. Through the scientific matching of tree species, establish a reasonable plant community structure, give full play to the role of natural control factors, promote the stability of the urban garden ecosystem, and improve the plants' self-regulation ability against pest and disease damage.

3.3.3 Reasonable fertilizer and water measures If organic fertilizer is used for ornamental plants, it should be fully decomposed, so that the pathogens and pests in the organic matter can be thoroughly killed. When using inorganic fertilizer, the ratio of nitrogen, phosphorus and potassium should be reasonable, and appropriately increasing the application of phosphorus and potassium fertilizer can improve the disease resistance of plants. For ornamental plants, whether it is the watering method or the amount and timing of watering, all affect the occurrence of diseases. Methods such as sprinkler irrigation and flooding will aggravate the occurrence of leaf diseases, so furrow irrigation and drip irrigation are best. The watering time is best chosen in the morning on a sunny day, so that the humidity on the leaf surface can be reduced in time, which can improve the disease resistance of plants.

3.3.4 Strengthen the tending and management of garden plants Prune in a timely manner to strengthen tree vigor, and combined with pruning, remove plants, diseased branches and residues infected by pests and diseases, so as to reduce the sources of pests and diseases.

3.3.5 Clean the garden and nursery Most pathogens (fungi) or overwintering eggs of pests and diseases overwinter in the dead branches, fallen leaves or weeds in the garden and nursery. Therefore, in winter, thoroughly clearing and destroying the dead branches, fallen leaves and weeds in the garden and nursery and improving sanitation can greatly reduce various sources of pests and diseases. Many weeds are wild hosts of plant diseases; for example, weeds such as plantain are wild hosts of root-knot nematodes. Overgrown weeds also increase the humidity of the microclimate, which is conducive to infection by pathogens.

3.3.6 Trunk whitewashing Trunk whitewashing can not only effectively prevent frost damage and sunscald of trees in winter, improve the disease resistance of trees, destroy the overwintering sites of pests and diseases, and kill mites, scale insects and others overwintering in the bark, but also prevent adult longhorn beetles from laying eggs the following year, playing a dual role of both frost protection and insect killing.

3.4 Promote and apply natural enemy control techniques Pollution-free control will not destroy the ecological balance, will not pollute the environment, and will not harm natural enemies, and is the main direction of future research on pest control. Research in this area should also be strengthened in the control of garden plant pests, such as using insects to control insects, using fungi to control insects, and using birds to control insects, as well as using black light lamps, sex pheromones, lasers and other modern science and technology to eliminate pests, or to make them produce hereditary physiological defects that lead to male sterility, so as to improve the level and effect of pest control.

3.4.1 Using insects to control insects Control pests by protecting and utilizing parasitic or predatory natural enemies, such as using the Turkish grain beetle to control the cypress bark beetle; using Trichogramma wasps to control the Chinese pagoda tree looper; and using the red-margined ladybird to control the giant mealybug.

3.4.2 Using birds to control insects Protect and utilize beneficial birds to control pests, such as using woodpeckers to control the double-striped cedar longhorn beetle; using grey magpies to control pine caterpillars; poultry can also be used, such as raising chickens to control the Chinese pagoda tree looper.

3.5 Choose and use biological pesticides Biological pesticides can effectively protect natural enemies and eliminate pests in the process of pest and disease control, cause little environmental pollution, and compared with chemical pesticides, their control effect on pests and diseases is lasting. For example, using Bt emulsion to control the Chinese pagoda tree looper requires only two sprays per year to control its damage; whereas with chemical pesticides, each generation of the pest must be controlled with more than two sprays. In addition to Bt emulsion and diflubenzuron, biological pesticides such as Huabao and tobacco-alkali extract produced in recent years are all preferred plant insecticides for controlling garden pests and diseases.

3.6 Physical and mechanical control methods According to certain habits of pests, use tools, equipment or create material conditions that pests like, and use light, heat, radiation and other mechanical, physical and manual control methods to control pests. Because this method is simple, easy to carry out and pollution-free, it is particularly suitable for urban gardens.

3.6.1 Light trapping and killing Taking advantage of the phototaxis of pests such as noctuid moths, slug moths, tussock moths, snout moths, lappet moths, leafhoppers and adult scarab beetles, set up black light lamps to trap and kill them during the peak period of adult occurrence.

3.6.2 Trap attraction Taking advantage of the characteristic of pests (such as willow tussock moth larvae, pine caterpillars, spider mites, etc.) of descending the tree to overwinter in autumn, tie straw ropes around the trunks to attract the pests to overwinter in them, and remove the straw ropes the following spring to kill the pests.

3.6.3 Using hormones to control insects Use insect sex pheromones as attractants to trap and kill pests. At present, more than 1,000 insect sex hormone compounds have been artificially synthesized, of which 280 have been commercialized. In China, sex pheromones of the cotton pink bollworm, cotton bollworm and pear fruit moth have been widely used for pest forecasting.

