Scab immune apple varieties for new orchards

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					EC 1334 • Reprinted June 1993                                                                                            $1.00



Scab-immune apple varieties
for new orchards
R.L. Stebbins



   In a wet-climate area such as
western Oregon, apple scab is the
apple disease that requires the
greatest number of fungicidal sprays
for control. Apple scab is caused by
the fungus Venturia inaequalis, which
attacks the young leaves and fruit as
they develop in spring and early
summer.
   Susceptible apple varieties may be
defoliated by apple scab in seasons
with long rainy periods. The surface
of fruits of scab-susceptible varieties
may be covered with olive or dark
brown spots that distort their shape,
lead to fruit cracking, and—in
general—destroy the value of the
fruit.
   Controlling apple scab with
protectant fungicides means applying
sprays at prepink, pink, and calyx
stages, and at first and second cover
spray. Additional sprays may be
needed during wet years. This
procedure can have its problems:
                                          One of the largest scab-immune apples, Freedom has very short stems.
• During the early growth stages,
   periods without rain may be too
   short to apply a fungicide to a        fungus Podosphaera leucotricha. This         In the United States, breeding for
   large orchard.                         disease occurs somewhat less com-         apple scab resistance began in Illinois
• Sprays to control apple scab may        monly and can be controlled with          in 1943. Breeding in the United States
   constitute 10% or more of the total    fewer fungicide sprays.                   and Canada has resulted in release of
   cost of production.                       If the variety has shown only a low    12 named varieties and nearly 30
• Many of the fungicides that have        amount of powdery mildew, you can         advanced selections for testing in
   been used to control apple scab        also control it by promptly removing      numerous locations.
   may be lost because of the reregis-    infected parts through pruning.              Since 1985, Oregon State Univer-
   tration process. The newer sys-                                                  sity has tested eight of the scab-
   temic fungicides cost more than                                                  immune varieties, plus Chehalis, a
   the older materials.                   Origin of                                 chance seedling resistant (but per-
   For growers starting new orchards,     scab-immune varieties                     haps not immune) to apple scab.
                                                                                    They were grown at Corvallis on two
an alternative to using fungicides is        Most apple varieties immune to
to plant scab-immune varieties.           apple scab resulted from hybridiza-
   Some of the scab-immune varieties      tion with a crabapple clone, and they     Robert L. Stebbins, Extension horticulture
are not resistant to another disease,     contain a single gene for resistance to   specialist emeritus, Oregon State
powdery mildew, caused by the             the disease.                              University.
Table 1.—Characteristics of some apple varieties immune to apple scab

                                                               Fruit           Maturity
Variety               Mildewa          Fruit size              color           season            Comments

Redfree               Moderate         Medium-small            Red             Late August       Sweet, crisp
Chehalis              Low              Medium-large            Yellow          Late August       Pick before full yellow or soft
Prima                 Low              Medium-large            Red             Early September   Bitter pit
Priscilla             Low              Small                   Part red        Mid-September     Good flavor
Nova Easy
  Gro                 None             Medium                  Dull red        Mid-September     Good flavor
Sir Prize             Low              Medium-large            Yellow          Late September    Soft
Jonafree              Low              Small                   Part red        Late September    Too tart
McShay                Low              Medium                  Part red        Mid-September     Poor keeper
Liberty               Moderate         Medium                  Red             Early October     Best flavor; very firm
Freedom               Moderate         Medium                  Part red        Early October     Good flavor; poor keeper
MacFree               High             Medium                  Part red        Mid-October       Mediocre
a
    Refers to the extent of mildew infestation observed in the plot at Corvallis.



