Posted: 05/08/2012 at 08:52
Don't know if any of you get the Barnsdale Gdns newsletter emailed to you but this was featured in the latest one.
This is a terrible disease that can vary year on year in its severity and because of all the dampness this year we are seeing quite a bit already. Being organic we generally rely mostly on hygiene to keep diseases at bay and roses are no different. We collect all the fallen leaves each autumn to prevent the blackspot spores from overwintering and being ready to re-infect the roses the following year. However, even doing this job each year does not guarantee that this disease will still not strike. If it does, then a good organic way of keeping it from spreading is to use skimmed milk! Dilute equal parts of the skimmed milk with water and spray it directly onto the leaves of the roses. The solution will coat the leaves and prevent the blackspot spores from attaching themselves to the leaves, therefore preventing further spread of the disease. The method will not cure the leaves of blackspot but it will halt its progress. It is important to use skimmed milk as the higher level of fat in other types of milk actually reduce the effectiveness of the spray. If it rains heavily then the solution will need to be reapplied, otherwise spray every 10-14 days.