Sunday, April 27, 2014

Diseases of Apple: Collar Rot Management

This is in continuation to my earlier post on Diseases of apple: Collar rot Description. This disease is generally diagnosed wrongly for white root rot and we treat it for the same by drenching with carbendazim, that further worsen the situation and plant dies pre-maturely. If diagnosed with the symptoms explained in my previous post i.e. coffee brown colour and late bud break, more number of spurs, small and sparse leaves, it should be managed in holistic way

  1. Phytosanitation: Free water or flood irrigation high moisture content near the trunk are major pre-disposing factors for the disease to spread. So keep the cultivation area free of diseased material like diseased bark and roots, etc. The cleanliness reduces the primary inoculum of the disease causing agents. This simple principle should be followed as soon as the first symptom in the form of late bud break or purple veins appears on lower side of leaves. This is the best way to manage the diseases on small farms and helps in reducing the costs.

  1. Cultural Practices: Alter the environment in which disease is appearing i.e. high moisture level in the basin and nearby trunk. Add gravels and sand near the trunk, remove soil from graft union. Improve drainage from the basin area. Since this also removes the primary inoculum as well as modifies the environment for disease proliferation again without enhancing the cost to a greater level.

  1. Biological Control: Introduction of biological control agents in the soil e.g. Trichoderma viride, and its variants help the plant in fighting with plant pathogen and grow healthy with a little cost. If consortium of different soil inhabiting biocontrol agents is available it will help better in managing the disease.

  1. Chemical Control: Agrochemicals should be the last priority to manage the disease and that too after the proper diagnosis. As the application of a wrong chemical will not only worsen the situation but also pollute the soil and soil microflora. i.e. soil health. In turn increase the cost without preventing the damage caused by the insect-pests or disease. Different combiproducts have been reported to control the disease among these, combinations of metalaxyl + mancozeb, moxymate + mancozeb, and dimethomorph are very effective.
In my comng post I shall be discussing about white root rot of apple.


Sunday, April 20, 2014

Diseases of Apple: 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.

Saturday, April 19, 2014

Diseases of Apple: Powdery Mildew Management

This is in continution to my yesterdays post on Diseases of Apple: Powdery Mildew Disease Cycle. Today I am going to give you few tips how to manage this disease that causes various economic losses to the crop including the quality detrioration of the fruit.

Before talking on the Powdery Mildew disease management, I would like you to remind one of my post on Principles of disease management, where we have talked about four major principles. Here we shall be taking all the principles one by one and see how we can use these principles to manage the disease.

1. Phytosanitation: The twigs that are showing infections should be removed during the maintenance pruning. The cleanliness reduces the primary inoculum of the disease causing agents. This simple principle should be followed as soon as the first symptom appears on the farm. The precuation that should taken care of while removing the infected twings during spring season you should remove these twigs before the sun rise when dew is on that will not allow the conidia of the fungus to germinate (leaf wetness plays an important role). This is the best way to manage the diseases on small farms and helps in reducing the costs.

2. Cultural Practices: Alter the environment in which disease is appearing by using some cultural operations like removing some of diseased portions and altering the drainage of the soil or using some inter-cropping pattern's or using some other crop as barrier crop or trap crop etc. Since powdery mildew is dry weather disease, this can be managed by altering the disease favouring envrionment the disease can be managed easily. If we go through the literature, dry weather doesn't mean that low humidity but it means no leaf wetness. Powdery mildew appears at about 25oC and RH is above 80% but no leaf wetness. This condition suggests that if we have provisioned the air circulation in the orchard that will not only reduce the relative humidity but also lower down the temperature, thus becomes unfavourable for the disease development. This also removes the primary inoculum as well as modifies the environment for disease proliferation again without enhancing the cost to a greater level.

3. Biological Control: Introduction of biological control agents directly on the phylloplane (leaf area) helps the plant in fighting with plant pathogen and help the plant to grow healthy with a little cost. Ampelomyces spp; Pseudozyma spp; Tilletiopsis spp and Verticillium lecanii are few examples of Biological control agents that plays an important role in nipping down the powdery mildew fungus.

4. Chemical Control: Agrochemicals should be the last priority to manage the disease and that too after the proper diagnosis. As the application of a wrong chemical will not only worsen the situation but also pollute the environment. In turn increase the cost without preventing the damage caused by the insect-pests or disease.

Annual spray schedule devised for apple scab control also includes fungicides specific to powdery mildew. However, powdery mildew is economically important disease to affect pink to petal fall stages. At this stages specific group of fungicides like EBI (Score, Topas, Contaf) and benzimidazoles (Benlate, Carbendazim) are effective.

In coming posts I shall be talking about collar rot of apple.

Friday, April 18, 2014

Diseases of Apple: 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 2-10oC 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 –24oC and, although not well studied, it appears that temperatures around –12oC 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

Thursday, April 17, 2014

Diseases of Apple: 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
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