The Secret to Successful Fresh Market Tomatoes
A Higher Score growers  bible

by Henry G. Taber, Mark L. Gleason, and Donald R. Lewis
Iowa State University

SPONSERED BY: PLANTMEDS RESEARCH; PLANTMEDS.COM
 

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 INTRODUCTION

Tomatoes rank as one of the top two vegetable crops in farm value in the United States and are the most popular home garden vegetable. They are native to South America in the Peru-Bolivia-Ecuador area of the Andes Mountains. In the wild, tomato fruits are about the size of large pearls or cherries. A relatively new crop to the United States, tomatoes were not established here until the late 1800s. Before that time, they were considered poisonous.

No tomato varieties were developed in the U.S. before 1860. The first improvement was made by Henry Tilden of Davenport, Iowa, in 1865 and appropriately was called "Tilden."

Tomato production is usually most profitable when the crop is planted early, if frost protection is available. The tomato is a warm-season plant and is very sensitive to chilling and freezing temperatures. The optimum temperature for growth is between 70 degrees and 80 degrees F and most varieties will not set fruit if the night temperature falls below 50 degrees F. Also, excessively high daytime temperatures approaching 100 degrees F could result in poor fruit set. Low temperatures (below 40 degrees F) at spring transplanting may result in plant damage or death, particularly if the transplants are weak or leggy. Rough and pithy fruit with poorly developed color on the first cluster results from growing plants below 60 degrees F in cold, damp soil. It is advisable to not transplant too early in the spring.

A good, stocky plant set out about mid-May in central Iowa is likely to do better than a young transplant set out in mid to late April under cool, windy conditions.
 

PLANTING

Site Selection
Tomatoes are fairly adaptable and can be grown in soil types ranging from light, sandy soil to heavy, silty clay loam soil if the site is well-drained. A well-drained soil that warms up in the spring is the most desirable. On loam or heavier soils, the site should be plowed 8 to 10 inches deep in the fall and disked well in the spring to produce a plant bed. Rotate crops so that tomatoes are not grown in the same soil more than 3 to 4 years. Avoid soils that have been planted with other Solanaceae crops, such as potatoes, eggplant, or peppers, because of potential disease infestation.

A light, sandy soil on a sheltered, gently sloping site with a southern or southeast exposure is preferred for earliest production. Using a rye cover crop in the fall and rotovating only the strip where the tomato row will be works best. The rye strip between every row will decrease wind problems on tender new transplants.

Some growers have used plastic row covers or hot tents to hasten early fruit production. This is not always effective because the high temperatures under some row covers and hot tents cause poor fruit set on the first clusters. If you do use a row cover, be sure to provide plenty of ventilation.

Plastic Mulch

Black plastic and straw mulches aid in weed control, soil moisture retention, and fruit disease control. Black plastic has an additional advantage in slowing soluble nitrogen fertilizer losses.

Black plastic mulch, laid before planting, aids in weed control, reduces root pruning, and gives a profitable increase in early yields some years. It is not always possible to enhance early yields by the use of black plastic. Research at the Iowa State University Horticulture Research Station in central Iowa shows inconsistent results from year to year. Plastic mulch may be beneficial because soil moisture is retained, less fertilizer is lost, and nitrogen sidedressings are often unnecessary.

Try to lay the plastic as early in the season as possible, such as late April or early May. It should be laid as soon as the ground can be worked after a heavy rain. It is very important that the plastic be laid over moist soil. If the plastic is laid over dry soil, it will delay subsequent transplant growth. It is advisable to lay the plastic at midday when it is warm enough to allow the plastic to be stretched tightly. Do not overdo stretching because cool nights may cause the plastic to tear.

The seedbed should be as fine as possible for good covering. Rototilling is preferred. The plastic is laid by burying about 2-4 inches of each edge.

Transplant Production
Disease-free seed is the key consideration in raising transplants. It is important to use seed treated with hot water to kill seed-borne bacterial diseases, such as spot, speck, and canker, which is more prevalent in the Midwest. A hot water treatment also kills anthracnose.

Treat the seed as follows to ensure disease-free seed.

