To study the important disease of fruit and plantation crops
Mango Anthracnose: Colletotrichum gloeosporioides
- Produces leaf spots, blossom blight, wither tip, twigs blight, and fruit rot.
- Small blister-like spots develop on the leaves and twigs. Young leaves wither and dry Tender twigs wither and die back symptom appears.
- Affected branches ultimately dry up. Black spots appear on fruits.
- The fruit pulp becomes hard, crack and decay at ripening. Infected fruits drop
- Spray fluorescens (FP 7) at 3 weeks intervals commencing from October at 5g/like on flower branches.
- 5-7 sprays one to be given on flowers and bunches.
- Before storage, treat with hot water, (50-55°C) for 15 minutes or dip in Benomyl solution (500ppm) or Thiobendazole (1000ppm) for 5 minutes
Mango malformation : Fusarium moliliforme var. subglutinans
- Three types of symptoms: bunchy top phase, floral malformation, and vegetative malformation.
- In the bunchy top phase in nursery bunching of thickened small shoots, bearing small rudimentarily leaves. Shoots remain short and stunted giving a bunchy top appearance.
- In vegetative malformation, excessive vegetative branches of limited growth in seedlings. They are swollen with short internodes forming bunches of various sizes and the top of the seedlings shows a bunchy top appearance.
- In malformation of inflorescences, shows variation in the panicle. Malformed head dries up in black mass and persists for a long time.
- Secondary branches are transformed into a number of small leaves giving a witch Broome appearance
- Diseased plants should be destroyed
- Use of disease-free planting material
- Incidence was reduced by spraying 100-200ppm NAA during October.
- Pruning of diseased parts along the basal 15-20 cm apparently healthy portions.
- This is followed by the spraying of Carbendazim (0.1%) or Captafol (0.2%).
Bunchy Top: Banana bunchy top virus
- Initially, dark green streaks appear in the veins of the lower portion of the leaf midrib and the leaf stem
- Dark green, hook-like extensions of the leaf lamina veins can be seen in the narrow, light-green zone between the midrib and the lamina.
- On mature plants infected with BBTV, new leaves emerge with difficulty, are narrower than normal, are wavy rather than flat, and have yellow (chlorotic) leaf margins.
- They appear to be “bunched” at the top of the plant, the symptom for which this disease is named.
- Severely infected banana plants usually will not fruit, but if the fruit is produced, the banana hands and fingers are likely to be distorted and twisted.
- Use virus-free planting materials
- Remove and rouging of infected banana plants
- Chop, dry and bury the infected plants
- Maintain clean, weed-free field for early detection of infected suckers
- Avoid banana cultivation in sugarcane and cucurbitaceous areas as sugarcane mosaic virus or cucurbit mosaic virus can easily spread to banana
- The plants should be injected with 4 ml of Fernoxone solution(50g in 400 ml of water)
- Insertion of Fernoxone capsules (containing 200 to 400 mg of chemical per capsule) into the pseudostem by using the banana injector or capsule applicator
- For vector controls Injection of plants with monocrotophos 4 ml (1:4) at 45 days interval from 3rd month till flowering
- Spraying plants with phosphomidon 1ml /l or Methyldemeton 2ml/ l or monocrotophos 1ml /l
- Panama Wilt of banana: Fusarium oxysporum sp. cubense
- Externally, the first obvious signs of disease in most varieties are wilting and light yellow colouring of the lower leaves, most prominent around the margins. They eventually turn a bright yellow colour with dead leaf
- Splitting of pseudostem base is a characteristic symptom.
- When a cross-section is cut, the discolouration appears in a circular pattern around the centre of the rhizome where the infection concentrates due to the arrangement of the vessels. As symptoms progress into the pseudo-stem, continuous lines of discolouration are evident when the plant is cut longitudinally
- Practice proper crop rotation with paddy/sugarcane once or twice followed by a banana for 2-3 cycles
- Plant wilt resistant cultivars such as Poovan and Nendran in endemic areas
- Proper care should be given when planting susceptible cultivators such Rasthali, Monthan, Karpuravalli, Kadali, Pachanadan by selecting healthy suckers from disease fields
- Remove and destroy infected plant material after harvest
- When only 1-3 plants are infected, kill and chop up the diseased plants and stew all the material in water at a temperature of at least 70 deg C for 30 minutes.
