Tomatoes, tree tomatoes (also called tamarillos), tomatillos, husk
tomatoes (also called ground cherries) and the Japanese Lantern plant are all in the Solanaceae family.
The tomatillo and related husk tomato belong to a different genus (Physalis) and differ from
tomatoes in that their fruit is encased in a thin husk.
Tomatillos produce large branched plants. The fruit are picked when they have reached full size and
are still green. After the husk is removed, the fruit is often mixed with
hot peppers and other ingredients to make green salsa. Varieties of tomatillo are: Tomatillo Green,
Tomatillo Purple (purple fruit), and Rendidor (commonly used in Mexico).
The husk tomato or ground cherry fruit is much smaller than the
tomatillo, is very sweet and used mainly for jam and preserves after the fruit has ripened and turned yellow.
Varieties of husk tomato are: Husk Tomato Goldie, Husk Tomato Strawberry.
The Japanese Lantern plant is used as a cut ornamental and is most often marketed in the fall. The
ornamental portion is an expanded calyx enclosing a pea-sized, globose berry.
The tree tomato belongs to still another genus, Cyphomandra
betacea, and is a tropical plant not
suited for outdoor production in the Pacific Northwest. Its fruit, promoted
by New Zealand, is marketed in the U.S.A. under the trade name Tamarillo. The fruit is egg-shaped,
may be red or yellow, and is bland or semi-sweet. Tree tomato plants are a small perennial bush or
shrub 6 to 10 feet tall, frost sensitive, and bear after the second year.
Tomato varieties mature over a wide range, commonly from 75 days for
early cherry types to 85 days for early full size fruit types, 100 days for medium, and 110 days for
later, full season varieties from direct seeded plantings. Transplanted plantings would be about
25 days less.
Anti-oxidant and anti-cancer compounds found in tomatoes and other vegetables have become important considerations
in the choice of varieties. Tomatoes with high levels of Vitamins A and C
are being developed. Two high-color lines, utilizing the "Crimson" gene are available (see varieties list, below).
Watch catalogs for these new types and consider testing them in your production situation.
Long shelf-life varieties:
Increased understanding of the genetics of fruit ripening has now
procedures and conventional breeding methods to be used to develop a new
generation of varieties that produce "long-life" fruit, that is fruit that is slow to soften
once it reaches the red-ripe stage. The extra shelf life amounts to about 10-20 days.
Varieties that are available to commercial growers: Elanor, Lenor, and
T1011. These are all
mid-season to late in maturity and are suggested for trial only since market
suitability for production in the Pacific Northwest is not known. They are
available through Ochoa Seed Co., Gilroy, CA, and Frontier Seed Co., Glendale, AZ, only.
Five other varieties known by the designation "Flavr Savr" are not
available to commercial growers except by special license from Calgene Inc., Davis, CA.
Curly-top virus resistance:
In the arid, irrigated areas east of the Cascades tomato production may
be severely limited by curly top virus. Commercial production is limited to the use of varieties
with resistance. Resistant varieties have been developed and released by Dr. Mark Martin
through the A.R.S., U.S.D.A. curly top breeding program at the Irrigated Agriculture Research and
Extension Center, Prosser, WA. These varieties are all red-fruited: Columbia, Rowpac, Roza,
Saladmaster, released in the 1960s for fresh market, and a "CVF" series released in the
1980s for processing and fresh market. Limited quantities of seed and descriptions of these varieties is
Dr. Erik Sorensen, WSU Cooperative Extension, Courthouse,
Pasco, WA 99301, 509/545-3511
Dr. Dennis Johnson, WSU, Rt. 2, Box 2953-A,
Prosser, WA 99350-9687, 509/786-2226
Mr. Gary Pelter, WSU Cooperative Extension, Courthouse,
Ephrata, WA 99882, 509/754-2011 ext.412
Standard tomato varieties, red:
Bush types: Early to Mid-season - Santiam, Oregon Spring, Oregon Star,
Oregon Pride (all seedless, with the latter two being large-fruited, resembling paste tomatoes);
Fireball, Willamette. For trial: Agriset 761, Coldset, Earlirouge, Equinox, New Yorker,
Pilgrim (early, multiple disease resistance), Solar Set, Springset.
