Fire Blight on Fruit Trees and Woody Ornamentals

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					                                         A L A B A M A   A & M      A N D   A U B U R N   U N I V E R S I T I E S

                                         Fire Blight on Fruit Trees
                                         and Woody Ornamentals
F   ire blight, caused by the bac-
    terium Erwinia amylovora, is
a common and destructive dis-
ease of pear, apple, quince,
hawthorn, firethorn, cotoneaster,
and mountain ash. Many other
members of the rose plant family
as well as several stone fruits are
also susceptible to this disease
(Table 1). The host range of the         Spur blight on crabapple
fire blight pathogen includes             cv ‘Mary Potter’.
nearly 130 plant species in 40
genera. Badly diseased trees and         symptoms are often referred to
shrubs are usually disfigured and         as blossom blight. The blossom
may even be killed by fire                blight phase of fire blight affects
blight.                                  different host plants to different
                                         degrees. Fruit may be infected
                                         by the bacterium directly
Symptoms                                 through the skin or through the
    The term fire blight describes        stem. Immature fruit are initially      Severe fire blight on crabapple
the blackened, burned appear-            water-soaked, turning brownish-         cv ‘Red Jade’.
ance of damaged flowers, twigs,           black and becoming mummified
and foliage. Symptoms appear in          as the disease progresses. These            Shortly after the blossoms
early spring. Blossoms first be-          mummies often cling to the trees        die, leaves on the same spur or
come water-soaked, then wilt,            for several months.                     shoot turn brown on apple and
and finally turn brown. These                                                     most other hosts or black on
Table 1. Plant Genera That Include Fire Blight Susceptible Cultivars.
Common Name                    Scientific Name           Common Name                           Scientific Name
Apple, Crabapple                  Malus                     Jetbead                           Rhodotypos
Apricot, Cherry, Plum             Prunus                    Kageneckia                        Kageneckia
Avens                             Geum                      Loquat                            Eriobotrya
Brambles                          Rubus                     Medlar                            Mespilus
Chokeberry                        Aronia                    Mountain Ash                      Sorbus
Cinquefoil                        Potentilla                Mountain Avens                    Dryas
Cliff Rose                        Cowania                   Ninebark                          Physocarpus
Cotoneaster                       Cotoneaster               Osteomeles                        Osteomeles
Cratnegomespilus                  Cratnegomespilus          Pear                              Pyrus
Creambush                         Holodiscus                Pearlbush                         Exochorda
Dichotomanthes                    Dichotomanthes            Peraphyllum                       Peraphyllum
Docynia                           Docynia                   Photinia                          Photinia
False Spirea                      Sorbaria                  Quince                            Cydonia
Firethorn                         Pyracantha                Rose                              Rosa
Flowering Quince                  Chaenomeles               Serviceberry                      Amelanchier
Goatsbeard                        Aruncus                   Spirea                            Spiraea
Hawthorn                          Crataegus                 Stranvaesia                       Stranvaesia
Indian Hawthorn                   Rhphiolepis               Strawberry                        Fragaria
Japanese Rose                     Kerria                    Toyon                             Heteromeles

