From: Brian Lo <dragon@csulb.edu>
Newsgroups: rec.gardens
Subject: FAQ: Tomatoes: Greenhouse
Date: Wed, 1 Mar 1995 09:08:47 -0800
GREENHOUSE TOMATO PRODUCTION
Midwinter greenhouse tomato production is not generally recommended for
western Oregon. Poor light intensity and high humidity often result in poor
fruit set and quality. Effective lighting and humidity control is not
considered to be economical. Heating and other production and marketing
costs, and competition from outdoor production from California, Arizona and
Mexico, and the availability of greenhouse tomatoes from Canada at competative
prices, make profitable greenhouse production in western Oregon difficult.
Greenhouse production in British Columbia is possible because of their high
inputs and the technical level of management possible in large operations (the
trend is to shift to operations of over 2 acres), and the high quality glass
greenhouses being used in the great majority of the operations, and their
strong marketing organiztion.
Tomato is the most commonly produced greenhouse vegetable crop.
Although claims by greenhouse promoters are made that 30 or more lbs. of
marketable fruit can be expected per plant (or plant-space) per year, such
production is only possible with very high inputs in quality facilities and
cultural practices. Production in western Oregon of about 20 to 25 lbs. would
be more realistic. A one crop schedule (December to December) is used by some
Pacific northwest growers and is common in British Columbia, Canada. Growers
there start their crop in January and harvest usually from March through
November. A two-crop system is recommended under western Oregon conditions.
This would consist of a fall (August to December) and a spring (January to
June) crop. A two crop system is at less risk from crop pests, and allows
fruit set and harvest when environmental conditions are best, and competition
from outdoor productions is lowest.
Depending on the number of units purchased, double polyethylene green-
house costs in 1994 would run about $6.00 to $7.00 per square foot. Hydropon-
ic equipment will cost another $1.50 to $2.00 per square foot. Land cost,
site preparation, foundations, concrete floors and electric, water and gas
service may cost another $3.50 to $4.00 a square foot. A number of different
materials are used in greenhouse structures and coverings which can result in
a wide range of total construction cost. This guide does not address green-
house engineering or coverings.
Approximately 25,000 to 35,000 square feet of greenhouse tomato produc-
tion is considered to be the minimum size economic unit. Smaller units are
often used for part time or hobby production. In Oregon, total greenhouse
vegetable production was just under one acre in 1994. This is similar for the
state of Washington.
Plants have been commonly grown in well fertilized, well drained soil
(ground- bed production). This conventional system is now largely replaced by
a soilless culture system. Soilless culture utilizes totally artificial means
of providing plants with nutrients and anchor. A major advantage is the
elimination of the need for soil sterilization, by steam or chemicals.
Due to environmental concerns, restrictions may be in place regarding
the disposal of excess fertilizer solutions and growing media. Possible
options are to discard fertilizer solutions by using it on pastures or in
other agricultural applications, and to recycle growing media by blending it
with other potting mixes or agricultural soils. Consult appropriate agencies
for available options.
SOILLESS CULTURE
Soilless culture is more demanding and less forgiving of mistakes than
conventional soil culture. Good nutrient media composition and nutrient
balance through the entire crop cycle are mandatory.
Soilless culture methods allow production of tomatoes in areas where
suitable soil is not available or where disease or other conditions make
ground production unfeasible. Although the system can be automated to mini-
mize irrigation and fertilization labor input, continuous monitoring of most
aspects of plant growth and culture media, nutrient balance, and a thorough
understanding of the crop and its physiology is critical. Costs of the au-
tomatic devices and special nutrient media are substantial.
All other aspects of production remain the same as with conventional
culture. There are little, or no yield or quality advantages over conven-
tional production if the quality of management is equal.
Excellent books on this subject are:
Hydroponic Food Production by Howard M. Resh, Woodbridge Press Publish-
ing Company, Santa Barbara, CA 93160.
A Guide for the Hydroponic & Soilless Culture Grower by J. Benton Jones,
Jr., Timber Press, POB 1631, Beaverton OR 97075.