rootstocks, dwarfing M26 and                           with acceptable dessert quality.          upright, branching freely near the
semidwarfing M7.                                          Yield is fairly light, which is        end of a year’s growth. This habit
    From planting until present, the                   typical for many early-maturing           gives a bushy tree with few openings
trees received no fungicide applica-                   varieties. There is little preharvest     between branches. Lower limbs tend
tions. None of these varieties has                     drop. The trees do not have blind         to be thick and strong.
shown symptoms of the disease,                         wood; they have wide-angled                  Chehalis tends to be moderately
despite weather that has been condu-                   crotches and enough (but not exces-       slow to begin production, and it
cive to apple-scab infection. Nearby                   sive) branching.                          tends to be a light cropper in most
trees of susceptible varieties have                       Branches are not especially thick,     years. Powdery mildew has rarely
become infected with apple scab.                       and they tend to produce shoots near      been seen on Chehalis.
Certain of the scab-immune apples                      the end of the previous year’s
have been infected with powdery                        growth. Full bloom was 1 to 4 days        Prima
mildew.                                                later than red Delicious. After a            Prima is a medium to large,
    Table 1 summarizes some facts                      moderately large crop, which was          truncate-conical red apple that
about those varieties tested at Corval-                thinned by hand but not chemically,       matures in early September. The skin
lis.                                                   cropping was light to moderate.           has an abundance of bright striped
                                                                                                 and blushed red color over light
                                                       Chehalis                                  greenish-yellow undercolor. It has a
Descriptions                                              Chehalis is a large, round-truncate    pleasant perfume aroma. The flesh is
                                                       yellow apple with no red blush. The       moderately firm, tart/sweet, and
of varieties                                           dots (lenticels) on the fruit skin tend   crisp. It makes good apple sauce. It
   These descriptions are based on                     to be corky when the spring has been      doesn’t hold up very well in cold
observations made in Oregon’s                          rainy. Splashes of russet may occur       storage.
Willamette Valley. In different                        near the calyx end.                          Large Prima fruits often have bitter
climates, these same varieties might                      Fruit that are fully exposed to the    pit, a physiological disorder of the
perform differently.                                   sun in very hot weather tend to           fruit manifested by dark, sunken
                                                       sunburn and may develop water core        spots on the skin and brown corky
Redfree                                                (a translucence of the cortex that        spots in the flesh under the skin. The
    Redfree is a small to medium,                      often leads to internal breakdown).       flesh is yellowish, slightly coarse, but
nearly round apple with red blush                         Because of its low acid content and    with good flavor when still crisp.
and stripes on all surfaces of the skin                crisp, juicy flesh, Chehalis can be          Full bloom of Prima occurs about
exposed to sunlight. There are no                      picked from mid- to late August.          3 days before red Delicious. On a tree
noticeable calyx lobes, and the basin                  Once the skin is fully yellow, it         trained to a central axis, crotch angles
is small. Fruit finish is smooth and                   acquires an unpleasant greasy             are wide, and limbs are spreading.
attractive with little tendency to                     texture, and the flesh is quite soft.     The branches tend to be thin; they
sunburn.                                               The fruit are easily damaged by           form shoots readily near the end of
    Fruits mature in mid- to late                      rough handling.                           the previous season’s growth, and
August at Corvallis. Fruit are moder-                     Full bloom of Chehalis is about        they bend downward under the
ately firm, sweet, mild, rather insipid,               3 days after red Delicious. It produces   weight of a crop. Branches tend to
crisp, and juicy. Redfree is the earliest              many branches on the central axis.        have a moderate amount of bare or
maturing scab-immune red apple                         Branches are somewhat stiff and           “blind” wood.
    Prima is fairly precocious but only   speckles of dull red over dull green-
moderately productive. After a            ish yellow, overlaid by a waxy
moderately large crop, which was          bloom. The fruit don’t sunburn             Use pesticides safely!
thinned by hand but not chemically,       easily, but they turn orange on the
a light crop was set. Prima has not       sides exposed to sun during hot            • Wear protective clothing and
shown any powdery mildew.                 weather.                                     safety devices as recommended on
                                              There are no noticeable calyx            the label. Bathe or shower after
                                          lobes, and shape is quite regular.           each use.
Priscilla                                 Well-exposed fruit may be fully            • Read the pesticide label—even if
   Priscilla is a small to medium red     colored, but color tends to be highly        you’ve used the pesticide before.