- Grow healthy plants with proper fertilization, irrigation, weed control
- Provide good drainage especially during the rainy season
- Soil application of rice chaffy grain or dried banana leaf formulation or well-decomposed compost around the plants
- Machinery and equipment should be treated with a sanitary solution such as Farmcleanse.
- Footwear, which may have contacted banana plants or soil around banana plants elsewhere, should not be worn on the farm.
- Provide mechanical barriers in and around the infected plants
- Application Pseudomonas fluorescens @ 2.5kg/ha bactericide can also be applied along with farmyard manure and neem cake.
- About 60 mg of Pseudomonas fluorescens (in a capsule) can be applied in a 10 cm deep hole made in the corm.
- Application of bio control agents like Trichoderma viride @ 25 g for 4 times once at the time of planting in the planting pit and remaining doses at third, fifth, and seventh month after planting
- Application of harzianum Th-10, as dried banana leaf formulation @ 10g/plant in basal + top dressing on 2,4, and 6 months after planting
- Application of 2 percent of Carbendazim as injection of Carbendazim 50 ml capsule application
- Paring (praline removal of roots and outer skin of corm) and dipping of the suckers in clay slurry and sprinkled with Carbofuran granules at 40g/corm
- Soil drenching of Carbendazim 0.2 percent solution alternated with Propiconozole 0.1% around the pseudostem at bimonthly intervals starting from five months after planting
- Application of urea + sugarcane trash (250g/pit) followed by lime (1Kg/pit) and neem cake (1-2Kg/pit)
- Application of neem cake @ 250 Kg/ha was most effective in controlling Fusarium wilt in Rasthali cultivar
Algal leaf spot of guava: Cephaleuros virescens
- Disease symptoms are exhibited on both abaxial and adaxial leaf surfaces as orange, rust-colored, dense silky tufts ranging from 5 to 8 mm in diameter.
- Upon scraping away these spots, a thin, grayish-white to dark-colored, necrotic crust remains on the leaf.
- These spots usually come together to form large irregular patches on a leaf. As the spots mature they take on a dull, grayish-green color.
- Algal leaf spot can be reduced by maintaining tree vigor with cultural techniques such as proper fertilization and irrigation, proper pruning to enhance air circulation within the canopy, and sunlight penetration, managing weeds, and wider tree spacing.
- Managing insect, mite and other foliar diseases increases tree vigor and lessens susceptibility to this disease.
- Spray Copper oxychloride 0.25%.
- Downy mildew of Grapes: Plasmopara viticola
- 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
- 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 percent
- Spray Bordeaux mixture 1 % or Metalaxyl + Mancozeb 0.4 %.
Powdery mildew of grapes: Uncinula necator
- Powdery growth mostly on the upper surface of the leaves.
- Malformation and discolouration of affected leaves.
- Discolouration of the stem to dark brown.
- Floral infection results in the shedding of flowers and a poor fruit set.
- 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.
- Spray Inorganic sulphur 0.25 % or Chinomethionate 0.1 % or Dinocap 0.05 %.
Gummosis of citrus: Phytophthora parasitica, P. palmivora, P. citrophthora
- The first symptoms are the dark staining of bark which progresses into the wood.
- The bark at the base is destroyed resulting in girdling and finally the death of the tree.
- Bark in such parts dries, shrinks, and cracks and shreds in lengthwise vertical strips.
- Later profuse exudation of gum from the bark of the trunk.
- Infection extends to crown roots.
- Prolonged contact of the trunk with water as in flood irrigation; waterlogged areas and heavy soils.
- Soil inhabitants.
- Sporangia spread by splashing rainwater, irrigation water, and wind.
- Irrigation water and wind.
