Pest and disease management in organic agriculture is a complex process and requires integration of all management components including use of resistant varieties, biological diversity on farm, balanced nutrition, steady supply of nutrients and use of preventive and curative steps.
Most pest management practices require long term continuous planning and implementation of activities that aim at preventing and controlling pests and diseases and include both preventive and curative strategies.
Preventive management focuses on keeping existing pest populations and diseases low. Control, on the other hand, focuses on killing pests and diseases. The general approach in organic agriculture is to deal with the causes of a problem rather than treating the symptoms, an aspect that also applies to pests and diseases.
Continuous monitoring, at least once a week of soil, water, pests, natural enemies, weather factors etc. is essential. The health of a plant is determined by its environment, which includes physical factors (such as soil, rain, sunshine hours, wind etc.) and biological factors (such as pests, diseases, weeds, diversity, naturally occurring organisms etc.).
All these factors play an important role in the balance, which exists between herbivorous insects and their natural enemies. Organic pest management strategies largely rely on understanding the intricate interaction of the ecosystem, which play a critical role in pest management.
Understanding and conserving the natural enemies/ defenders is important. In orchards, there can be various types of insects out of which some may be beneficial and some are harmful. Fanners need to understand the difference between the two and try to keep on monitoring the population of friendly insects. Sweep nets, visual counts etc. can be adopted to arrive at the number of pests (P) and defenders (D). The natural enemies can be divided into 3 categories- 1. Parasitoids 2. Predators and 3. Pathogens.
The general rule to be adopted for management decisions is relying on the P:D ratio of 2:1. This means 1 predator is competent to take care of 2 pests. However, some of the parasitoids and predators will be able to control more than 2 pests. Whenever the P:D ratio is less than 2:1 then there is no need for any control measures. In case if it goes beyond 2:1 (i.e. 3.1 and above) then resort to inundative release of parasitoids and predators depending upon the type of pest.
In addition to inundative release of parasitoids and predators the usage of microbial biopesticides can be resorted to. Use of botanicals and organically acceptable chemical formulations be adopted only as last resort.
Preventive Measures for Controlling Disease in Organic Plants:
Thorough understanding about plant health and occurrence of pests and diseases helps growers to choose effective prophylactic measures. As there can be many factors that influence the development of a pest and disease, it is most important to provide necessary interventions at the most sensitive time. This can be accomplished through correct timing of management practices, a suitable combination of different methods, or the choice of a selective method.
Some important preventive crop protection measures are as follow:
(a) Selection of adapted and resistant varieties.
(b) Selection of healthy and disease free seed and planting material.
(c) Selection of optimum planting time and spacing.
(d) Integration of diversity through rotations, intercrops, alley cropping, multi- tier cropping etc.
(e) Balanced nutrient management and addressing secondary or micronutrient deficiency.
(f) Maintenance of soil health and biological activity through timely incorporation of organic manures.
(g) Timely weed management.
(h) Effective water management, preferably through efficient irrigation systems.
(i) Conservation and promotion of natural enemies.
(j) Use of proper sanitation measures and timely removal of infected plant parts from the ground to prevent the disease from spreading, eliminating residues of infected plants after harvesting.
Role of Diversity in Containing Pests for Organic Plants:
Studies have indicated that enhanced diversity in a particular field or plantation helps in containing pests. Diversity can be enhanced by planting border plants, planting on bunds, intercrops, rotation, alley cropping, multitier cropping etc. Several types of plants like nitrogen fixing plants, plants of pesticidal value, insectary plants which specifically attract useful insects because of their pollen nectar, can be planted.
It has been observed that in mono-cropping the host plants are concentrated in time and species whereas intercrops or border crops increase the diversity in the field and act as barriers for colonization and movement of insect pests. Also many flowering plants planted in the orchard act as attractants for many natural enemies. In conclusion, enhanced diversity creates natural habitat conditions which results in increase, in natural enemy populations ultimately resulting in lower insect pest level.
Planting Material Treatment for Organic Plants:
Seeds and planting material such as cuttings etc. can be treated to protect against pests and diseases in the soil that can attack seeds, roots or young seedlings (soil-borne diseases).
There are four main methods for seed treatment in organic farming:
1. Physical – Heat sterilization by soaking seed in hot water (typically 50- 60°C),
2. Botanical – By coating seeds with a layer of plant extract, such as turmeric powder, crushed garlic or clove-cinnamon extract,
3. Biological – By coating seeds with a layer of antagonistic microorganisms such as Trichoderma or Pseudomonas fluorescens,
4. Organically acceptable chemicals – By coating/treating seeds with vinegar, copper salts or baking soda and mineral oil etc.
