Apple Tree Diseases: Apple Mosaic Virus

This is in continuation to my previous post on Diseases of apple: Management of SootyBlotch and Fly Speck. In today’s post we are going to discuss about the Apple Mosaic Virus.

Apple Mosaic

Causal Organism: Apple mosaic virus (ApMV)

Description: In the spring, pale yellow to cream-coloured areas develop on expanding leaves of infected apple trees. These areas may appear as small spots, flecks, irregular blotches, vein-net patterns, line patterns, or bands along major veins. As the season advances, they turn from pale yellow or cream to a lighter chrome yellow or white and then soon become necrotic. Severely affected leaves abscise prematurely.

Economic Impact

In general, ApMV does not have much affect on fruit production and quality. However, severely infected Lord Lambourne trees often produce fruits with cream coloured blotches.  The virus results in yield reductions varying from slight to 50 per cent.  Crop losses of up to 42 per cent were recorded in infected hazelnut and average losses of 25 per cent were recorded from almonds affected by almond mosaic, a complex disease in which ApMV plays a major etiological role.

In my coming post I shall be discussing about apple cholorotic leaf virus

Apple Tree Diseases: Sooty Blotch and Fly Speck

This is in continuation to my previous post on Diseases of apple: Management of PrematureLeaf Fall. In today’s post we are going to discuss about the Sooty Blotch and Fly Speck.

Sooty Blotch

Causal Organism: Gloeodes pomigena

Description: Sooty blotch colonies appear as shades of olive green on mature fruit. They vary from discrete almost circular colonies to large colonies with diffuse margins, which are sooty in appearance. Large amorphous colonies that cover large portions of the fruit surface result from secondary spread on the fruit.  The fungus is found on the upper surface of fruit, which can be easily removed by rubbing leaving behind slight depression. No permanent spot is found on the fruit surface. This disease is found on late maturing varieties and under storage conditions. The fungus survives from one season to the next as mycelium and pycnidia on infected twigs of apple and numerous forest trees. The fungus is dispersed as chlamydospores or conidia during rains in the spring and early summer. Most conidia are liberated by early summer, but extensive secondary spread by chlamydospores and mycelial fragments occur throughout the seasons. The infection can also be seen on new twigs, on which it remains active. During the months of May and June, low temperature and rains are necessary for disease development. For the fungus development 18.3ºC is favourable. The disease is more prevalent in low and shady area of the orchard.

Fly Speck:

Causal Organism: Zygophiala jamaicensis and Mycrotheria spp.

Description: Symptoms of flyspeck on apple are approximately described by the name. Black spots are formed on fruits. Colonies are characterized by well-defined groups of 6, 8 or sometimes 50 shiny, black, superficial pseudothecia on the surface of the fruit. This disease is found abundantly during rainy days and in less windy regions. Sooty blotch and flyspeck colonies commonly occur on the same fruit, but the colonies are mutually exclusive.

Though these diseases do not cause much harm to the fruit yet it deteriorates the market quality thus affects the price of the produce.

In my coming post I shall be discussing about Management of Sooty Blotch and Fly Speck of apple.

Apple Tree Diseases: Disease Monitoring System for Farmers

This is in continuation to my previous post on Diseases of apple: Disease Cycle of Premature Leaf Fall. In today’s post we are going to discuss about the Disease Monitoring System for farmers.

Disease cycle

The fungus overwinters in the form of apothecia on fallen leaves. Primary infection is caused by ascospores produced on the overwintered leaves. The ascospores discharge begins during spring season but causes infection at a particular leaf age stage.

During first one month after full bloom when temperature generally hovers around 20^oC, but humidity is low therefore, leaves are not vulnerable to the infection.

It’s the first fortnight of June when temperature starts rising fast, pre-monsoon showers adds to the humidity in the orchards of shady areas. The infection initiates during this period rapidly and got established in 4-22 days (incubation period).

During second fortnight of June and July the symptoms begin with the response of the host. Less moisture, high humidity/foggy and temperature >20^oC initiate blotch and yellowing. Infection near to leaf petiole site initiates early defoliation.

From first week of August onwards when rains recede but temperature remains above 20^oC and humidity is above 90 percent, severity of the disease increases to epidemic level. During this period daily prevailing weather like light rains, partially sunny and foggy could predict the most suitable epidemic conditions.

In coming post we shall be discussing about the Management of Premature Leaf Fall disease of apple.

Apple Tree Diseases: Disease Cycle of Premature Leaf fall

This is in continuation to my previous post on Diseases of apple: Premature Leaf Fall. In today’s post we are going to discuss about the Disease cycle and predisposing factors of Premature Leaf Fall.

