Tomato Technical Bulletin
Syngenta’s Crop Management Strategies Help Protect Your Investment
Making Superior Vegetables a Reality

Syngenta/ROGERS® Brand is committed to providing growers with the highest-quality vegetable seed genetics for a wide range of greenhouse growing systems and environments.

Towards this end, we invest considerable resources in our seed production process, from breeding all the way through to delivery. Syngenta/ROGERS’ greenhouse vegetable breeding efforts are founded on global synergies in Holland, France, Spain, Morocco, and the United States, and we have a full staff of scientists and researchers as well as an unmatched germplasm base. Once a tomato variety has been developed, our optimized seed production and quality assurance protocols (which are supported by state-of-the-art seed physiology laboratories) help ensure that only the best-germinating, highest vigor, and disease-free seed goes into a ROGERS package.

We believe our commitment to quality positions ROGERS to be your preferred greenhouse vegetable seed supplier. Working together, we can make superior vegetables a reality.

Syngenta/ROGERs’ Greenhouse Tomato Disease Prevention and Detection Program

Greenhouse tomato production creates an environment that is especially conducive to some seed-borne diseases. Therefore, it is important that seed suppliers take measures to help ensure that the seed purchased by their customers does not contain any of these diseases.

Bacterial Canker in Mexico Greenhouse Tomato Productions

Several diseases in particular can be troublesome, even devastating, to tomato crops that grow for seven months or longer in greenhouses. These diseases include bacterial canker caused by Clavibacter michiganensis subsp. michiganensis, tobacco mosaic caused by tobacco mosaic virus (TMV), tomato mosaic caused by tomato mosaic virus (ToMV), and pepino mosaic caused by pepino mosaic virus (PepMV). The causal organisms of these diseases, once established, can spread very quickly and extensively on tools and hands during the daily vine pruning, training, and other handling that occurs with tomato plants.

In greenhouse tomato productions in Mexico, bacterial canker seems to be the most prevalent of the four diseases cited above. It is caused by a bacterium that can be moved easily from plant to plant during handling, and can even be taken up into the plant through the roots. Once inside the plant, the bacterium will begin to increase in population, and will eventually move into the vascular tissue. Over time it will likely spread up the stem and into the outer foliage. It can move into or otherwise infect the flower, causing possible fruit abortion, and reduced yield and fruit quality. The optimal temperature for growth of the bacterium is about 27 ºC (81 ºF).

Detecting Bacterial Canker

Early detection and diagnosis are the keys to controlling bacterial canker. The bacterium goes through a fairly lengthy process of increasing in population before entering the vascular tissue, so initial symptoms may take weeks to develop. As a result, infected seedlings may not show symptoms until several weeks after having been transplanted. Symptoms from new infections on older plants may not appear for weeks after infection, depending on temperatures, the amount of inoculum, and the location of the introduction of the inoculum.

Leaf symptoms may begin as a yellow-green color with browning along the margins, which most likely will be accompanied by wilting and distortion of the growth. The veins commonly have a yellow to brown discoloration if the outer epidermis is removed. A milky white cloud of bacteria often exudes out from the cut end if the leaf petiole is placed in water. The bird’s eye white spotting fruit symptom that is characteristic of fruit infection in the open field may not develop on greenhouse tomatoes unless there is splashing or free water on the fruit surface. As the infection progresses, a distinct canker can develop on the stem and severely infected plants may be killed.

Diagnosing Bacterial Canker

Rapid diagnostic tests such as Immunostrips and ELISA kits can be used to help confirm the identity of the disease. Additionally, samples for diagnosis can be sent to a lab where the bacterium can be isolated from the tissue, and characterized by such tests as PCR, immunofluorescence, and pathogenicity. Laboratories in the U.S., however, must now have an APHIS PPQ 526 permit in order to receive diseased samples from international sources.

Control measures, such as increased sanitation and perhaps even the exclusion or eradication of infected plants, should be implemented immediately if the presence of bacterial canker is confirmed. It should also be noted that the bacterium can survive for months in infected plant debris and soil, and for weeks on surfaces in the greenhouse. Therefore, these need to be thoroughly sanitized or cleaned before the introduction of a new tomato crop.