Some of the most widely practiced organic seed treatment options are as follows:
1. Beejamrit:
Made from cow dung, cow urine and lime is an excellent seed treatment formulation and is being used by large numbers of organic farmers in almost all crops. Beejamrit treatment provides protection against seed rot, seedling rot and some other soil borne diseases. Beejamrit treatment improves seed germination.
2. Cow Urine:
Dilute one part of cow urine with 5 parts water, soak the seeds for 15 min and then dry in sun. The treatment prevents soil borne diseases and increases germination.
3. Cow Milk:
Dilute one part cow milk with 5 parts water, soak the seeds for 15-20 min, sun dry and sow, this treatment helps in control of leaf spot diseases and prevents yellowing of leaves.
4. Horse Manure/Compost Tea:
Horse manure/compost tea is ideal for seedbed treatment in nurseries.
5. Wood Ash:
Mix 10 gm finely powdered wood ash in 500 ml water and treat the seeds. Dry in sun and sow immediately. The treatment helps in reduction of seedling rot.
6. Horsetail (Equisetum Arvense) Decoction:
Boil 500 gm plant parts in 5 lit water and boil till it becomes half. Filter and store. The extract can be used for seed treatment for protection against soil borne fungal diseases such as seedling rot.
7. Panchagavya Treatment:
3% solution of Panchagavya can be used to soak the seeds or dip the seedlings before planting. Soaking for 20 minutes is sufficient. Rhizomes of turmeric, ginger and sets of sugarcane can be soaked for 30 minutes before planting.
8. Turmeric Powder:
250 gm powder in 1 lit of water for 10 kg seed. Treatment provides protection against fungal rot and wilt diseases.
9. Asafoetida:
250 gm in one lit of water for 10 kg seed. Treatment provides protection against fungal rot and wilt diseases. The treatment also repels insects and ants.
10. Garlic Extract:
Crush 250 gm garlic cloves in 1 lit of mineral oil. Keep overnight and collect filtrate. 20 kg seed can be treated with this extract.
11. Garlic-Clove-Cinnamon Extract:
Crush 250 gm of garlic, 100 gm of clove buds and 100 gm cinnamon powder in 1 lit of mineral oil. Keep overnight and squeeze out the extract. 20 kg seed can be treated with this extract.
12. Steam Distilled Plant Oils:
Steam distilled oils of thyme, cinnamon, clove and garlic are effective against wide range of seed and soil borne fungal and bacterial diseases. 1-2% of such oils mixed with mineral oil or any other vegetable oil can be used for seed treatment.
13. Sodium Hypochlorite:
Hard seed coat seeds can be surface sterilized by using 5% solution of sodium hypochlorite for 5 minutes followed by several washings of clean water.
14. Vinegar:
Mix 1 tbsp of vinegar in 4 cups of water. Place the seeds in a small cloth bag and dip the seed bag into vinegar-water solution. Dry dipped seeds on old newspapers before sowing. Make sure that seeds are completely dry before storing.
15. Copper Salts:
Seed treatment with copper sulphate and lime or copper oxychloride is generally advised as last resort where other methods have failed.
16. Elemental Sulphur:
200-mesh fine powder of elemental sulphur at 20 gm per kg of seed is also effective against many seed and soil borne diseases. Lime sulphur can also be used in place of elemental sulphur.
Biological Seed Treatment Methods for Organic Plants:
Microbial inoculants in the form of bio-fertilizers and bio-pesticides are being used widely not only for growth promotion and nutrient mobilization, but also for protection of seeds against soil borne plant pathogens. These inoculants are applied both as seed and soil treatment.