- Injuries to crown roots or base of the stem during cultural operations should be
- If the lesion has girdled less than ½ the girth, remove the diseased bark with a knife along with ½” of uninvaded bark.
- The bark of the trunk should be coated with Bordeaux paste.
Citrus Canker: Xanthomonas campestris pv citri
- Acid lime, lemon, and grapefruit are affected. Rare on sweet oranges and mandarins.
- Affects leaf, twig, and fruits. In canker, leaves are not distorted.
- Lesions are typically circular with yellow halo; appear on both sides of the leaf, severe in acid lime (difference from scab) When lesions are produced on twigs, they are girdled and die.
- On fruits, canker lesions reduce market value.
- Streptomycin sulphate 500-1000 ppm; or Phytomycin 2500 ppm or Copper oxychloride 0.2% at fortnight intervals.
- Control leaf miner when young flush is produced.
- Prune badly infected twigs before the onset of monsoon
Greening: Liberobactor asiaticum ( Phloem limited bacteria)
- Stunting of leaf, sparse foliation, twig dieback, a poor crop of predominantly greened, worthless fruits.
- Sometimes only a portion of the tree is affected. A diversity of foliar chlorosis.
- A type of mottling resembling zinc deficiency often predominates.
- Young leaves appear normal but soon assume an outright position, become leathery and develop prominent veins and dull olive green colour. Green circular dots on leaves.
- Many twigs become upright and produce smaller leaves.
- Fruits are small, lopsided with the curved columella. The side exposed to direct sunlight develops full orange colour but the other side remains dull olive green.
- Infected budwood; psyllid vector-Diaphorina citri
- Control psyllids with insecticides.
- Use pathogen-free bud wood for propagation.
- 500 ppm tetracycline spray, requires fortnightly application.
Leaf curl: Papaya leaf curl virus
- Curling, crinkling, and distortion of leaves, reduction of leaf lamina, rolling of leaf margins inward and downward, thickening of veins.
- Leaves become leathery, brittle, and distorted. Plants stunted. Affected plants do not produce flowers and fruits.
- Spread by whitefly Bemisia tabaci.
- Uproot affected plants.
- Avoid growing tomatos, tobacco near papaya.
- Spraying with systemic insecticides to control the vector
- Stem rot / Foot rot: Pythium aphanidermatum
· Water-soaked spot in the stem at the ground level which enlarges and griddle the stem.
· The diseased area turns brown or black and rot.
· Terminal leaves turn yellow droop off.
· The entire plant topples over and dies.
· Forward by rain. R. solaniis favoured by dry and hot weather. Common in 2-3-year-old trees.
- Seed treatment with Thiram or Captan 4 g/kg or Chlorothalonil.
- Drenching with Copper oxychloride 0.25 % or Bordeaux mixture 1% or Metalaxyl 0.1%.
- Scab: Venturia inaequalis
- The symptom appears on leaves and fruits.
- On the lower side of the leaf, the lesion appears as olivaceous spots which turn dark brown to black and become velvety.
- On young foliage, the spots have a radiating appearance with a feathery edge.
- On older leaves, the lesions are more definite in outline.
- The lesion may form a convex surface with the corresponding concave area on the opposite side.
- In severe infection leaf blade curved, dwarfed, and distorted.
- Fruits show small, rough, black circular lesions.
- The centre of the spots becomes corky and on mature fruits, the yellow halo is seen around the lesions.
- Clean cultivation, collection and destruction of fallen leaves and pruned materials in winter to prevent the sexual cycle.
- Spray Tridemorph 0.1% before flowering.
- Spray Mancozeb 0.25 % at bearing stage.
- Spray 5 % urea prior to leaf fall in autumn and 2 % before bud break to hasten the decomposition of leaves.
- Commercial Fruits. By S. P. Singh
- A text book on Pomology, Vol,1. by T. K. Chattapadhya
- Tropical Horticulture, Vol.1, by T. K. Bose, S. K. Mitra, A. A. Farooqui and M. K. Sadhu