ASK THE CONSULTING ROSARIAN
by John Moe, Master Rosarian
Q – I
did enjoy the program on the link between soil and fertilizer,
and what can happen when everything does not go as planned. You
said that the leaves often give a clue as to those deficiencies,
and did give us a couple of websites where we could see photos
of nutrient deficiencies, but I didn’t have time to write them
down. Could you list them here?
– it isn’t always easy to write down a website when you hear it,
but these are two of the best that I have found to show the
deficiencies. Take a look at these and bookmark them so you can
get back to them when you need to.
Q – Before you started your program on
fertilizer, you had a slide on downy mildew and took a few
minutes to talk about it. I have heard that some of our members
have had this in their gardens. Is it as serious as you said,
and if so, if I find it in my garden, what can I do?
A – Yes, it is one of the most serious of rose
diseases. And yes, some of our members have said that they have
it, and are in the treatment process. So, if you had added any
new roses to your garden this spring, regardless of where you
purchased them, take special care to watch them for the early
signs. Favorable conditions for downy are humidity over 85% and
temperatures under 80°. There is a lot of it in CA, so roses
that came up to the nurseries here in WA are susceptible! It is
always the best policy that, whenever you bring in a new rose,
regardless of where you got it, you let it sit away from your
other roses for a several days to see if it is OK. Sort of
having your own quarantine area.
The symptoms of downy mildew begin as
purplish-red irregular spots primarily on new growth. When
a spot comes to a leaf vein, it follows it, but when a spot of
to a leaf vein, it crosses it. What you are looking for in your
new additions, and in your garden is what you see in this first
photo, from Nicole Ward Gauthier, University of Kentucky
Cooperative Extension Service.
As it progresses, you will see that purple to
red or brown irregular blotches that form have tended to follow
the leaf veins, as you see here, in this photo courtesy of Gail
Trimble. This is often when we first realize what we have, as
too often it is confused with blackspot. The leaves will yellow
and rapid defoliation will start from the top of the bush. Left
untreated downy mildew can destroy your entire rose garden.
Some fungicides that have shown to control
include; Aliette, Heritage, Compass, Subdue MAXX, and Daconil
Weather Stik, using repeated applications