spot on roses
year our roses are affected by black spot. Is there an organic spray
we can use? Also, is untreated sawdust a good mulch for the garden?
rose varieties are susceptible to black spot, but other than changing
your roses to more resistant ones, there are several actions you
can take to reduce the incidence of the disease.
In late winter, after
pruning, make sure you clean up all dead leaves and prunings from
the soil beneath the plants to get rid of much of the source of
reinfection. Cover the soil surface with clean mulch such as granulated
bark and change it each year after pruning. Then immediately give
your roses a thorough spray with a copper fungicide, mixed with
spraying oil, such as Eco Oil or Conqueror.
In spring, when new
growth appears, you could spray with a preventative fungicide such
as Nature's Way Fungus Spray, which contains both copper and sulphur,
or you could alternate between separate copper and sulphur sprays
in the form of Copper Oxychloride and Super Sulphur. These sprays
are organic in nature and safe to use as long as you follow the
Some gardeners report
several sprays of seaweedbased fertiliser during the growing season
helps reduce black spot problems, so that could be worth a try also.
Untreated sawdust is
fine as a mulch as long as you apply a nitrogenous fertiliser at
the same time to counteract the nitrogen "drawdown" effect that
can occur with wood products as they decompose. Check with your
local garden centre and get a fertiliser with the amount of N (nitrogen)
higher than P (phosphorous) and K (potassium). If you don't counteract
the nitrogen loss caused by the decomposing sawdust, plants in your
garden may eventually show nitrogen deficiency symptoms such as
poor growth and yellowing of leaves.
Gardener, Issue 189, 2005, Page 25
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.