2023 Solved Old Paper (BOT - 201) New
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Sugarcane:-
Grassy shoot disease:-
Pathogen:- The disease is caused by Mycoplasma like organisms. Mycoplasma cells are physically small – less than 1 µm – and they are therefore difficult to detect with a conventional microscope.
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Tundu disease of Wheat:-
Pathogen:- Clavibacter (= Corynebacterium) tritici
Symptoms:-
> The early symptoms of tundu disease are wrinkling of lower and twisting of the middle leaves generally evident when the crop is reaching maturity. This is followed by curling and twisting of spikes.
> What happens actually is that a bright yellow sticky slime exudes mainly from the ear and envelops it.
> In addition, the slime trickles down to glumes, stem, and leaf sheaths and envelop them. The slimy substance becomes deeper yellow, hard, and dry in dry weather resulting in retardation of plant growth and distortion of stem and ear.
Management:-
i. As soon as the symptoms appear, the infected plants should be uprooted and burnt.
ii. Seeds not contaminated with nematode galls should be sown preferably in non-infected fields. Seeds can be made gall-free by soaking them in strong solution of common salt (solution called ‘brine’) prepared at the rate of 40 lb. salt dissolved in 25 gallons of water. The galls float on the surface of the solution and are removed. This method is the most effective one and recommended strongly.
iii. In tropical countries, summer ploughing helps destroy bacteria and nematodes occurring in soil by heat and desiccation and thus reduces disease incidence in the next season.
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Bacterial Leaf Blight of Rice:-
Pathogen:- Xanthomonas oryzae pv. oryzae
Symptom of Damage:-
> Seedling wilt or kresek.
> Water-soaked to yellowish stripes on leaf blades or starting at leaf tips then later increase in lengthand width with a wavy margin.
> Appearance of bacterial ooze that looks like a milky or opaque dewdrop on young lesions early in the morning.
> Lessions turn yellow to white as the disease advances.
> If the cuts end of leaf is kept in water it becomes turbid because of bacterial ooze.
Management:-
Biological Method:-
> Spray fresh cowdung extract 20% twice (starting from initial appearance of the disease and another at fortnightly interval).
> Neem oil 60 EC 3% (or) NSKE 5% is recommended for the control of sheath rot, sheath blight, grain discolouration and bacterial blight.
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Tikka Disease of Groundnut:- The groundnut leaf spots (early leaf spot and late leaf spot) commonly called as “Tikka” disease.
1. Early Leaf Spot of Groundnut:-
Pathogen:- Cercospora arachidicola
Symptoms:-
> Infection starts about a month after sowing.
> Small chlorotic spots appear on leaflets, with time they enlarge and turn brown to black and assume sub circular shape on upper leaf surface.
> On lower surface of leaves light brown colouration is seen.
> Lesions also appear on petioles, stems, stipules.
> In severe cases several lesions coalesce and result in premature senescence.
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Bacterial Leaf Blight:-
Pathogen:- Xanthomonas oryzae pv. oryzae
Symptom of Damage:-
> Seedling wilt or kresek.
> Water-soaked to yellowish stripes on leaf blades or starting at leaf tips then later increase in lengthand width with a wavy margin.
> Appearance of bacterial ooze that looks like a milky or opaque dewdrop on young lesions early in the morning.
> Lessions turn yellow to white as the disease advances.
> If the cuts end of leaf is kept in water it becomes turbid because of bacterial ooze.
Management:-
Biological Method:-
> Spray fresh cowdung extract 20% twice (starting from initial appearance of the disease and another at fortnightly interval).
> Neem oil 60 EC 3% (or) NSKE 5% is recommended for the control of sheath rot, sheath blight, grain discolouration and bacterial blight.
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Scab disease:-
1. Common scab:- > Common scab of potatoes is a soil-borne disease caused by the bacteria-like organism Streptomyces scabies.
> The disease occurs throughout the potato growing regions of the world, including Africa.
2. Fungal scab:-
> Scab diseases of trees and shrubs are caused by a group of closely related fungi, mainly of the genera Venturia, Fusicladium and Fusicladosporium.