1. Place the seed in a cheesecloth bag of suitable size; fill the bag more than half full of seed.

2. Wet the seed and bag with warm water. Maintain the water temperature at 120 degrees F for 25 minutes. Do this by stirring the water several times. Be sure to use an accurate thermometer. If the water temperature is too high -- 130 degrees F -- it will not kill the tomato seed, but the seed must be planted within a few days.

3. Spread the seed out on a clean surface and allow to dry.

4. Treat the seed with 75 percent Thiram seed protectant at the rate of 1 teaspoon per pound of seed.

An excellent transplant for field production. Although expensive to produce, this stocky transplant will produce top yields.

Controlling temperatures, water, nutrients, and growing space produces a good, stocky transplant. Provide 6 to 10 square inches per plant in the flat. Daytime temperatures should be between 70 and 80 degrees F and nighttime temperatures should be lowered to 55 degrees F.

Transplant to the field after all danger of frost is past and the soil temperature is at least 60 degrees F. Use a fertilizer high in phosphate, such as 10-52-17 or 9-45-9 as a starter solution. Add a cup of starter solution to each plant.
 

SPACING & TRAINING

Indeterminate Varieties
Rows should be 5 to 6 feet apart with plants 30 to 36 inches apart in the row. If staking indeterminate tomatoes, rows can be 4 to 5 feet apart with plants 18 to 24 inches apart in the row.

Determinate Varieties
Rows should be 3 1/2 to 5 feet apart with plants 12 to 24 inches apart in the row.

The common planting system involves ground grown semi-determinate varieties, usually on plastic or straw mulch. The major training system used is wire cages.

Cages are the main training system for fresh market tomatoes allowing the semi-determinate varieties more foliage cover for fruit protection from the sun.

Plants grown in cages are usually not pruned. The individual wire cage supports the tomato plant, giving a higher marketable yield by keeping the fruit off the ground . The advantages of cages are ease of use, high yields, and excellent fruit quality. The disadvantages of cage-grown plants include greater difficulty in harvesting and storage and the cost of cages. Cages are made from reinforced concrete fencing (6 by 6 inch squares), 18 to 22 inches in diameter and 3 to 4 feet high.

Staking and training tomato plants offers the advantages of an increase in the percent of marketable fruit, easier harvesting, and reduced injury to both plants and fruit during harvest. The major disadvantage is the high cost of staking and pruning, which could eliminate any profit. The market outlet must justify this procedure.

In addition to being a costly operation, staking and pruning practices reduce the total yield per plant because laterals and potential flower clusters are removed. When plants are staked, the vines are usually pruned to two main stems. This is done by pinching out new shoots or suckers as they appear in the leaf axils, up to about the third flower cluster. Suckers should be removed by hand when they are relatively small, about 2 inches in length, but no more than 4 inches long. Break off shoots by hand, rather than using a knife, to avoid transferring disease organisms. The vines are tied to stakes of 1-inch square or larger at approximately 10-inch intervals. Staked tomatoes can be planted closer together, about 18 to 24 inches apart. This permits more plants to be grown in a given area, thus increasing total yield per acre.

Pinching out new shoots in the leaf axils of staked tomatoes

The pruning operation for staked tomatoes creates stress on the plant related to soil moisture supply. If heavily pruned, there will be an increase in cracked and blotchy ripened tomatoes. Staked and pruned plants must receive a continuous water supply of 1 inch per week. They require constant, even watering to prevent cracks, blossom-end rot, and blotchy ripening. Blotchy ripening is a physiological disorder that can be triggered by any condition that slows growth. Some major causes are low temperature, water stress, virus diseases, lack of nutrients or nutrient imbalance, and prolonged cloudy weather.
 

FERTILIZING

Lime
It is important to maintain minimum soil pH of 6.0 to 6.8. Caution: Many areas of the state, particularly in western Iowa, have high pH values over 7 and do not need lime.

Rates
N (nitrogen): Sandy soils; 60 to 70 lb. of N/acre, disked in before planting. Apply 30 to 40 lb. N/acre approximately 3 to 4 weeks after transplanting. Loam, silt loam, and silty clay loams; 60 to 80 lb. of N/acre, disked in before planting. Adjust rates according to previous cropping management.
P205 (phosphate): 50 to 160 lb./acre, adjusted according to soil tests.
K2O (potash): 50 to 250 lb./acre, adjusted according to soil tests.

