Considerable progress has been made in breeding disease resistance or tolerance to the more commonly occurring tomato plant viruses and diseases, such as the verticillium and fusarium wilts, tobacco mosaic virus, altenaria stem canker, stemphylium gray spot, septoria leaf spot, and bacterial speck.
Those seed borne diseases that can be controlled by heat treating the seed are bacterial cankcr, bacterial spot, bacterial speck, and anthracnose.
Most cultivars are not resistant to anthracnose, bacterial cancer, bacterial spot, late blight, and Southern stem blight, while many tomato cultivars are resistant to alternaria stem cancer, bacterial speck, bacterial wilt, early blight, fusarium wilt, gray leaf spot, tobacco mosaic, and verticillium wilt.
Gray mold ( Botrytis cinerea ) is a commonly occurring disease in warm and wet environments that primarily affects older leaf tissue. Best control is to keep the foliage dry by maintaining movement of dry air within the plant canopy.
A soil borne disease that can be severe in warm wet weather conditions is Rhizotonia which is best controlled by soil sterilization, and by keeping soil from making contact with plant foliage.
Phytium aphanidermatum is a serious root disease that occurs in warm wet conditions, frequently in those hydroponic growing systems in which the nutrient solution is recirculated. When occurring, the disease can quickly kill plants, and its control requires the dismantling of the entire hydroponic growing system for complete sterilization. In soilless medium systems, pinebark as an ingredient in the soilless mix, offers some control of this root disease.
Disease control requires constant plant observation and evaluation, and the use of control measures to prevent the introduction of disease organisms from outside sources.
Soil Borne Diseases
Sterilization is required when tomato plants are grown in soil to control such diseases as bacterial wilt, Southern blight, fusarium wilt, and fusarium crown rot. Field soil sterilization with methyl bromide has been the commonly used procedure. For greenhouse soils, steam sterilization is the common method. Since use of methyl bromide is being phased out, alternative methods of chemical sterilization are being sought
Although most diseases produce characteristic visual symptoms, proper identification by a skilled plant pathologist before a corrective chemical treatment is made is essential. Many colleges of agriculture or their agricultural extension services within the land-grant university system in the United States and some soil and plant analysis laboratories offer pathological services plus pest chemical recommendations. In addition, there are crop consultants in most of the major crop-producing areas of the United States who can field identify plant diseases. Most are usually familiar with current pest control regulations, and some crop consultants are also licensed pest chemical applicators.
Most tomato cultivars are not resistant to the following insects: aphids, cabbage looper, Colorado potato beetle, fall army worm, corn earworm, leaf miners, thrips, and tomato pinworm. Other insects that will attack the tomato plant are Colorado corn earworms, flea beetlcs, fruit flies, hornworms, spider, stick bugs, and whiteflies, i nsects that are becoming increasingly difficult to control, particularly in the field and in those areas of the United States where tomato crops have been produced for a long period of time. In addition, insects can carry diseases, such as various geminiviruses that are just now being specifically identified.
Another insect that is become increasingly difficult to control is the thrip, a very small insect that can damage the tomato plant as well as carry virus diseases. This insect, as well as others, should be prevented from entering the greenhouse by screening ventilation openings.
Insect Population Monitoring
The insect population in the greenhouse is best monitored by placing yellow- or blue-colored sticky boards at intervals within the plant canopy, and then daily examining these boards, noting the numbers and species of insects found on the board. As insect numbers accumulate, procedures for insect population control can be instituted by using chemical procedures or by introducing predator insects into the greenhouse. The use of these sticky boards is not a means for controlling insect populations.
Insect Control Using Predator Insects
The use of predator insects to control of various insect pests has a fairly long history of development and use. Some of the plant-damaging insects that can be controlled by predators are aphids, mealy bug, scales, spider mites, thrips, and whiteflies. Successful predator insect control is based on careful monitoring and introduction of predators before the target insects become out of control. Air temperature and humidity are important factors that can influence both the target insect and its predator, and therefore must be maintained at optimum levels. As with any pest problem, a combination of control factors becomes essential for success in keeping damaging insect populations from reaching damaging levels. Supplies of predator insects and instructions in their use are available from a number of sources.