> They are favoured by wet weather in spring and summer.
> Apple scab is a disease caused by the fungus, Venturia inaequalis, which spreads by airborne spores and survives the winter on fallen leaves. Expect scab marks to appear on leaves from mid-spring until leaf fall in autumn.
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Canker:-
Pathogen:- Xanthomonas campestris pv citri
Symptoms:-
i. Acid lime, lemon and grapefruit are affected. Rare on sweet oranges and mandarins.
ii. Affects leaf, twig and fruits. In canker, leaves are not distorted.
iii. Lesions are typically circular with yellow halo; appear on both sides of leaf, severe in acid lime (difference from scab) When lesions are produced on twigs, they are girdled and die.
iv. On fruits, canker lesions reduce market value.
Management:-
i. Streptomycin sulphate 500-1000 ppm; or Phytomycin 2500 ppm or Copper oxychloride 0.2% at fortnight intervals.
i. Control leaf miner when young flush is produced.
iii. Prune badly infected twigs before the onset of monsoon
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Chlorosis:-
> Chlorosis is a yellowing of normally green leaves due to a lack of chlorophyll. Many factors, singly or in combination, contribute to chlorosis.
> Yellowing of the entire network of veins in the leaf blade is the characteristic symptom.
> In severe infections the younger leaves turn yellow, become reduced in size and the plant is highly stunted.
> The veins of the leaves will be cleared by the virus and intervenal area becomes completely yellow or white.
> In a field, most of the plants may be diseased and the infection may start at any stage of plant growth.
> Infection restricts flowering and fruits, if formed, may be smaller and harder.
> The affected plants produce fruits with yellow or white colour and they are not fit for marketing.
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IPM (Integrated Pest Management):- IPM is that method of pest control, which utilizes all suitable techniques of pest control to reduce pest populations and maintain them below economic injury level.
Principles of IPM:-
> IPM is a decision-making process that helps to prevent pest problems.
> With IPM programs, all information and treatment methods are considered in order to manage pests.
> This should be effective, affordable, and safe for the environment.
> Elements of any IPM program include:
i. Prevention:- Organisms are kept from becoming problems by planning and managing ecosystems.
ii. Identification:- Pests and beneficial organisms are identified.
iii. Monitoring:- Pest and beneficial organism’s populations are watched, as well as pest damage, and the environment.
iv. Injury and Action Decision:- Injury and action thresholds are used to know when to treat pests.
v. Treatments:- Treatments (or a combination) are used, including cultural, biological, physical, mechanical, behavioural, or chemical methods. The goal is to control pests with little impact on the environment.
vi. Evaluation:- The effectiveness of pest management plans are considered.
Advantages of IPM include:-
> Long-term answers to pest problems.
> Protecting environmental and human health by reducing pesticide use.
> Reducing harm to beneficial organisms.
> Preventing creation of pesticide resistant pests.
> Providing a way to manage pests when pesticides cannot be used.
Components of IPM:- Various components and techniques that can be utilized in Integrated Pest Management programmes are as follows:
1. Cultural control:- Use of resistant varieties of crops is a promising technique in IPM. Moderately to low level of resistance is best integrated with chemical and biocontrol agents. Crop rotation and sanitation are also used to reduce the pest population to lower levels.
2. Mechanical control:- Use of screens or barriers or handpicking in nursery stage of the crops and use of light traps to kill egg-laying adults can bring down the population for the other methods to be effective.
3. Biological control:- Natural enemies are commonly utilized in IPM programmes. Emphasis is given to protection and augmentation of indigenous natural enemies and recolonisation of those that have been wiped out due to indiscriminate use of insecticides.
4. Chemical control:- Minimal use of insecticides is recommended in IPM. Rule of the thumb is not to use insecticides unless absolutely necessary. Application methods that do not bring insecticides in contact with natural enemies are favoured in IPM programmes.
5. Regulatory methods:- Plant and animal quarantines by the government and collective eradication and suppression in large areas help in providing long-lasting management. International efforts to suppress noxious pests like locusts have proved fruitful.