Application
Broadcast 50 to 75 percent of the fertilizer before plowing. Apply the remainder in bands 2 inches deep and 3 to 4 inches from the row at or near the time of setting plants in the field. When setting out transplants, apply a common starter solution such as 10-52-8, 9-23-7, or 10-34-0 at the rate of 1 pint of solution per plant. Starter solution is made by dissolving approximately 3 pounds of dry fertilizer in 50 gallons of water. Follow directions on the label.
 

VARIETIES

Radial (upper left) and concentric (upper and lower right) cracking are major varietal problems under Iowa growing conditions. Lower left is the desirable fruit.

Varieties should be chosen with care to obtain the best economic return. The major problems with most varieties under Iowa conditions are cracking, green shoulder, and blotchy ripening. Not all varieties will perform consistently in all areas and years.

When selecting varieties, consider the market outlet. If the intent is for early fresh market production, use a medium early (70 to 75 day) variety that will produce high yields of larger size fruit. Top considerations should be high yields with fruit of uniform color development throughout the outer and inner fleshy walls. Smooth surface, small seed cells, and firm flesh are also important. The plant should be well-developed, vigorous and produce heavy foliage to prevent sunscalding. The variety should be resistant to soil-borne diseases, such as fusarium and verticilliuim wilts.

The current trend in variety development by seed companies is producing a semideterminate or determinate vegetative type of plant with a heavy fruit load. This reduces space requirements and increasees production per acre because plants can be set closer together.

The determinate varieties are those with small, compact vines. The fruit clusters on these vines are concentrated at the ends of short branches, exposing them to direct sunlight. Thus, these varieties are typically early and fruit may be somewhat orange-red in color and tend to sunscald under Iowa conditions. The harvest duration of early determinate plants generally would be no more than 3 weeks.

Semideterminate growth habit, which has more foliage cover, is preferred. A good producer under Iowa conditions has been Mtn. Spring. Other varieties can be planted at the same time to extend the season until frost.

Indeterminate varieties normally have a long production season and have large, sometimes sprawling, vines. Yields are often heaver than those of determinate plants but the maturity date is late. The Jetstar variety has been the most consistent top quality producer under Iowa conditions.

Growers should plant small numbers of new varieties to determine the best type for their soil and location. Avoid large plantings until the variety has been proven for the site.

Fruit size is an important characteristic for the market place. Grocery stores usually prefer large tomatoes, whereas roadside stands, restaurants, etc., will often take smaller tomatoes. Markets refer to the sizes as 5 x 6, 6 x 7, etc.

Characteristics of suggested fresh market tomato varieties.

Resistance does not imply immunity. The degree of resistance or tolerance will vary with variety, disease pressure, and environmental conditions. F1= Fusarium wilt Race 1; F2= Fusarium wilt Race 2; V= Verticillium wilt; N= Nematode (primarily root knot species). Vine type growth habit: D= determinate, SD= semi-determinate, I= indeterminate.
 

IRRIGATION

As the fruit nears maturity, major problems experienced in Iowa are radial and concentric cracking, blotchy ripening, and blossom-end rot. Most often these problems are related to variety and fluctuations in soil moisture levels. Therefore, for top economic return, irritation should be applied before the soil dries beyond the point of less than 50 percent of the water at field capacity. One of the most practical ways of determining when to water is the "squeeze test." When a ball of soil is squeezed in the palm of the hand and still holds together, it is considered to have more moisture than 50 percent of field capacity. A better method is instrumentation. There are many good soil measuring devices available, such as tensiometers and soil moisture blocks.

Fruit size and quality can be greatly reduced because of inadequate irrigation. Tomato plants will require about 1 to 1 1/2 inches of water per week during the growing season. Overhead irrigation systems are popular and can be used for other crops. However, a fixed system may be needed if staking or trellising tomatoes.

The trickle system is gaining popularity in many parts of the country and is being used successfully in Iowa. The trickle system involves pumping water at low pressures through plastic tubing so that the water trickles slowly from small openings along the length of the tubing. Its advantage is that it will operate with low pressure and low flow rates. Water is kept off the plant foliage because the tubing lays directly on the soil near each row of plants.

PEST MANAGEMENT

For up-to-date pest management information obtain a copy of FG-600, titled: Midwest Vegetable Production Guide for Commercial Growers. The guide is updated annually. You can obtain a copy from your county extension office or write directly to: Ag Publications and Distribution Center, 119 Kooser Drive, Iowa State University, Ames, IA 50011.