Bush types: Mid-season to Late - Carmen, Celebrity. For trial: Better Boy, Carnival, Heinz 1350, Medford, Milagro,
Monte Carlo, Pik Red, Pik Rite, Setmore, Summerset, Sunny, Supersonic. Research in the Hermiston area indicates that Baja, Keno, Oregon
Spring, and Valerie performed well.
Also for trial (most are late varieties): Big Beef (All
America, medium-early beefsteak, VFF, Alt, St, N, TMV), Bonita (jointless VFF), Colonial (jointless stem, green shoulder, large), Daybreak (VFF, Asc, St),
Merced (tolerant to gray wall), Solar Set (reported high-temperature tolerance but susceptible
to gray wall), Spectrum 882 (solid, multi-purpose, medium to large oval fruit).
High Color Varieties: For trial: Spitfire, Cobia.
Staking: Early Girl. For trial: Keno.
Cherry type, red, indeterminate:
Sweet l00. For trial: Large German Cherry.
Cherry type, red, determinate:
Small Fry, Sweetie. For trial: Cherry Grande.
Indeterminate cluster tomatoes with some market potential. Suggested varieties
for trial are Santa and Juliet. Juliet fruit is larger and not as popular as that of Santa. Santa seed may
no longer be available because it has become a proprietary item.
Chico III, Heinz 2653, La Rossa, Milano, Oroma, Vega (VFF).
Large fruited types: Jubilee, Lemon Boy. For trial: Golden Boy, Orange Queen.
Cherry type, determinate: Gold Nugget.
Cherry type, indeterminate: Yellow Plum.
Yellow and red striped:
Greenhouse: See separate file on Greenhouse Tomato
White: Great White (beefsteak type), White Beauty.
Yellow: Italian Gold, a golden Roma type.
Pink - Ponderosa Pink (beefsteak type).
Yellow and red stuffing: Yellow Stuffer, a pepper-like tomato, hollow, for
VARIETY SELECTION FOR DISEASE AVOIDANCE
Varieties are listed below by their resistance to Verticillium and
Fusarium wilts and root-knot nematode.
Variety Maturity Date Resistance*
`Better Boy' Late VFN
`Better Boy F.' Early VFN
`Big Set' Late VFN
`Carmen' Late VFNT
`Carnival' Late VFNT
`Casino Royale' Mid VFNT
`Cavalier' Late VFNT
`Celebrity' Late VFNT
`Chico III' Mid F
'Fireball VF' Mid VF
`First Lady' Mid VFNT
`Heinz 1350' Mid VF
`Heinz 1370' Late F
`Jetstar' Mid VF
`Merced' Mid VFT
`Milagro' Late VFNT
`New Yorker' Early V
`Pik Red F.' Early VFN
`Pik Rite F.' Early VFN
`President' Mid VFNT
`Red Pak' Mid VF
`Rutgers' Early F
`Santa Fe' Late VF
`Small Fry' (cherry) Early VFN
`Spring Giant' Early VF
`Springset' Early VF
`Sunny' Mid VF
`Sunray' (yellow) Mid-late F
`Supersonic' Mid VF
`Toy Boy' (cherry) Early VFN
`VFN-8' Mid-late VFN
`VFN Bush' Mid VFN
`Wonderboy' Late VFN
* V = Resistant to Verticillium wilt
F = Resistant to Fusarium wilt
N = Resistant to root-knot nematode
T = Resistant to Tobacco Mosaic Virus
SEED AND SEED TREATMENT
Tomato seed numbers approximately 11,500 per ounce. Most of the new
hybrids are sold by seed
number. Use only treated seed from a reliable seed source. Some seed
companies now can
furnish tomato seed that has been "vigorized" or "conditioned" to allow
adverse (cool) temperature conditions.
Research in Indiana has demonstrated a benefit from starter or "pop-up" fertilizers.
In direct seeded plantings, spray directly on the seed a solution of 2-6-0 (made up of 1 part
10-34-0 : 4 part water) at 1 pint per 100 lineal feet of row (use 1/2 this rate on sandy soils).
To reduce risk from Verticillium wilt and other diseases avoid
using fields in your rotation plans in which eggplant, tomato, pepper, potato, strawberry, or caneberries have been
Use l or more ounces of seed per acre, depending on the variety and
required plant population. Sow
them in the greenhouse 6 to 8 weeks before field transplanting. Seedlings are
other flats when the first true leaf has formed. Veneer bands or jiffy pots
may be used to
advantage. Space between the plants should be 2 to 2.5 inches. Provide
adequate ventilation during
the heat of the day, particularly after watering, which should be completed
before l p.m. Water plants before signs of wilting appear.