Greenhouse Vegetable Production Guide for Commercial Growers 1993-1994
Edition. British Columbia Ministry of Agriculture, Fisheries and Food., 808
Douglas St. Victoria, British Columbia, Canada V8W 2Z7.
Two major soilless culture systems are used, those in which plant nutri-
ents are recirculated (closed-system hydroponics), and those that utilize
artificial media for plants to anchor but new nutrient solution is constantly
provided to the plants and the excess nutrient solution is not collected and
recirculated (open-system hydroponics or bag culture).
Closed-system hydroponic culture is the growing of plants in troughs or
tubes, where plants are anchored in gravel, sand, or artificial soilless
mixes; or without artificial media for anchor, such as nutrient-flow technique
(NFT). Any system used must be suitably built to allow proper application and
recirculation of the nutrient media. Flow rates of 1 1/2 to 2 quarts per
minute are most common. In a closed-system, the nutrient solution is regular-
ly monitored and adjusted for pH as needed. Because plants take up nutrients
at different rates, and roots exude certain chemicals, imbalances and problems
can occur. To prevent undesirable build up of certain elements, the nutrient
solution may need to be changed every 2-3 weeks with changes as often as once
per week during periods of peak growth. By careful monitoring of nutrients in
sloution and especially the electrical conductivity (EC) daily, and by
installing activated charcoal filters to remove certain toxic root exudates, a
large reservoir of nutrient solution may be maintained for one crop cycle (up
to 10-11 months). The EC should be maintained at 2.5, so that fresh water is
added when EC exceeds 2.5 and new, complete nutrient solution is added to
bring the EC back to 2.5.
Bag Culture uses artificial media (usually rockwool) packaged in 3 or 4
cubic foot bags. Rockwool comes in two densities, standard and low density.
The low density is used for one year and discarded. The standard density may
be sterilized and reused for up to three crops. Two common trade names are
Redi-Earth and Metro-Mix. The 4 cubic foot bags are best for tomatoes. Two
rows of tomatoes are usually planted per bag with plants spaced 16 inches
apart in each row with rows 16 inches apart. Bags are placed in rows 6 feet
apart, and spaced down the row to allow a uniform 16 inch spacing between
plants. A drip irrigation system with spaghetti drippers for each plant is
used to distribute the nutrient solution. A 10%-20% excess solution is
applied during cloudy cool periods and 25% to as high as 50% under sunny, warm
conditions to provide drainage and prevent salt buildup. This excess should
be collected and discarded or may be reused with certain restrictions.
Common modifications of this system (to reduce cost) utilize 3-5 gallon
plastic bags or pails with saw dust, pine bark or rice hull media. Western
Hemlock and Douglas-fir are most commonly available and the main ones used in
the Pacific Northwest. Avoid western red cedar because of possible toxicity
from chemicals in it. Use a medium-fine grade of horticultural grade (guaran-
teed to be free of toxic chemicals that may be used by the lumber industry).
If too fine a grade, the saw dust will limit oxygen exchange as it breaks down
resulting in root suffocation. Prior to using saw dust, test leachate conduc-
tivity for any salt accumulation and leach bags with fresh water if needed.
Modifications of the fertilizer program are necessary to compensate for
specific media. Of particular concern is possible manganese toxicity since
manganese can accumulate in wood to toxic levels. Check the first leaf tissue
samples and adjust manganese applications as needed.
Commercial fertilizer mixes are available through horticultural supply
companies. Follow directions carefully in preparing and dispensing the nutri-
ent solution. Choose a high quality fertilizer injection pump and system to
minimize fertilizer distribution problems. The major advantage of bag-
culture, is the reduced management of nutrient solution monitoring, and the
elimination of nutrient circulation, that is required in "closed" hydroponic
systems.
Hydroponic greenhouse promoters have often failed to present their
product fairly and have created unrealistic expectations. None of the package
offers of equipment and technical services guarantees success. Investigate
thoroughly before making financial investments.
