In this article we will discuss about:- 1. Introduction to Integrated Pest Management 2. Considerations for Pest Management in Greenhouses 3. Management Practices of Specific Greenhouse Insects 4. Management Practices of Important Greenhouse Diseases.
Introduction to Integrated Pest Management:
Although greenhouse vegetable cultivation is expanding leads and bonds every day, but diseases, insect pests, nematodes limiting the production. These constraints should be minimized to produce the high quality and residue free vegetables for internal and export markets. The unique weather conditions which prevail in greenhouses make their ecosystem different from open-growth conditions which may be congenial for certain pathogens to develop.
Variable climate of the greenhouse especially with respect to humidity, moisture, light intensity quality and temperature promote the variety of diseases and insects. Soil wetness and moderate temperature affect soil-borne plant pathogens. Besides, the disease may vary on the same host in different types of greenhouses.
Greenhouse factors that affect the development of pests comprise specific systems of heating, architecture of the greenhouse and covering material, systems of ventilation and irrigation, growth medium, general crop management, and factors which condition the interaction between pathogens and their hosts.
Besides providing appropriate conditions for plant growth, the controlled environment of the greenhouse also provides congenial congenial conditions for disease and insect pest development. Therefore, the management and control of insect-pests and diseases can be challenging, even under optimum conditions.
The strategies adopted to combat these problems, mainly, include use of pesticides viz.-insecticides, fungicides, nematicides, acaricides, etc. The indiscriminate use of chemicals is expensive, hazardous, pollutant and act as product quality deterioration. Therefore, the growers should focus on managing pests with safer pesticides.
Integrated pest management (IPM) is a useful approach for producing greenhouse vegetables. It involves the integrated use of different methods and techniques (cultural, physical, mechanical, chemical and biological) to maximize productivity in a way that is ecologically sound and safe.
The term IPM implies the management of all crop pests including insects, mites, diseases, nematodes and weeds. The integrated approach is the most economical and effective way of limiting most of the pests below economic thresholds, resulting in higher economic returns and sustaining the eco-system.
Considerations for Pest Management in Greenhouses:
It is imperative to realize the impact of pests in limiting the greenhouse crop production and planning their management accordingly. A greenhouse provides a protected environment in which pests can thrive. Pests that may inhabit a greenhouse are protected from the harsh environmental factors (extreme heat, cold, rain and other environmental factors) that normally aid in their control when a crop is grown out doors or under field conditions.
The direct sun, ultraviolet rays and constant changes in temperature also play an important role in overall natural pest control often obtained under field conditions. The greenhouse protects the plants and consequently their respective pests from these environmental conditions. There is lack of specific chemicals suited for greenhouse conditions because most pesticides used under field conditions cannot be used in greenhouse situations.
The toxic fumes liberated by pesticides do not escape and become hazardous to the greenhouse workers. Many greenhouse grown vegetables require frequent harvesting over a long period of time which limits the use of many potent pesticides that have a longer waiting period for consumption after their application.
Further, the greenhouse grower is frequently not able to use large sprayers due to limited space. Therefore, the grower must be extra careful in the long range planning, selection, use and application of pesticides in greenhouse vegetable production system.
For the successful management of pests in greenhouses, the following considerations should be included during planning of the production system for vegetable crops:
(i) Design of greenhouse construction (especially height, heating, insect screens and ventilation components) and an irrigation system that minimizes least wetness and humidity at the plant canopy level.
(ii) Selection of pest resistant varieties.
(iii) Pest-free and healthy seedlings that minimize introduction of plant pathogens, nematodes and insects.
(iv) Optimum fertilizer schedule which results in healthy growth of plants.
(v) Timely monitoring for diseases, nematodes and insects during the growing season.
(vi) Follow sanitation practices including removal of all plant materials after final harvest that minimize microorganisms and pest propagules movement from diseased plants to healthy ones.
(vii) Adopt proper harvesting and shipping/transport practices that maximizes the quality of the product.
Management Practices of Specific Greenhouse Insects:
Many insects that feed on plants grown under field conditions also damage such plants in a greenhouse. However, several insects and mites seem to be a perpetual problem for greenhouse growers. Gaining control or successfully managing insect problem in the greenhouse can be more difficult than the open field conditions. Therefore, the grower must know tactics, schemes and methods that are legal and play a role in the overall reduction or control of a pest.
The important specific insects of a greenhouse can be controlled or managed by following these measures:
A. Aphids (Aphis Gossypii, Myzus Persicae, Brevicoryne Brassicae):
1. In greenhouse conditions aphid population should be kept under control by using beneficial insects such as lady bird beetles, wasps, lacewings and other insects.
2. Spray the crop with malathion (0.1 %) or endosulfan (0.05 %) or monocrotophos (0.05 %). However, insecticides with systemic action are limited for greenhouse use.
B. White Flies (Bemisia Tabaci):
1. New Crops should not be planted in or near greenhouses that currently have a white fly problem.
2. Greenhouse owners that grow seedlings should take extra precautions to keep the seedlings free of white flies.
3. Workers should not wear yellow clothing because white flies are attracted to yellow colour.
4. Control or destroy volunteer host plants including weeds, both during production as well as lean period.
5. Sanitation should always be practiced and infested plants and their parts should be destroyed as soon as the crop is harvested.