Syngenta/ROGERS – Protocols for Ensuring Healthy Seed

Syngenta/ROGERS takes the responsibility of providing customers with healthy seed very seriously. Beginning at the earliest stages of production, we implement a series of protocols that help ensure the quality of our greenhouse tomato seed. Various elements of our program are outlined below.

Stock Seed

• Produce crops primarily in our greenhouse in Holland.

• Repeatedly inspect productions for disease and other problems.

  • Sample of seed is tested for multiple diseases prior to the disinfection/cleaning treatments. 

• Treat all seed.

Commercial Seed

• Produce crops in the greenhouse to allow for better control of the environment. As compared to open field production, greenhouse production also reduces the likelihood of introducing diseases.

• Produce crops under strict sanitation and pest control conditions that include:

  • General disinfection of the greenhouse, including spraying with a disinfectant.

  • Soil disinfection with fumigation.

  • Continuous disinfection of shoes and hands upon entering, including disinfection mats and buckets with bleach.

  • Sanitation of tools during the pruning and staking of plants. This can include using bleach, milk, quaternary ammonia, or other compounds.

  • Using clean trays for transplants.

  • Using clean media for transplant trays.

  • Applying pest and disease control sprays, and other measures, as needed.

• Provide personnel trained in pest and disease identification to inspect each seed crop a minimum of three to four times during the growing cycle. The advantages of our inspection process include:

  • It allows for a complete evaluation of the crop.

  • Plant health in general is monitored, and adjustments can be made to the fertility program and plant architecture as needed.

  • It provides for control of diseases that are not seed transmitted, but could affect plant health and the resulting seed quality.

  • It is pro-active for detection of possible new diseases.

• Extract the seed, soak it in disinfectants, and rinse and dry it under controlled conditions.

• Sample the seed for disease testing using a method to get a representative sample.

• Test each lot of greenhouse tomato seed for the following diseases:

  • Bacterial Canker – 50,000 seeds

  • Bacterial Speck – 30,000 seeds

  • Bacterial Spot – 30,000 seeds

  • PepMV – 3,000 seeds

  • TMV – 3,000 seeds

  • ToMV – 3,000 seeds

By Wayne Wiebe, Ph.D., Seed Technology Leader
January 2006

common physiological disorders affecting tomatoes grown under passive greenhouse conditions in Mexico

Over the past decade, tomato growers throughout Mexico have increasingly adopted methods for cultivating tomatoes in a protective growing environment. This is because it allows them to overcome unfavorable climatic conditions, protect their crops from vectors spreading diseases and viruses, and helps reduce the incidence of physiological fruit disorders. In a recent report presented in Mexico, the Asociacion Mexicana de Productores de Hortalizas en Invernaderos, A.C. (AMPHI) estimated that by the end of 2005 there would be close to 3,000 hectares of vegetable crops in Mexico growing under some type of greenhouse culture.

A majority of the total greenhouse acreage planted in Mexico is devoted to tomatoes, including beefsteak, saladettes, and cocktail types. In part, this is because greenhouse-grown tomatoes are often considered to be more profitable than field-grown tomatoes or other conventional vegetable crops.

Just as with open field tomato production, however, there are common physiological disorders that can affect the harvest quality of tomato crops. A well-planned greenhouse management program can often minimize the negative impact of these disorders, especially when compared to a tomato crop produced under open field conditions.

Several of the most common disorders affecting greenhouse tomato crops are provided below, along with a review of the most commonly accepted best practice crop management techniques for their prevention (this is not an exhaustive list of techniques).

BLOSSOM DROP

One of the initial challenges of growing tomatoes in the warmer climates of northwestern Mexico are the extreme variances in day and nighttime temperatures experienced during the transplanting and early flowering periods. It is common for daytime temperatures inside a passive greenhouse to exceed 40 ºC (104 ºF) High temperatures such as these can inhibit pollination and fertilization, leading to blossom drop and the subsequent abortion of flowers. Other factors that commonly contribute to early flower drop are excessive nitrogen fertilization and high relative humidity.

