> My employer has a problem here on Vancouver Island with powdery mildew. The
> greenhouses are full of frost. We have tried Benomyl and Foped but with poor
> results. The talk at the garden suppliers is that this year has been the worst
> remembered for this disease.
> Our roses were so bad that we gave up and burned them all. We have cleaned the
> greenhouses out and have opportunity now to disinfect with anything that will
> work. Even the wooden structure of the greenhouses has mildew growing on there.
> The mildew has infected many outdoor plants. Clover, hardwood trees and other
> plants show the white fuzz. I understand that there are hundreds of varieties of
> powdery mildew. Is it more likely that several strains are infecting these
> different plants or that it is one organism that is responsible?
> Is there anything that we can use to disinfect the empty greenhouses,
> effectively treat diseased plants, or prevent it?
> Please email
Sounds like you should read up on powdery mildew from a regular textbook
or from the American Phytopathological Society (APS) Compendium of rose
Diseases or from a book on greehouse fungal diseases from the AARS.
There are lots of basic information that you should know if you are a
greenhouse manager. Also, you might want to look at the greenhouse
structure itself and see if you have proper heat & ventilation to dry up
There are many species of "powdery mildew" as well as many strains of
the powdery mildew that attacks roses. On the other hand, not all fungi
that have whitish mycelia are powdery mildew. Also, the regular "mildew"
that you mention growing on the walls of your greenhouse, is not a
"powdery mildew"! The species that attacks roses also attacks many other
plants. My greenhouse manager was just commenting to me this morning on
the numbers of plant species that she has seen powdery mildew on in our
I personally think that you went overboard with getting rid of your
roses that were infested with powdery mildew as well as completely
scrubbing the greenhouse with a sterilant/fungicide. There are excellent
products for controlling powdery mildew in greenhouses. Contact a pest
control advisor or agriculture agent to recommend the fungicides that
are available to you in Canada. You definitely need to change from
Benomyl as this fungicide is one of the oldies and it has been
discontinued by many growers as many fungi have developed resistance and
growers could not get adequate control of their fungal diseases. I am
not familiar with "Foped" but you might want to try newer fungicides
such as Rubigan, Systhane (Eagle), Bayleton, etc. if available in your
area. There is also an eradicant fungicide that is available for
greehouse growers only with a permit. I can't think of the name of the
fungicide at this time, but ask me later and my brain might be in better
shape to remember.
Baldo Villegas (Bugman), Entomologist/ARS Consulting Rosarian
Home Page: http://www.concentric.net/~bugman/