Common Pest And Diseases Of Vegetable Crops Pdf
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- Vegetable diseases, pests and disorders
- Greenhouse vegetable and floriculture crops
- Chapter VII: Disease Management
Vegetable diseases, pests and disorders
Diseases can occur at any stage during the course of plant growth. The rapid, accurate diagnosis of the cause of a disease, along with the implementation of a rapid treatment, is essential to ensure the protection of the crop.
Certain infectious diseases caused by living, microscopic organisms have the potential to rapidly ruin a crop. However, for any particular vegetable, these diseases are not that numerous and, so, it would not be difficult for a grower to become familiar with them and take proper preventative action.
Diseases caused by nonliving things i. Usually, it is easier to rule out an infectious agent as the cause of a disease before investigating possible nonliving abiotic causes.
This stresses the need for the grower to become familiar with the more common infectious diseases that can occur on the crop.
This chapter provides an overview of the science of diagnosis and treatment of vegetable diseases. The grower is advised to consult other references listed at the end of the chapter for more detailed information related to a particular crop.
Disease is the outcome of an interaction between the host, the disease agent, and their environment. If the cause of infectious disease, the pathogen, is next to the host, nothing will happen unless environmental factors are favorable for its infection and development within the plant. With foliar pathogens, there is usually a minimal period of leaf wetness required to stimulate spore germination and infection.
For some soilborne pathogens, infection occurs in combination with high soil moisture and certain critical soil temperatures. Knowledge of conducive environmental factors for the more important vegetable diseases presents an opportunity for more effective management: the disease can prevented by altering some of the environmental factors, or, when such factors cannot be altered, steps can be taken to minimize the impact e.
Not all diseases are caused by pathogenic organisms. Determining whether a disease is caused by a pathogen, or has nonliving abiotic causes requires not only the examination of individual plants, but also, noting the pattern of symptom occurrence in a field. Examine individual plants for unusual symptoms, such as leaf spots, wilts, stunting, fruit rots, misshapen leaves, cankers and stem blight.
Roots should be examined for galls, root rot and necrosis dead areas. Fields should be observed to determine if the problem is widespread and whether different plants species in and around the field are affected, which could indicate an abiotic cause. Symptoms with a nutritional or physiological cause have a more widespread occurrence within a field than infectious diseases. Initially, most disease causing pathogens will be isolated in areas and spread outward from those areas.
Also, weeds or nonrelated crops are not typically affected. Soilborne pathogens are even more restricted within a field than foliar pathogens.
Table VII-1 lists characteristics to consider when diagnosing the cause of a plant disease. Fungi are multicellular microscopic organisms that can grow to their food, usually in the form of filamentous strands. Their growth pattern is radial, so on surfaces such as plant leaves, the effects of their growth may be seen as circular spots.
However, fungal infections of other plant parts, such as roots, may produce no visible structures. Some symptoms can indicate these infections. For example, browning of the water-conducting tissues of the stem, in combination with wilt, can indicate infection by the Fusarium wilt fungus. Other disease symptoms, such as blight a general death of tissue , which can have a variety of causes, may require laboratory testing to confirm fungi as a cause. Fungi can produce specialized structures, such as spores, which are used for reproduction, dissemination through space and time, and survival.
Sclerotia are structures that function in the long term survival of many soilborne pathogens. The southern blight fungus which infects many vegetables forms sclerotia resembling mustard seeds. Most fungi that infect leaves require free moisture to initiate infection, with the exception of powdery mildew fungi, which need only high humidity to initiate infection.
Bacteria are single celled microscopic organisms, which survive by becoming dormant. The most notable exception to this is the pathogen that causes common scab on potato: this is a filamentous, multicelled bacterium that produces spores. They can be transported by wind driven rain, by insects, or the movement of infected plant parts, including seed. They can also cause soft rots of vegetative parts that are usually characterized by a foul smell.
Other bacterial diseases that produce symptoms such as wilt require laboratory analysis for diagnosis. Mycoplasmas are bacteria-like, only structurally simpler and smaller than bacteria. They are transmitted by leafhoppers. The most notable disease of vegetables caused by a mycloplasma is aster yellows, which affects carrots, celery and related plants. The symptoms of aster yellows are distinctive: leaves have a bronzed appearance and flowers are abnormal leaf-like tissue grows from them, instead of petals.
