Keeping Blackspot on roses at bay

It looked like autumn last week as the dead leaves damaged by the winds floated down to the ground. Don’t let this fool you into thinking that things are slowing down in the garden. Quite the opposite. Everything’s shooting up. There’s a new problem coming to light, blackspot on roses. I have asked the help of James Kilkelly from Gardenplansireland to give us some help at combating this perennial problem... organically.

Halt the rise of black spot, organically.

Its back! Black spot has once again raised its ugly mottled head to infect the roses of Ireland (including mine), causing leaf loss, and die back of the plants stems. Black spot (Diplocarpon rosae) is a fungal disease encouraged by much the same conditions that encourage potato blight, which are warm, moist locations with stagnant air. Most Irish roses especially those grown in areas of high rainfall are destined at some stage of their growing life to play host to blackspot.

Maybe you are lucky enough to have never had a run in with blackspot, and therefore you require an introduction to help you identify this plant ill. Blackspot is aptly named, initially appearing as purple or black circular spots with yellow-fringed halos. Over a short period of time these halos spread and join up causing the leaves they appear on to yellow and shed prematurely.

Although blackspot will rarely kill a rose outright, it will however leave you with a sickly, twiggy rose, which flowers poorly due to a lack of its life-giving leaves. Now, there are many combined chemical products available in your garden centre for the control of blackspot, for example Rose-clear, Benlate or Multirose, to name a few. But you may actually have all the raw materials already within your kitchen to create your own homemade, organic and most importantly safe black spot spray.


Method 1, Milk.
Walk across your kitchen as far your fridge. Mix equal parts milk and water, then apply this each week with an atomiser or a sprayer to the upper and lower section of the roses leaves. This milky solution causes an invisible and friendly fungus to form, which will help prevent the formation of the dreaded black spot.


Method 2, Baking soda.
Mix one tablespoon of baking soda or baking powder into one litre of water and add a drop or two of washing up liquid for stickiness. Again, apply this each week with an atomiser or a sprayer to the upper and lower sides of the roses leaves. The baking soda (Sodium bicarbonate) causes the rose leaf surface to become exceedingly alkaline which again prevents the blackspot from thriving. Both method 1 and 2 are effective only if used at the first sign of symptoms.

Method 3, The rake and clippers.
It is important to rake up the withered rose leaves and petals that litter your beds and borders, as these can act as a breeding ground for the blackspot fungus. Also, pick or snip off any live leaves that exhibit black spots, as well as looking unsightly they aid the spread of the disease. All infected rose leaves and clippings should be burnt not composted.

Method 4, The shovel.
When all is said and done, probably the best method of organic black spot control is to plant roses resistant to the disease. And there are quite a few.
Black spot resistant roses include...
Amber Queen (golden yellow),
Iceberg (white),
Trumpeter (red),
Electron (Deep pink),
Helmut Schmidt (Golden yellow),
Just Joey (Creamy peach),
Keepsake (Dark pink),
Las Vegas (Dark peach with yellow highlights),
Peter Frankenfeld (Dark pink),
Polarstern (White),
Precious Platinum (Medium red),
Silver Jubilee (Salmon pink),
Voodoo (Orange),
Love (Crimson red with white backs),
New Year (Orange),
Tournament of Roses (Rose pink),
Bonica (Rose Pink),
Escapade (Mauve-pink),
Europeana (Dark red),
Impatient (Orange-red),
Liverpool Echo (Orange),
Matangi (Red),
Orangeade (Orange-red),
Play Girl (Bright pink),
Playboy (Reddish orange),
Redgold (Golden yellow edged in dark pink),
Regensberg (Pink and white),
Sarabande (Orange-red),
Sexy Rexy (Rose-pink),
Showbiz (Scarlet red),
Viva (Red).


Top Tip
Gareth Austin from Newtowncunningham has a good tip for us too.
“I have another practice on keeping roses disease free, and it comes from the old method of preventing blight on potatoes.
Use Sulphate of Potash in Spring and early summer as a feed for the roses. The growth which develops is less soft and more disease resistant. Also as the foliage is harder they are less prone to pest attack. This method can also be used on your spuds. Mulch in Autumn with Turf or wood ash as a soil improver.”

Photo: Wild roses (dog rose) don’t seem to suffer from blackspot although the leaves did go brown after the cold winds recently.