For seed treatment 5 gm of inoculant is adequate for treating one kg of seed. In case of multiple inoculations 5 gm of each inoculant is used per kg of seed. Treatment is done by making slurry of the inoculant and sticker (like sugar, jaggary or gum Arabic) in water and then mixing it with seeds. Treated seeds are dried in shade and sown within 4-6 hrs of treatment.
i. Biofertilizers such as Rhizobium, Azotobacter and PSB:
Act as nutrient mobilizers and growth promoters. Very high microbial population around seeds creates a barrier for pathogens to reach seeds. Azotobacter releases some fungistatic complex, which helps in reduction of soil borne pathogen attack.
ii. Trichoderma Viride:
The fungal inoculants are being used as biological control agents against plant pathogenic fungi and are effective as seed dressing in the control of seed and soil-borne diseases including Rhizoctonia solani, Macrophomina phaseolina and Fusarium species. On application to seed it colonizes on the seed surface and kills not only the pathogens present on the cuticle, but also provides protection against soil-borne pathogens.
iii. Trichoderma Harzianum:
It is also used as bio-fungicide and is suitable for application as foliar application, seed treatment and soil treatment for suppression of various diseases caused by fungal pathogens including Botrytis, Fusarium and Penicillium sp. and also nematodes.
iv. Paecilomyces Lilacinus:
It is used as effective control agent against root knot nematodes as seed and soil treatment. It can be used alone or in combination with Trichoderma viride.
v. Pseudomonas Fluorescens:
Effective strains of P. fluorescens possess excellent bio-control properties and on application as seed or soil treatment protect the roots of plants against pathogenic fungi such as Fusarium and Pythium. P. fluorescens has also been found to be effective against some phytophagous nematodes.
vi. Bacillus Subtilis:
Some strains of Bacillus subtilis are effective biofilm producers around roots of treated plant thereby protecting their roots from various soil borne fungal pathogens. Bacillus subtilis inoculants have been specifically found very effective in nurseries and in protected cultivation.
Weed Management for Controlling Organic Plants:
Weed management under organic management is one of the most challenging tasks and requires long term planning and adoption of various cultural methods.
Besides the cultural and agronomic options, weed management is generally addressed through following practical solutions:
1. Manual weed removal.
2. Mechanical scraping or cutting through hand or motor operated weeders, bullock operated scrapers or tractor mounted weeders and smotherers.
3. Mulching – keeping the soils covered with organic/biological mulch is the best strategy not only for weed suppression but also for soil fertility management. In vegetables covering the vacant spaces by crop residue, dried leaves and degradable waste, immediately after transplanting is the most effective strategy.
4. Intercropping with legumes and cover crops also prevents weed growth.
5. Use of plastic mulch is highly effective, but being cost intensive is resorted to only in cash crops.
6. Flaming of weeds between the rows of fruit plants is a viable option and is very effective in new as well as old orchards with woody plant stand.
7. Use of organically acceptable chemicals such as vinegar and salt for suppressing the weed growth.
Curative Pest Control Measures for Organic Plants:
If preventive crop protection practices fail to sufficiently prevent economic losses then, it may be necessary to take curative action. Curative action means controlling the pest or disease once it has already infested the crop.
Several options exist in organic agriculture:
1. Mechanical control with traps, sticky plates or hand picking.
2. Biological control with natural predators or antagonistic microbes.
3. Natural pesticides based on herbal preparations or other natural products.
4. Organically acceptable chemical alternatives such as copper sulphate, lime and elemental sulphur
Mechanical Control Measures for Organic Plants:
1. Removal of Affected Plants or Parts:
The virus affected diseased plants should be removed from the field; it prevents the transmission of disease to other plants.
2. Collection & Destruction of Egg Masses and Larvae:
Keep surveillance of the crop for pest monitoring and during survey collect the egg masses and larvae from the field and destroy them. This practice helps in minimizing the pest load.
3. Light Traps:
Among the most widely used constructed traps are kerosene lamp traps or light traps. Ultraviolet lamps are much more effective than ordinary electric bulbs. These traps should be used at appropriate time, depending upon the life cycle of the insects.
The best time is immediately after the emergence of moths, before they lay the eggs. In these traps the light source is kept over a shallow wide bowl of water added with few spoonful of oil or kerosene. Moths that attract towards light fall in this bowl and will not be able to fly. From there they are collected and destroyed.
4. Pheromone Traps:
Sex pheromones are synthetic chemicals that are basically used to attract and trap insect pests so as to reduce the insect population. Since sex pheromones are not sprayed directly on to the crop, there is no pollution problem.
5. Use of Sticky, Coloured Plates and Other Physical Traps:
Different species of insects are attracted by different colours. The results indicated that yellow plastic plates coated with grease or any sticky substance and insecticide were effective in controlling leaf miner. This method avoids environmental pollution since the insecticide is not sprayed directly onto the crop. Different colours may attract different insects. Appropriate colours need to be identified for the purpose.
