Title

Developing an Integrated Pest Management (IPM) programme for large scale production system

of greenhouse tomatoes (Solanum lycopersicum) for a farmer based in Chinhoyi, Zimbabwe.

Keywords: IPM, greenhouse tomatoes

Introduction

Greenhouse tomato growers around Chinhoyi farms produce vine ripe tomatoes at a time of year

when homegrown tomatoes are not available. Many disease and insect pests can attack

greenhouse grown tomatoes and hurt both production and quality. Greenhouse tomato producers

must be able to accurately scout for and identify these pests and know how to effectively and

economically control them. Growers who successfully combat greenhouse tomato pests rely on

integrated pest management (IPM).

IPM simply means that growers use a combination of biological, cultural, and chemical methods

to suppress pest populations, rather than relying only on one method, such as repeated insecticide

use. This integrated approach uses preventive measures to avoid likely insects and diseases, crop

monitoring to allow early detection, biological control when possible, and pesticides when

needed. A sound IPM program reduces pesticide use, allows more timely application of needed

pesticide treatments, and improves pest control (Abrol 2013, p.31).

Pest Spectrum for Greenhouse Tomatoes

Table 1 | Pest and Disease Spectrum for tomatoes in greenhouse (Czosnek 2007, p.277)

Insects and mites Diseases

Aphis spp. (aphids) Grey mold

Bradysia coprophila (fungus gnats) Powdery mildew

Tetranychus urticae (red spider mites) Pythium root rot

Scatella stagnalis (shore fly) Bacterial blight

Heliothrips haemorrhoidalis (greenhouse thrips) Alternaria leaf spot

Table 1 “continued”

Bemisia tabaci (whiteflies) Sclerotinia stem rot

Liriomyza sativae (leaf miners) Downy mildew

Phytonemus pallidus (cyclamen mites) Impatiens necrotic virus

Planococcus citri (mealy bugs) Black root rot

Coccoidea spp. (scale insects) Phytophthora damping off

Cultural approach for pest management

Many of the insect pests that attack field grown tomatoes also attack greenhouse tomatoes,

because of the enclosed, controlled environment of the greenhouse, insect management is

different from what is used in the field. The most important components of insect management in

greenhouse tomatoes which farmers should follow are discussed below.

Keeping insects from entering the greenhouse (exclusion) is a key part of greenhouse insect

management. Many common pests that attack greenhouse tomatoes are small flying or wind-

borne creatures that can easily be sucked into the greenhouse through ventilation fans and

cooling pads or can easily enter through other openings (Ciancio and Mukerji, 2007). If growers

build greenhouses that are “bug tight,” it will avoid many serious insect infestations. It is

important to install proper screening over air intake vents or cooling mats.

Many greenhouse insect pests are so small; it takes very fine screening to exclude them. Bemisia

tabaci (thrips) are the smallest insect pests that need to be screened out, and obviously, screening

that keeps out thrips also keeps out larger pests, such as aphids and whiteflies. Though it requires

additional planning and expense, building an insect-proof greenhouse is an investment towards

pest management (Hill, 2008).

Sanitation is another major part of greenhouse pest management which farmers should adhere to.

Many tomato pests also occur on other crops or broadleaf weeds. For this reason, it is important

to avoid growing other crops next to the greenhouse and to prevent heavy growth of

broadleaf weeds around the outside edges of the greenhouse (Albajes et al, 2006). Elimination of

weeds and volunteer plants growing inside the greenhouse during either cropping or non-

cropping periods is even more important, because such plants can serve as hosts for a number of

pests and can let pests survive inside the greenhouse during non-cropping periods.

One of the most important practices in sanitation is to begin with insect-free transplants of

tomatoes and avoid bringing other plants into the greenhouse once you plant the crop (Pimentel

2002, p.110). Serious infestations of insects or diseases can be introduced on new plants. If new

plants are introduced, quarantine them in another location and closely observe them for several

days to be sure they are pest-free. The farmer should keep the greenhouse clean and free of

debris, promptly removing pruned leaves and overripe tomatoes. Pruning lower leaves after

harvesting lower fruit clusters is a helpful measure in greenhouse tomato production and disease

management. This can also aid in insect control by removing large numbers of developing leaf

miners and whiteflies.

