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					                                                                                                                  6/20/2010




                                                           Ornamentals
                                                             ◦ Powdery mildew
                                                             ◦ Black spot on rose         Vegetables
                                                             ◦ Root rots                   ◦ Leaf spots (tomato
                                                           Fruit Trees                      and cucurbits)
                                    Tamla Blunt              ◦   Powdery mildew            ◦ Virus diseases
                      CSU Plant Diagnostic Clinic            ◦   Fireblight                  (tomato and
                                                             ◦   Peach leaf curl             cucurbits)
                                                             ◦   Leaf spots (Cherry,
                                                                 Apple, Grape)?




   Field patterns
                                                       Wide host range
   Look for mottling,
                                                            ◦ Tomato, potato,
    mosaic, stippling                                         beans, beets,
   Serological, DNA tests                                    pumpkin




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   Virus vectored by
    the beet leafhopper
   Leafhopper
    movement
   „Wave‟ years
    associated with
    insect populations




                          UC Davis




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•   Control weeds around perimeter                                        Tolerant tomato cultivars
•   Floating row covers for early planting                                 ◦ Avoid Roma types
•   Reflective mulches ineffective                                         ◦ CVF 111
•   Insecticide control?                                                     Compact, semi determinant unusual looking growth
                                                                              early - uniform shape - round and soft when ripe -
    – Has not been very effective
                                                                              good flavor fair shelf life and cracks in 1st picking,
•   Resistance?                                                               none thereafter- decent yield
•   Tomatoes –                                                             ◦ Saladmaster
    – Delayed Planting „May 15?‟                                             Small fruit, round, indeterminant, good flavor, not a
    – „Wall of Water‟                                                         commercial variety - but good for some home
                                                                              gardeners




   Beet Leafhopper
    Transmitted                                                           Mechanically
    Virescent Agent                                                        transmitted
   Phytoplasma                           Eggplant sample from SW CO
                                                                          Leaf yellowing and
   Vectored by beet                                                       mottling
    leafhopper                                                            Fruit distortion
   Diagnosed by PCR                                                      Resistant varieties
   Symptoms look
    similar to BCTV
                              J. Eggers, OSU HAREC




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   Transmitted by thrips during          Start with clean
    seedling production                    transplants
                                           ◦ Avoid growing seedlings
   Symptoms include stunting,               next to bedding plants
    fruit distortion, leaf flecking,      Control thrips during
    dieback                                seedling production
                                           ◦ Insecticides
                                           ◦ Cultural practices
                                          Inspect seedlings for
                                           spotted wilt symptoms
                                          Destroy tomato plants
                                           exhibiting virus
                                           symptoms




       Many different
        viruses affect
        squash and
        pumpkin
        ◦   cucumber mosaic
        ◦   squash mosaic
        ◦   watermelon mosaic
        ◦   zucchini yellows
            mosaic virus
       Primarily
        transmitted by
        aphids
       Symptoms variable
        depending on virus,
        time of infection




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•   Reflective mulches and
    mineral oils?
•   Insecticides?
•   Avoid planting next to           Patterns on leaves
    other cucurbit crops              ◦ Location
    – Early and late crops?           ◦ Distribution
•   Weed control                     Fungal fruiting
    – wild legumes (WMV)              structures
    – many hosts (CMV)                ◦ Hand lens
•   Resistance                        ◦ Microscopic
    – traditional breeding
      techniques
    – Transgenic (coat protein)
     • Freedom II yellow squash
                                                           Photo by Bill Willis




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    •   Major plant pathogens
        and many are allergens   •   Common on
         – Foliar diseases           tomato and potato
         – Seed rot              •   Characteristic
         – Fruit rot                 bulls-eye leaf
                                     symptom




       Survival in crop         •   Resistance
        debris                   •   Nitrogen management
       Symptoms                     – Maintain optimal levels
        ◦ Relatively large,          – Don‟t let plants run out at end of season
          target shaped          •   Fungicides
          lesions on leaves;
          lesions surrounded         – Time applications to host development or by
          by yellow border             forecasting models-Tomcast
        ◦ Progressions from          – New strobilurins (Heritage, etc.) excellent but
          lower to upper               resistance may develop quickly
          leaves
        ◦ Normally doesn‟t
          affect fruit