Note:- In most of the cases, chemical, biological and varietal resistances are combined to manage the population of pest species.
Examples of IPM:-
1. Cotton pest control in Peru:-
> Developed by Wille (1951) in Canete Valley which is a self-contained ecosystem surrounded by arid areas.
> Due to extensive use of organic insecticides and subsequent resistance developed by the cotton pests, the valley was led to the brink of disaster.
> The following steps were taken to save the crops:
i. Prohibition of ratooning.
ii. Prohibition of synthetic organic insecticides and return to the old calcium and lead arsenates and nicotine sulphates.
iii. Repopulation of the area with; natural enemies introduced from the surrounding regions.
iv. Establishment of deadlines for planting, ploughing, irrigation, pruning and harvesting.
v. Employment of cultural practices, which led to the establishment of healthy, uniform stands.
> As a result of this IPM programme, the pest problem was solved and the whole agro-ecosystem twined into a self-balanced system.
2. Integrated Pest Management in Paddy:- FAO developed an intercountry programme for IPM in South and Southeast Asia by integrating biological, chemical and cultural control methods.
3. Integrated Pest Management in Sugarcane:-
> Chemical control is not successful in sugarcane fields because of technical and mechanical problems of insecticide applications and also insecticide contamination eventually reaching humans.
> Integration of biological contraol, particularly the egg parasite, Trichogramma species and modification of cultural practices has been found to keep the pest densities below economic injury levels.
4. Integrated control of locusts:-
> FAO undertakes constant surveillance throughout the breeding areas and follows the following IPM programme:
- Eggs are destroyed by ploughing or flooding (mechanical control).
- Nymphs are controlled either by direct spraying by aircrafts or by barrier spraying, baiting, trenching or burning by flame-throwers.
- Repellents like neem-oil are sprayed on crop at the time of swarming.
- Swarms are either sprayed while resting on ground or by aircrafts while migrating.
- Some biological control is achieved by conserving predators in the breeding grounds.
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Ergot disease of Bajra:-
Pathogen:- Claviceps fusiformis
Symptoms:-
> Small droplets of pinkish sticky fluid oozes out of the spikelets. The affected spikelets turn black and several such dark sticky patches are seen on the earhead.
> Grain formation is inhibited.
> The honey dew contains large number of hyaline single celled conidia.
> Later infected ovaries get converted into sclerotia.
Management:-
1. Seed treatment:-
> Removal of ergot / sclerotia to prevent primary infection Dissolve 1 kg of common salt in 10 litres of water. Drop the seeds into the salt solution. Remove the ergot and sclerotia affected seeds which
will float. Wash seeds in fresh water 2 or 3 times to remove the salt on the seeds. Dry the seeds in shade.
> Treat the seeds with Thiram @ 2g /kg of seed.
2. Spray of Fungicides:- Spray any one of the fungicides like Carbendazim 500g or Mancozeb
1000g /ha when 5 - 10% flowers have opened and again at 50% flowering stage.
Smut of Bajra:-
Pathogen:- Tolyposporium penicillariae
Symptoms:-
> The disease becomes apparent at the time of grain set.
> A few grains, sporadically distributed on the earhead are replaced by green to black sori, which are much bigger than normal grains.
> The sorus wall is tough, surrounding the powdery mass of smut spores which are in balls.
> Favourable Conditions:- High relative humidity; Successive cropping with pearlmillet.
Management:-
> The only control measures recommended strongly for this disease are the removal of smutted ears, use of clean seeds, hot weather deep ploughing, field sanitation, and crop rotation.
> Attempts are required to raise resistant varieties of this crop against smut disease.
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Early Blight of Potato:-
Pathogen:- Alternaria solani
Symptoms:-
> It is present in both hills & plains.
> Brown-black necrotic spot-angular, oval shape characterized by concentric rings.
> Several spot coalesce & spread all over the leaf.
> Shot holes on fruits.
Management:-
> Disease free seed tubers should be used for planting.
> Removal and destruction of infected plant debris should be done because the spores lying in the soil are the primary source of infection.