The farmer should also take some restrictive measures for entry into growing areas to necessary

personnel and supervise all visitors. Everyone should clean shoes before entering the greenhouse

by removing soil, then use foot baths with a disinfectant at each entry point in a greenhouse

Scouting and early detection are critical to successful insect control. Purposefully the farmer

should inspect plants one to two times per week to check for developing insect problems. This is

done by walking through the greenhouse, making random stops, and visually examining both

upper and lower leaf surfaces as well as buds, blooms, and fruit for insect pests. Extra attention

should be done to plants or areas that show unusual symptoms or appearance. Many insect

infestations begin in isolated spots within the greenhouse but quickly spread if not controlled.

There are a number of pest management tools which a farmer can use in addition to visual

scouting. Yellow sticky cards can help detect whiteflies and many other greenhouse pests early.

Pheromone traps available for tomato pinworm can allow critical early detection if used

according to directions and replace the lure as required.

Biological approach for pest management

Biological control is the use of living organisms to control crop pests. Biological control of

greenhouse insect pests can be achieved through release of bio-control agents like predatory

mites, pirate bugs (Anthocoridae spp.), soil-dwelling mites, and parasitic insects.

Successful biological control requires frequent scouting, accurate pest identification, and

knowledge of the pest biology, knowledge and understanding of the biology of the bio-control

agents used, and careful selection and timely release of bio-control agents. It is important for a

farmer to understand that biological control of pests is not meant to eliminate all insect pests.

Biological control can be a viable alternative to using insecticides in greenhouse tomato

production and works especially well with using bumble bees (Bombus fervidus) for pollination.

Low levels of pests must be present to provide food for the biological control agents. It is

important to begin releases of biological control agents when pest populations are low to keep

them from reaching damaging levels. The farmer should keep in mind that biological control

agents are living organisms, and the quality of the agents can differ between sources. Success of

bio-control often depends on careful management of environmental conditions, especially

temperature and humidity.

One of the major factors affecting success of biological control efforts is insecticide use. For

example, you cannot conduct a successful biological control programme against whiteflies if

broad-spectrum, long residual insecticides are being used regularly in the greenhouse to control

other pests.

When insecticide sprays are required, the farmer should carefully select products compatible

with any biological control agents being used, a number of biopesticide and insect growth

regulator (IGR) type products meet this requirement (Smith and Leggitt 2000, p.354).

Chemical approach for pest management

Insecticides, pesticides, fungicides and nematicides are the last resort in any IPM system.

However, chemical use is often needed by the grower to keep pest populations from reaching

damaging levels.

Most insect pests of greenhouse tomatoes occur on the undersides of leaves, and the farmer will

not get good control unless he sprays the bottom side of the leaves. Since pest populations are

often highest on the lower, older leaves, it is especially important to be sure to treat the

undersides of lower leaves. Using adequate spray volume and taking the time necessary to treat

the leaf undersides thoroughly, especially lower leaves is critical for achieving good control with

insecticide sprays (Benton 2007, p.295).

Although the pest spectrum for greenhouse tomatoes is broad, they are some serious pests with

high population densities that should be controlled using pesticides so as to keep their population

below economic threshold.

Aphids (Myzus persicae) have a very successful population due to their special reproduction

characteristic of telescoping generations. In the event that cultural and biological pest control

measures for aphids become fruitless, the farmer should use the following insecticides;

malathion, pyrethrins or Beauvaria bassiana (a fungal disease that infects aphids) (Matthews,

2000).

Whiteflies (Bemesia tabaci) are also the most common and most problematic insect pests of

greenhouse tomatoes. Each female whitefly lays about 150 eggs, usually attached to the

undersides of leaves. In greenhouses, eggs hatch in four to seven days into tiny, white, oval

crawlers (Czosnek, 2007). This simply suggests that they have high population density like

aphids.