3.7 Manual control

   Scrape off gypsy moth eggs from trunks or buildings, dig out the pupae of the Chinese pagoda tree looper from the loose soil near pagoda trees, pick off the larval nests of the poplar notodontid moth, shake down and kill the larvae of the Chinese pagoda tree looper, Chinese pine caterpillar and tent caterpillar, scrape off scale insects on trunks, and prune out diseased branches and leaves.

3.8 Correct use of chemical pesticides

   Chemical control should be carried out only when necessary for emergency response, implement targeted control, and choose agents with strong selectivity, low toxicity and little environmental pollution as much as possible. The method of using chemical agents to control pests and diseases mainly serves to deal with sudden or large-scale serious outbreaks of pests and diseases. Its advantages are that it is fast-acting and convenient for mechanization and large-area application, with fewer affected factors, but it also has obvious side effects such as killing natural enemies, inducing resistance, and polluting the environment. Therefore, when using chemical pesticides, the correct method of use must be mastered. First, one must have a correct understanding of pesticides and their formulations, the control targets and the various methods of using pesticides, and the toxicity of pesticides; second, one needs to be familiar with and master the performance of various pesticides, clearly understand the impact of pesticides on the protected plants (such as stimulating growth and development, the plant's tolerance and the conditions for causing phytotoxicity, etc.), and investigate and analyze the occurrence patterns of pests and diseases in different regions, as well as meteorological conditions (light, temperature, humidity, wind, etc., and their impact on the occurrence and development of pests and diseases and on the effectiveness of pesticides). Third, the various conditions and safety protection measures required for using pesticides must be prepared, and at the same time operators must receive strict technical training.

3.8.1 Grasp the meteorological conditions favorable for pesticide application; changes in meteorology directly affect the effectiveness of pesticide use As far as temperature is concerned, the suitable application temperature for most pesticides is 2O~3O℃; too high or too low a temperature will affect the exertion of the pesticide effect. Generally, application should be chosen before 1O a.m. or after 15 p.m. on a sunny day. Rainfall has a great impact on the effectiveness of pesticide use; rainwater can dilute and wash away the pesticide on the leaf surface, so if it rains within 24h after spraying, the pesticide needs to be re-sprayed.

3.8.2 Grasp the weakest link of pests and diseases and the timing most favorable for killing them in large numbers Generally, diseases show significant differences in their response and sensitivity to pesticides at different stages of the entire infection cycle or life history. At the early stage of disease onset or when pathogen spores germinate and invade the plant, this is the weakest link in their life history, they are relatively sensitive to the agent, and their resistance is weakest, making this the key period for control; pests have the weakest resistance from initial hatching to before the 3rd instar, and especially the egg hatching period and the larval molting period are the best times for pesticide application.

3.8.3 Grasp the period when the protected object is insensitive to the agent for pesticide application Different growth stages of plants and different plants react differently to pesticides. Seedlings and the flowering stage have poor tolerance, and plants with very weak growth and poor nutrition are even more prone to phytotoxicity.

3.8.4 Grasp the safe period for natural enemies for pesticide application In the prevention and control of pests and diseases, attention should be paid to protecting natural enemies in order to maintain ecological balance. For example, applying pesticide during the egg stage or pupal stage of natural enemy insects can achieve the purpose of controlling pests while protecting natural enemies.

3.8.5 For pests and diseases that can be controlled together, carry out combined control and minimize the number of pesticide applications Avoid polluting the environment and the development of pest and disease resistance, and accurately master the use concentration and limit concentration of each agent for each control target.

3.8.6 Pay attention to the alternating use of agents, slow down the development of resistance in the control target as much as possible, and at the same time, according to the purpose of control, choose suitable pesticide formulations to improve the control effect For different control targets, different pesticide formulations should be selected for control according to their characteristics, the plant and environmental factors. For example, for controlling leaf-eating pests, emulsifiable concentrates and wettable powders are generally used; for controlling underground pests, powders, emulsions, etc. are generally used to make toxic soil for soil treatment.

3.9 Improve pesticide application techniques

At present, urban pest and disease control mostly uses conventional spraying methods. According to estimates, with conventional spraying, only 25%-50% of the pesticide sprayed out by the application equipment is deposited on plant leaves, less than 1% of the pesticide is deposited on the target pests, and only 1%~3% of the agent can play an insecticidal role. This application method is not only inefficient and causes waste of pesticides, but also causes a large amount of pesticide to flow into non-target environments, causing poisoning of humans and livestock and environmental pollution. Therefore, the application (especially spraying) techniques of chemical pesticides must be improved to increase the utilization rate of pesticides, reduce the amount of pesticides released into non-target environments, and protect the environment on which we depend for survival.