Downy mildew garlic (peronospora)

Peronospora or false garlic mildew it is a common fungal disease, which agent is Peronospora destructor Casp. In some cases leads to the destruction of much of the harvest crops.

 
 
 
 



 
 
 
 

This fungus affects plants onion family such as garlic, onions, shallots, onions, welsh, leeks.

 

Name

Generally Powdery mildew is a group of plant diseases caused by pathogenic fungi. There are of two types – downy mildew and powdery mildew present. They are united by symptoms the affected plant parts (leaves, stems) generated white or grayish bloom. But different pathogens.

Downy mildew in garlic it is a fungus Peronospora destructor Casp (downy mildew family the class Oomycetes)

True mildew in garlic it is a mushroom Leveillula taurica (family Eryzyfovi (Erysiphales) in the class of ascomycetes (Ascomycota))

 

Scientific name

  • Peronospora destructor (Berk.) Casp.
  • Synonym: Peronospora schleidenii

In other languages

  • Spanish: Mildiu Algodonoso, Mildiu Lanoso

 

Damage from peronospora

As an example.

In the Georgia, USA in 2012 an epidemic of downy mildew caused loss of 20-25% of the crop of onions (about $ 18.2 million). Because of the epidemic disease producers had to harvest two weeks earlier, ended up with smaller size bulbs. Infection fields ranged from 10 to 100%.

Downy mildew epidemic provoked weather conditions – continuous periods of wet, cool weather with average low night temperatures of 10 to 11 ° C, followed by high humidity morning fog.

 

 

Downy mildew garlic – Symptoms

  • the leaves or garlic arrows formed oval or cylindrical affected areas of pale green, yellow or brown (Fig. 1, Fig. 2).
  • by favorable weather (cool and wet) infected leaves covered with a mass resolution of gray to purple (Fig. 3).
  • leaves curl and dried up (Fig. 4, Fig. 5).
  • disease begins to hit targets areas of the field (Fig. 6, Fig. 7) or disease

Лист лука с симптомами заболевания - пероноспороз ложная мучнистая роса чеснока и лука

 

Лист лука с симптомами заболевания - пероноспороз ложная мучнистая роса чеснока и лука

 

симптомы заболевания пероноспороз ложная мучнистая роса чеснока и лука

 

Лист лука с симптомами заболевания - пероноспороз ложная мучнистая роса чеснока и лука

 

Лист лука с симптомами заболевания лука и чеснока -пероноспороз (ложная мучнистая роса)

 

Поле лука с очагом заболевания - пероноспороз ложная мучнистая роса чеснока и лука

 

Поле лука с очагом заболевания - пероноспороз ложная мучнистая роса чеснока и лука

 
 
 




 
 
 

Cycle of the disease

Dormant period

It is believed that the fungus Peronospora destructor winters mainly in the form of mycelium in infected bulbs that remain in the field or in the remains of plants collected but not destroyed and left near the fields.

The originator can also spend the winter in perennial bulbs in home gardens.

It is suspected that the fungus spores stored in the soil can directly infect the roots of young plants onions or garlic.

These plants are infected system and serve as centers of infection at the industrial crops of garlic and onions.

 

Primary infection

Favorable conditions for

  • temperature – night from +5 to + 10 ° C with a further increase in daytime and + 15 C +18 °
  • a letter of moisture within 1.5 to 7 hours

Under these conditions downy mildew garlic can develop very quickly from initial infection to air disputes epidemic.

A critical aspect of Peronospora can be a time when high humidity is kept at least 11 hours under these conditions the fungus affects the plant for 3 days.

Spores can travel long distances in moist air.

If the weather is hot and dry, the development and progression stops and often stops completely.

 

The primary source of the disease:

  • diseased plant material
  • crop residues on the field
  • Tools and machinery
  • presence of perennial bulbous patients on adjacent fields

 

By spreading

In case of favorable environmental conditions after winter, the fungus mycelium from systemically infected plant spreads spores. After spreading through the air these spores infect leaves bulbous plants.

Spores produced at night when there is high humidity and average temperature around 9 C.

Disputes ripen early and are spread throughout the day. Spores can survive for four days.

Germination occurs in free water on the plant with the optimum water temperature range of 7-16 C. Thus for the spread of infection need not be rain and quite abundant dew or dense fog overnight and in the morning.

 

 

Secondary infection

Mycelium Peronospora destructor infested plants in the leaves of garlic or onion produces a new crop of dispute, called conidia. The cycle of approximately 11-15 days.

As soon as the upper part of the sheet dies garlic fungus affects the lower part of the next letter in each subsequent cycle saprogenic.

These cycles can be repeated several times until the letter is completely cut off.

These repetitive cycles saprogenic can lead to serious and prolonged epidemics downy mildew on garlic if there is favorable weather conditions persist.

 

 

Methods of prevention and control

Prevention

  • acidic soils promote the development of mildew and generally not effective for growing garlic (PH indicator needs at least 6)
  • use of healthy planting material from proven manufacturers with quality that is laboratory confirmed
  • landing an hour for a good ventilating (correcting the scheme of settlements etc.)
  • Plant inspection – checking tip sheets twice a week
  • Avoid watering top. If you still use sprinkler irrigation, then do it early in the day so the leaves can dry in the evening. Downy mildew spores forms of garlic active at night, when the leaves are wet.

 

Physical control

Processing cloves before planting fever:

  • Dry heat treatment bulbs – at 40 ° C for 8 hours contributes to the destruction of any internal mycelium
  • Wet processing – at a temperature of 42 ° C to 50 ° C for 15-30 minutes, followed by drying

 

Chemical control

Fungicides to combat by peronospora (downy mildew) garlic and onion

Rydomil Gold MC 68 WG – production Syngenta, Switzerland. Active ingredients Dymetomorf, 640 g / kg Mankotseb 40 g / kg metalaxyl-M. The rate of application of 2.5 l / ha, the maximum multiplicity processing 3, no later than 30 days before harvest.

VG Gold Areva – production ADAM, Israel. Active ingredients Dymetomorf 90 g / kg + mankotseb, 600 g / kg. The rate of application of 1.8 – 2 l / ha, the maximum multiplicity processing 3, no later than 30 days before harvest.

Kvadris 250 SC – Production Syngenta, Switzerland. Active ingredients 250 g / l Azoksystrobyn. Normal use of 0.8 – 1.2 l / ha, the maximum multiplicity processing 3, no later than 14 days before harvest. Handling – at the first signs of disease or prophylactically.

 


Author photo

  • Gerald Holmes, California Polytechnic State University at San Luis Obispo,
  • Howard F. Schwartz, Colorado State University
  • Claudia Nischwitz, Utah State University

 


The information was prepared by Andrew Marchenko


 

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