Gardening News - Halt the rise of black spot, organically.

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Written by Staff Reporter

Wednesday, 20 August 2008

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. Black spot 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 black spot 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. Black spot resistant roses include Amber Queen (golden yellow), Iceberg (white) and Trumpeter (red). I believe the saying is “a good start is half the battle”, how true it is.

Until next week, happy gardening and remember that a weed is just a plant in the wrong place.

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