apple that matures in mid-Septem-         variable.                                    Follow closely the instructions on
ber. The flesh is firm, sometimes             This apple is not very attractive.       the label (and any other directions
tough, crisp, sweet/tart, flavorful.      Nova Easy Gro matures in mid- to             you have).
However, the fruit is poorly colored      late September. It’s firm and has a
and not very attractive. Its shape is     high sugar content. The flesh is crisp     • Be cautious when you apply
roundish-conic, sometimes slightly        and juicy, with a mild flavor superior       pesticides. Know your legal
ribbed, and with moderately promi-        to many scab-immune varieties. It            responsibility as a pesticide
nent calyx lobes.                         “tastes better than it looks.”               applicator. You may be liable for
   Priscilla’s color is broad splashes        Full bloom of Nova Easy Gro              injury or damage resulting from
of dull red over dull green. It stores    occurs with red Delicious. After a           pesticide use.
well and hasn’t been noticeably           moderately large crop, which was
prone to physiological disorders. In a    thinned by hand but not chemically,
taste test after storage, Priscilla was   a light to moderate crop was set.
rated equal to Golden Delicious.          There has been little preharvest drop.
   Priscilla’s tree tends to be some-         On a tree trained to a central axis,   growth and bend downward under
what sparsely branched with a fair        crotch angles are wide, and limbs are      the weight of a crop. It has little blind
amount of bare wood on the limbs          spreading. Branches tend to be thin;       wood.
and trunk. It tends to become tall        they form shoots readily near the end
quickly and to bend over when             of the previous season’s growth and
cropping. Priscilla crops lightly.        bend downward under the weight of          Jonafree
                                          a crop.                                       Jonafree is a small round apple
                                              Nova Easy Gro has a light to           with a red blush on all exposed
Nova Easy Gro                             moderate amount of bare wood. It’s
  Nova Easy Gro is a medium-size                                                     surfaces. There are no noticeable
                                          precocious, fairly productive, and         calyx lobes, and shape is quite
round apple with splashes and             hasn’t shown symptoms of powdery           regular. Well-exposed fruit may be
                                          mildew.                                    fully colored, but color tends to be
                                                                                     highly variable. When fully mature,
                                                                                     the skin may have a greasy feel.
                                          Sir Prize                                     This apple is only moderately
                                             Sir Prize is a medium to large,         attractive. Jonafree matures in early
                                          long, truncate yellow apple with           October. It’s firm and has a high
                                          large calyx lobes and long stems.          sugar content. The flesh is hard and
                                          There may be a slight blush on some        juicy with a tart flavor. It was rated
                                          fruits. The fruit don’t sunburn easily.    well below Golden Delicious in a
                                             Sir Prize matures in late Septem-       taste comparison with stored fruit.
                                          ber. It has a high sugar content. The         Full bloom of Jonafree occurs with
                                          flesh is crisp and juicy, with a tart      red Delicious. After a moderately
                                          flavor, especially when slightly           large crop, which was thinned by
                                          immature. Because it becomes soft on       hand but not chemically, bloom has
                                          the tree when fully mature and             been sparse. Jonafree is precocious
                                          shows bruises due to rough han-            but not very productive. There has
                                          dling, it’s not suitable for shipping.     been little preharvest drop.
                                             Full bloom of Sir Prize occurs a           On a tree trained to a central axis,
                                          few days after red Delicious. After a      crotch angles are wide, and limbs are
                                          light crop, which was not thinned, a       spreading. Branches tend to be thin,
                                          very light crop was set. It’s not very     form shoots readily near the end of
                                          productive.                                the previous season’s growth, bear
                                             There has been little preharvest        fruit on the ends of shoots, and bend
                                          drop. On a tree trained to a central       downward under the weight of a
                                          axis, crotch angles are wide, and          crop.
                                          limbs are thin and spreading.                 Jonafree has a moderate amount of
                                          Branches form shoots readily near          bare wood. It hasn’t shown symp-
Liberty is well-adapted to central axis
                                          the end of the previous season’s           toms of powdery mildew.
training.
McShay                                     varieties. In several taste tests,                 Full bloom of Freedom occurs a
    McShay is a medium to large,           Liberty’s flavor has been rated equal           few days after red Delicious. After a