Weed Control

Effective weed control is possible with careful planning and use of several weed control strategies. The first step in achieving acceptable weed control is field selection and preparation. Tomatoes should not be planted in fields infested with high populations of difficult to control or perennial weeds. Efforts to control these weeds (hemp dogbane, quackgrass, yellow nutsedge, velveetleaf, etc.) should be made either while producing crops such as corn and soybeans where more control options are available, or by leaving the land fallow and concentrating control efforts while the land is idle.

The type of control program selected depends on the size of operation, equipment available for use, and severity of weed problems. Cultural strategies, such as cultivation, hand weeding, and the use of mulches, may provide adequate control when weed pressures are low or the operation is small enough to allow several timely cultivations. Herbicides may be needed to supplement cultural control measures where weed populations are high or labor is limited. The grower should not abandon the use of appropriate cultural strategies when herbicides are used.

Herbicide Selection
Modern herbicides have been developed that provide consistent weed control with minimal risk of injury to the crop or the environment. However, unfavorable weather conditions before or after application, or misapplication of a herbicide may result in poor weed control or severe crop injury. The grower should be aware of these inherent risks before using any herbicide. It is recommended that a tomato producer use a new chemical on a limited basis until experienced in the use of that herbicide.

Several types of herbicides are available to the vegetable producer. Selection of a specific chemical should be based on cultural practices, weed species present, soil type, and the type of equipment that is available. Certain chemicals may be used on both direct-seeded and transplanted tomatoes. while others may be used only on transplants.

Preemergence Herbicides
Preemergence herbicides normally are applied before either the crop or weeds emerge through the soil and are effective only against germinating seedlings. They have little or no effect on established weeds. Some of these herbicides may be mechanically incorporated into the upper layer of soil before planting the crop (preplant incorporated). Incorporation places the herbicide into the soil zone where most weed seeds germinate, and also prevents the loss of volatile herbicides (Treflan, Tillam, and others) from the soil surface. The herbicide label will provide instructions regarding requirements for and methods of incorporation.

Many preemergence herbicides can be left on the soil surface following application. Surface-applied herbicides require rainfall to be activated. If rainfall fails to occur within 7 days of application, control may be improved if the herbicide is worked into the soil. This can be done either with overhead irrigation or, if cultural practices allow, by using a rotary hoe.

Postemergence Herbicides
Portemergence herbicides are applied directly to the foliage of established weeds. Contact postemergence herbicides kill only the portion of the plant that is wetted by the spray (such as Gramoxone). None of the herbicide is moved through the plant to the root system. Thus, these herbicides are generally only effective against small annual weeds. Translocated postemergence herbicides are absorbed by the foliage and move throughout the plant. They can be effective against many perennial species. Metribuzin (Lexone, Sencor) and Poast are herbicides cleared for postemergence use in tomatoes.

Selective herbicides normally control a fairly specific group of weeds. Because of this, it is important to choose a herbicide that is effective against the predominant weeds found in a specific field. A combination of herbicides may be required in certain fields to provide adequate control of all the weeds present.

Sprayer calibration and maintenance are other important aspects of herbicide use. Consistent results can only be obtained when a herbicide is uniformly applied at the recommended rate. A sprayer capable of applying spray volumes ranging from 20 to 50 gallons per acre at pressures between 20 and 50 psi will be adequate. Flat fan nozzles are well adapted for most herbicide applications. Herbicides should not be applied at the high pressures (80-120 psi) used to apply many fungicides and insecticides. Do not use a sprayer for applying fungicides or insecticides if it has been used to spray 2, 4-D or related compounds.
 

Tomato Diseases

Diseases are often a limiting factor in tomato production in Iowa. The development of a control program requires recognition of disease symptoms and proper identification of the cause. The symptoms, biology, and control of the important wilts, blights, fruit rots, and virus diseases are outlined in this section.

Most of the diseases discussed below can be introduced into a planting through infected seed or on diseased transplants. Yield losses can be large if diseases are established early in the growing season and continue to build up until harvest. All seed and transplants should be of high quality and disease free. Transplants should be checked for mottling or deformation of foliage, leaf spots, and wilting before planting. Roots also should be examined for root rot and swelling or knots that may indicate root knot nematode is present. Some diseases may be present on transplants without causing observable symptoms. Periodic scouting of fields after planting will help identify disease problems before they reach damaging and unmanagable levels.