Nematodes that attack tomato roots are the root knot ( Meloidogyne spp.), sting ( Belonoclaimus spp.), and stubby root ( Trichodorus spp.). There are tomato plant cultivars that have resistant to the root knot nematode, otherwise chemical control is needed when nematodes are present in the rooting media.
A new line of pesticide chemicals is being developed containing naturally occurring fungus organisms that can invade the insect’s body as a means of controlling insect pests in the tomato greenhouse. Some products are quite new and use experience by growers has not been well documented.
Insecticidal soap is another control chemical that will kill aphids, mealy bugs, whiteflies, and mites. The plant must be completely saturated with the insecticidal soap in order to be effective, and repeated applications may be needed to control an insect infestation. Another form of an insecticidal soap is neem oil insecticidal soap, a new product, with possible control of a wide range of insects commonly occurring in the greenhouse. Neem-containing materials have had a long history of use in various developing countries around the world. Neem oil is extracted from the fruit of the neem ( Azadiruchta indica ) tree.
W EED CONTROL
Chemical soil weed control is the normal practice, methyl bromide being a control method when soils are sterilized with this agent. Although herbicides can be effective in controlling weeds cultural practices, such as crop rotation, tillage practices, and seedbed preparation, are equally important means of control. Therefore, a combined strategy of non-chemical and chemical techniques can effectively control most weed problems.
CHEMICAL PEST CONTROL
Most diseases, insects, nematodes, and weeds can be controlled chemically. However, the use of chemicals for control can render fruit less desirable in the marketplace. In addition, pest chemicals vary widely in their effectiveness, method and time of application. State and federal law require that pest control chemicals be applied by those licensed to do so, Today, both federal and state laws require registration of most pest chemicals which regulate their use. Therefore, the user of these chemicals needs to be aware of these regulations by following label instructions.
Chemicals that are approved for specific use are constantly changing as older products are removed from the market and new ones introduced. A pest chemical label can be changed, removing its use for a particular crop or pest, although it still may be suitable for use on other crops or pests. Therefore, before selecting and using any pest chemical, its use must conform to label requirements. Use and restriction information concerning pest chemicals can be found in various state agency publications. Growers need to have access to the latest versions of these pest control publications for their region to ensure that the label is still applicable for its intended use.
In all forms of pest control, the timing of applied control measures can determine the success of an applied treatment. Strategies for dealing with insects and diseases need to be formulated and carefully followed. For example, it is important to know the life cycle of a plant-damaging insect in order to apply control measures that will prevent the development of that form of the insect that harms the crop or when the applied chemical will be most effective. Each stage of insect development is different, and a particular control measure may be effective against one stage of development but not another. Professional assistance is important in order to correctly identifying the insect in question and then selecting those control measures that will be provide the desired con trol.
INTEGRATED PEST MANAGEMENT
Integrated pest management (IPM) involves the use of a combination of procedures, cultural, chemical and non-chemical, in order to control both insects and diseases. An IPM program is normally for a specific crop, such as tomato, or for a system of growing, such as hydroponic.
Carefully maintaining the plant environment and the health of the plant itself is as important as non-chemical means of disease and insect control. Air and rooting temperature, relative humidity, airflow in the plant canopy, soil moisture, and plant nutrition, for example, are factors that contribute to the well being of plants. A vigorously growing healthy plant is less likely to be disease prone. Stressed plants are more likely to be affected by the presence of disease and insects than a healthy plant
As with any infestation, prophylactic procedures are essential to prevent disease organism and insect introduction since most disease and insect problems are difficult to control after the fact. The environment, such as air and root temperature, soil moisture, relative humidity, air movement within the plant canopy, the presence of host plants, and cultural practices will influence the initiation or control of diseases and insects. The use of insect traps and frequent monitoring of the tomato plant can warn of a developing insect or disease infestation in order that control measures can be taken before the infestation reaches plant-damaging levels.
For the greenhouse grower, controlling access to the greenhouse, screening to keep insects from being drawn into the greenhouse through the ventilation system, and the sterilization of clothes and tools are important measures. Only disease- and insect-free plant material should be brought into the greenhouse. By combining chemical, non-chemical, and prophylactic procedures, a grower should be able to produce a tomato crop free from damaging pests.