Management Tips for Prevention of Blossom Drop

1.     Choose varieties based on growing conditions. The optimum temperatures for tomato pollination are between 21ºC (70 ºF) to 28 ºC (82 ºF), with an optimum relative humidity around 70%. Extended periods of relative humidity under 60% may result in the stigma drying out to that extent that the pollen cannot stick to it. At relative humidity levels above 80%, the pollen grains stick together and do not disperse well, thus causing poorly pollinated flowers.

2.     Monitor ventilation and crop cooling. Effective ventilation is critical to helping reduce the air temperature inside the greenhouse. By moving air through the crop, the plants can become active and increase their rate of transpiration, thus helping create a cooling microclimate inside the greenhouse. The inside temperature of a passive greenhouse will never be cooler than the outside air temperature, so it is wise to adopt shade curtains or micro-foggers as a means to reduce the inside greenhouse temperature.

3.     Manage nutrients. High levels of nitrogen (N) can contribute to early and excessive vegetative growth and throw plants out of balance. It is recommended that growers consult with a crop nutrition specialist to develop a fertilization program that provides the proper quantity and ratio of the nutrients required for each specific stage of plant and fruit development. Levels of boron must also be sufficient and well balanced.

4.     Utilize approved hormones. The use of approved fruit setting agents and hormones can aid the grower to set early flowers under extreme heat conditions. These fruit are not usually of export quality, but the technique is useful as its helps balance the plant in its early stages of development and can contribute to an overall better quality crop.

5.     Work with bees (Bombus terrestis). Use a minimum of four hives per hectare. Bees will not work under extreme temperatures, so in extremely hot conditions mechanical means such as vibrators should be used to pollinate crops.

GRAY WALL

Fruit showing graywall in center pith area*

Gray wall is commonly observed in west Mexico and the northern coastal Baja tomato growing areas during periods of low light and morning fog, and during the winter and spring tomato production windows.

The exact cause of gray wall is elusive. The fruit defect is associated with a wide variety of environmental conditions including, but not limited to, high nitrogen, low potassium and compacted soil conditions or growing medium. TMV, certain bacteria and fungi are also thought to be contributing factors to the development of gray wall.

Also called blotchy ripening, gray wall symptoms usually appear on immature tomato fruit as blotchy gray or brownish-gray spots. As the tomato matures to red, the discolored areas remain gray or turn yellowish, resulting in fruits that do not ripen evenly. The dark brown tissue can also be seen in the walls of the tomatoes when they are cut open, making them less desirable to consumers.

Management Tips for the Prevention of Gray Wall

1.     Use gray wall tolerant varieties
Syngenta/ROGERS offers tomato growers a wide selection of new commercial indeterminate tomato varieties that are widely adaptable and have shown tolerance to gray wall. One such variety is Silvana (41564).

2.     Plant only varieties that offer TMV resistance
Academic research indicates a greater incidence of gray wall in non-TMV resistant varieties.

3.     Watch the weather
An awareness of predicted cold fronts or rainy conditions allows the grower to implement early preventative crop management steps that may help reduce gray wall. Such steps may include de-leafing above the bottom truss to allow more light penetration to the crop, increasing K fertilization levels, and reducing the frequency of irrigations. Growers can stay apprised of weather conditions by watching local television reports and viewing such websites as www.wunderground.com/global.MX.html and www.accuweather.com.

RUSSETING or MICRO CRACKING (Crazing)

In Mexico, russeting in passive greenhouses is common. A close examination of tomatoes with russeting reveals fruit with hundreds of minute cracks on the surface, creating a dull red color and rough texture. In addition to the generally undesirable appearance, the shelf life of affected tomatoes is greatly reduced due to water escaping through the minute surface cracks. Upon losing 5% of their weight from water loss, tomatoes shrivel, become soft, and break down.

