Pest identification: plant pathogens

California PCA Exam Helper: Category B

The list below includes all the plant pathogens contained in the knowledge expectations for the Category B California PCA exam.

Remember, in addition to knowing these organisms, there are many other knowledge expectations for this exam. Get the complete list of knowledge expectations from DPR.

Each pathogen is linked to pages within the UC IPM Web site that contain information and photos to help you identify it and understand the basic biological and management information specified in the knowledge expectations. For some pathogens, a number of links are available. If a pathogen causes disease in several crops, links are listed to the UC IPM Pest Management Guidelines for crops where it is most important. It is important to be aware of pathogens that have a broad host range, although not necessary to learn details of every disease situation. Use the knowledge expectations to determine what information you should focus on. Pathogens which are also problematic in urban situations such as gardens and landscapes are linked to Pest Notes.

Definitions for many terms can be found in the Glossary.

Information pertaining to these pathogens is also in the recommended study guide, Plant Pathology, 4th Edition, G.N. Agrios, which is a comprehensive textbook that contains much more information than you will be required to know. Always use the knowledge expectations to determine what information you need to focus on.

Specific fungal diseases

For each of the following pathogens and associated disease, identify:

  • the common name of disease
  • the genus of the causal agent
  • the class of the causal agent
  • the biology
  • life cycles
    • the sexual structure
    • the asexual structure
    • the resistant survival stage
  • host range
  • signs and symptoms of the disease
  • methods of control

Be prepared to identify the following pathogens when presented with a photograph, common, or Latin name.

Class Pathogen Disease Photos, description, and management information
Plant diseases caused by fungi
Plasmodiophoromycetes
  Plasmodiophora brassicae
  clubroot in cole crops      
Zygomycetes
  Rhizopus sp.
  soft rot in strawberry in sugarbeet in peach & nectarine  
Oomycetes
  Phytophthora sp. Phytophthora sp. causes disease on many other plants/crops
  late blight of potato in potato in tomato    
  Pythium sp.
  damping-off in floriculture & nurseries in cotton in cucurbits  
  Bremia sp.
  downy mildew of lettuce in lettuce     Several other genera of downy mildew exist which affect a wide variety of plants/crops
Ascomycetes
  Erysiphe necator
  grape powdery mildew in grapes     Several other genera of powdery mildew exist which affect a wide variety of plants/crops
  Taphrina sp.
  peach leaf curl pest note in peach and nectarine    
  Venturia sp.
  apple scab pest note in apple   A different species of Venturia occurs on pear causing pear scab
  Colletotrichum acutatum
  strawberry anthracnose in strawberry      
  Sclerotinia sp.
  watery soft rot, cottony rot in floriculture & nurseries in cole crops in lettuce  
  Monilinia sp.
  brown rot in peach & nectarine in cherry in almond  
Basidiomycetes (class)
  Ustilago sp.
  common smut of corn in corn     other species of Ustilago cause smut on other grains and grasses
  Puccinia sp.
  stem rust of wheat in grains     other species of Puccinia cause rust on other grains and grasses
  Armillaria sp.
  oak root fungus in grape in walnut in pear Armillaria causes disease on most perennial plant species
  Sclerotium sp.
  stem rot, southern blight, white rot of onion in onion & garlic in potato in carrot Sclerotium spp. causes disease on many other plants/crops
  Rhizoctonia sp.
  damping-off, soreshin, brown patch in lettuce in cotton in turfgrass Rhizoctonia spp. causes disease on many other plants/crops
Fungi Imperfecti (class)
  Botrytis sp.
  gray mold in strawberry in grape in floriculture & nurseries Botrytis spp. causes disease on many other plants/crops
  Alternaria sp.
  tomato black mold in tomato     Alternaria spp. causes disease on many other plants/crops
  Verticillium sp.
  verticillium wilt in floriculture & nurseries in cotton in apricot Verticillium spp. causes disease on many other plants/crops
  Fusarium sp.
  fusarium wilt and root rot in floriculture & nurseries in tomato in cotton Fusarium spp. causes disease on many other plants/crops

Plant diseases caused by bacteria

For each of the following bacterial diseases, identify:

  • the common name of the disease
  • the genus of the causal agent
  • the disease cycle
  • means of survival
  • method of dissemination
  • mechanism of inoculation and infection
  • environmental conditions favorable for disease
  • symptoms and signs of disease
  • host range
  • methods of control

Be prepared to identify the following pathogens when presented with a photograph, common, or Latin name.