Disease cycle

The fungus overwinters in the form of apothecia on fallen leaves. Primary infection is caused by ascospores produced on the overwintered leaves. The ascospores discharge begins during spring season but causes infection at a particular leaf age stage. The disease first attacks plants growing in shady and high moisture conditions

Air temperature, light intensity and soil moisture are the predisposing factors to trigger the disease outbreak, however, severity index increases with the maturity of the leaves.  The disease is severe when a cool, rainy period of 4 to 5 days proceeds several hot sunny days in the orchard. The inoculum of the disease get released at the pink bud stage but it causes the infection only at a particular leaf maturity stage when plant physiological processes start producing ethylene, the ripening / ageing hormone. The pathogen therewith the hormonal changes induce yellowing and abscission of the leaves and defoliation occurs.

The scientists have developed disease cycle key on the rate of infection conditions for this new disease on apple plant to monitor it. It therefore concludes that the blotch started its symptoms on the upper side of the leaf first in the 2^nd week of June irrespective of the weather conditions. However, the disease symptom on leaves followed by temperature above 20^oC and relative humidity above 70 per cent continuously for 5-6 days, induce yellowing and defoliation process. Prolonged hot and dry weather affect the primary infection and disease conditions adversely. Under favourable weather conditions the leaves start defoliation within 3-5 days whereas under interrupted/un-favourable conditions the infected leaves could retain up to 3 months.

In coming post we shall be discussing about the disease monitoring system for farmers.

Apple Tree Diseases: Premature Leaf Fall

This is in continuation to my previous post on Diseases of apple: White root rot Management. In today’s post we are going to discuss about the Premature Leaf Fall.

Description:  Pre mature defoliation in all apple-growing states of Himachal Pradesh, Jammu and Kashmir, Uttarakhand and North- east in recent years. The disease is caused by fungus, Marssonina coronaria and Alternaria mali resulting in mid-season pre mature defoliation. Its affects all the commercial cultivars grown in India.  Disease appears both on leaves and fruit. Dark brown patches having pin head fruiting structures, develop on upper surface of leaves varies from 5-10 mm diameter typical blotch symptoms. Various small and large blotches depending on the climatic conditions after the initiation of disease coalesce to form large dark brown blotches and the surrounding areas turn yellow. The yellowing advances towards petiole end, developing abscission layer and induce mid season defoliation. It reduces the fruit size and delays ripening. The fruits are poorly coloured and lack flavour. Irregular necrotic blotches on mature leaves characterize the disease. The blotches develop suddenly and increase rapidly during June-July (high humidity and high temperature) and cause yellowing and defoliation. The mid-season defoliation may be responsible for poor growth and development of fruiting buds and result into low productivity in ensuing year. Infection of the fruit appears in the harvested fruits and dark brown depressed spots are most common on ‘Golden Delicious’.

In coming post we shall be discussing about the disease cycle of premature leaf fall.

Apple Tree Diseases: White Root Rot Pre-disposing Factors

This is in continuation to my previous post on Diseases of apple: White root rot. In today’s post we are going to discuss about the pre-disposing factors for the disease development.

Pre-disposing factors:

Soil moisture is the major key factor for the proliferation of the disease as the fungus is of polyphagous. The mycelium could grow in soils with 6-89.2 percent water content, but the fungal mats developed most vigorously at 70 percent. Soil type influences greatly the period of survival and spread of soil-borne fungi. The occurrence of white root rot disease of apple trees was closely related to soil conditions. In alluvial areas and regions with non-volcanic ash soils, the pathogen was associated with sandy soils over gravel where available water was the limiting factor. In upland regions, the disease was prevalent on shallow soils overlying stony sub-soils. Of the several factors examined in Himachal Pradesh for their possible role in the longevity and survival of the root rot pathogen, clay loam soil was reported better than clay soil for its longer survival at all temperature ranges and soil moisture regimes. Temperature has been known to play an important role in the survival and spread of the pathogen, 17^oC is an optimum temperature level. Of the two factors i.e. temperature and soil moisture, the latter plays more decisive role in increasing the longevity of the pathogen than the former.

The prevalence of white root rot in Himachal Pradesh is limited to high hill soil texture varies from loam to clay loam. The soil reaction is slightly acidic and this zone is ideally suited for apple cultivation. It receives an average of 100-140 cm rainfall per annum. The rainy season in the apple zone is during June to September, when also a higher incidence and severe symptoms of root rot are observed, indicating that the disease spread and severity are related to excessive soil moisture regimes at higher temperature. The higher elevation range was observed favourable for the spread of D. necatrix being high rainfall area and low temperature conditions prevailing for long durations. Besides soil, pH also seems to have a strong relationship with the survival of the pathogen flourishing best in 6- 6.5 pH range. Incidentally the larger area under apple cultivation in Himachal Pradesh also falls within this pH range.