> Very early spraying with Zineb or captan 0.2% and repeating it for every 15 – 20 days gives effective control.
> The variety Kufri Sindhuri possesses a fair degree of resistance.
Late Blight of Potato:-
Pathogen:- Phytopthora infestans
Symptoms:-
> It affects leaves, stems and tubers.
> Water soaked spots appear on leaves, increase in size, turn purple brown& finally black colour
> White growth develops on under surface of leaves.
> This spreads to petioles, rachis& stems.
> It frequently develops at nodes.
> Stem breaks at these points and the plant topples over. In tubers, purplish brown spots and spread to the entire surface on cutting, the affected tuber show rusty brown necrosis spreading from surface to the center.
Management:-
> Protective spraying with mancozeb or zineb 0.2 % should be done to prevent infection of tubers.
> Tuber contamination is minimized if injuries are avoided at harvest time and storing of visibly infected tubers before storage.
> The resistant varities recommended for cultivation are Kufri Naveen, Kufri Jeevan, Kufri Alenkar, Kufri Khasi Garo and Kufri Moti.
> Destruction of the foliage few days before harvest is beneficial and this is accomplished by spraying with suitable herbicide.
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Little leaf of Brinjal:-
Pathogen:- Mycoplasma like organism (MLO)
Vector:-
> The disease is transmitted through by the vector Brown leaf hopper (Cestius phycitis).
> Probably during the season of Brinjal crop, the causal agent survives on weed hosts and from there it is transmitted to main crop by its insect vector.
Symptoms:-
> The main symptom of the disease is the production of very short leaves by affected plant.
> The petioles are so much reduced in size that leaves appear sticking to the stem. Such leaves are narrow, soft, smooth and yellowish in colour.
> Newly formed leaves are further reduced in size.
> The internodes are shortened and at the same time large number of axillary buds are stimulated to grow into short branches with small leaves. This gives whole plant a bushy appearance.
> Usually such plant unable to form flowers.
> Fruiting is very rare.
Management:- No effective control method is found.
Physical methods:-
> Plant disease-resistant varieties such as Padagoda.
> Avoid cultivating alternative host plants like Chilli/Pepper.
> Provide adequate space while planting ideally 90x75 cm.
> Adjust sowing time to avoid the insect vector's peak season.
> Regularly monitor the field for signs of leafhopper infestation ensure it is disease-free.
> Remove and destroy the infected plants immediately.
> Get rid of susceptible host plants (weeds).
> Use barrier crops around your field that hinder the vector to directly infest your crop.
> Conserve natural enemies and beneficial insects.
Chemical method:- Tetra-cycline has been reported to control the disease.
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Downy Mildew of Grapes:-
Pathogen:- Plasmopara viticola
Symptoms:-
> Irregular, yellowish, translucent sports on the upper surface of the leaves.
> Correspondingly on the lower surface, white, powdery growth on leaves.
> Affected leaves become, yellow, brown and gets dried.
> Premature defoliation.
> Dwarfing of tender shoots.
> Brown, sunken lesions on the stem.
> White growth of fungus on berries which subsequently becomes leathery and shrivels.
> Later infection of berries result in soft rot symptoms.
> No cracking of the skin of the berries.
> Spread:- Through sporangia by wind, rain etc.
> Survival:- As oospores present in the infected leaves, shoots and berries. Also as dormant mycelium in infected twigs.
> Optimum temperature:- 20-22°C
> Relative humidity:- 80-100 per cent
Management:- Spray Bordeaux mixture 1 % or Metalaxyl + Mancozeb 0.4 %.
Powdery Mildew of Grapes:-
Pathogen:- Uncinula necator
Symptoms:-
> Powdery growth mostly on the upper surface of the leaves.
> Malformation and discolouration of affected leaves.
> Discolouration of stem to dark brown.
> Floral infection results in shedding of flowers and poor fruit set.
> Early berry infection results in shedding of affected berries.
> Powdery growth is visible on older berries and the infection results in the
> Cracking of skin of the berries.
