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3 Grape diseases and their management


Welcome to the third talk of this week. In the last class we talked about important apple diseases and their management. And today we are going to talk about important Grapes diseases and their management. Grape is a very important commercial crop and it is affected by a series of diseases and on the basis of their severity they are categories to be very highly damaging and those include Downy Mildew, Powdery Mildew, Pierce’s Disease and Grey Mold. These are the most highly rated disease as they cause severe damage to the grape growers.

Downy Mildew of grape is caused by a fungus Plasmopara viticola. Here the symptoms appears as light yellow coloured on the top surface of the leaf, on the bottom surface we can see that there is growth of Downy Mildew pathogen in the early morning season and slowly the pathogen or symptom progresses to the brown color from the initial yellow color. The pathogen may also affect the young developing grapes and that is why it can cause a significant damage to the growers of grapes. The pathogen survives as oospores in fallen and dead leaves and this is why it is important that we should take care of this initial source of inoculum.

There are IPM practices that are recommended for management of this particular disease and that includes some cultural practices and some chemical practices. Cultural Practices include elimination of humidity and moisture around the impacted plants because this favours growth and development of the pathogen and that is why it is important that there should be less moisture around the grape plants. Selective pruning is important to improve air circulation because ones we prune some undesired branches then it will improve the air flow and that will help us in maintaining their moisture level in the grape canopy. Instead of irrigation we can go for drip irrigation because it will also reduce the moisture content in the grape growing areas or within the micro canopy of the grapes. Enclosed environments like houses or Greenhouses aid in reducing humidity and thus reducing the chance of this mildew from harming the grapevines. So indoor cultivation in greenhouses has better advantage in managing the humidity level and thereby we can reduce the infestation of grape to a great extent. Some chemicals have proved effective in managing or reducing the disease severity and that includes copper fungicides along with dithiocarbamates, mancozeb and all these chemicals give good control over the disease. So these are some of the important Cultural and Chemical management practices that help us to tackle the Downy Mildew problem in Grape.

The next important disease of Grape is Powdery Mildew. It is caused by fungus Uncinula necator and the disease is very easy to identify by looking at the white powdery masses that appears in the leaf surface and all parts of the plant rather including the grape bunches. So it is a disease which can be easily detected and that can be adequate control measure can manage the disease to reduce the severe damage to a great extent. The pathogens survive in infected plant tissues so it can migrate from one plant to another plant or since it is travelled the conidia are air borne in nature the conidia may of the powdery mildew fungus may arrive from a distant place as well.

So IPM practices are recommended which includes some Cultural practices, Use of Resistant varieties, Resistant cultivars and some Chemical methods and combination of these methods can have a effective control over the pathogen. Cultural control method are Canopy management and row orientation because this is most important to minimize the light and air movement to the canopy. Conditions that increase direct sunlight and air movement within the canopy are not favourable. So that is why we need to have excess branches in a way so that there should not be direct sunlight that enters the canopy. At the same time there should be less air flow within the canopy.

This Cultural practices help us to reduce the severity of the disease to a significant level. Some genetic stock has been identified and this genetic sources should be used for management of the orchards. Chemicals that include Sulphur fungicide are prove to be very important and essential and they are used as along with silicone which in combination give protection to the plants against the Powder Mildew pathogen. Strengthening – it also helps the strengthening of epidermal cells and that is how the pathogen is unable to invade the plants very easily. Along with this sulphur fungicide silicon, Tebuconazole can also be sprayed on the on the leaves surface or on the foliar’ s of the plant so that it can also have good impact on lowering down the disease severity. So this chemical methods along with resistance stocks or cultural practices if we combine them together we can have a good control over the pathogen and we can save the farmer’s income before a severe loss.

The next important diseases of grape is Pierce’s Disease. It is caused by a bacterium known as xylella fastidiosa. This particular disease is important and the symptoms can be easily identified by looking into the Browning of the leaf tissues which usually starts from the margins and then slowly the entire leaf may get affected and at the end of the season we can see that the entire plant is getting affected. So this is one of the important disease because this pathogen is xylem inhabiting and it is vector-transmitted. So it is very very difficult to manage no chemical has been identified that can manage this disease in a significant way or there is no genetic stock that has also been identified that can manage this disease or suppress this disease to a great extent. So there are only few process that has been developed so far and that includes use of certain viruses that kills the bacteria. Sometimes this viruses which are also known as bacteriophages, they can be used alone or they can be used in combination with another bacteriophages that are responsible for suppressing of the disease symptoms in the plants but besides these there is no other effective chemical or biological sources that can suppress the disease to the great extent. So it is a challenge to the grape growers or to researchers to develop others management strategies so that this important disease can be handled better in future.

So next important disease of grape is Grey Mold. This is caused by Botryotinia fuckelina and this particular disease is important because it also cause severe loss to the grape growers. The disease can be easily identified by observing the Grey Molds on the fruit brunch and it can affect the entire grape bunch and it can be hundred percent damaging to the growers. The pathogen it survives in infected trees and soil as sclerotia. So it is very important to manage this infected trees and sclerotia that are present in soil. There are certain IPM practices that are recommended and this practices include some Cultural, Biological and Chemical methods and among the cultural measures pruning and staking of plans to improve air circulation is very important. Pruning it will improve the air flow and that is how it is helping the pathogen not establish properly within the canopy. Keeping the soil under plants clean and raking up of any fallen debris is very important because this fallen debris can harbor the pathogen for fresh infection. Adding a good amount of organic compost or mulch under plants is also very effective because it reduces or suppress the inoculum that is fallen on the ground or on the leaf.

Mulching prevents them burying under the mulches and there by this inoculum does not get available for its infection in the new growing season. Water in early morning hours is recommended because it is found to be effective when the irrigation or watering of plants are done early in the morning hours. Some Biocontrol agents has also given very effective and good control over the pathogen that include bacillus subtilis. So application of bacillus subtilis has significantly lower the inoculum that are particularly present on the soil. Chemicals includes Copper fungicide and they have found to be effective in managing the pathogen and thereby suppressing it to a great extent .

So these are some of the important diseases of grapes and we have seen how this particular diseases can be managed by adopting certain Cultural, Biological and Chemical measures and when all these are used in an effective manner we can have good control over this pathogens and save the loss for the growers.

Thank you.



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