and black spot on roses
roses are a problem. I did spray with winter oil and copper oxychloride
etc, but with wet weather, some varieties now have severe rust and
others have black spot. I have been spraying every 7-9 days with
super shield and trying to collect the infected leaves and pruning
the dead heads. All seem to make no difference. One rose bush I
have just severely pruned again it was so infected. I did speak
to the gardeners at the Wellington Botanic Gardens and they have
a commercial spray you cannot buy but suggested I spray with milk
or baking soda?
sounds like you are doing all the right things regarding sprays.
In fact, you might be doing a bit too much. Removing diseased leaves
and dead flowers is definitely a good idea I assume that
you are destroying them?
I wouldn't bother with
milk or baking soda in addition to your other sprays, they are really
just a safer alternative rather than a panacea for your problems.
The bottom line is that
roses do not generally grow well in wet climates. Some cultivars
are more disease resistant than others, but some of the older varieties
are very susceptible to rust and/or black spot, and will keep becoming
reinfected. You may have to bite the bullet and replant with more
If, however, your roses
are precious, you could look at the part of the garden they are
growing in. Do they get enough sun? Have they had enough fertiliser?
Is the soil well-drained? Is there enough airflow around the plants
to reduce humidity? You could also have a look at neighbouring plants
to see if they are harbouring disease and spreading it.
by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor
of Resource Management.
with permission from NZOOM Home and Garden content,
from the previous
The views expressed here are not necessarily those of the RNZIH