In this article we will discuss about the major diseases and deficiencies of apple.
Diseases of Apple:
i. Scab:
The causal fungus is Venturia inaequalis. Typical scab symptoms appear on the leaves and fruits. Light brown or olive green spots which soon turn black appear either on or both sides of the young leaves in spring. The affected leaves may dry up or fall prematurely, resulting in loss of vigour and reduced yields. Affected fruits show scabby, knotty, mis-shapen appearance. Mild temperature and rainy weather are most favourable for the severity and spread of the disease.
To control scab disease follows clean cultivation practices. Collect all affected plant parts, fallen fruits and destroy them. Spray Bordeaux mixture (4:4: 50) when the buds are showing pink colour, when petals have fallen and about three weeks later. Spray at least three times Dithane M-45 (Mancozeb) at 0.5 per cent or Bavistin at 0.05 per cent.
ii. Pink Disease:
It is caused due to Corticium salmonicolor. Light brown lesions appear on twigs and stem. Affected bark gets broken after sometimes into small protuberances of white or buff coloured fungal structures. It spread from June to September. The disease is favoured by over-crowding of branches, poor drainage, warm and humid conditions.
Remove the affected plant part. To large cut ends apply Bordeaux paste. Application of Triademefon 2% on scarified cankers followed by Triademefon @ 0.05% spray soon after harvest in rainy season is very effective.
iii. Powdery Mildew:
The disease is caused by fungus Podosphaera leucotricha Salm. The disease mainly affects the new shoots and the affected leaves and produces white powdery patches. The affected terminals remained stunted and die, while the leaves curl and crinkle. The fruits of Jonathan cultivar show russeting. The leaves fall and the plant is robbed of its carbohydrates production. The blossoms are deformed and fruit setting is reduced drastically. Dry weather with mild temperature conditions favour disease development.
Prune the affected twigs in winter to reduce the disease. Spray with wettable sulphur (300 g/100 litres of water) or carbendazim fungicide (50 g/100 litres of water) i.e-(i) During the late dormancy, (ii) At bud swell, (iii) At petal fall and (iv) Two weeks later.
iv. Silver Leaf Canker:
The disease is caused by fungus Chondrostereum purpureum. Silvering of foliage appears soon after petal fall. The wood of dead tissue turns black. Toxic substances produced by the fungus on translocation to leaves, induce silver leaf symptoms.
Prune the affected plant parts and wounds should be covered with Bordeaux paint. Young trees show recovery when their vigour increase by fertilization and other cultural practices. Post-harvest spray of carbendazim (0.05%) or Blitox (0.3%) on trees can check the infection. Also spray these chemicals on ground to reduce the inoculum in the orchard.
v. Sooty Blotch and Fly Speck:
Sooty blotch is caused by Gloeodes pomigena and fly speck by Microthyriella rubi. Sooty blotch is characterised by dull black to grey spots with indefinite outline. Fly specks appears as definite circular specks black in colour. Both spots make fruit skin smoky and reduces its market return. To control three diseases, give two sprays of Captafol/Mancozeb/Zineb/Captan at fortnightly interval 15-20 days prior to harvest.
vi. Brown Rot:
The disease is caused by Monilinia fructigena. The fungus is winters in mummified fruits. It hibernates in the fruiting spurs and branches and producing canker on the base of the spur. During summer remove all affected spurs and branches. Discard all affected fruits and destroy them properly.
vii. Root Rot:
The disease is caused by Dematophora necatrix. Affected trees show sparse foliage, slow growth and bronzing and yellowing of leaves. Ultimately such plant die. The roots turn brown and remain covered with white cottony mycelial mat of the fungus in rainy season. Heavy, water-logged soils favour the development of the fungus and the disease.
Improve drainage of the orchard for the control of disease. Cut the affected roots during November-December. Apply Brassicol paint (10 kg/litre linseed oil) on the cut ends and the healthy portions of the roots. Uproot and burn the dead plant and treat the soil with 1 per cent Brassicol solution. Give atleast 3 drenching of carbendazim (10 g/10 litres water) at 15-20 days interval during monsoon.
viii. Collar Rot:
It is caused due to Phytophthora cactorum. The disease spread maximum in poorly drained soils. It manifests itself in the form of brown, soft, spongy, cankered area around the collar of the tree at or below soil level. The girdled trees succumb to attack.