Wilt Diseases

Bacterial Canker

Bacterial canker typically produces a wide range of symptoms on tomatoes. The bacterium, Clavibacter michiganense, is systemic and initially causes leaflets to wilt on one side of a leaf. Wilting of branches or entire portions of young and old plants develops as the disease progresses. Vascular discoloration may accompany wilting although it rarely extends to the soil line (see Fusarium and Verticillium wilts). Infection in older plants causes leaflets to brown from the markin inward to the midrib. Entire leaves and branches eventually die, brown, and hang from the plant. Cankers, if present, develop as white to yellow streaks on petioles and stems. The streaks brown and crack to form elongate cankers that may reveal decayed internal stem tissues. Infection of green and ripe fruit is common. Fruit spots are circular, raised, and have a rough tan to brown center and a white halo. The white halo symptom distinguishes bacterial canker fruit infection from backterial spot infections.

Clavibacter michiganense is often introduced on infected transplants, although it can survive in infested residues and seed. Natural spread of the bacterium occurs during hard or driving rains. The bacterium also can be spread during pruning and trellising or on tools, people, or equipment moving in fields while foliage is wet.

For control of bacterial cancer, rotate crops, control weeds, and be sure all seed and transplants are disease free.

Fusarium Wilt

Fusarium wilt is one of the most serious tomato diseases. The fungus, Fusarium oxysporum f. sp. lycopersicae, causes plants to progressively yellow and wilt from the lower branches upward. Yellowing of lower leaves usually begins on one side of a leaf, branch, or portion of a plant. Eventually, entire branches, stems, or plants yellow, wilt, and die due to the Fusarium infection. Moderately infected plants may be stunted, wilt during periods of water stress, or yield poorly. Discoloration of the water conducting or vascular tissues can be observed when stems are split or cut in cross sections. The browning in the vascular tissues is most intense near the soil line.

The Fusarium fungus only affects tomatoes and can survive for extended periods in soils. The disease progresses rapidly and is most severe during periods of high temperatures and on warm, sandy soils. Many tomato varieties have resistance to race one or two of the fungus. New races of Fusarium can develop with time and may overcome resistance present in current varieties.

For Fusarium wilt control, use a resistant variety, rotate crops, and use disease-free transplants.

Verticillium Wilt

Verticillium wilt is the prevalent wilt disease in northern tomato growing areas. The fungus Verticillium albo-atrum causes symptoms similar to Fusarium wilt. The first symptom of the wilt is yellowing of lower, older leaves that may occur in blotches. Leaves may then brown along veins or in blotches before foliate completely yellows, withers, and drops. Defoliation often progresses up the plant until only a few leaves remain at the tips of stems. Plants infected with Verticillium exhibit vascular discoloration similar to those infected with Fusarium wilt. Verticillium wilt usually does not cause unequal symptom development observed with the Fusarium disease.

Verticillium wilt has an extremely wide host range and can persist in the soil for extended periods. Soil fumigation or long crop rotations are needed to reduce populations of the fungus in soils. The fungus can survive cold winter temperatures and can develop under cooler weather and soil temperatures than Fusarium wilt.

For Verticillium control, use long crop rotations with nonhost species such as cereals or grasses, disease-free transplants and a resistant veriety.

Foliar Diseases

Septoria Leaf Spot

Septoria leaf spot or blight, caused by the fungus Septoria lycopersici, is one of the common leaf spots found in Iowa. Leaf spots are found early in the season on lower leaves within the canopy. Mature spots are mostly circular, about 1/8 inch in diameter, and have dark brown or black margins and sunken white to gray centers. Numerous spots may be present on a single leaf. Small, black fungal fruiting structures develop within the spots during wet weather. Spores from these fruiting structures are spread by splashing rain water, wind, farm equipment, and people working when foliage is wet. The disease quickly spreads from lower leaves to the rest of the plant during periods of moderate temperatures and wet weather. Premature defoliation due to Septoria increases chances of sun damage to developing fruit. The fungus survives between crops in infected plant residues, on related weed species and on seed.