Tomato is a warm-temperature vegetable and requires a long growing
season. Transplants should
be kept close to the following temperatures: 64 to 70 F during the day, 55 to
61 F at night until the seedlings are thinned out.
When the first true leaf has formed, early flowering can be increased by
a one-week cold treatment at 54 F. Caution: Do not subject transplants with 4-5 true leaves
to cold temperatures (around 50 F nights and 60-65 F days) for more than a week since this will
increase catfaced fruit.
Condition transplants for 1-2 days before transplanting to the field by
slightly reducing the moisture and maintaining approximate outdoor temperatures. Do not over-harden
(see note on catfacing above). Thoroughly water plants l2 to l4 hours before transplanting
to the field. Plants should be dug or cut loose from the soil when being transplanted; ensure the
roots are not exposed to sun or drying wind.
Apply a starter fertilizer solution to the transplants when
transplanting to the field. Select starter
fertilizers that have the highest level of phosphorus available, such as
10-52-17, 11-48-0, 11-55-0 dry fertilizers or 10-34-0 liquid fertilizer. Make up a stock solution of 3
lbs of the dry, such as 10-52-17, or 2 pints of liquid 10-34-0 per 50 gallons of water. Use 1/2 pint
of this stock solution per plant, applying the solution directly to the plant roots when
setting in the field.
Use rows 4-5 feet apart and space transplants 12 to 48 inches apart in
the row, depending on
Direct seeding should be done with early varieties only. Drop 1-3 seeds
per hill and space 9-12
inches apart in rows spaced 48-60 inches.
Tomatillos are usually grown from transplants planted in rows 5 feet
apart with a 2.5-foot spacing
in the row.
Recent research indicates that a temperature of 68-78 F is ideal for
Use windbreaks as necessary especially in eastern Oregon. Grain
windbreaks have been found effective when grain rows are used for each tomato row. Winter wheat
varieties, rye, or oats can be used. Spring barley may be used for February plantings. Seed grain
thickly, 2-3 seeds per inch. This requires about 10 lb of barley, 9 lb of wheat, or 8 lb of rye to
seed grain rows 12 feet apart. Windbreaks may be cultivated out after the tomato plants are well established.
If they are not, windbreaks should not be allowed to touch the tomato plants because abrasion of the
enlarging fruit can cause that fruit to be misshapen.
A soil test is the most accurate guide to fertilizer requirements. As a
general guideline before
transplanting, broadcast and disc in the following:
Nitrogen: 75-100 (N) lb/acre
Phosphate: 100-150 (P2O5) lb/acre
Potash: 100-150 (K2O) lb/acre
Sulfur: 25-30 (S) lb/acre
Side dress with 25-50 lb N/ acre when first fruits appear.
Where mulching and trickle irrigation are practiced, additional nitrogen
can be fed through the
trickle irrigation system at 15 lb/acre when the first fruit begins to set and
an additional 15 lb/acre
four weeks after. To prevent clogging or plugging from occurring use soluble
forms of N
(urea or ammonium nitrate), and chlorinate the system once a month with a l0
to 50 ppm.
chlorine solution. Chlorinate more frequently if the flow rate decreases.
Avoid excessive nitrogen applications, which can cause excessive vine
growth and delay maturity.
PLASTIC GROUND MULCHES AND ROW COVERS
The use of black plastic ground mulch is recommended, especially in
Western Oregon, to enhance earliness and yield. Plastic
mulch controls weeds, conserves moisture, may increase soil temperature, and
protects fruit from
ground rots. For black plastic mulch to increase soil temperature, it is
critical that the soil surface be smooth and that the plastic be in close
contact with the soil. This can only be achieved by laying the plastic with a
machine designed and properly adjusted for this task. Clear plastic much is
superior for heat transfer to the soil but does not control weeds.
A new generation of plastic mulch films allows for good weed
control together with soil warming that is intermediate between black plastic and clear film.
These films are called IRT (infrared-transmitting) or wavelength-selective films. They are more
expensive than black or clear films, but may be cost-effective where soil warming is important. (See
also section on spacing).