PLANTING
Greenhouse tomatoes are always grown from transplants. Use a special
part of the greenhouse to grow these transplants. This can be a separate
greenhouse, or an area divided off from the main greenhouse where day and
night temperatures can be separately, and accurately maintained.
Plant the spring crop in early December, so harvest will begin in mid-
March. For this crop, seed into flats, then transfer seedlings to 4 inch
containers set close together when the first true leaf has formed. Space the
containers at an 8 x 8 inch spacing two to three weeks later to finish growing
the transplants. Set plants in their permanent location about mid February.
Although three and a half to 4 square feet of space per plant is often
used in other areas, about 4 1/2 to 5 square feet per plant would be more
appropriate under western Oregon conditions. Plants should be trained to a
single stem and supported by strings hanging from overhead wires.
Vines are usually removed by the end of July or early August when
outdoor tomatoes become available locally. From seeding, it takes about 5
months for a spring crop to begin to fruit.
Plant the fall crop in mid June, and set the plants in their permanent
location about August 1. It takes about 3 1/2 to 4 months from seeding until
first pick for a fall crop, which should begin in early October, after local
tomatoes are no longer available. Aim for a production peak around Thanks-
giving, terminating after Christmas or when heating costs and lighting con-
ditions become limiting in December.
VARIETIES
Variety selection is made to fit light intensity, fertility and disease
resistance requirements. Check variety descriptions for diseases to which the
variety is resistant, and the season to which it is best adapted.
Varieties such as Dombito, Belmondo, Jumbo and Trend are best adapted to
areas west of the Cascade Mountains and varieties such as Perfecto and Capello
to areas east of the Cascades. Caruso, which has sparse foliage is best
adapted to fall cropping, and may produce yellow-shouldered fruit under high
light intensities. Some varieties may be too vigorous, and can become too
viney under high water and fertilizer programs. Always test a variety in the
season it will be produced before committing to it.
Varieties (in the 6.5-7.5 ounces fruit range) that have been used in the
Pacific Northwest are: Laura, Capello, Cobra, Trust and Trend (all uniform
ripening); Caruso (semi-green shoulder) Dombito and Jumbo (green shoulder).
Varieties suggested for tried are: Belmondo, Boa, Carmello, Contento, Larget-
to and Match (all uniform ripening); also Dombello, Peto 109, Peto 656, Peto
761 (all green-shoulder). In all these varieties, provision for fruit set must
be made (see section on "pollination" below).
Parthenocarpic varieties needing little or no mechanical vibration for
pollination: Carpy, Quasar, Barry (these produce 4.0 to 5.0 ounce fruit) which
may be too small for most domestic markets.
Tomatoes for the U.S. market must be of a large size. Many European
varieties are not large enough. Know your market requirements for fruit
color, size and shape, and the variety fruit characteristics before selecting
the varieties to use. Fruit under 4 ounces is considered small, 4-6 ounce
fruit is marketable, and fruit over 6 ounces (large) is preferred.
SEED COMPANIES
Asgrow Seed Co., 7000 Portage Rd., Kalamazoo, MI 49001. 616/385-6665; or
Salinas, CA: 408/424-6905
Bruinsma Seeds b.v. (refer to Asgrow) or POB 1463 High River, Alberta T0L 1B0
CANADA ph: 403/652-4768
Crop King. POB 310, Medina, OH 44256 ph: 216/725-5656
DeRuiter Seeds Inc. POB 20228 Columbus, OH 43220 614/459-1489
Enza Zaden Seeds POB 7, 1600 AA, Enkhuisen, The Netherlands
Petoseed Co. Inc. 1905 Lirio St. POB 4206, Saticoy, CA 93007-4206.
ph: 805/647-1188
Rogers NK, P.O.B. 4727 Boise ID 83711-4727
Stokes Seeds Inc. Buffalo, NY 14240-0548 ph: 416/688-4300
Vilmorin Inc. 6104 Yorkshire Ter. Bethesda, MD 20814
Zenner Bros. Seed Co., Inc. 1311 S.E. Gideon St. Portland, OR 97202
ENVIRONMENTAL CONTROL
Accurate temperature, humidity, and carbon dioxide control are impor-
tant. Environmental control is accomplished in many ways ranging from totally
manual, to sophisticated computer-assisted control. Computers are also used
to monitor fertilizer and water applications.