Remove the soil around the collar region during November-December and expose the affected portion to sun. Remove the cankered area to the healthy portion and apply copper oxychloride paint (Blitox in linseed oil). Drench 30 cm radius around tree trunk with Mancozeb (300-400 g/ 100 litres water) or copper oxychloride (500-1000 g/100 litres water) or Brassicol (1 kg/100 litres water). Always keep graft point 20-25 cm above the soil level at the time of plantation.
Nutrient Deficiencies of Apple:
The deficiency symptoms of different elements are given below:
i. Nitrogen:
The deficiency of nitrogen may cause restricted growth, narrowing of top-root ratio, less elongation of branches and reduction in size and colour of fruits. The bark of the tree may be reddish or yellowish green in early stages, but later developing tints of yellow.
ii. Phosphorus:
Shoots are short, thin and upright. Leaves are small with dull purple and bronze tints, early defoliation of older leaves. Opening of buds in the spring is delayed. Lateral buds may remain dormant; therefore, few lateral shoots appear.
iii. Potassium:
Deficiency of potassium is seen on spurs of old branches which progressed towards the younger leaves as the season advances. The first evidence of scorch might be loss of normal green colour at the widest part of the leaf margin, accompanied by a water-soaked or stained appearance, which was followed by necrosis. Severely affected trees were mostly stunted in growth with small-sized leaves. The fruits in affected trees do not develop properly, remain small in size with poor colour development.
iv. Calcium:
The young foliage of calcium-deficient plants showed an upward cupping of the margins. In older leaves, the margin turns necrotic and they may fall. Death of growing points, followed by die-back. In better pit, slight indents appear on the skin usually towards the clayx end of die fruit. The areas turn brown and the flesh below these areas also turns brown and corky. Symptoms become more pronounced in the storage conditions. In cork spot, hard brown spots appear on the surface skin. Flesh and these spots become hard due to abnormal tissue proliferation. Measles on the bark result from a complex involving low calcium, high manganese and sometimes low boron. The deficiency can be corrected by giving one spray of 0.5 per cent calcium chloride.
v. Magnesium:
In severe cases, the symptom shows marginal scorching of leaves. Severe defoliation of terminal shoots progresses from base to tip. Green colour starts fading on the terminals of older leaves progressing interveinally towards the base and midrib, giving the very typical ‘Herringbone’ appearance to the leaves. In severe cases, the fruit may fail to mature and drop early.
vi. Zinc:
Buds along shoots fail to develop. Leaves remain small and narrow (little leaf) tending to form rosettes at tips. Foliage is sparse throughout the tree. Older leaves may fall in severe cases leaving tufts or rosettes at the terminals. Fruits become small, pointed and misshapen. The deficiency can be corrected by spraying 0.5% ZN SO4 in two sprays at 15 days interval during May to July.
vii. Boron:
Symptoms normally appear on the fruits before vegetative parts are affected. Fruits do not develop normally and become misshapen caused by depression usually under-laid by hard corky tissues which rapidly turn brown when exposed. Surface colour is dark green.
Leaves become dark green, thick and brittle, starting at shoot tip. Boron deficiency is also known as corky pit, corky core, spot necrosis and drought spot. For the correction of Boron deficiency give one or two sprays of 0.1 per cent Boric acid at 15 days interval in the month of July.
viii. Iron:
The deficiency symptoms first appear on young leaves at tip of the shoot. It is characterised by interveinal chlorosis of young leaves. In severe cases, the new leaves may unfold, but completely devoid of green colour. The veins, however, may turn green later.
ix. Manganese:
The characteristic chlorosis first appears at the leaf margins and progresses interveinally towards the midrib. Early defoliation occurs particularly on the top of the tree. Fruits remain poorly coloured. Give one or two sprays of 0.4 per cent manganese sulphate at 15 days interval in June.
x. Copper:
Whither tip, leaf margins burned and ragged with some cuping. Tree defoliation progresses from tip to the base of the shoots.