Class Pathogen Disease Photos, description, and management information
Plant diseases caused by bacteria
  Pseudomonas sp.
  bacterial canker of stone fruits in peach & nectarine in plum & prune in almond bacterial canker causes disease on many other tree crops
  Clavibacter sp.
  bacterial canker of tomato in tomato      
  Erwinia sp.
  fire blight pest note in apple in pear  
  bacterial soft rot in potato in onion & garlic in carrot bacterial soft rot occurs on many other crops
  Xanthomonas sp.
  black rot of crucifers in cole crops     Xanthomonas spp. causes disease on other crops
  Agrobacterium sp.
  crown gall in floriculture & nurseries in walnut in peach & nectarine crown gall can occur on most perennial, woody plants

Plant diseases caused by fastidious vascular bacteria

Be prepared to identify the following diseases when presented with a photograph and recognize the pathogen, life cycle, insect vector, and disease reservoir.

Class Pathogen Photos, description, and management information
Plant diseases caused by fastidious vascular bacteria
  Xylella fastidiosa
  Pierce's disease in grape
  Almond leaf scorch

in almond

Plant diseases caused by phytoplasmas

Be prepared to identify the following diseases when presented with a photograph and recognize the pathogen, insect vector, disease reservoir, and alternate hosts.

Class Pathogen Disease Photos, description, and management information
Plant diseases caused by phytoplasmas
  Corn stunt (corn leafhopper vector) in corn

   
  Cherry X-disease (leafhopper vectors) in cherry

   
  Aster yellows (leafhopper vectors) in lettuce

in celery

in ornamentals & nurseries

Plant pathogenic viruses

For each disease listed below, identify

  • symptomology
  • disease cycles
  • host range
  • methods of control
  • how the virus is spread
Class Pathogen Disease Photos, description, and management information
Plant pathogenic viruses
Arthropod vectors
  Tomato spotted wilt tospovirus
  tomato spotted wilt (thrips vector) in lettuce

in ornamentals & nurseries

in tomato

tomato spotted wilt tospovirus occurs on other crops

  Beet curly top geminivirus

  curly top disease  (leafhopper vectors)

in potato

in cucurbits

in sugarbeet

 
  Cucumber mosaic cucumovirus (CMV)

  cucumber mosaic (aphid vectors)

in cucurbits

in spinach

in peppers

 
Soilborne vectors

  Beet necrotic yellow vein furovirus

  rhizomania of sugarbeets (soilborne fungus, Polymyxa betae vector)

in sugarbeet

     
  Grape fanleaf nepovirus

  grapevine fanleaf (nematode vectors)

in grape

     
Seed transmission

  Lettuce mosaic potyvirus

  lettuce mosaic (aphid vectors)

in lettuce

     
  Bean common mosaic potyvirus

  bean common mosaic (aphid vectors)

in dry bean

     
Graft transmission

  Citrus tristeza closterovirus

  citrus tristeza (melon aphid vector)

in citrus

     
Mechanical transmission

  Tobacco mosaic tobamovirus / tomato mosaic tobamovirus

  tobacco and tomato mosaic (insect, mechanical transmission; often by man and tomato seed)

in tomato

in peppers

in floriculture & nurseries

 

Plant diseases caused by parasitic seed plants

Recognize the following parasitic seed plants. Know their host range and methods of control. Be prepared to identify them when presented with a photograph, common, or Latin name.

Class Pathogen Disease Photos, description, and management information
Plant diseases caused by parasitic seed plants
  Arceuthobium sp.

  dwarf mistletoe

pest note

     
  Phoradendron sp., Viscum sp.

  true or leafy mistletoe

pest note

     
  Cuscuta sp.

  dodders

pest note

weed gallery

in tomato

in alfalfa

Abiotic plant diseases

Describe the types of symptoms associated with

  • herbicide injury
  • mineral excesses and deficiencies
  • wind
  • excess soil moisture
  • low soil moisture
  • air pollution and other toxic chemicals
  • high temperature
  • low temperature
  • sunscald
  • edema
  • etiolation

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