Downy mildew of grapes

  1. Downy mildew of grapes occurs in the most part of theworld where the grapes are grown humid condition.
  2. The disesase attacks on leaf and fruits of the grapes plants and also cause dwarfing and killing the young shoots.

Symptoms 

  1. Yellowish gray spot develop on the upper surface of the bay leaf from the lower surface of the spores downy growth of fungus appear these nacrotic areas may causes.
  2. Turn brown and the infected leaf may finally die. Barriers may also be attacked and turn brown.
  3. Storage decay is not indused by mildew pathogen.

Causal Organism

  1. Plasmopora viticola
  2. The branches of the conidiophore at the right angle and are irregularly spaced.
  3. Mycelium ranifies within the intercellular space and sets globose haustoria into infected tissue.
  4. Usually 4-6 sporangiophores arise through 1 stoma each producing 4-6 branches nearly right angle to make branch, further 2-3 Secondary branches are produce from each such branch.
  5. Sporangia germinates through zoospores or resting spores are produce as a result of fertilization between Anthredia and oogonia.

Disease Cycle

The fungus over twinter through. Oospores on the infected plant. Oospores germinates at a temp range of 20°c to 25°c penetration take place through stomata on lower surface of the leaves. The incubation periods for the production of sporangial, after infection 5-8 days, depending upon the temp and humidity.

Secondary infection occurs through sporangia which germinates by means by zoospore.

Controls

  1. Sanetery precaution infected leaves and fallen things should be destroyed.
  2. Fungicides spray are most commonly used, Bordeaux mixture, Captan, Biltox 50 etc