pear. The stems and midribs of             Soft, succulent shoots are very    Control
diseased leaves often turn black      vulnerable to the disease. Mature
                                                                                    A control program combining
as well. As the twig and leaf         apple and pear tissues are much
                                                                              resistant varieties, sound cultural
blight phase progresses, leaves       more resistant to infection than
                                                                              practices, sanitation, fertilization,
die, curl downward, and cling to      young tissues. Cultural practices
                                                                              and pesticides is needed to pro-
the blighted twigs. Succulent         favoring rapid shoot growth in-
                                                                              tect plants from fire blight. Culti-
twigs, shoots, and water sprouts      crease the plants’ susceptibility to
                                                                              vation and fertilization practices
are easily infected. The tips of      attack. These practices include se-
                                                                              that produce rank, succulent
blighted twigs, shoots, and           vere pruning, excessive nitrogen
                                                                              growth increase the possibility
sprouts droop, producing the          fertilization, and an unbalanced
                                                                              that the disease will develop. Do
typical “shepherd’s crook.”           fertility program.
                                                                              not cultivate pear and apple or-
Leaves may be infected through             Warm, moist conditions, par-       chards late in the season, and do
pores as well as wounds.              ticularly during flowering, greatly      not severely prune susceptible
    Cankers form at the base of       increase incidence of the disease.      cultivars. Regulate plant growth
blighted twigs and spurs. The         Blight development can occur at         and apply fertilizers so that mod-
bark surrounding a developing         temperatures between 65° and            erate shoot growth is maintained.
canker first appears water-            95°F, but the 75° to 81°F range is      Beginning in late winter to early
soaked, then later sunken and         most favorable. Temperature ex-         spring and continuing through the
dry. The surface of bark cover-       tremes will slow development of         growing season, remove all root
ing the canker is usually smooth      the disease. In regions with mild       sprouts and suckers from trees.
and sometimes has a purple            winter temperatures, cankers may        All diseased tissue (blighted twigs
color. Reddish-brown streaks can      increase in size during the fall        and branches) should be re-
be seen in the sapwood under          and winter on trees with a sou-         moved as soon as possible to
the discolored, sunken bark.          therly exposure. Rain is critical to    slow the spread of the disease.
Amber-colored discharge can           the spread and development of           Prune diseased wood about 12 to
often be seen near blighted tis-      the disease. Fire blight outbreaks      14 inches below visible cankers
sues of the plant at any stage of     are encouraged by warm, cloudy          during the growing season, and 6
infection.                            weather following a rain. A             to 8 inches below cankers in the
                                      humid environment promotes              fall or winter months. Clean your
Characteristics                       bacterial growth and spread.            tools with a solution of isopropyl
                                      Other weather events like frost,        alcohol or other disinfectant after
     The fire blight pathogen,         high winds, and hail create
Erwinia amylovora, is a rod-                                                  each cut to avoid spreading the
                                      wounds through which the bacte-         bacteria.
shaped bacterium that overwinters     ria can enter the plant.
in tissues around the edge of                                                       The first chemicals used for
cankers on large branches and                                                 the control of fire blight were
limbs. A gummy, amber-colored                                                 copper fungicides like copper hy-
discharge oozes from cankers dur-                                             droxide (Kocide 101 at 2 to 4
ing warm, humid weather. The                                                  pounds per 100 gallons of water
discharge, which contains bacte-                                              between silver-tip and green tip
ria, is dispersed by insects or                                               on apple and pear) and copper
splashing rain to blossoms, leaves,                                           sulfate (Tri-Basic Copper Sulfate
and shoots (see drawing on next                                               at 1⁄ 2 pound per 100 gallons of
page). Dried bacterial discharge                                              water on pear only). Recommen-
often forms strands which are car-                                            ded spray schedules are listed on
ried by wind.                                                                 the product labels. These com-
     Susceptibility to fire blight                                             pounds provide effective control
                                      Typical ‘Shepherds Crook’ often         under light to moderate disease
depends on: (1) cultivar charac-      seen at the end of fire blight-
teristics, (2) maturity of tissue,                                            pressure but can cause fruit rus-
                                      damaged shoots. The brown color
and (3) weather conditions. Pear      of the blighted leaves indicates that   seting on some apple and pear
flowers are invaded very rapidly       this blighted shoot is on apple or      varieties. Copper fungicides that
through nectaries and pistils,        crabapple.                              are cleared for fire blight control
which are ideal sites for growth                                              on woody ornamentals may be
of the bacteria. Apple flowers                                                 phytotoxic to crabapple and
are usually invaded through stig-                                             some other plants.
mas and anthers.                                                                    Copper hydroxide (Kocide
                                                                              2000 T/N/O at 0.75 pounds per
                                                                              100 gallons of water or 1.5
Disease Cycle of Fire Blight
                                                                                      Blossom and
                                                                                      leaf blight

                                                    Bacteria enter
  Bees carry bacteria                               uncuticularized
  to blossoms                                       flowering parts

