Major diseases of Grapes- their Identification and Prevention

Diseases of grapes
Diseases of grapes

This blog talks in detail about a few major diseases of grapes- Anthracnose, Downy Mildew, Powdery mildew, and Grey Mould.

Grapes are one of the most commercially grown crops in the world. In India, it is majorly grown in the regions like Tamil Nadu, Karnataka, Andhra Pradesh, and Maharashtra.

One of the challenges in the production of grapes is the invasion of a wide variety of insect pests and diseases at different crop stages. Identifying diseases in the vineyard as soon as possible is essential to stop significant outbreaks and quality losses. But the need for a cure is not always implied by the presence of a pathogen or sickness. Disease severity varies from year to year, mostly based on the weather, the presence of inoculum (the disease’s history), and the vulnerability of the vines. Therefore, a disease may be fatal in one year and insignificant in the near future. Therefore, from season to season, different steps may need to be taken to avert losses.

Major diseases of grapes are:

  • Anthracnose
  • Downy Mildew
  • Powdery mildew
  • Grey Mould

1. Anthracnose

This disease is widespread throughout the nation’s grape-growing regions, primarily damaging leaves, and young shoots. 

Identification guide:

  • Little light brown or greyish black lesions appear on sensitive stems, young leaves, blossoms, and young berries.
  • As a result, short holes are made in the leaves, decreasing the functional leaf area.
  • Affected flowers do not produce fruit. 
  • Additionally, the fungus creates cankers on the petioles and veins, and the leaves twist and distort. 
  • The disease results in round, brown sunken patches on berries that have dark brown edges. Berries may crack and reveal the seeds if they are attacked severely. Berries in anthracnose-affected bunches lose their value as exports. 
  • The spread of the disease is greatly facilitated by rain and dampness.

General preventive measures:

Preventative actions must be taken to ensure control. 

  • When pruning, all twigs or canes with cankers should be eliminated. 
  • The twigs and leaves that have been clipped should be burned or buried far underground. 
  • In the months of October and November, this disease is more severe. Sprays of protection should be applied to the young branches and new shoots during this time.
  • Spraying Bordeaux combination at 0.8 percent, Copper Oxychloride at 0.25 percent, or Carbendazim at 0.1 percent on grapevines at the 3–4 leaf stage is beneficial against this disease.

2. Downy Mildew

The development of the disease is favored by light, persistent rainfall or heavy dew along with high relative humidity and chilly temperatures. The immature fruits, flowers, clusters, and leaves are all affected by the disease. 

Identification guide:

  • Young, mature leaves first show signs of light yellow dots on their upper surface and similar white patches on their underside. 
  • Due to decreased photosynthetic activity, the affected leaf sections turn brown and cannot sustain the bunch’s development. 
  • There are significant losses when the clusters are damaged before the fruit set. 
  • Whole clusters dry out, decompose, and collapse. 
  • Small, infected berries turn brown and desiccate. Berries no longer get an infection after they start to soften and change color.
Downy Mildew of Grapes

General preventive measures:

  • To reduce the damage caused by this disease, vines should be pruned after the second week of October. 
  • At the time of pruning, all afflicted vine parts should be cut off and immediately killed.
  • Effective treatments for this disease include Bordeaux combination (1%), Copper Oxychloride (0.2%), Mancozeb (0.2%), Metalaxyl (0.2%), or Fosetyl Al (0.2%). 
  • Compared to non-systemic ones, systemic fungicides are more efficient. 
  • Systemic fungicides shouldn’t be sprayed more than 2-3 times.

3. Powdery mildew

It is the second most devastating disease after downy mildew, but it is more significant from the standpoint of exporting fresh grapes because it taints and deforms the infected berries. Warm, dry circumstances favour the development of the disease. This disease also develops more quickly in the presence of shade or indirect light.

Identification guide:

  • The disease can be identified by areas of white, ash-like powder on the undersides of leaves, young shoots, and immature berries. 
  • The affected leaves become pale in colour and curl up. Affected shoots tend to be immature and frail. 
  • After being pruned in October, the damaged buds from the growing season do not sprout. 
  • As a result, both the cane’s productivity and the number of productive canes are decreased.
  •  Blossoms that are harmed are unable to produce fruit. Young berries become corky when they are attacked. 
  • They become covered in a white powdery layer after being extensively damaged, and eventually, they fracture.
Powdery Mildew of Grapes

General preventive measures:

  • Spraying Wettable Sulphur (1.5kg/200 liters of water) will quickly and effectively eliminate powdery mildew.
  • Spraying should be done carefully because it can burn the berry skin and leave tiny black flecks.
  • The dust should be evenly distributed across the sections of the damaged plants.
  • The disease can be controlled more effectively and for a longer period of time using systemic fungicides like Bayleton (1g/liter of water), Calaxin (3-4 ml/10 liters of water), or Benomyl (5g/10 liters of water.

4. Botrytis Rot/Grey Mould

It is among the most significant storage-related diseases and can thrive at low temperatures. 

Identification guide:

  • In vineyards, the fungus damages the shoots and clusters or eats away at the stalks, causing early fruit drop.
  •  The skin of the impacted berries becomes loose right below the infection in the early phases of the disease. 
  • The firm pulp is exposed when the skin of the berry is rubbed with fingertips. 
  • The diseased berries shrivel, decay, and turn dark brown, revealing the presence of a fungus growth that is greyish in colour.

General preventive measures

  • The disease can be controlled with careful field handling, pre-cooling, and refrigeration. The humidity around the clusters is decreased through vineyard pruning and thinning.
  • The growth of the fungus during transit and storage is reduced by preventative sprays containing Captan (0.2 percent) and Benomyl or Bavistin (Carbendazim) (0.1 percent).
Botrytis Rot/Grey Mould of Grapes

How can Fasal assist?

  • In just a few days, devastating vine diseases and disorders can entirely and rapidly destroy entire vineyards. With the use of Fasal’s technology, diseases like anthracnose, powdery mildew, downy mildew, and others are no longer a threat to your vineyards.
  • Based on the idea of precision agriculture, the technology from Fasal suggests site-specific, time-specific, location-specific, and crop-specific solutions.
  • Fasal’s technology analyses rainfall, humidity, temperature, the anticipated temperature at the canopy level, and a microclimatic prediction for grape diseases to warn farmers when conditions are favorable for pest invasion.
  • Fasal’s technology develops several management plans and suggests remedies based on the particular characteristics of a farm.

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