Physico-environmental conditions viz., soil type (loam and clay laom), soil reaction (pH6-6.5), soil moisture (>70%) and Temperature (17^oC) play an important role in incidence and survival of Dematophora necatrix.

In coming post we shall be discussing about the management of the white root rot disease.

Apple Tree Diseases: White Root Rot

This is in continution of my previous post on Diseases of Apple: Collar Rot Management. By now you know about the collar rot symptoms and its managment practices. But a small description about white root rot here will help you distinguish between the two.  White root rot is taking heavy toll in wet temperate zone of Himachal Pradesh, besides fallacy in the diagnose is further making the situation worse. It is important to understand the disease symptoms and how to distinguish the intermingling symptoms. The description on white root rot is given below

Symptoms:

White root rot as name indicates the white fluffy growth of mycelium can be seen on roots during monsson months this mycelial mat can be seen on soil level. The disease caused by Dematophora necatrix, a polyphagus fungus that can infect more than 173 plant species. The fungus has been increasingly imposing problem and resulting in the death of plants. Further, death of a tree, due to root rot in an orchard does not mean the end of losses, instead the incitant being soil borne also spread to neighbouring sites. The economic losses, therefore, are likely to multiply in compound manner within and outside the infected orchards.

The fungus first invades feeder roots and disease symptoms can be ascertained on lateral roots, which turn into dark brown colour and become infested with white flocculent fungus during monsoon months. The earliest above ground manifestation of the disease is bronzing of the leaves, stunted growth and size. There is progressive decline in foliage and twig growth. White root rot affected trees are usually associated with a heavy weak blossom and fruiting next year, however in succeeding years, few leaves emerge and much of the immature fruits induce early colouration and fail to reach maturity. Severity in years leads to die-back/drying of twigs and branches. Fibrous roots are completely devoured in advance stage, and the tree dies as cortical and phloem cells are ruptured, which disrupt the translocatory system. Infected trees often persist for 2-3 years depending upon the infestation of the fungus and young trees if infested may die quickly with necrotic leaves still on the dead plant is a characteristic symptom.

In coming post I shall be dealing with the predisposing factors of the disease.

Apple Tree Diseases: Collar Rot Description

This is in continution to my previous post Diseases of Apple: Powdery Mildew Management. Here we are going to talk about the Collar Rot that is similar to Root Rot and Crown Rot. This disease is tedious to be managed but if understood throughly it can be managed.

Description 

The disease is caused by Phytophthora cactorum and infection starts from the collar region i.e. soil line and spread mostly to the underground parts and the above ground stem portion is also infected in highly susceptible scion cultivars. The fungus attacks the cambium thusrequires wounds to cause infection, once infected  bark at the soil level becomes coffee brown in colour, slimy and rots resulting in cankered areas. The wounds are irregular in outline but usually roughly oval which extend rapidly, often resulting in girdling of the tree. The attacked trees are recognized by sparse foliage, purple colour of the leaf veins in attcked tree, more number of spurs than normal, fruit size remain small in such trees as nutrition uptake is reduced due to rot.

In coming post we shall be talking about the Collar Rot Management.

Apple Tree Diseases: Powdery Mildew Disease Cycle

This post is in continution to my previous post on Diseases of Apple: Powdery Mildew. In this post we are going to discuss about how disease causing propagules overwinters (survive) and cause primary and secondary infections. 

Disease cycle:  

The powdery mildew fungus overwinters as mycelium in infected buds or as cleistothecia on the surface of infected twigs. Infected terminal buds are more susceptible to winter injury than healthy buds, typically bud break in the spring is 5-8 days later than healthy buds, and are more susceptible to spring frost than healthy buds. In fact, healthy buds may survive at temperatures 2-10^oC colder than infected buds. As a result, many infected buds will not survive through a cold winter. This is important to keep in mind because a hard winter can dramatically reduce both disease pressure and the need for control measures during the subsequent season. The survival rate of infected buds is less than 5 per cent when temperatures drop below –24^oC and, although not well studied, it appears that temperatures around –12^oC will kill the mycelium in infected buds and allow the bud to produce healthy leaves. The cleistothecia, which form the sexual stage of the fungus and produce ascospores, apparently do not play an important role.