For Septoria control, use adequate planting widths, control weeds, rotate crops, and apply a recommended fungicide.

Early Blight

Early blight can be found in most tomato growing areas and also affects potato, eggplant, and other related hosts. The fungus, Alternaria solani, first infects lower, older foliage and then may spread up the plant to leaves, stems, and fruit. Leaf spots are irregular, dark brown, and develop a concentrically ringed or target-like pattern. Leaf tissue around spots may yellow and spotted leaves usually die prematurely. Total defoliation and fruit infection occur if plants are weakened from poor growing conditions. Fruit infections may develop on the stem end and appear as dark, leathery, sunken areas with concentric rings.

Alternaria solani produces large numbers of wind- and water-spread spores on the edges of leaf spots. Extended periods of wet foliage from rain, dew, or irrigation and plants in poor vigor contribute to early blight outbreaks. The fungus survives at least 1 year in infected plant residues and can be seed borne.

For Alternaria control, use crop rotation with unrelated crops, control weeds, maintain plant vigor with proper fertilization and cultural practices, and use a recommeded fungicide.

Bacterial Speck and Bacterial Spot

Bacterial speck, caused by Pseudomonas syringae, and bacterial spot, caused by Xanthomonas vesicatoria, can infect all above ground portions of tomatoes. Bacterial speck appears as numerous, small, black specks on leaves, stems, and fruit. Bacterial spot typically causes larger water-soaked or greasy spots that develop a narrow, yellow halo. Severe bacterial spot infections result in ragged appearing leaves and early defoliation. Both bacteria cause flower abortion and fruit spots. Bacterial speck fruit infections are small (1/16 inch diameter), slightly raised black specks on the fruit surface. Bacterial spot infections are raised, distinct spots, up to 1/4 inch in diameter, that turn brown and become rough or scabby.

Bacterial speck and spot overwinter in infected plant residues and seed. Build-up of the disease usually occurs after severe or driving rainstorms that spread the bacteria and aid in the infection of plants. The bacteria also are spread on tools, equipment, and people if present within a field when foliage is still wet from dew, rain, or irrigation.

For control of bacterial speck and spot, use disease-free seed and transplants, rotate with unrelated crops, and apply a copper containing fungicide.

Late Blight

Late blight is a destructive disease of potatoes and tomatoes in areas with cool, wet weather during the growing season. Warmer, drier conditions in Iowa limit development of the fungus Phytophthora infestans and therefore the disease is infrequent. Foliage, stems, and fruit are often quickly killed by the disease. Leaflets first develop irregular, water-soaked or greasy spots that enlarge from the margin inward. The blighted areas turn brown and may cover a large part of the leaf. On the lower leaf surface, a white, downy mold appears near the margin of infected tissue and is characteristic of late blight. Similar symptoms also may occur on stems and fruit.

The late blight fungus overwinters in potato cull piles and southern potato and tomato growing areas. Outbreaks occur during cool, wet weather when tomatoes are grown near potato cull piles, infected potato fields, or when infected transplants are used. These conditions are rare in Iowa and control measures for late blight are seldom needed. If late blight develops, fungicides are effective in controlling the disease.

Fruit Rots

Anthracnose

Anthracnose, or ripe rot, caused by the fungus Colletotrichum coccodes, is the most common and important fruit rot. Symptons appear after tomatoes ripen and are initially small, circular, and slightly depressed spots on the fruit surface. The spots gradually enlarge, develop a dark center, and often merge together. Numerous spots may cover the fruit and cause general decay. Anthracnose infections also allow entry of soft rot organisms that further decay the fruit during transport and storage.

Anthracnose overwinters in infected plant residues, in the soil, and in and on seed. Before fruit ripens, the fungus colonizes and produces spores on early blight spots, insect damaged foliage, and other damaged leaf tissue. Green fruit is infected although symptoms do not develop until ripening. Warm, wet weather during fruit ripening, overripe fruit and fruit in contact with the soil favors the development of anthracnose.

For anthracnose control, rotate crops and maintain a regular spray schedule through harvest.

Buckeye Rot
Buckeye rot occurs sporadically on tomatoes, peppers, and eggplant and is caused by the fungus Phytophthora parasitica. The disease obtains its common name from brown concentric rings on the fruit surface that may appear similar to markings on a buckeye nut. The rings initially develop from gray to brown water-soaked spots that are most common when the fruit is touching or near the soil surface. The zonate discoloration may cover more than half the surface and then can extend into the center of the fruit.