> It spread through air-borne conidia
> Through dormont mycelium and conidia present in the infected shoots and buds.
> Sultry warm conditions with dull cloudy weather, highly favourable.
Management:- Spray Inorganic sulphur 0.25 % or Chinomethionate 0.1 % or Dinocap 0.05 %.
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Angular Leaf Spot of Cotton:- Also called as Bacterial Blight of Cotton.
Pathogen:- Xanthomonas campestris p.v malvacearum
Symptoms:- The bacterium attacks all stages from seed to harvest. Five common phases of symptoms:
1. Seedling blight:-
> Small, water-soaked, circular or irregular lesions on the cotyledons.
> Infection spreads to stem through petiole and cause withering and death of seedlings.
2. Angular Leaf Spot:-
> Small, dark green, water soaked areas develop on lower surface of leaves.
> The spots become angular restricted by veins and veinlets and are visible on both the surface of leaves.
> Later they turn reddish brown colour and infection spreads to veins and veinlets.
3.Vein necrosis or Vein banding:-
> Blackening of the veins and veinlets, gives a typical ‘blighting’ appearance.
> On the lower surface of the leaf, bacterial oozes are formed as crusts or scales.
> The leaves become crinkled and twisted inward and show withering.
> The infection also spreads from veins to petiole and cause blighting leading to defoliation.
4. Blackarm:-
> On the stem and fruiting branches, dark brown to black lesions are formed.
> Girdle the stem and branches to cause premature drooping off of the leaves.
> Cracking of stem and gummosis, resulting in breaking of the stem and hang typically as dry black twig to give a characteristic “black arm” symptom.
5. Square rot or boll rot:-
> On the bolls, water soaked lesions appear and turn into dark black and sunken irregular spots.
> Infection slowly spreads to entire boll and shedding occurs.
> Infection on mature bolls lead to premature bursting.
> The bacterium spreads inside the boll and lint gets stained yellow because of bacterial ooze and loses its appearance and market value.
> The pathogen also infects the seed and causes reduction in size and viability of the seeds.
Survival and Mode of Spread:-
> The bacterium survives on infected, dried plant debris in soil for several years. The bacterium is also seed-borne and remains in the form of slimy mass on the fuzz of seed coat.
> The primary infection is through seed-borne bacterium.
> Secondary spread is through wind, windblown rain splash, irrigation water, insects and other implements.
Favourable Conditions:-
> Optimum soil temperature of 28˚C.
> High atmospheric temperature of 30-40˚C.
> Relative humidity of 85 percent.
> Poor tillage, late irrigation.
> Potassium deficiency in soil.
> Rain followed by bright sunshine during the months of October and November.
Management:-
> Delint the cotton seeds with concentrated sulphuric acid at 100ml/kg of seed.
> Treat the delinted seeds with Carboxin or Oxycarboxin at 2 g/kg or Carboxin 37.5% + Thiram 37.5% WS @2.5 g/ kg.
> Remove and destroy the infected plant debris.
> Rogue out the volunteer cotton plants and weed hosts.
> Follow crop rotation with non-host crops.
> Early thinning and early earthing up with potash.
> Spray Streptomycin sulphate @ 100g +Copper oxychloride@500 g/acre.
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Red Rot of Sugarcane:-
Pathogen:- Glomerella tucumanensis. (Older name = Colletotrichum falcatum)
Symptoms:-
> The affected canes exhibit leaf colour change, from green to orange and then to yellow in the third or fourth leaf. Then the leaves start drying from bottom to top.
> If the fungal spores enter the leaf sheath through the leaf midrib, then reddish spots can be seen on the back side of the leaf midrib also.
> The external symptoms appear only after16 - 21 days after infection and drying of entire cane takes another 10 days time.
> When the affected cane is split opened, the inner region is reddish in colour with intermittent white tinges across the cane length.
> Sometimes, the pith inside the cane is filled with blackish brown liquid and exhibited alchohol odour.
Management:-
i. Cultural method:-
> The best way to control red rot is to select setts for planting from healthy plants in a disease- free area.