A major consideration in environmental control is that of providing
temperature and humidity conducive to active movement of water and nutrients
through the plant for optimum growth. This is done by maintaining a humidity
of between 605 and 80% during daylight hours. In the Pacific Northwest, light
intensity and duration are limiting factors in winter making the economics of
supplemental lighting an important consideration. Light intensity is influ-
enced by external factors such as cloud cover and fog and also the quality of
the greenhouse covering and its condition. Dirt, dust, condensation and
degradation of the covering material itself can seriously reduce yields.
If a greenhouse is to be kept closed for long periods (several days at a
time) to conserve heat, you should provide suitable carbon dioxide generating
equipment (see below). Management of irrigation to control increased humidity
and control of increased disease problems also become critical in houses with
reduced ventilation.
Temperature Requirements
Temperature requirements for major greenhouse vegetables differ. In
general, the cooler temperatures are used when light intensities are low. For
tomatoes, days, 70 to 75 F.; nights, minimum 62-65 F. Where day temperatures
might exceed 85 to 90 F., cooling equipment is needed to prevent fruit set
failure and to allow proper red color developing in the maturing fruit.
Carbon dioxide enrichment
Carbon dioxide is normally present in the atmosphere at a concentration
of 300 parts per million parts of air. Carbon dioxide levels in greenhouse
air may be depleted to levels that may limit plant growth, especially in
tightly sealed greenhouses and when ventilation is restricted during daylight
hours. Addition of carbon dioxide to greenhouses has been demonstrated to im-
prove vegetable yields. Concentrations of 1,000 ppm. or more in greenhouse
atmospheres have given the best results. Yield increases of 20% or more have
been reported for tomatoes under certain conditions. Carbon dioxide generat-
ing and monitoring equipment is readily available. Flue gasses from certain
types of heaters and fuels, and even liquid carbon dioxide are used. Investi-
gate the various models and types before purchasing.
Concentrations should be adjusted for light intensity and growth stage as
follows:
Bright, sunny weather 1000 ppm
Cloudy weather 750 ppm
Young plants 700 ppm
During moderate ventilation 350 ppm
Light supplementation
Light intensity during seedling growth is directly related to the number
of days to flower and yield. Low light intensities delay flowering and reduce
fruit set and total yield. Under western Oregon winter conditions, light
levels are not adequate for good commercial production. This is due to both
the shorter days of winter and to frequent cloud cover and fog. Based on
research from Canada, winter light conditions in western Oregon can be
expected to result in as much as a 20 day delay in flowering and a 50% reduc-
tion in early yield for a crop intended for late winter and spring harvest.
Supplemental lighting becomes very important during this period and also when
plant populations are increased (and less than 4.5 to 5.0 square feet per
plant is used).
Light quality affects plant growth. Most high pressure sodium lights,
designed to produce high levels of photosynthetically active radiation (PAR),
tend to produce excessively elongated internodes. To compensate for this
metal halide lights which provide a greater portion of the blue spectrum may
be used. Light placement and lighting schedules also affect growth and
pollination.
Light intensity is a function of lamp wattage and distance from the
plant canopy. About 650 foot candles at the leaf surface are considered
necessary for normal growth. With one design, a 1000 watt metal halide lamp
covers approximately 112 square feet when 600 foot candles are desired. This
translates to approximately 32 fixtures needed for a 30' x 120' greenhouse!
Since each 1000 watt fixture gives off about 3750 btu. per hour, fuel savings
would also be realized during the time the lights were operating. Growers
must carefully evaluate supplemental lighting and test its efficacy under
their conditions.
Although supplemental lighting increases yield under adverse sunlight
conditions when all other production conditions (carbon dioxide, etc.) are
optimal, the increased cost of installation, operation and maintenance of the
lights and price competition from other tomato production areas makes the
economics of supplemental lighting marginal in Oregon.