In the event that exclusion and sanitation were not viable in reducing the whiteflies population,

the following insecticides may be used for control. Paraffinic oil and potassium salts of fatty

acids provide contact control of adults and crawlers. Pyrethrins will provide short-term control of

adults, but these products will not control immature whiteflies. Effective control of whiteflies

depends on controlling the immature stages (Dent, 2000).

Thrips (Frankliniella fusca) are tiny insects, less than one-sixteenth of an inch; they feed on plant

leaves, blooms, and fruit with “punch and lap” mouth-parts. They reproduce on a wide variety of

crops and weeds. They lay eggs, which are inserted into plant tissue, hatch into elongate, spindle-

shaped larvae and starts feeding on the undersides of leaves by puncturing cells. The following

chemicals can be used to control thrips; azadirachtin, chlorfenapyr, malathion, pyrethrins and

spinosad (Pimentel, 2002).

Leaf miners (Liriomyza sativae) feed on a variety of weeds and vegetable crops, including

tomatoes. In the field, naturally occurring parasites and predators often keep leafminer

populations in check. However, leafminers can be significant pests in greenhouses because the

naturally occurring parasites and predators are excluded. Hence the farmer can turn from

biological control for leafminers and use insecticides such as azadirachtin, pyrethrins, and

spinosad (Hill, 2008).

In summer, spider mites (Tetranychus urticae) are the most problematic pests. They reach

damaging populations under hot, dry conditions. Initial signs of infestation are leaves that look

stippled. In general the farmer should know that mites can develop on many other species of

plants, good sanitation practices are a key to avoiding infestations. If the population density for

mites reaches extremes, miticides such as acequinocyl, bifenzate, chlorfenapyr, etoxazol, or

fenproximate usually give best control (Ciancio, 2007).

Conclusion and Recommendations

The farmer might get confused on determining the actual starting point when he want to employ

the IPM system for pest management. These IPM principles and practices are combined to create

IPM programs which are viable to greenhouse tomato farmers. While each situation is different,

five major components are common to all IPM programs:

1. Pest identification

2. Monitoring and assessing pest numbers and damage

3. Guidelines for when management action is needed

4. Preventing pest problems

5. Using a combination of biological, cultural, physical/mechanical and chemical tools

REFERENCES

Abrol, D.P. (2013) Integrated Pest Management: Current Concepts and Ecological

Perspectives. 3rd

Edition. London. Academic Press Elsivier. pp.561.

Albajes, R., Gullino, M.L. and Elad, Y. (2006) Integrated Pest and Disease Management in

Greenhouse Crops. Moscow. Kluwer Academic Publishers. pp.489.

Benton, J. (2007) Tomato Plant Culture: In the Field, Greenhouse, and Home Garden, 2nd

Edition. CRC Press, London. pp.401.

Best, G.A. And Ruthven, D.A. (1995) Pesticides: Developments, Impacts and Controls. The

Royal Society of Chemistry, UK. pp. 179.

Ciancio, A. Mukerji, K.G. (2007) General Concepts in Integrated Pest Management and

Disease Management. India. Dehli University, Springer. pp. 359.

Czosnek, H. (2007) Tomato Yellow Leaf Curl Virus Disease: Management, Molecular Biology

Breeding for Resistance. 5Th Edition. Israel. Hebrew University of Jerusalem. pp.447.

Dent, D. (2000) Insect Pest Management. 2nd Edition. CAB International, Oxford United

Kingdom. pp.410.

Hill, D.S. (2008) Agricultural Insect Pests of the Tropics and Their Control. New York.

Cambridge University Press. pp.715.

Matthews, G.A. (2002) Pesticide Application Methods, Third Edition. Imperial College, United

Kingdom. John Wiley and Sons. pp.432.

Pimentel, D. (2002) Encyclopedia of Pest Management. CRC Press, Cornell University, New

York City. pp.883.

Smith, S. and Leggitt, M.C. (2000) Greenhouse Gardener's Companion: Growing Food and

Flowers in Your Greenhouse and Sunspace. Revised Edition. Fulcrum Publishing,

Colorado. pp.480.