Plastic, spunbonded, and non-woven materials have been developed as crop covers for use as
windbreaks, for frost protection, and to enhance yield and earliness. They complement the use of
plastic mulch and drip irrigation in many crops. Some sources of these materials and information on their
American AgriFabrics, Alpharetta, GA. Phone 770-663-700, fax: 770-663-7690, email: firstname.lastname@example.org.
Ken-Bar, Inc., Reading, MA. Phone: 800-336-8882, fax: 781-944-1055, email: email@example.com.
Non-woven or spunbonded polyester or propylene, and perforated
covers, may be used for 4 to 8 weeks immediately after transplanting or direct seeding. Covers should
be removed when plants begin to flower or if temperatures become excessive under the covers.
Do not allow temperatures to exceed 90 F for more than two or three consecutive days. Row
covers increase heat unit accumulation by 2 to 3 times over ambient. Two to four degrees of
frost protection may also be obtained at night. Soil temperatures and root growth are also
increased under row covers as are early yields, and in some cases total yields.
Apply water uniformly to reduce incidence of blossom end rot. Irrigate
carefully after fruit ripens
to reduce fruit decay and cracking. A total of 12-15 inches may be needed in
western Oregon. Approximate summer irrigation needs for the Hermiston area have been found to
be: 3.5 inches in May, 5.0 in June, 7.5 in July, and 7.0 in August. Research has shown that the
use of drip irrigation under black plastic mulch is superior to
sprinkler irrigation with black plastic mulch. Yields usually increase
Soil type does not affect the amount of total water needed, but does
dictate frequency of water application. Lighter soils need more frequent water applications, but less
water applied per application.
CHEMICAL FRUIT RIPENING
Ethephon (Ethrel) may be used for uniform ripening for once-over harvest and to
enhance ripening in late varieties, or during late seasons, or when
ripening is delayed. The proper use of Ethrel can advance harvest about 5-7
days. Fruit do not increase appreciably in size after ethephon treatment
Several factors must be considered for effective use of Ethrel:
- Because Ethrel can cause some defoliation and increase incidence of sunburned fruit, do not treat fields
where growth is poor or the plants are stressed.
- Do not apply Ethrel if temperatures are expected to exceed 90 F.
- Apply when fruit is at 5 to 10% red/pink/breaker stage. Ethrel is effective only on fruit that is at least mature-green
(fruit has gel inside). The key to good results is good coverage.
- Apply 1.25 to 1.75 pints Ethrel (2 lb/gal formulation) in 40-80 gal water/acre. Use higher rates when day
temperatures are less than 64 F and tomato growth is dense. Ideal temperature range is 75-85 F.
- Avoid spraying more than can be harvested in one day as sprayed fields do not "store" as well as unsprayed.
- Varietal differences in foliage vigor and leaf characteristics affect Ethrel uptake and potential for fruit injury and ripening
response. Experiment carefully and know how your variety responds.
- Do not exceed 6.5 pints/acre total, or excess residues may develop.
Consult product label for full instructions and cautions.
Harvest fruit at proper maturity, generally l4 to 2l days after
treatment. Observe treated fruit frequently for condition of crop ripening. Cool temperatures can slow Ethrel
absorption and color development and extend the period between treatment and harvest.
HARVESTING, HANDLING, AND STORAGE
Tomato yields vary with area and number of harvests. Yields may range
from 230 to 270
cwt/acre, or about 1200 20-lb boxes/acre. With appropriate plasticulture
techniques, yields of as high as 3200 20-lb boxes/acre have been reported.
Tomatoes may be harvested at the mature green stage (when the fruit
cavity is filled by gel),
semi-ripe (with different amounts of red pigmentation) or fully ripe,
depending or marketing
requirement. They are very perishable and subject to surface and internal
damage, and must be
handled accordingly. Tomatoes are sensitive to chilling injury, which differs
with maturity of the fruit. Proper temperature management for ripening and storage are critical to
STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)
Store mature-green tomatoes at 55 to 70 F; ripe fruit at 45 to 50 F and
a relative humidity of 90
Mature-green tomatoes cannot be successfully stored at temperatures that
greatly delay ripening.