Viruses are submicroscopic entities that can only replicate inside living plant cells. They require agents such as insects to transmit them to plants. A typical virus symptom is a mosaic pattern on leaves, but viruses may cause other symptoms, such as necrotic lesions and stunting, which can have other causes. Insect vectors of viruses include by aphids, leafhoppers, white flies and thrips.
Viruses often have wide host ranges, including weeds that are not botanically related to the crop, and symptoms are not always produced in these plants. Although some viruses can tentatively be identified by symptoms produced on plants particularly mosaic or ringspots , accurate diagnosis requires laboratory testing. Nematodes are microscopic roundworms that feed on the roots of plants. The root knot nematode produces root galls and deformed roots on a wide range of crops. Heavy infestation can lead to wilting and death of plants.
Nematodes can also cause stubbiness, necrosis and stunting of roots, but these symptoms are not distinctive. Soil or root analysis is required to confirm diagnosis. Soil temperatures that are suboptimal for seed germination and seedling growth can favor the development of damping off pathogens, such as Pythium and Rhizoctonia.
Often, the impact of these pathogens can be reduced by delaying planting, until the soil temperature increases. Foliar pathogens have different optimal temperatures for development.
Symptoms of bacterial diseases on leaves are produced at high temperatures, at which a fungal disease like downy mildew might be halted. These temperature requirements are known for many diseases and with a disease like late blight of potato, can be used to accurately apply fungicides when they are needed. Moisture is the driving force for foliar diseases. Free moisture on the plant surface is necessary for growth and infection of many bacteria and fungi.
There is usually a minimum, critical time requirement. Moisture can also infect spore production by fungi. This characteristic is the basis of a predictive system for fungicide choice for management of purple blotch of onion. Saturated soil moisture conditions can create an environment conducive for root-rotting pathogens such as Pythium or other fungi that cause fruit rot. Soil pH affects the activity of some soilborne pathogens. Diseases caused by the cotton root rot fungus tend to occur in alkaline soils, while Fusarium wilt diseases are more prevalent in acidic soils.
The growth of the common scab pathogen of potato is reduced in acidic soils. However, it is generally not feasible to alter soil pH to manage disease.
In some cases, vegetable cultivars may be resistant or tolerant to important diseases. Resistant cultivars have no or low severity of disease, while tolerant cultivars may become diseased without incurring yield loss. The use of these cultivars does not necessarily eliminate the need for other disease management approaches, such as the use of fungicides.
Several pathogens can be spread by contaminated seed, for example, the bacteria causing leaf spot of pepper and tomato, black rot of crucifiers and fruit blotch of watermelon; and fungi causing gummy stem blight and anthracnose on watermelon.
Some seed companies indicate whether seed lots have been tested for these pathogens. However, low levels of seed contamination could increase if transplants are produced from the seed. Infected transplants may have slight or no symptoms. The use of a soilless mix and good sanitation practices during the production of the transplants will greatly reduce the risk of infection by soilborne pathogens. The risk of introducing a foliar epidemic, such as gummy stem blight, can be minimized by inspecting transplants and making preventative applications of fungicides or bactericides copper-based early in the season.
Many pathogens which cause disease survive in the soil, on crop residue. Rotation with nonsusceptible crops, or fallowing, can reduce the pathogen population. Rotation is not a practical alternative for some soilborne fungi, such as Fusarium wilt fungi and the southern blight fungus, because their survival structures persist for years in soil.
White rust, an important fungus disease of spinach, mustard, turnip and swiss chard, forms survival structures in the leaves of diseased plants that require 2 to 3 years to die out. Burial of crop residue can augment the beneficial effects of crop rotation. Many foliar pathogens can survive in crop residue, but only for one or two years. Burial of crop residue decreases pathogen survival and physically removes their access to the new crop.
Shredding of crop residue can speed up the decomposition of certain pathogens. For example, the bacterium that causes black rot of cabbage can survive in plant residue for nearly a year, but if the residue is shredded, the survival time decreases to less than 2 months.