Mycelia in infected buds produce conidia to initiate primary infections and these infections can be found as early as the tight cluster stage. There is often an abundance of susceptible tissue for the conidia to infect because infected buds break later than healthy buds. Conidia are disseminated by wind and can infect young leaf tissue, blossoms, and fruit. Leaves become increasingly resistant to infection as they age and become nearly immune once they have matured, although infection can occur through injuries on older leaves. Symptoms may develop as early as 5 days after infection. Numerous secondary cycles can occur under favorable conditions and, like many powdery mildews, cooler temperatures rather than relative humidity drive early secondary infections. Like other powdery mildews, P. leucotricha exhibits a diurnal periodicity in that the highest concentration of airborne conidia is found from midday to early afternoon. Infections that result in fruit russet occur primarily during the pink stage of bud development.

Apparently, infection of lateral and fruit buds occurs within 1 month after they are formed. The infections remain latent until bud break the following spring where they will serve as the initial source of inoculum. The lateral buds are susceptible to infection longer than the terminal buds, however, it is the terminal buds that are the likely source of overwintering of the fungus as infection can be greater than 50 percent by terminal bud set.

In coming post we are going to discuss about the management of the disease

Apple Tree Diseases: Powdery Mildew

Diseases play an important role in low productivity of any crop in the form of yield losses. Generally about 33% losses are due to diseases and insect pests. There are some diseases which not only impair with the yield losses but these also contribute towards poor quality of the produce. The question now arises that, What is Disease?: 

Disease is an impairment of health or a condition of abnormal functioning.

Diseases of Apple

Powdery Mildew
Collar rot
White Root Rot

Premature Leaf Fall
Sooty Blotch and Fly Speck
Apple Scab
Apple Mosaic Virus

In this post we are going to talk about the powdery mildew disease of apple. This disease is very common in Kinnaur district of Himachal Pradesh as dry weather plays an important role in the appearance of the disease.

Description: The disease infects leaves, blossoms, green shoot, and the fruit. On the leaves, the fungus can appear as felt-like patches or as a solid mat on the surface, particularly on the undersurface of the leaf. Initial infections on the underside of the leaf may cause chlorotic patches or spots to occur on the upper side of the leaf. This symptom, however, is not unique to powdery mildew so inspection of the underside of the leaf is necessary to confirm that powdery mildew is the cause of these symptoms. Under favorable environmental conditions, the disease spreads over the entirety of the leaf and progresses down the petiole on to young, green shoots. Infected leaves tend to crinkle, curl, or roll upwards along the edges giving them a narrow appearance. If the infection is severe, infected leaves will usually drop prematurely during the summer.

Shoot infections are the typical result of overwintering infections of the fungus in buds. When the terminals push in early spring, the fungus grows along with the new succulent growth and infects this tissue immediately. These shoots may be killed outright in the spring, or may survive throughout the season and die in late fall or winter. The initial growth of the fungus on newly infected twigs appears powdery white but eventually turns a darker brown. Small black fruiting bodies, called cleistothecia, can appear in the mycelial mat and function as the source for sexual reproduction and the eventual production of ascospores.

The blossoms, petals, sepals, receptacles, and peduncles may become infected and covered with the fungus. Blossom infections are less common but are important because infected blossoms will either fail to set fruit or produce small, stunted and/or russetted fruit. These fruit are unmarketable for fresh market consumption. 

In my next post I shall be talking about the 
Disease Cycle of Powdery Mildew, 
Management of Powdery Mildew

Environmental Factors- Contributing Factor towards Low Productivity in Apple

This post is in continuation of our earlier post on Old and Senile Orchards - Contributing to low productivity in Apple part of our series on Low Productivity in Apple: Contributing factors in Himachal Pradesh

Pest and Diseases

A number of pests and diseases have been found to affect the apple orchards. Besides apple scab, which first appeared in epidemic form during the year 1985-86, the emergence of some new pests and diseases like premature leaf fall and red spider mite, has been one of the most potent reasons for low productivity.

Adequate measures need to be taken to control these serious pests, in order to improve productivity and reduce losses.

Environmental Factors

The changing weather pattern seems to be the most important single factor responsible for the declining productivity of apple crops in the state. The reduction in annual snowfall and prolonged dry spells in the winter have become a regular feature, leading to a wide variation between day and night temperatures. Fluctuating temperatures during flowering period, particularly rains accompanied by low temperature, adversely affects the pollination due to restricted bee activity and retarded pollen tube growth. The occurrence of hail in many areas is a regular feature, and heavy losses are incurred due to these natural calamities thereby contributing to low productivity.

This post is part of our series on Low Productivity in Apple: Contributing factors in Himachal Pradesh. Entire series is coverted through following topics

1. Genetic potential of the cultivar
2. Management Practices
3. Pollination Problems
4. Inadequate Nutrition
5. Poor Canopy Management
6. Moisture Stress
7. Old and Senile Orchards
8. Environmental factors

to be continued with the strategies to over come these bottlenecks..............................