6. Physical Barriers:
The flat snail (Bradybaena similaris) is widely distributed in Taiwan, Mainland China, Japan and India. Recently, a method has been developed for controlling the snail by the use of disposable plastic soda bottles made into traps. These prevent the snails from climbing up onto the grapevine. The traps are made by cutting off both ends of the bottle and splitting one side of the body longitudinally to allow it to be sleeved around the stem of the grapevine.
The bottles are then stapled firmly around the stem at a height of 1 m above the ground. Since the bottles are tightly fixed around the grape stem, the snails cannot pass through the neck to infest the vines. Unable to descend, all the snails are trapped in the bottle and soon die of starvation. These traps give a control rate of more than 94.8%. This is a very cheap and effective method of controlling flat snail, and there is no threat to the environment. It can thus be widely recommended to grape farmers.
Bagging Fruits:
Bagging prevents insect pests, especially fruit flies damaging the fruits. The bag provides physical protection from mechanical injuries (scars and scratches) and prevents egg laying activities of female flies, latex burns and fungal spots on the fruits.
Although bagging is not widely practiced due to involved costs and difficulties in bagging so many fruits, but it is widely practiced in banana world over and is also economical. Wherever possible it can be used and gives reliable estimate of projected harvest.
How to make a bag?
1. Cut old newspapers measuring 15 x 22 cm or 12.5 x 27.5 cm for mango and for fruits of similar size.
2. Double the layers, as single layer break apart easily.
3. Fold and sew or staple the sides and bottom of the sheets to make a rectangular bag.
4. Fruit bags can also be made of plastic film or fine net mesh.
5. Ready-made fruit nets/sleeves are also available in the market.
How to bag a fruit?
1. Blow in the bag to inflate it.
2. Remove some of the fruits, leaving 1 on each cluster.
3. Insert one fruit per bag then close the bag using coconut midrib or firmly tie top end of bag with string or wire or staple it.
4. Push the bottom of the bag upwards to prevent fruit from touching the bag.
5. Use a ladder to reach as many fruits as possible. Secure the ladder firmly on the ground and for bigger and higher fruit trees, secure or tie the ladder firmly on big branches to ensure safety of workers.
Remember:
1. Bagging works well with melon, bitter gourd, mango, guava, star fruit, and banana.
2. Start bagging bitter gourd when the fruit is 2-3 cm in length. Tie the bag with a string around the stalk. The bag is formed like a cylinder and must be longer than the anticipated size of the fruit when it matures.
3. Start bagging the mango fruit 55-60 days from flower bloom or when the fruits are about the size of a chicken egg.
4. When using plastic bags, open the bottom or cut a few small holes to allow moisture to dry up. Moisture trapped in the plastic bags damages and/or promotes fungal and bacterial growth that cause diseased fruits. Plastic also overheats the fruit.
5. Bags made of dried plant leaves are good alternatives to plastic.
6. Remove the bags during harvest and dispose them properly.
Biological Alternatives for Controlling Pests in Organic Plants:
Nature has its own device to balance the ecosystem. Spiders, insect predators, parasitoids and insect pathogens are present in nature and are playing major role in maintaining the pest population in undisturbed ecosystems. The potentiality of such system can be harvested for maintaining the pest population below economic injury level in our agricultural fields. Natural enemies are highly specific and safe to non-target species. Once established they survive in nature till the pest is prevalent and are self-perpetuating in nature.
Use of Pest Predators and Parasites:
Mass production of predators, parasites and pathogens and their augmentation in the infested or infected field, effectively controls the pest population below economic injury level.
With the help of inundative release of Trichogramma sp. @40,000 to 50,000 per hectare, Chelonus blackburni @ 15,000 to 20,000 per hectare, Apanteles spp. @ 15000-20000 per ha and Chrysoperla sp. @ 5,000 per ha, 2-3 times a year can effectively check the spread of large number of insect pests and helps keep their population below economical threshold limit.
Use of Biopesticides:
Biopesticides or pesticides of microbial origin are emerging as sustainable non-chemical alternatives in pest management. Trichoderma viride or T. harzianum or Pseudomonas fluorescens formulation @ 4 gm/kg seed either alone or in combination can manage most of the seed borne and soil borne diseases.
There are other formulations viz. Beauveria bassiana, Metarhizium anisopliae, Nomitraea rileyi, Verticillium sp., which are available in the market and can manage their specific host pest. Discovery of isolates like Bacillus thuringiensis, B. tenebrionis and B. thuringiensis san-diego acting against Coleopterans as well other species has extended the scope of bacterial insecticides.