6. Use yellow sticky traps regularly in greenhouse which reduces the menace of white fly.
7. Spray either malathion (0.1 %) or moriocrotophos (0.03 %) during active period.
8. Use the parasitic wasp (Encarsia formosa) in greenhouse.
9. Use of bio-agents like Verticillium lecanii is quite effective.
C. Thrips (Scirtothrips Dorsalis):
1. Prevent the thrips from flying or moving into the greenhouse using small mesh screens.
2. Daily misting and a relative humidity of 90% or higher reduce the population of thrips and spider mites.
3. Spray the plants with dimethoate (0.05%) or imidacloprid (0.04%) or fipronil (0.0075 %).
4. A predacious mite (Neoseiulus cucumeris) can be very effective but it must be released over a period of several weeks to control thrips.
D. Tobacco Caterpillar (Spodoptero Litura):
1. Growers must make every effort to prevent the cut worm from entering or becoming established in the greenhouse.
2. Workers should burn pruned plants parts as well as whole plants after final harvest.
3. Spraying of SNPV at 500-600 larval equivalents with proper POB counts when the larvae are not more than one cm long is suggested.
4. Since the older larvae of this species have a habit of hiding under clods/fallen leaves on the soil and climbing on to the top plants during night. To kill the hidden larvae, food bait can be effectively used. The bait can be prepared by mixing 10 kg rice bran, 1 kg jaggery and 150 ml monocrotophos with a small quantity of water. Small pallets of this bait are distributed on the soil throughout the greenhouse.
5. Spray endosulfan (0.05%) or dichlorvos (0.05%) thoroughly covering the leaves and developing fruits.
E. Fruit Borer (Helicoverpa Armigera):
1. Prevent the entry of adult moths into the greenhouse through large openings by covering the doors and by poly sheets or mesh.
2. Spray HNPV of 500-600 Les/ha to eliminate the already existing larvae. Preferably, spraying should be undertaken when the larvae are not more than one centimeter long. If larval of all sizes are noticed, the spray should be repeated after 15-20 days.
3. Spray the formulation of bioagents, Bacillus thuringiensis @ 500g a.i./ha of greenhouse at 10 days interval.
4. Inundative release of egg parasitoids such as Trichogramma chilonis and T. brasiliensis.
5. Foliar spray of methomyl (0.025 %) is also recommended.
F. Two Spotted Spider Mite (Tetranychus Urticae):
1. Follow prevention and sanitation measures.
2. Sprinkler irrigation system is found detrimental to mites and aid in control and in delaying buildup of mite populations.
3. Spray the greenhouse grown vegetables with dicotol @ 0.04 %.
4. Predacious mites can be released to control mites if the infestation is light. The mite percolator, Amblyseius longispinous is effective in suppressing the population of the spider mite.
G. Serpentine Leaf Miner (Liriomyza Trifolii):
1. Adopt preventive measures to avoid the establishment of leaf miners.
2. Release natural enemies in the greenhouse e.g. Diglyphus spp.
3. In severe infestation, spraying of fenthion (0.01%) or triazophos (0.04%) + decamethrin (0.0014%) should be done.
H. Nematode Management Strategies:
In addition to the common insects in greenhouse, nematodes often pose an additional problem. These microscopic worms feed on or in plant roots, disrupting plant root growth and function. They reproduce well at 20-90°F and cause significant problems on many of the vegetables most popular in greenhouse production systems. Nematodes are easily spread with contaminated water, soil or growing media and plant tissues.
The following management practices should be adopted to keep the greenhouse free from nematodes:
(a) Follow plant quarantine measures for instance restrict the use of seed tubes of potato from Nilgiri Hills of Tamil Nadu as the golden nematode is endemic to this area. Check the imported plant material carefully.
(b) Physical Methods:
1. Solarization of the greenhouse soil during off-season.
2. Use nematode free planting material
3. Give not water treatment to planting material.
4. Sanitation and destruction of infected plants.
(c) Cultural Methods:
1. Grow nematode resistant tomato varieties like Pusa-120, PNR-7 and Hisar Lalit.
2. Follow long term crop rotation.
3. Follow deep ploughing during summer keeping greenhouse doors closed so that nematode gets killed due to desiccation and solarization.
4. Apply organic amendments like neem cake or mathua cake @ 500 kg/ha, or at lower doses to the soil in case of row application.
5. Trap crops can also be raised in greenhouse if sufficient space is available.
Marigold is a good companion trap crop tomato as it reduces rook-knot nematode actively in tomato drastically.
(d) Chemical Methods:
Fumigation of the soil with DD mixture or nemagon @ 5 kg a.i./ha has been effective. The other fumigants used are chloropicrin, EDB and methyl bromide. Incorporate the non-fumigants like carbofuran @ 1-2 kg a.i./ha in the soil before planting. Furadan 3 G may be applied @ 1-2 kg a.i./ha at the time of planting in the furrows.