FERTILIZER
Tailor fertilizer programs for specific crops and soil fertility situ-
ations. Proper fertility is necessary for success. Plants have different
fertilizer requirements during different stages of their growing cycle.
Whether you use soil or a soilless system, no single set of recommendations
will apply, so use soil tests to determine initial applications, and monitor
fertility levels by leaf analysis throughout the growing season. Both soil
tests and leaf analyses are available through Oregon State University Exten-
sion offices.
In conventional soil culture, a routine fertilizer program would be the
addition of 0-20-20 fertilizer at 1,000 to 2,000 pounds per acre before the
fall crop, and 650 to 1,000 pounds before the spring crop or, you can supply
phosphorous by applying 46 percent triple super phosphate at 300 to 500 pounds
per acre and potassium by using potassium sulfate at 300 to 400 pounds.
Add nitrogen as ammonium nitrate, calcium nitrate, or potassium nitrate
before planting and throughout the season, depending on the amount of organic
matter in the soil. Feed weekly with solutions of balanced fertilizers.
Proper feeding of tomatoes with nitrogen in critical. Too much nitrogen
when the plants are small will result in soft growth, small flower clusters,
and poor set. Apply nitrogen in limited quantities before planting, at about
50 pounds per acre, and apply weekly as necessary to maintain adequate
nitrogen levels in the leaves. Nitrogen levels may be monitored by regular
leaf-petiole analysis.
Micronutrients are normally provided by the soil's clay and organic
fractions. Soil tests are necessary to determine which if any micronutrients
must be added.
In soilless culture, all major and micro-nutrients must be added, and
kept in balance. A number of soilless culture systems are available. These
are variations of the "closed" or "open" systems described earlier. Fertiliz-
er proportioners are used to accurately inject the proper amount of nutrient
concentrate into the water stream used for irrigating the plants.
Totally soluble hydroponic fertilizer mixtures are available from
regional horticultural supply houses. Follow manufacturer's recommendations
carefully and completely as outlined specifically for tomatoes. Improper
alterations of formulas or instructions for their use, can result in serious
production problems.
Most commonly at least two stock tanks are needed to prevent insoluble
precipitates from forming when the nutrients are mixed and injected. One
stock tank is usually used to mix potassium nitrate, calcium nitrate and iron
chelate. The other contains the phosphorous source, magnesium sulfate,
potassium chloride and the rest of the micronutrients. This is done to
prevent the formation of insoluble precipitates that most commonly occur from
the mixing of calcium nitrate and phosphorous materials.
The use of more expensive "technical grade" fertilizer salts eliminates
sludges from forming. Where "fertilizer grade" materials are used, sludges
will form in the potassium nitrate, calcium nitrate tank due to insoluble
additives used in these fertilizers to prevent caking and dust.
For a check on crop progress leaf samples should be taken at regular
intervals beginning at about the time the third cluster begins to set. Sample
the whole leaf with petiole, choosing the newest fully expanded leaf below the
last open flower cluster. Sufficiency leaf analysis ranges for newest fully-
expanded, dried whole leaves are*:
Macronutrients (percent) Micronutrients (parts per million)
Prior to fruiting During fruiting Prior to fruiting During fruiting
N: 4.0-5.0 3.5-4.0 Fe: 50-200 50-200
P: 0.5-0.8 0.4-0.6 Zn: 25-60 25-60
K: 3.5-4.5 2.8-4.0 Mn: 50-125 50-125
Ca: 0.9-1.8 1.0-2.0 Cu: 8-20 8-20
Mg: 0.5-0.8 0.4-1.0 B: 35-60 35-60
S: 0.4-0.8 0.4-0.8 Mo: 1-5 1-5
Toxic levels for B, Mn, and Zn are reported as 150, 500 and 300
ppm respectively*.
* Taken from J.M. Gerber 1985. Plant growth and nutrient formulas.
pp.58-69. In A.J. Savage (ed.). Hydroponics Worldwide: State of
the art in soilless crop porduction. Int'l Ctr. for Special
Studies, Honolulu, Hawaii).