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                                             Powdery mildew fungi
                                              grow on the surface
                                              of plants
                                              ◦ Obligate parasites
                                              ◦ Host specific
Puccinia                      Puccinia
opizii                        aristidae




   Improve air circulation
                                              Colletotrichum
   Resistant varieties                   
                                              coccodes
    when available                           Primarily a fruit rot
   Sulfur applications                      Overwinters on infested
                                              debris (fruit) – conidia
                                              are splashed by rain,
                                              irrigation onto fruit
                                             Very common in home
                                              vegetable gardens
                                              where overhead
                                              irrigation is used
                                             Controlled by:
                                              ◦ Avoid overhead irrigation
                                              ◦ Routine fungicide sprays
                                              ◦ No resistant varieties!




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                                                                                                Cucurbit
                                                                                                anthracnose on
   Colletotrichum                                                                              cantaloupe and
    orbiculare
   Melons, watermelon                                                                          watermelon
   Lesions light brown
    to reddish, often
    associated with leaf
    veins
   Leaves may be
    distorted
   Disease favored by
    extended periods of
    leaf wetness
   Many races of
    anthracnose fungus
                                Photo APS




                                                                Fusarium wilt
                                                          Fusarium oxysporum
       Plant resistant cucumber varieties                   f.sp. lycopersici
        ◦ not with muskmelon, watermelon                                                          Note vascular discoloration
       Crop rotation (3-4 years) or clean up old
        debris
        ◦ Fungus survives on debris
       Deep-plow crop debris (not always feasible
        in a home garden)
       Fungicides at regular intervals to protect
        leaves


                                                     Other important Fusarium wilts: cotton, cucurbits, banana, mimosa,
                                                     coffee, many ornamentals, etc




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                                       Long crop rotations
                                        ◦ 5 + years because fungus survives very well
                                       Resistant varieties
                                        ◦ Race specific genes
                                        ◦ Prevalence in home gardens increasing?
                                          Use of heirloom varieties
                                       Fumigation or solarization
                                       Fungicide applications or drenches are not
                                        effective




   Probably most common
    and widespread disease             Overwinters in plant
                                        debris
    of vegetables,                     Infects petals, flower
    ornamentals and fruit               stalks, fruit
    ◦ Often attacks senescing
                                       Light brown rotted
                                        areas that may be
      plant parts such as flowers       dusted with gray
    ◦ Important storage rot             spores
    ◦ May be a problem on              Development favored
                                        by wet conditions
      vigorously growing plants         and cool
                                        temperatures




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                                                   Sanitation
                                                    ◦ Removing old leaves
                                                      during renovation
                                                   Fertility
                                                   Weed control
                                                   Mulch
                                                    ◦ Straw, not plastic
                                                   Irrigation
                                                    ◦ Avoid overhead
                                                      irrigation
                                                    ◦ Avoid prolonged leaf
                                                      wetness
                                                   Control movement
                                                    of people and
                                                    machinery




                                                   Bloom is most
                                                    critical period for
   Pick fruit frequently and early                 fungicide control
   Handle berries carefully during harvest         ◦ 7-10 day application
   Remove diseased berries from field             Botrytis develops
   Store berries in cool place as quickly as       resistance to certain
    possible                                        fungicides very
                                                    quickly
   Market as fast as possible                      ◦ Example
                                                      benzimidazoles
                                                   Use different classes
                                                    of fungicides in
                                                    rotation or as
                                                    mixture




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   Septoria lycospersici              •   Septoria tritici
   Most common fungal                 •   Leaf spot of
    leaf disease                           grains during
   Survival in crop debris                cool, wet
   Symptoms                               weather
    ◦ Multiple, small black spots      •   Often seen on
      develop on leaves and                grasses in
      stems; development starts            winter
      on lower leaves and
      progresses upward
    ◦ No fruit spotting




                                    Rhizoctonia-right angle
                                    branching




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 •   Sanitation
     – Clean potting mix
     – Clean tools and pots
 •   Fungicide drenches                                            Bean
                                                                                                  Peanut
 •   Biological controls
     – a fungus called
       Trichoderma is antagonistic                     Rhizoctonia solani AG-4
       to Rhizoctonia                                  causes root rot on bean,
     – Commercial potting mixes                        peanut, soybean
       often contain Trichoderma