The Phytophthora fungus is soil borne and requires wet soil conditions or extended warm wet weather to cause significant losses. The disease can be avoided by selecting well-drained planting sites, controlling weeds, and rotating with unrelated crops.

Virus Diseases

Tobacco Mosaic Virus
A number of virus diseases affect tomatoes and can cause significant losses. Tobacco mosaic virus (TMV) is the most common and important of these viruses. Light to dark green mottling of foliage and occasionally on fruit is one symptom of TMV. Varying degrees of puckering, curling, and malformation of leaflets also may occur. Plants infected when young may be stunted and bear few, small, or poor-tasting fruit. Infections later in the season may cause only foliar symptoms and have little impact on yield. Different strains of the virus exist and the severity of symptoms may be related to the strain of virus present.

TMV is highly infectious and is spread mainly on hands, tools, clothing, and farm equipment that contact foliage. Insect vectors play only a minor role in the spread of TMV but are extremely important in the spread of other tomato virus diseases. The hands of workers who use cigarette, pipe, or cigar tobacco are a common source of TMV. Ground cherry, horsenettles, and other related weeds also harbor the virus.

Prevention is the best method of control for TMV and other virus diseases. All people handling plants should wash their hands thoroughly before working. Weed control, use of disease-free transplants and control of insects (primarily aphids) will help avoid most viruses. Resistance to TMV is present in some varieties.

(The disease management section information partially provided by Pm1266, ttitled: Tomatoe diseases and disorders).

Insects

(section to completed at a later date)

HARVEST

Fruits in various stages of ripeness are harvested for market -- from mature green to vine ripe. Eating quality, however, is usually related to the degree of color when picked. Vine ripe fruits are more flavorful than those picked at the mature green stage.

For local marketing during cool weather, tomatoes should be harvested at the pink or firm red stage. When it is hot and/or the time between harvest and sale is 3 days or more, tomatoes should be picked at the turning or breaker first color stage. Tomatoes for distant or delayed markets are often picked at the mature green stage. It is important for pickers to identify this stage accurately since the fruit can gain as much as 10 percent of its final weight in the 4 days before the first appearance of skin color.

Today's market place emphasizes uniformity of color, size, and shape and freedom from defects. Market tomatoes must be graded. Those with cracks, sunscald, blossom-end rot, catfacing, or fruit diseases should be eliminated. It also is important to place fruits of uniform size in one container.

Size standards can be confusing because U.S. and Michigan standards are based on maximum and minimum diameter sizes, whereas Florida sizes are designated according to the number of tomatoes it takes to fill a standard carton. A carton that contains layers of seven rows of tomatoes, each with seven tomatoes, is referred to as 7 x 7. The 7 x 7 is Florida's small size and 5 x 6 is extra large.

Tomatoes are usually packed in 20- or 25-pound cardboard cartons. They should be packed as tightly as possible without bruising. Grade standards are usually established by the market outlet. Be sure you know the size requirements for the market before starting the growing season.

YIELD

For fresh market tomatoes an average yield is about 12-16,000 lbs per acre or 6-800 boxes. However, growers using top management practices typically obtain 30,000 lbs or 1500 boxes or lugs per acre.

POST HARVEST CARE

Mature green and breaker stage tomatoes are highly susceptible to chilling injury so storage temperatures below 50 degrees F for more than a day should be avoided. Prolonged exposure to low temperatures will prevent ripening even after transfer to proper conditions. At 55 degrees to 60 degrees F, less than 10 percent of the fruits will usually be red ripe after 10 days, and only about half will be at the turning stage. Optimum storage condition for firm, slightly colored or mature green tomatoes is 60 degrees to 65 degrees F at 85 to 90 percent relative humidity. As tomatoes ripen, they become less susceptible to chilling injury and can be stored at lower temperatures. Ripe tomatoes can be stored at 45 degrees F and 80 to 85 percent relative humidity. For best eating quality, tomatoes picked at any stage of maturity should be ripened at 65 degrees to 70 degrees F. However, in mid-July, temperatures above 90 degrees F often occur and red color development is inhibited and the fruit remains yellow-orange.