Transcript Apple Scab
Pome fruits Grown in the temperate zones in both hemispheres. Most production is in the cooler sections of US, Canada and Europe. Not below Memphis and Fort Smith AR. ► Apples #1 pome fruit with most production in the Pacific NW, in the valleys where climate is dry and the crops are irrigated. ► 1991 – 9,871 million pounds ► Leading States 71% of total production ► Washington 4,300 million lbs ► New York 1,050 million lbs ► Michigan ► Calif. ► PA, VA, NC, WVA, OR, ID, OH, and IL ► Most popular varieties Red and Yellow Delicious ► McIntosh ► Rome Beauty ► York ► Jonathan ► Recently Granny Smith, Gala, Fiji ► Fresh market = highest prices, remainder of crop is process for juice, sauce, jelly or jam. Apple Diseases ► Apple Scab ► Fire Blight ► Cedar Apple Rust ► Black Rot Apple Scab Pathogen – ► Venturia inequalis –sexual ► Spilocaea pomi -asexual ► Responsible for crop failures in the late 1800s. Present in all countries where apples are grown. Not a problem in dry, irrigated locations, but where cool moist wet spring months are common James Peale, 1824 Symptoms – ► Fruit, leaves, leaf petioles, and young twigs attacked causing scabby lesions in which tissues may be killed. ► Leaf - spots, black in color and appear on both surfaces and leaf may curl or distort ► Fruit Scabs - appear similar on fruit but the fungus stimulates cork formation beneath spots that may cover the fruits and result in severe fruit disfiguration ► Twigs – infections easily overlooked as the lesions look like enlarged lenticels ► Fungus attacks only current season growth Symptoms Symptoms Signs pseudothecia Signs Symptoms Economic impact ► Greater than most diseases because: ► Crop reduction (Defoliation- weakening) ► Lowering of fruit grade ► Foliage loss ► Increase in production costs – Fungicides – Prior to fungicides, total fruit drop – appeared dormant in June. Disease Cycle ► ► ► ► ► ► ► ► ► Fungus overwinters in leaves on ground and sometimes on apple buds Late fall – spring pseudothecia are produced in leaves – Primary infection in new growth Olive, two-celled ascospores –Primary Inoc. Ejected into air Conidia produced in apple bud scales Ascospores and conidia infect flowers and leaves Secondary cycle – conidia produced in primary lesions, 7-9 days after infection Spread by splashing rain and by wind. Infected fruit may not show symptoms until storage after several months Inoculum level in spring may be high after spray –because overwintering in leaves Disease Cycle – Apple Scab Control ► Hosts – Cultivated apple and crab apple species. Not to pear ► Resistance ► Sanitation – not feasible ► Chemical - #1, protectant – prevent spores from germinating, postinfection fungicides – some resistance in fungal populations Cedar Apple Rust – Gymnosporangiuim juniperivirginianae Basidiomycete ► Name comes from fact that red cedar (Juniperus viginianae) is alternate host ► Other species cause quince rust and hawthorn rust ► Pathogen ► Economic impact – due to apple tree defoliation that results in fruit yield and size reduction and also a reduction in tree vigor Symptoms – Apple ► ► ► Leaf - bright yellow leaf spots that turn orange as enlarge and age. Fruit and twig – infections occur These symptoms caused by fungus aecial stage. Cedar ► ► Leaf - Brown to reddish brown leaf galls -During periods of rain, galls produce orange, gelatinous spore-horns from the gall surface that contain masses of teliospores. Teliospores – germinate and each cell produces 4 basdiospores that are airborne to apples Symptoms – Disease Cycle Two host and three fruiting structures Apple, cedar - telia, aecia, and pycnia OW in reddish brown galls – cedar apples in cedar tree Wet in spring – horns with teliospores, each =produces 4 basidiospores Air currents (3-5 kilometers) – germ tubes – leaf and fruit of apples, temp and wetting conditions 4-8 d old leaves spermagonia that is fertilized by compatible spermatia = production of aecia July and August windborne aeciospores (produced in chains) from apple infect cedar leaves 1-3 weeks = rust lesion fungus grows in tissue in winter18 months after infection production of galls Disease Cycle Control Eradication 1-2 miles of orchards – red cedars, 4-5 miles more effective Resistance Chemical Fireblight Pathogen – Erwinia amylovora – bacterium ► This was the first plant disease proven to be caused by a bacterium ► Pear industry in Eastern U.S. was essentially wiped out by this disease in 1900’s ► Pear is considerably more susceptible than apple, - most destructive disease of apple ► ► ► Economic impact – Results from killing of flowers, fruit spurs, twigs and girdling of large branches and trunks that results in death of the trees Young trees in nursery or orchard can be killed in a single season. Hosts – over 75 rosaceous plant species are susceptible Symptoms ► Flower and twig – blight appears in spring, blackening of flowers and leaves = curled leaves hanging from twigs and small branches ► Fruits – first as watersoaked lesion, then mummifies and turn black and may be tree for several months ► Fruit spurs and terminal twigs – Infections and symptoms progress to supporting branches where cankers are formed. ► Sign During humid conditions, milky bacterial ooze may appear on surface of infected part – rod-shaped with flagella Symptoms Apple Shoot Pear Blossom Symptoms (Shepard’s Crook) Symptoms Burnt Appearance Diseased shoot on left Disease Cycle ► ► ► ► Bacteria overwinter in canker margins in branches Warm spring weather = multiplication Sticky bacterial exudates is present insects are attracted and pickup ooze on their bodies and transfer to flowers where new infections take place Splashing rain may also spread the bacteria (enter through natural and wound openings) Disease Cycle – Fire Blight Control 3 Areas of Importance I. Reducing bacterial inoculum ► Removal by pruning the overwintering cankers ► Weekly inspection of orchards in summer, and removal of infected spurs and terminals ► Disinfect tools II. Properly timed application of bactericides during flowering to control blossom blight phase ► Cu ► Streptomycin 2-3 applications III. Insect control esp. aphids and plant bugs to prevent infections IV. Avoid planting susceptible cultivars – V. Apples more resistant VI. Over stimulation (succulent growth part. Susc.) with high N should be avoided Black Rot ► Pathogen – Botryosphaeria obtuse- Economic Effects ► Limb Canker phase is most important in the northeastern and north central applegrowing regions of the United States ► Leaf Spot and fruit rot phase are most important in the southeast Symptoms – Appear 1 to 3 weeks after first petal fall -leaf infections begin as small purple flecks rapidly enlarging to 1/8 to 1/4 in. diameter. -Margins remain purple, center turns brown; “frog eye appearance” Infections on young fruit -reddish flecks, developing into purple pimples -enlarge to dark brown necrotic areas Infections on more mature fruit -Black, irregularly shaped -surrounded by red halo -enlarging; characterized by series of concentric rings alternating black to brown Infected fruit mummify and remain attached to tree Limbs and branches -reddish brown and slightly sunken cankers large and small -branches weak & break with heavy crop load Symptoms Symptoms Symptoms Disease Cycle -Over-winters in dead bark, twigs, cankers, and mummified fruit -Ascospores (spring) and conidia released during rainfall; washed or blown onto fruit or foliage -Sepal infection occurs after bud break -Fruit infection occurs during growing season -Leaf infection common after petal fall -Early season infection may result in fruit drop Control -Removing dead wood, mummies & cankers from trees -Current season prunings should be removed form the orchard or chopped with a flail mower -Fungicides, applied from silver tip until harvest required to control disease