                                                                          Soybean




                                     Weak growth           Fungicides
                                                            ◦ PCNB, benzimidazoles, carboxins, iprodione,
                                                              strobilurins
Stem cankers                             Black scurf       Biological controls
                                                            ◦ hypovirulent strains-Rhizoctonia decline
                                                            ◦ Bacillus sp.
                     Knobby tubers                          ◦ Trichoderma-T22 acid soils




                                      Sclerotia




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     Most plant pathogenic bacteria cannot                                   Internal and
      produce spores                                                           external plant
     Will not survive once outside the host                                   symptoms such as
                                                                               wilting or
     Plant pathogenic bacteria cannot enter an                                discolored vascular
      intact plant                                                             system
     Must enter through natural opening or wound                              ◦ Smell test is usually
                                                                                 fairly effective
                                         Clavibacter michiganensis            Pathogenicity tests
                                         subsp. sepedonicum on                 on various species
                                         potato                                and varieties of
                                                                               host plants




                                      Bacterial signs
                                        “Streaming” from freshly
                                          cut stem in water.            Leaf spots and
                                        “Stringing” from cut             blights
                                          stems pushed together,
                                          then pulled apart.
                                                                        Soft rots of fruits,
                                        Bacteria “flow” observed         roots and storage
                                          from tissue mount on           organs
                                          compound microscope.
                                        Bacterial ooze can be           Wilts
                                          observed on-site with         Overgrowths
Bacterial streaming from tomato           some diseases
infected by Ralstonia                                                   Scabs
solanacearum.
Used by permission of M. Williamson
                                                                        Cankers




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                                Bacterial diseases are
                                 usually very difficult
                                 to control
                                 ◦ Clean seed/planting
                                   stock
                                 ◦ Sanitation
                                 ◦ Rotation
                                 ◦ Resistant varieties
                                 ◦ Chemicals (not very
                                   successful)                  Xanthomonas on Geranium
                                 ◦ Cultural practices
                                   (fertilization/watering)




   Pathogen is Erwinia         Symptoms:
    tracheiphila                 ◦ Drooping of one or more
                                   leaves
   Cucumber, cantaloupe,        ◦ Collapse of all vines
    squash and pumpkin           ◦ Cut stems of infected
    are susceptible                plant may show threads
                                   of bacterial ooze or white
   Watermelon are                 droplets of bacterial ooze
    resistant or immune            on cut end
   Occurs in US, Europe,        ◦ Fruits develop internal
                                   slime rots with surface
    South Africa and Japan         dark spots or blotches




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   Bacterium survive                                            Insects feed and
    only for a few                                                cause deep wounds
    weeks in crop                                                 on leaves
    debris                                                       Deposit bacteria in
                                                                  the wounds with
   It survives over                                              their feces
    winter in the                                                Bacteria enter the
    intestines of striped                                         xylem, multiply
    and spotted                                                   rapidly and spread
    cucumber beetles                                              to all plant parts




   Control
    ◦ Controlled best by controlling the cucumber
      beetles, especially the early ones, with insecticides
    ◦ Resistant varieties
    ◦ Pick only fruit from healthy plants




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                                         Plants grow poorly
   General yellowing,
                                         Leaves are bluish-
    often more severe on
                                          green with purple
    lower leaves                          tints
   Stems are short and                  Lower leaves
    slender                               sometimes turn
   Look for patterns                     bronze with purple
   Soil, tissue analysis                 or brown spots
                                         Shoots are short
                                          and thin, and
                                          upright and spindly




       Interveinal
       Most pronounced on
        youngest leaves
        ◦ Iron not mobile in plant
       Iron rapidly forms
                                     Blossom end rot of tomato
        solids in combination                                      Cat-face tomato
        with oxygen, and
        hydroxide and
        carbonate ions
       Solids not water
        soluble, can‟t be
        absorbed
       Adding more iron to
        high pH soils won‟t
        help
        ◦ Iron will precipitate                    Grape chimera    Tomato sunscald




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                                                                     Virus, Yellows diseases
                                                                      ◦ Often marginal
Physiological cracking of tomato                                      ◦ Look for mosaic symptoms
                                                                      ◦ Serological, DNA tests     Barley yellow dwarf
                                   Hail damage to Grape & Hosta
                                                                     Root rots




    Yellow shoulder of tomato                                                                                 Western X




   Chemical damage                                                      Several fungal,
   Powdery mildew                                                        bacterial diseases
                                                                          (often on fruit)
   viruses




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