Tomatoes held for 2 weeks or longer at 55 F may develop abnormal amount of
decay and may fail
to develop a deep red color. The optimum temperatures for ripening
range from 65 to 70 F. Tomatoes will not ripen normally at temperatures above
80 F. A
temperature range of 57 to 61 F is probably most desirable for slowing
ripening without increasing
decay problems. At these temperatures the more mature fruit within the
mature-green range will
ripen enough to be packaged for retailing in 7 to 14 days.
Fruit held below 50 F become susceptible to alternaria decay during
Increased decay during ripening occurs after 6 days of exposure at 32 or 9 days
at 40 F.
Mature-green tomatoes may also be damaged by low temperatures in the field. A
of tomatoes exposed to temperatures below 50 F for a week before harvest would
develop alternaria rot even at recommended storage temperatures. Some loss
due to chilling can
be expected in fall-grown tomatoes exposed for over 95 hours to temperatures
below 60 F during
the week before harvest. Severity of chilling increases with increases in
exposure time, so 135
hours exposure to below 60 F may result in heavy losses.
Chilling periods for fruit while in the field, during transit, and in
storage have a cumulative effect.
Thus, fruit chilled for only a short period in the field can become very
susceptible to decay when
held for only a short period at chilling temperature during transit or
storage. Tomatoes should be
kept out of cold, wet rooms because in addition to potential development of
extended refrigeration damages the ability of fruit to develop desirable fresh
Ripening of tomatoes is initiated by the ethylene they produce.
However, in commercial practice,
mature-green tomatoes are commonly treated with supplemental ethylene to
within a lot. For treatment, tomatoes are exposed to 100 to 150 ppm ethylene
for 24 to 48 hours
at 68 to 77 F and 85 to 95% relative humidity. Ethylene is applied in a
fairly airtight room by a
shot method, a generator, or a flow-through system. Immature tomatoes may
supplemental ethylene, but the ripened fruit will lack quality. Fruit beyond
the breaker stage do
not benefit from supplemental ethylene because their ripening processes
already have been
initiated by their own ethylene.
Semi-ripe tomatoes with 60 to 90% color can be held up to a week at 50
F. If held longer, they
will probably not have a normal shelf life during retailing. Riper tomatoes
will tolerate lower
temperatures. For example, "firm-rip" tomatoes can be held a few days at 45
to 50. Long
holding of ripened tomatoes at low temperatures (40 and below) results in loss
of color, shelf life,
Fully ripe: When it is necessary to hold fully ripe tomatoes for the
longest possible time before
their immediate consumption upon removal from storage, as for example, for
overseas use, they can be held at 32 to 35 F for up to 3 weeks. Such
acceptable, would not be of high quality and would have little if any shelf
life remaining. Mature-green, turning, or pink tomatoes should be ripened
before storing at such low
A storage temperature of 50 to 55 F is recommended for semi-ripe to
fully ripe greenhouse-grown
tomatoes. Ripening of less mature tomatoes at 70 F is recommended before
storage at 50 to 55
Research showed that an atmosphere with 3% oxygen and 97% nitrogen
extended the life of
mature-green tomatoes up to 6 weeks at 55 F and that the flavor of the ripened
fruit had no
off-flavor and was acceptable to the taste panel. A 1% or lower oxygen level
off-flavor. Increased carbon dioxide levels provide no benefit; in fact,
levels of 3 to 5% have been
reported to cause injury at 55 F.
Cherry tomatoes are commonly packaged in 8-lb baskets.
Mature green tomatoes are commonly packaged in 30-lb cartons and
Pink and ripe tomatoes are commonly packaged in 20-lb two-layer flats
and cartons, tray pack; or
28-lb three-layer lugs and cartons, tray pack; or 30-lb cartons, loose
NON-PATHOGENIC FRUIT DISORDERS
Blossom End Rot
Cause: Calcium deficiency aggravated by widely fluctuating soil moisture
conditions-nonpathogenic. Calcium in the fruit may be deficient because (1)
insufficient calcium in
the soil, (2) excess N, Mg, K or Na has been applied as fertilizer, (3) very
wet or very dry soils
interfere with uptake of calcium, (4) combinations of (1) to (3).
Symptoms: Black leathery lesions form on blossom end of fruit. The affected
area shrinks and
causes misshapen fruits. Only some fruits on a plant may be affected. Green as
well as ripe fruits
may be affected.
1. Add lime to adjust pH of soil to 6.8 to 7.2. Mix lime thoroughly in top 8
to 12 inches of soil.
Lime is best applied in fall.