MULCHING
If mulches are used, apply to the soil when tomatoes are about two feet
high. Straw mulch is most common, used at about 200 bales per acre. The
mulch reduces evaporation of water from the soil and prevents compaction of
the surface. White (reflective) plastic mulches are recommended to control
weeds, conserve moisture, reduce humidity, and improve light conditions.
WATERING
Maintain an adequate supply of water to plant roots. Excess water re-
duces soil aeration. Young plants put in the greenhouse in mid-winter May
need to be watered only once every 10 to 14 days. The same plants in mid-
summer may need water every two or three days in ground beds. A fall crop
would need a total of about 15 to 18 inches; a spring crop may need 20 to 25
inches of water.
With bag culture, mature plants may need to be watered several times a
day. One to 3 quarts per plant per day may be needed depending on growth
stage and plant size.
POLLINATION
Tomatoes are self pollinating under open field conditions. Pollen sheds
and fertilization occurs as a function of normal air movement and its agi-
tation of the plants and flowers. Under greenhouse conditions, flowers need
to be agitated mechanically, or fruit needs to be set using plant chemical
hormones that are sprayed on flower clusters on a regular basis.
A few new varieties have been developed that are parthenocarpic (need no
pollination, and are seedless). These generally have small to medium size
fruit and have not been tested adequately in the Pacific Northwest (see
section on "varieties" above).
Pollination by mechanical vibration is recommended with the large
fruited U.S. and European varieties. This is accomplished using a hand
operated electric vibrator available from horticultural supply companies.
These vibrators operate on 110 volt or battery power. The battery powered
models use a 6 or 12 volt motorcycle battery. Units using flashlight batter-
ies have insufficient action for best pollination. Many other methods have
been tried or tested. None have been as good.
Timing is important when using mechanical vibrators to set fruit.
Pollen sheds most readily when temperature is at its peak, and relative
humidity lowest on a given day. The optimum time for that is between 11 a.m.
and 3 p.m. during winter and early spring. Each flower cluster needs to be
vibrated every day, as long as flowers are still opening in that cluster, to
accomplish pollination of the flowers that open on that day.
Note: Special bees (bumble bees) are now being used for pollination.
These bees mechanically agitate tomato flower clusters to acquire pollen
and thus accomplish pollination. Currently, the high cost of obtaining
these bees has limited them to use in very large interconnected green-
house ranges. The bees would have to be obtained from special bee
keepers. Research is also underway at Oregon State University to test
the efficacy of leaf-cutter bees for mechanically agitating tomato
flower clusters for pollination.
Chemical fruit set is commonly used in European greenhouse tomato pro-
duction on varieties that have been specifically developed to produce high
quality fruit with this method. Most large fruited varieties used in the U.S.
will develop hollow, soft and misshapen fruit with the use of chemical setting
agents, therefore chemical fruit setting is not recommended.
PRUNING AND TRAINING
Auxiliary branches must be pruned as the plant is trained to a single
stem, supported by string to an overhead wire. In rare occasions, especially
when grafted plants are used, plants may be trained in a double stem configu-
ration.
With varieties that tend to produce small fruit, cluster pruning is used
to increase fruit size, and limit the number of fruit per cluster. Generally,
3-4 fruit per cluster are allowed to develop with these varieties.
To reduce the likelihood of disease spread (especially Tobacco Mosaic
Virus), exercise careful sanitary procedures. Workers should use disposable
gloves, disposing them, and sanitizing pruning instruments at the end of each
row. No tobacco products should be allowed in the greenhouse, and users of
such products must not handle TMV susceptible tomato varieties.
PEST CONTROL
Proper control of plant disease is critical in greenhouse environments,
where high temperatures and humidity are ideal for diseases to develop.
Insect and nematode infestations can also become rampant under confined
greenhouse conditions.
