Powdery Mildew

Identification and  damage


Powdery Mildew on a Rosa species .

As you  can see Mildew  comes  in  a white powdery  mycelia and spore growth that forms on leaf surfaces and shoots and sometimes on flowers and fruits.These  are  the  fruiting of  the  fungus.

It  can  severely  effect  woody  plants  as  young  sapping which  would  dwarfed.


Downey Mildew  thrive  in  temperatures ranging  from  50 to  60  degrees  wuth  humidity  of  90%

It  can  be  recognized  by  only  being  specific  to  the  leaves  &  not  like  its  other  relation Powdery  Mildew  which  effect  the  stalks  as  well.

And  require  the  opposite it  needs  free  water  and  temperatures  ranging  from

60 -80  degrees  to  germinate.


Prevention  is  the  only  way  with  this  I’m  afraid  :-

  • Make  sure  that  the  air  is  well  circulated  either  out  doors  or  inside
  • water  the  plant  in  the  morning  and  in  the  evening  if  necessary.
  • apply  fungicide  at  the  first  sign  of  attack   and  remove  and  dispose of  infected  leaves
  • As  it  wind  blown  and  dependent  on  climate  make  sure  that  the  plant  is planted  in  the  right  environment &  that  there  isn’t  any  other  plant  that  is  infected  with  it  near  by .
  • Plant a  species  that  is  immune  to  it  if  possible for  example  Rosa  rogusa  or  aImage


    Rosa Rugosa alba

Cultural Practises

As  Mildew  seem  to  thrive  in  shady   moderate  temperatures ( esp Powdery Mildew)  place  plants  in a sunny  area  with  good  circulation

Avoid  over  feeding  the  plants  with  fertilizer  as  this  will  make  sappy  growth .giving  the  plant  an  over  head  watering  will  wash  of  the  spores  and   kill  them  in  the  soil

Fungicides  applications  

In  severe  cases  when  roses  and  other  woody  plants  are  infected  spraying  with  fungicide  will  be  the  only  alternative.

These  are  classified  as  :-

  • Preventive
  • Eradicator


These  fungicides  are  applied  to  new  growth  before  mildew  has  a  chance  to  get  a  foot  hold.

These  include :-

  • Horticultural  oils  like  neem,jojoba (read  My  article  on  neem  oil  )
  • Powders  like  sulphur , potasium  bicarbonate
  • and  Biological    with  serenade

For Mild to  heavy  infestation  spray  with  the  plants  natural  product  ie  Neem  oil. Becareful  never  to  apply  a  oil   spray  within  2  weeks  of  sulphur  spray  or  it  will  burn  the  leaves.

Also  never  apply  oil  sprays  when  the  temperature  has  reached  90  degrees 



An Organic Sulphur Spray

Copper fungicide

An H&S approved copper fungicide

Sulphur  sprays  have  been  used  for  centuries  and  rather  ironic   that  in  the  days  of  the  smug  plant  diseases   never  appeared  cause  the  sulphur  was  believed  to  keep  it  at  bay

The  best  sulphur  to  buy  are  the  wettable  kind  cause  the  dust  can  be  toxic  to  humans

Copper  Formulations

Although  copper  has  been  used  for ages  as  an  effective  fungicide  when  it  mixed  with  a  another  formulation  like lime it acts a bactericidal thus  killing  off leaf  spot  and  fireblight


Vitax Bordeaux Mixture
(Disolve in Water and use a spray)
Contains Tetra-copper Tricalcium Sulphate

Vitax Bordeaux Mixture should be mixed with water and then applied, without drenching, as a fine spray to both sides of affected foliage.  The actual dilution rates vary from plant to plant and full instructions are provided on the product label.



Contrary  to the  myth  Sodium  Bicarbonate    found  in  Baking  Soda  actually  restricts   fungus  growth  due  to  its  alkalinity &  there  fore  only  useful  as  a  preventive measure.

Also available to licensed applicators only is a fungicide containing potassium bicarbonate (e.g., Kaligreen).

Sprays of potassium bicarbonate can injure the plant, so use these products with caution.overuse should be avoided because of possible negative effects (sodium accumulation and alkaline pH) on the soil

Biological Fungicides

5878321_2 Biological fungicides (e.g., Serenade or UK  Myclobutanil ) are commercially available beneficial microorganisms formulated into a product that, when sprayed on the plant, destroys fungal pathogens. The active ingredient in Serenade is a bacterium, Bacillus subtilis, that helps prevent the powdery mildew from infecting the plant.

Myclobutanil is a triazole chemical used as a fungicide. It is a steroid demethylation inhibitor, specifically inhibiting ergosterol biosynthesis. Ergosterol is a critical component of fungal cell membranes.

These products have some effect in killing the powdery mildew organism but are not as effective as the oils or sulphur in controlling it.


2 thoughts on “Powdery Mildew

  1. Pingback: Plant Diseases: Powdery Mildew | Grower Direct Fresh Cut Flowers Presents…

  2. Pingback: The 6 main pest and diseases of rose & how to treat them. | RS Garden Care Services

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