A pathogen that attacks one member of a plant family frequently will infect other members of that family or group. Table VII-2 lists vegetables which are susceptible to similar diseases. A standard rotation program should use only one member of each group on a site in a 2 to 3 year period. An exception to this recommendation is the Fusarium wilt fungus. There are variants of this fungus that infect one crop only. Thus, the Fusarium wilt fungus that infects watermelon will not infect cantaloupe or other cucurbits and these crops can be grown in soils where Fusarium wilt of watermelon was a problem.
Rotation is important in the control of root knot nematodes. If susceptible crops are grown repeatedly on nematode infested land, production levels decrease until susceptible crops are no longer economical. Onions, shallots, garlic, leek or sweet corn should be grown on sites where root knot nematodes are a known problem.
Fallowing can also reduce populations, but the fallow land must be kept weed free, since many weeds are also hosts for this nematode. Planting when the soil temperature is optimum for seed germination and seedling growth will reduce seed decay and damping off. In areas normally experiencing heavy rainfall, vegetables should be planted on raised beds to allow for drainage of excess water from the root zone.
Greenhouse vegetable and floriculture crops
This page provides an overview of the bacterial diseases in vegetable crops. The related tools listed at the end of the page provided detailed information about the identification, symptoms, and management of bacterial diseases. It is important to have a plant diagnostics laboratory confirm the pathogen causing any diseases in a crop so that the disease can be appropriately managed. Pathogenic bacteria cause many serious diseases of vegetables. They do not penetrate directly into plant tissue but need to enter through wounds or natural plant openings. Wounds can result from damage by insects, other pathogens, and tools during operations such as pruning and picking.
Although there are many insect pests and diseases of brassicas aka crucifers , most can be prevented from damaging the crops by adhering to a few basic guidelines. In general, a preventative management approach involves a combination of the following practices:. Other methods can also be employed, but the above four are fundamental to management of the most common problems listed below. Crop rotation. Seedlings of direct-seeded crops are more vulnerable to damage — get a head start against flea beetles and other pests by using transplants. Weed control. To reduce potential feeding sites in the spring, control weeds, especially those in the brassica family, and distance any garden flowers you are growing that are in the same family.
This page provides an overview of the fungal diseases in vegetable crops. The related tools listed at the end of the page provided detailed information about identification, symptoms, and management of fungal diseases. It is important to have a plant diagnostics laboratory confirm the pathogen causing any diseases in a crop so that the disease can be appropriately managed. Fungi constitute the largest number of plant pathogens and are responsible for a range of serious plant diseases. Most vegetable diseases are caused by fungi. Sources of fungal infections are infected seed, soil, crop debris, nearby crops and weeds. Fungi are spread by wind and water splash, and through the movement of contaminated soil, animals, workers, machinery, tools, seedlings and other plant material.
PDF | Vegetables are important source of dietary fibers, minerals, antioxidants and In addition, they can exacerbate pests and diseases problems by Identification of Plant Growth Promoting Rhizobacteria(PGPR's) against.
Chapter VII: Disease Management
Content Content 1. Diseases - Bacterial. Pests - Insects. See questions about Cauliflower. Cauliflower plant.
Phytophthora blight is perhaps the most serious disease of cucurbits in Indiana. The plastic-covered structure blocks rain, snow and strong wind that crops are exposed to when growing in the open field. Free Download Boxwood Blight Product Code: BPW This publication provides information about boxwood blight a fungal disease that affects boxwood plants ; images of the symptoms and signs of this fungal disease and management options. This publication examines how fungicides are classified and recommends management practices particular to pome fruit that can prevent fungi from developing resistance to these products.
In Texas, the greatest challenge to vegetable producers is in the area of pest control. The mild climate prevalent in most of the state is extremely favorable for all forms of crop pest to flourish weeds, insects and diseases.
Common Insect Pests of Brassicas
We are currently updating and migrating the resources on this site to the Cornell Vegetable Resources website. Visit that site's Disease factsheets page for the latest information. The addition of color photographs enhances the use of these sheets for plant disease diagnosis. Navigating through this web site is very easy. By clicking on Diseases by Crops on the sidebar, seed packets of your favorite vegetables appear, and by clicking on the crop of interest, a listing of the current fact sheets available is displayed. Magnification of the photos provided in each sheet is possible.
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