(e) Biological Methods:
The predators (Fungi, predacious nematodes) and parasites (Bacteria- Bacillus thuringiensis and Protozoa) can be used to control the nematodes in greenhouse.
The integrated management of nematodes found in greenhouses has been given below:
1. Follow sanitation and soil solarization measures.
2. Deep ploughing should be done during hot summer.
3. Application of carbofuran at 0.8 kg a.i./ha in combination with neem cake and urea at transplanting reduces the nematode population.
4. Seed treatment with 5% aqueous extract of neem leaf/neem cake containing spares of Paecilomyces lilacinus if found effective.
(I) Reniform Nematode (Rotylenchulus Reniformis):
1. Give solarization treatment and incorporate mahua cake to the soil of greenhouse.
2. Combined use of Paecilomyces lilacinus and carbofuran @ 1kg a.i./ha is found effective.
3. Application of neem cake/neem leaf extracts with spores of Paecilomyces lilacinus in the nursery bed and subsequent root-dip treatment protect the crop.
Management Practices of Important Greenhouse Diseases:
Production areas should be examined for the initial symptoms of disease during routine crop maintenance activities. The earlier the disease is found and identified, the more effective removal of infected plant parts will be to stop or slow down the disease progress.
The more common diseases affecting greenhouse vegetables are described as under:
A. Damping off (Pythium spp., Rhizoctonia spp., Fusarium spp.):
1. Sowing of seed should be done in pre-planting media within clean trays or flats.
2. Seed treatment with captan or thiram @ 2 g/kg seed should be done before sowing.
3. Seeds should be grown physically apart from any crop so that there is no chance for pathogen movement from the old crop to the new crop.
4. Avoid excessive watering or overdoses of fertilizers that may lead to plant root or shoot damage.
5. Drench the soil with formaldehyde before sowing of seeds.
B. Root Rot (Pythium Aphanedermatum):
1. Use only pathogen free planting material.
2. Follow bag system of cultivation as it encourages less incidence of the disease than nutrient film system.
3. The system must be inspected for possible points of entry of unsterilized soil or poor quality water that may introduce Pythium spp.
4. No fungicides are legal for this disease in greenhouse.
C. Sclerotinia Stem Rot (Sclerotinia Sclerotiorum):
1. Sanitation of infected plant parts or entire plants effectively prevents the spread of disease.
2. Judiciously destroy the infected plant parts.
3. Use forced air and heat to lower the humidity as high humidity is a pre-requisite of fungus invasion. Infected plants from the bags should be removed and bags should be fumigated prior to their reuse.
4. Use only labeled fungicides as a part of disease control programme.
D. Botrytis Blight (Botrytis Cinerea):
1. Sanitation of the infected material should be done to remove the fungal inoculum from the greenhouse.
2. Grower should prune off lower canopy to improve drying and air circulation.
3. Temperature and humidity (<90%) must be controlled to dis-favour fungus.
4. Fans should be used to provide air circulation.
E. Downy Mildew (Pseudoperenospora Cubensis):
1. Minimize condensation development in the greenhouse which provides leaf wetness for infection.
2. Keep the adjacent areas free from wild or cultivated cucurbits which act as reservoirs of the fungus.
3. Grow resistant/tolerant varieties.
4. No fungicide control measures are available for greenhouse use.
F. Early Blight (Alternaria Solani):
1. Remove severely affected plants to decrease the inoculum of the fungus.
2. Lower down the humidity of the greenhouse.
3. High fertility level of soil may decrease the plant susceptibility to the disease.
4. Treat the seeds with captan or thiram @ 2 g/kg seed and spray the crop with Dithane M-45 (0.2%) and repeat the spray, if needed.
G. Fusarium Wilt (Fusarium Oxysporum F. Sp. Lycopersici):
1. Thorough sanitation must be performed prior to the planting of the next crop.
2. Discard the infested bags or fumigate them suitably.
3. Follow proper drainage system to avoid the spread of disease.
4. Fumigation of the soil should be done with formaldehyde or any other suitable fumigant.
H. Bacterial Wilt (Pseudomonas Solanacearum):
1. Heating and sealing of the greenhouse during summer reduces the bacterial survival.
2. Grow resistant or tolerant varieties, if available.
3. Disinfect the irrigation water with a suitable disinfectant.
4. Spray the crop with Streptocycline @ 0.25%.
I. Cucumber Mosaic Virus:
1. Rogue out all affected plants as soon as possible to reduce the risk of spread.
2. Adequate weed control must be maintained around the production area to eliminate possible weed reservoirs of this virus.
3. Minimize the aphid population using suitable control measures .to restrict the secondary spread of the virus with the greenhouse.
J. Leaf Curl Virus:
1. Use virus free seedlings for transplanting.
2. Rogue out infected plants.
3. Raise the nursery in disease free area. Use highly UV-reflective mulches which repel the whitefly.
4. Clean the greenhouse immediately after harvesting.
5. Resistant/tolerant varieties should be used, if available.