                                     Primary          splashed            Secondary
                                     Cycle            to blossoms           cycles
                                                      and twigs
                                                                                                  Blighting of
                                                                                                  twigs and
Insects pick up ooze                         Bacteria oozing from
from edge of holdover                        infected cortex
                                                                                           Canker at base
               Bacterial cells                                                             of diseased

teaspoons per gallon) and cop-                                               Spray (0.5 teaspoon per gallon
per sulfate pentahydrate (Phyton                                             of water) are recommended
27 at 20 to 40 fluid ounces per                                               every 4 to 5 days during the
100 gallons of water) will give                                              bloom period. Begin spraying
some protecation from fire blight                                             just before the center flower in
on woody ornamentals. See the                                                the cluster opens and continue
comments for streptomycin sul-                                               applications through petal fall.
fate for instructions on optimum                                             For best results, make applica-
application timing for the control                                           tions in the late afternoon or
of fire blight. Kocide 2000 will                                              early evening because strepto-
damage the foliage of crabapple                                              mycin breaks down in sunlight.
but is safe to use on Indian                                                      Aphids, leafhoppers, flies,
hawthorn, loquat, hawthorn,                                                  and ants play a major role in
photinia, pyracantha, and flow-                                               spreading the bacteria from
ering pear. Refer to the label of                                            cankers to blooms and new
each fungicide for additional                                                growth in the spring. These in-
directions on product use.                                                   sects should be monitored and
    The antibiotic streptomycin                                              controlled with insecticides if
(Agrimycin 17) will give better                                              necessary before bloom occurs.
control under higher disease         The surface of this perennial fire       Bees do not feed on bacterial
pressure than the copper com-        blight canker on the main trunk of      ooze but will spread the disease
pounds, and does not cause fruit     pear is cracked and dry. Note the       from infected to noninfected
russeting. When using these          dead branch stub in the center of       blossoms during pollination.
products, start spraying as soon     the canker.                             Insecticides used during bloom
as bloom begins because strep-                                               will kill the bees, but pollination
tomycin is ineffective against fire                                           will also be prevented, greatly
blight once infection occurs.                                                reducing fruit set.
Protective sprays of Agrimycin                                                    Many popular trees and
17 at 100 ppm (8 ounces of for-                                              shrubs are resistant to fire blight.
mulated product per 100 gallons                                              Establishment of disease-resistant
of water or 1 tablespoon per 21⁄ 2                                           plants is an inexpensive, easy,
gallons of water) or Fireblight

and effective means of control-                Resistant firethorn cultivars
ling fire blight without the need          include Pyracantha coccinea cv.
for chemical treatments. Some             Sensation, P. koidzumii cv. Santa
shrubs and small trees resistant          Cruz Prostrata, and hybrids San
to fire blight are listed in Table         Jose and Shawnee. The firethorn
2. Refer to Table 3 for reaction          cultivars Apache, Fire Cascade,
of some apple and pear varieties          Mohane, Navaho, Pueblo,
to fire blight.                            Rutgers, Shawnee, and Titon are
     The reaction of selected             resistant to both fire blight and
crabapple and flowering pear               scab. Cotoneaster selections re-      Note the reddish-brown discol-
cultivars to fire blight is listed in      sistant to fire blight include C.      oration of the bark covering this fire
                                          apiculatus, C. dialsianus, C.         blight canker.
Table 4. Crabapple cultivars re-
sistant to fire blight, as well as         foveolatus, C. franchetti, C. inte-
apple scab, powdery mildew,               gerrimus, C. nitens, and C.
                                          zabelli. Severe outbreaks of fire          Among Indian hawthorn selec-
cedar-apple rust, and frog-eye
                                          blight have been noted on             tions, ‘Jack Evans’ and ‘Janice’ are
leaf spot are Adams, Candied
                                          Cotoneaster dammeri in both           highly sensitive to fire blight. Also,
Apple, Centennial, Centurion,
                                          production nurseries and land-        significant fire blight damage has
Dolgo, Liset, Sargent, Sugartyme,
                                          scape plantings.                      been seen on the cultivars ‘Olivia’
and Zuni.
                                                                                and ‘Majestic Beauty’. Most other
                                                                                Indian hawthorn selections, includ-
Table 2. Fire Blight Resistant Members of the Rose Family.                      ing ‘Clara’, ‘Elenor’, ‘Tabor’, ‘Indian
Scientific Name                         Common Name
                                                                                Princess’, and ‘Snow’ are highly
Cercocarpus betuloides                 Mountain-mahogamy                        resistant to fire blight and typically
Exochorda racemosa                     common pearl bush                        suffer very little damage in land-
Fragaria chiloensis                    beach strawberry                         scape plantings.
Photinia serrulata                     Chinese photinia
Physocarpus capitatus                  ninebark
Potentilla fruiticosa                  bush cinquefoil
Prunus americana                       American plum
Prunus cerasus                         sour cherry
Prunus dulces                          almond
Prunus hortulana                       wild-goose plum
Prunus mahaleb                         St. Lucie cherry
Rosa californica                       California wild rose
Rosa gymnocarpa                        wood rose
Spirea prunifolia                      bridal wreath