> The red rot affected field must be rotated with rice for one season and other crops for two seasons.
> Growing of recommended resistant and moderately resistant varieties viz., Co 86032, Co 86249, CoSi 95071, CoG 93076, CoC 22, CoSi 6 and CoG 5.
ii. Physical method:-
> Removal of the affected clumps at an early stage and soil drenching with Carbendazim 50 WP (1 gm in 1 litre of water).
> The cut ends and entire setts should be dipped in a fungicide solution, such as one per cent Bordeaux mixture.
> If the disease is noticed in the field, the leaves and canes should be collected and destroyed by burning.
iii. Chemical method:-
> Adopt sett treatment with Carbendazim before planting (Carbendazim 50 WP (0.5 gm in 1 litre of water) or Carbendazim 25 DS (1gm in 1 litre of water) along with 2.5 kg of Urea in 250 litre of water.
> Use fungitoxic chemicals like Bavistan, Benomyl, Topsin and Aretan at 0.1 per cent for 18 min. at 52ºC for dipping setts which gave almost complete elimination of rot infection.
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Plant Disease control by Biological methods:- Biological control involves the use of one living organism to control another.
Biological Control Agents:-
a Parasitoids
b. Pathogens
c. Predators
d. Antagonists of Plant Diseases
a Parasitoids:-
> Each parasitoids requires only one host, which it kills for its development into a free living adult.
> Parasitoids are of the same size as the hosts, or sometimes even smaller.
> Mechanism:-
- The Female parasitoid lays eggs inside or on an insect host.
- Legless larva on hatching feed on the hosts internally or externally.
- Many adult parasitoids feed on nectar or pollen and serve as important pollinators.
> Examples:- Trichogramma,Ichneumoid,Scelionoid,Braconid, Encryrtid,Eulophid,Chalcid wasps and Tachinid Flies.
> Revolution of Trichogramma chilonis:-
- Trichogramma chilonis has been successfully released in Jammu & Kashmir, Himachal Pradesh, Punjab, Haryana, Gujrat , Uttrakhand , Uttar Pradesh, Bihar , Karnataka, Tamil Nadu ,Maharashtra and few other states.
- It has given 56-82% protection against the sugarcane tissue borers.
b. Pathogens:-
> Pathogens are disease causing organisms e.g. Bacteria, Fungi, Viruses ,Protozoa and Nematodes in Insect Pests which kill their host or debilitate the future generation.
> Mechanism:-
- The infected insects are unable to feed properly ,remain stunted, lose their body colour and get paralysed.
- Dead insects are often found hanging on the plants, or a fungal growth on the body of dried insect could be easily located in the field.
- Caterpillar, Pseudoplusia includens , killed by entomopathogenic fungus Nomuraea rileyi , white-disease in soybean crop.
c. Predators:-
> These are free living and larger in size than their prey, requiring several preys to complete their life cycle.
> Some smaller predators release a powerful poison, use a trap or hunt in groups to be more effective.
> Mechanism:-
- Green lacewings (very common and important predator of crop pests).
- The female lays small pale green, oval shaped eggs at the end of long silken stalks, which ultimately turns grey.
- The larva have well developed legs and pincer like jaws with which they suck the body fluids from the prey.
d. Antagonists of Plant Diseases:- The microorganisms used in biological suppression of plant diseases which grow in association with plant diseases are termed as antagonists.
An antagonist microorganism adversely affects the disease causing organism by following:-
i. Competition:- The competition which takes place between two organisms in terms of nutrients etc.
ii. Antibiosis:- An association between organisms that is injurious to one of them. Antibiosis, is provided by marigold (Tagetes species) roots, which release terthienyls, chemicals that are toxic to several species of nematodes and fungi.
iii. Hyperparastism:- The parasitic habit of one species upon another parasitic species which is harmful to one of them.
iv. Mycoparasitism:- A parasitism of a fungus(host) by another fungus(mycoparasite). Trichoderma harzianum, used as seed treatment against pathogenic fungus(Sclerotium rolfsii) on chickpea and sugarbeet.