2. Use only moderate amounts of additional fertilizers to keep plants normally
green and vigorous
but not luxuriant.
3. Do not plant tomatoes where drainage is poor, surface water accumulates, or
soil is droughty.
1. Mulch plants with black plastic or loose organic materials.
2. Fertilize with nitrogen side-dressing only if it is required to maintain
green color and
moderate-growth. Use calcium nitrate or ammonium sulfate at rate of 0.25 lb to
100 sq ft (100
3. Maintain uniform soil moisture. Apply water to wet all soil in root zone
every 7 to 10 days.
About 24 hours after watering, dig a small hole with a trowel to a depth of 1
foot to be certain
water has penetrated to that level.
4. If symptoms of blossom end rot are detected, spray the leaves and fruit
with calcium chloride at
the rate of 2 Tbs in 1 gal water (4 lb in 200 gal water/A). Apply two or more
sprays at 1-week
intervals. The spray may cause some injury to the margins of the leaves.
Gray-Wall or Blotchy Ripening
This disorder appears as gray or brown blotchy areas in the fruit wall
tissue, beginning when the
fruit is green. It can occur on more than half of the fruit of a particular
field. Cross-sections of
fruit show blackened tissue. This causes the external fruit color to look
somewhat gray. When the
fruit ripens, the area remains firm and turns from green to yellow, rather
than red. Fruit thus
ripens unevenly. The affected area appears woody when cut. White wall tissue
considered to be an early stage of gray wall, but may also be related to other
"internal white tissue" section below). A definite cause for gray wall has
not been defined but a
number of factors play a role in predisposing fruit to gray wall, these are
listed in their considered
lessening degree of importance:
1. Low light or prolonged cloudy periods.
2. Excess nitrogen causing excessive plant vigor.
3. High soil moisture from excess rain or irrigation.
4. Potassium deficiency.
5. Soil compaction.
6. Temperature fluctuations, particularly unusually cool nights and
Tobacco mosaic virus is also reported to be involved in gray wall. In
those cases the disorder is
also called internal browning. That tobacco mosaic virus is involved in a
disorder called internal
browning is not in dispute. What is in dispute is whether the two disorders
are the same or separate. In a few other cases certain bacteria and fungi are thought to also
be implicated. Another confusion is that gray wall is also sometimes called blotchy ripening!
Information from Florida indicates that the varieties Merced and
Floridade may have tolerance to the conditions that predispose tomatoes to gray wall
Internal white tissue
The expression of white tissue varies widely, and is considered dependent on
environmental conditions. It is sometimes attributed to gray wall. Potassium
deficiency and high
temperatures are believed to aggravate the problem.
Solar yellowing (also called yellow shoulder, yellow top and
persistent green shoulder)
This problem occurs most commonly on fruit ripening in late May and June
when days are
longest, sunlight is most intense, and temperatures exceed 85 F. Under such
(the red pigment in tomato) fails to develop normally in some varieties,
leaving only the carotene
(yellow) pigment to show at the shoulder or, with green-shoulder type
tomatoes, where the dark
green portion was. Even with temperatures under 85 F the surface temperature
of exposed fruit,
especially those with dark green shoulders can become high enough to inhibit
normal red color
development. In other parts of the day or night, when temperatures do not
exceed 85 F some red
color may develop, resulting in an orange rather than a yellow abnormality. To
problem, choose uniform-ripening varieties and protect fruit surfaces from
radiation by choosing varieties having good fruit cover or, by the use of
wash applied when fruit are at the mature-green stage. The white wash will
have to be removed
before the fruit is marketed.
Mature green and tomatoes just turning red are most susceptible. Fruit
develops white necrotic
tissue surrounded by a yellow halo. The area may be sunken and wrinkled.
Damage is confined
mainly to the upper portion of the fruit, and is seen where fruit that has
been covered by leaves is
suddenly exposed to light. The area can later be covered by a black fungus
when the rest of the
fruit turns red.
Roughness and scars
Varieties differ in susceptibility. associated with large fruit.
Particularly severe when young
plants are exposed to cool temperatures, and night temperatures below 50 F
when flower clusters
Varieties differ in susceptibility. Promoted by fluctuations in soil
moisture and temperature.
Often seen when varieties developed for hot, arid climates are subjected to
humid, wet conditions.
Cracks may be radial or concentric.
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