Management Tips for the Prevention of Russeting

1.     Avoid conditions that cause condensation on the fruit. Consider improving poorly ventilated greenhouses.

2.     Avoid significant temperature and humidity fluctuations. In the morning, after the suns rises, increase the greenhouse temperature slowly to avoid a rapid decrease in ambient humidity and a rapid increase in inside temperature. Use thermal curtains or shade cloths if available.

3.     Create a favorable microclimate. Increase the total head population of the crop up to 5% by leaving an extra shoot during a cropping period conducive to russeting. This can help create a favorable microclimate inside the greenhouse.

4.     Manage irrigation schedules. Better manage your crop irrigation schedule by using tensiometers. Consider revising your irrigation program.

5.     Maintain optimum K levels. Maintain K levels at the optimum levels for the appropriate stage of your crop’s development.

BLOSSOM END ROT (BER)

Fruit on plant showing BER on sidewall*

Cross section of fruit showing internal BER*

Fruit showing symptoms of BER: top left fruit showing mild BER, others showing severe BER*

Blossom end rot is one of the most common fruit disorders. Best known to tomato growers worldwide by its symptoms, tomato BER is not caused by an organism but is rather the result of an insufficient amount of calcium reaching the blossom end of the tomato fruit to maintain cell integrity. It usually appears as a light tan, brown, or black sunken area on the outside of the blossom end of the tomato fruit, but sometimes occurs on the inside of the fruit as well. It is not soft, but firm, and has a leathery texture.

Although adequate calcium may be applied in the nutrient solution, insufficient water may prevent it from reaching the fruit. If plants have reached the point of wilting due to stress caused by high temperature (greater than 28 ºC), high humidity, rapid plant growth, excessive salinity, or high nitrogen, it is very difficult for nutrients to reach the fruit and they may show the symptoms of BER.

Management Tips for the prevention of Blossom End Rot

1.    Choose varieties with a strong root system. Syngenta/ROGERS’ Charleston, Silvana, Pascaline, and Tsarine varieties are good options.

2.    Watch N levels. Avoid the use of excess N, especially in the ammonium form, as it increases the demand for calcium.

3.    Consider using grafted tomato transplants. Many Mexican greenhouse growers are adopting this crop management technique as a means to control BER. Rootstocks can offer the scion variety a greater root mass and greater root pressure, thereby providing more efficient translocation of water and nutrients up the tomato plant to the tomato fruit during stressful growing conditions late in the growing season.

4.    Avoid wide fluctuations in your irrigation program. Use tensiometers to monitor the need for irrigation.

5.    Consider foliar sprays. Consider applying high quality, well balanced foliar nutrients sprays to complement your fertilization program.

6.    Manage the crop. Remove and discard any immature fruit that show BER symptoms. Once a fruit has blossom end rot, it will not go away.

Plan for Success

Unlike field-grown tomatoes, the complex cropping requirements of greenhouse tomatoes require regular management and attention. There are no simple formulas for successfully raising greenhouse tomato crops, but there are several important management steps growers can take to increase the chance of a strong harvest. Taking the time to create a well thought out and comprehensive crop management program is one important factor. It is also important to stay vigilant and anticipate fruit disorder problems before they occur.

Technical Resources cited

Jones, J.B, R.E. Stall, and T.A. Zitter, editors, Compendium of Tomato Diseases, The American Phytopathological Society, 1997.

Marlow, Douglas, Greenhouse Crops in North America: A Practical Guide to Stonewool Culture, 1993.

Estevez, Juan Carlos, Manajo eficiente del cultivo de tomate en el sur de Sonora, 2005

Snyder, Richard, Greenhouse Tomato Handbook, Mississippi State University Cooperative Extension Service, 1997.

Greenhouse Tomato Proceedings, American Society for Horticultural Science, 1995.

Gabor, Brad and Wayne Wiebe, Tomato Diseases: A Practical guide for Seedsmen, Growers, and Agricultural Advisors, 1997.

Gill, Allen and Vicente Zamudio, Field Trial Observations and Research, Syngenta Seeds, Inc., 2000- 2005.

By Allen Gill, Syngenta Greenhouse Business Manager, Mexico
October 2005