Table 3. Reaction of Various Apple and Pear Varieties to Fire Blight.*
                           Moderately                             Moderately                         Highly
                           Resistant                              Susceptible                        Susceptible
Apple                      Empire                                 Freedom                            Golden Delicious
                           Liberty                                Golden Delicious                   Granny Smith
                           Priscilla                              Jonafree                           Jonathan
                           Redspur                                McIntosh                           Julyred
                           Red Delicious                          Prima                              Lodi
                           Topred                                 Redfree                            Mutsu
                           Yates                                  Stayman                            Paulared
                           Arkansas Black                         Turley                             Rome
                                                                  Winesap                            Transparent
                                                                  Jonagold                           Tydman’s Red
                                                                                                     Mollies Delicious
Pear                       Ayers                                  Seckel                             Bartlett
                           Keiffer                                                                   Bosc
                           Moonglow                                                                  Red Bartlett
*This is only a partial list of common varieties. Actual reactions may differ depending on environmental conditions. Contact your
local county agent for information on overall quality of a variety before planting.

Table 4. Reaction of Crabapple and Flowering Pear Cultivars to Fire Blight.
                               Resistant-                             Slightly to
                               Moderately                             Moderately                  Highly
                               Resistant                              Susceptible                 Susceptible
Crabapple                      M. Baccata ‘Jackii’                    Red Jewel                   Klehm’s Imperial Bechtel
                               Coral Burst                            Red Baron                   Golden Raindrops
                               Pink Princess                          Tea                         Doubleblooms
                               Spring Snow                            Royalty                     Snowdrift
                               Jewelberry                             Hopa                        Silver Moon
                               Robinson Dwarf                         Brandywine                  Professor Sprenger
                               Adams Dwarf                            Winter Gold                 Indian Magic
                               Radient                                Candied Apple               Siami Fire
                               Velvet Pillar                          Selbirk                     Sentinel
                               Pink Spires                            Sugar Tyme                  Purple Prince
                               Liset (Dwarf)                          Ormiston Roy                Mary Potter
                               Profusion                              Red Jade
                               Bob White
                               Indian Summer
                               Sargentii (Dwarf)
                               Zumi var. Calocarpa
                               White Angel
                               Red Splendor
                               Donald Wyman
                               Strawberry Parfait
Flowering Pear                 Bradford                               Capital                     Aristocrat
                                                                      Cleveland Select            Autumn Blaze
                                                                      Earlyred                    Fauriei
                                                                      Whitehouse                  Redspire

          Austin Hagan, Extension Plant Pathologist, Professor, and Edward Sikora, Extension Plant
          Pathologist, Professor, both in Entomology and Plant Pathology at Auburn University, and
          William Gazaway, former Extension Plant Pathologist. Originally prepared by Nancy Kokalis-
          Burelle, former Graduate Assistant, Plant Pathology, Auburn University.
          Trade names are used only to give specific information. The Alabama Cooperative Extension
          System does not endorse or guarantee any product and does not recommend one product
          instead of another that might be similar.
          For more information, call your county Extension office. Look in your telephone directory
          under your county’s name to find the number.
          Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June
          30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama
          Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs,
          materials, and equal opportunity employment to all people without regard to race, color, national origin, religion,
ANR-542   sex, age, veteran status, or disability.                                   7M, Revised July 2004, ANR-542

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