EC 1334 • Reprinted June 1993 $1.00
Scab-immune apple varieties
for new orchards
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
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
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
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
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
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.
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 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
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