You can control most fungus and virus diseases with resistant varieties,
fungicides and proper sanitation and sterilization of soils, growth media, and
equipment. The most serious fungus diseases on tomatoes are leaf mold
(Cladosporium), early blight (Alternaria), leaf spot (Septoria), gray mold
(Botrytis), and the wilt diseases (Fusarium and Verticillium).
Tobacco mosaic virus resistant varieties are available. When suscepti-
ble varieties are grown, this virus disease can be serious and several other
virus diseases may occur. Resistant varieties, proper sanitation to reduce
spread by workers, soil sterilization, and control of insect vectors are some
of the methods of control.
Early control of white fly, aphid, and spider mite infestation is im-
portant. Several biological agents and chemicals are available to control
these pests.
Nematodes and several fungus diseases may become a problem in either
soil or hydroponic culture. Sterilization of soil or hydroponic media is used
as a preventative measure.
Control of pests in greenhouse production is different from that used in
open field production and requires pesticide lables and uses specifically for
greenhouses. Current recommendations on pesticides are available from your
county Extension agent or pesticide dealer. Always follow label instructions
and safety precautions precisely.
NON-PATHOGENIC FRUIT DISORDERS
Blossom-End Rot: Varieties differ in susceptibility. Caused by calcium
imbalance or deficiency during critical stage of fruit differentiation and
expansion, usually induced by water stress.
Gray-Wall: Linked to high plant vigor, associated with high rates of
nitrogen fertilization with high soil moisture and low temperature. In some
cases certain bacteria, fungi and/or tobacco mosaic virus are thought to be
involved in gray wall. Often associated with blotchy ripening (see below).
Blotchy Ripening: Promoted by low potassium levels in the fruit, high
soil moisture and humidity and fluctuating temperatures during fruit ripening
(above 85 F.) and low sunlight levels, or shaded areas in the plant canopy.
Aggravated by compacted soils.
Solar yellowing: 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 conditions, lycopene (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 toma-
toes, 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 abnormali-
ty. To reduce this problem, protect fruit surfaces from short-wave solar
radiation by altering pruning practice in March and April by allowing two
leaves to form on axillary branches rather than removing the axillary branch-
es. The use of non-phytotoxic white wash will also help if applied when fruit
are at the mature green stage. The white wash will have to be removed before
the fruit is marketed.
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 are
differentiating.
Fruit cracks: Varieties differ in susceptibility. Promoted by fluctua-
tions in soil moisture and temperature. Often seen when varieties developed
for hot, arid climates are subjected to humid, wet conditions.
HARVESTING HANDLING AND STORAGE
Yields from a two-crops-per-year system would be about 8 pounds of fruit
per plant from the fall crop, assuming a 2 to 3 month harvest period ending in
late December (0.8 lbs/plant/week is considered very good). Approximately
12-15 pounds of fruit per plant may be realized from the spring crop assuming
a 4 month harvest period ending just after the July 4th holiday.
Yield from a single-crop-per-year system, where harvest begins about mid
October and ends in July the following year, could produce a total of about
25-27 lbs./plant (based on 0.5-0.75 lbs./plant/week). The lower output per
week per plant shown is due to adverse winter climatic conditions (cloudiness
and high humidity) generally experienced west of the Cascade mountains.
Fruit is harvested when mature green if it is to be held before market-
ing. Mature green fruit have well developed internal gel, and may have inter-
nal tissues that are beginning to turn red. Vine ripe fruit ranges from fruit
just turning red to fully ripened, depending on market requirement. When har-
vesting and handling, avoid bruising fruit.
The USDA Grade Standards for Fresh Tomatoes recognize 6 official color
designations:
1) Green - surface of the tomato is completely green;
2) Breakers - a definite break in color from green to tannish-yellow,
pink or red on no more than 10% of the surface;
3) Turning- more than 10% but less than 30% of the surface, in the
aggregate, shows change as in 2) above;
4) Pink- more than 30% but less than 60% of aggregate surface shows
pink or red color;
5) Light Red - more than 60% of aggregate surface is reddish pink or
red provided that not more than 90 % is red;
6) Red- more tan 90% of surface in the aggregate show red color.