round-conic apple with bright red          to that of Empire (a new scab-                  very large crop, which was thinned
blush over a greenish-yellow under-        susceptible variety with excellent              by hand but not chemically, there
color. It has a moderately large           flavor), and superior to that of red            was no bloom on the M7-rooted trees,
amount of waxy bloom. It has no            Delicious.                                      but a good fruit set on the M26-
noticeable calyx lobes, and shape is          Full bloom of Liberty occurs a day           rooted trees. There has been little
regular. Stems are fairly short. Well-     or two before red Delicious. After a            preharvest drop.
exposed fruit may be fully colored,        moderately large crop, which was                   On a tree trained to a central axis,
but color tends to be highly variable.     thinned by hand but not chemically,             crotch angles are moderately wide,
    McShay can be very attractive. It      bloom has been ample. There has                 and limbs are moderately spreading.
matures in late September. It’s only       been little preharvest drop.                    Branches tend to be thin, to form one
moderately firm and doesn’t have a            On a tree trained to a central axis,         or two shoots near the end of the
high sugar content. The flesh varies       crotch angles are moderately wide,              previous season’s growth, and to
from crisp to soft. Because these          and limbs are moderately spreading.             bend downward under the weight of
observations were made on fruit from       Branches tend to be thin, to form one           a crop.
the first, very light crop, it seems       or two shoots near the end of the                  Freedom doesn’t have much bare
likely that McShay’s fruit quality will    previous season’s growth, and to                wood. It’s precocious, productive,
be rated more highly in future years.      bend downward under the weight of               and susceptible to powdery mildew,
    On a tree trained to a central axis,   a crop.                                         but it doesn’t become as extensively
branches are numerous, crotch angles          Liberty doesn’t have much blind              infected as Jonathan or MacFree.
are narrow, and limbs are upright.         wood. It’s precocious, productive,
Branches tend to be thin, and they         and susceptible to powdery mildew,
don’t form shoots readily near the         but it doesn’t become as extensively            MacFree
end of the previous season’s growth.       infected as Jonathan or MacFree.                   MacFree fruits mature in mid- to
McShay doesn’t have bare wood and             Because of its regular production            late October. They’re small to me-
isn’t precocious. It’s too early to rate   and excellent fruit quality, Liberty is         dium, not well colored, and of poor
its productivity. Full bloom is a few      the most promising late variety in our          quality. Although the tree is resistant
days later than red Delicious.             scab-immune collection.                         to apple scab, it’s highly susceptible
                                                                                           to powdery mildew. I don’t suggest
                                                                                           that you plant this variety.
Liberty                                    Freedom
    Liberty is a small to medium,             Freedom is a medium-size, round
round-conical apple with a red blush       apple with red stripes over yellow.
over greenish-yellow overlaid by a         The fruit don’t sunburn easily. There
waxy bloom. The fruit don’t sunburn        are no noticeable calyx lobes, and              Summary
easily.                                    shape is quite regular. Well-exposed               Anyone who wishes to grow
    There are no noticeable calyx          fruit may be fairly well colored, but           apples with a relatively low chemical
lobes, and shape is quite regular.         shaded fruit are not.                           input should plant only scab-immune
Well-exposed fruit may be fully               It matures in late September to              varieties. Early, midseason, and late-
colored, but shaded fruit are not.         early October, and it has a high sugar          maturing scab-immune varieties are
Liberty is fairly attractive. It matures   content. The flesh is firm, crisp, and          available.
in late September to early October.        juicy at harvest time, but it tends to             If you successfully control pow-
It’s very firm and has a high sugar        break down in storage. Severe rus-              dery mildew by pruning, you won’t
content.                                   seting has been noted where the stem            need any fungicide sprays during the
    The flesh is crisp and juicy, with a   end presses against the shoot, due to           growing season to produce attractive,
flavor superior to many scab-immune        the fruit’s very short stems.                   disease-free fruit.




                                           Extension Service, Oregon State University, Corvallis, O.E. Smith, director. This
                                           publication was produced and distributed in furtherance of the Acts of Congress of
                                           May 8 and June 30, 1914. Extension work is a cooperative program of Oregon State
                                           University, the U.S. Department of Agriculture, and Oregon counties.

                                           Oregon State University Extension Service offers educational programs, activities, and
                                           materials—without regard to race, color, national origin, sex, age, or disability—as required
                                           by Title VI of the Civil Rights Act of 1964, Title IX of the Education Amendments of
                                           1972, and Section 504 of the Rehabilitation Act of 1973. Oregon State University
                                           Extension Service is an Equal Opportunity Employer.

				
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