STORAGE (quoted form USDA Ag. Handbook # 66):
Store mature-green tomatoes at 55 to 70 F; ripe fruit at 45 to 50 F and
a relative humidity of 90 to 95%.
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 mature-green tomatoes 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
subsequent ripening. Increased decay during ripening occurs after 6 days'
exposure at 32 or 9 days at 40 F. Mature-green tomatoes may also be damaged
by low temperatures in the field. A high percentage of tomatoes exposed to
temperatures below 50 F for a week before harvest would probably 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 in storage and during transit, have a cumula-
tive effect. Thus, fruit chilled for only a short period in storage can
become very susceptible to decay when held for only a short period at chilling
temperature during marketing. Tomatoes should be kept out of cold, wet rooms
because in addition to potential development of chilling injury, extended
refrigeration damages the ability of fruit to develop desirable fresh tomato
flavor.
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-ripe" 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, and firmness.
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 ship-board or overseas use, they can be held at 32 to 35 F.
for up to 3 weeks. Such tomatoes, although acceptable, would not be of high
quality and would have little if any shelf life remaining.
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 ship-board or overseas use, they can be held at
32 to 35 F for up to 3 weeks. Such tomatoes, although 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
temperatures.
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 F.
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 can cause 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.
PACKAGING
One function of post-harvest handling in packing houses today is the
washing, brushing and cleaning of produce to remove any pesticide residues
that may be on the fruit. Tomatoes lend themselves well to such procedures.
Package tomatoes by size in 8-10 pound, single layer cartons, or 20 lbs.
double layers. Use only containers intended for greenhouse-produced fruit,
and so designated. In general only top grade fruit is marketed. Greenhouse
tomato fruit is usually individually differentiated with stick-on lables.
Misshapen and defective fruit should be removed from vines as soon as it is so
recognized.
PEST CONTROL FOR GREENHOUSE TOMATO PRODUCTION
USE PESTICIDES SAFELY!
Wear protective clothing and safety devices as recommended on the label.
Bathe or shower after each use.
Read the pesticide label--even if you've used the pesticide before. Follow
closely the instructions on the label (and any other directions you have).
Be cautious when you apply pesticides. Know your legal responsibility as a
pesticide applicator. You may be liable for injury or damage resulting from
pesticide use.
PEST CONTROL
Proper control of plant disease is critical in greenhouse environments,
where high temperatures and humidity are ideal for diseases to develop.
Insect and nematode infestations, too, can become rampant under the confined
greenhouse conditions.
You can control most fungus and virus diseases with fungicides and proper
sanitation and sterilization of soils, growth media, and equipment. The most
serious fungus disease on tomatoes are leaf mold (Cladosporium), early blight
(Alternaria), leaf spot (Septoria), gray mold (Botrytis), and the wilt
diseases (Fusarium and Verticillium).
Tobacco mosaic virus can be serious and several other virus diseases may
occur. Proper sanitation to reduce spread by workers, soil sterilization, and
control of insect vectors are some of the methods of control.
Powdery mildew (Erysiphe) is a common fungus disease on cucumbers;
chemical controls are available. Several virus diseases also affect cucum-
bers.
Bottom rot (Sclerotinia) is a troublesome lettuce disease which can be
difficult to control. Few other diseases are troublesome in greenhouse
lettuce.
Early control of white fly, aphid, and spider mite infestation is im-
portant. Several chemicals are available to control these pests.
Nematodes may become a problem in either soil or hydroponic culture.
Sterilization of soil or hydroponic media is used as a preventative measure.
Current recommendations on pesticides are available from your county Extension
agent. Always follow label instructions and safety precautions precisely.
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This information was prepared by the Oregon State University
Extension Service from Oregon and Pacific NW publications as well
as other vegetable production guidelines from public insti-
tutions in the U.S. and Canada. These guidelines are intended as
a general guide for Oregon commercial vegetable producers.
Address comments or questions to your County Extension Agent or
Dr. N.S. Mansour, Department of Horticulture, Oregon State
University, Corvallis, OR 9733l
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