Roses - Treating Black Spot21-Dec-2011
Roses - the world's favourite flower.
Black spot - the scourge of rose growers.
Black spot a fungal disease that thrives in warm humid climates.
Starts off as a black spot in the leaf and then turns yellow and eventually the leaf falls off.
Appears as circular black spots on the leaves which are fringed with yellow margins - spots can also appear on the stems.
The leaves will fall prematurely and if left unchecked can lead to defoliation of the plant
If it's really bad, the plant can die.
Controlling or Reducing Black spot
Firstly - open up the rose bush to create more air movement through the middle and that minimises the risk of humidity.
Areas with high summer rainfall and high humidity usually have the highest incidence.
Never water the foliage - Watering the rose foliage creates the right environment for the disease to multiply -infections take hold when the water remains on the leaf for about 6-7 hours
Always water around the roots of the rose and give it a good soaking.
When the black spot spore lands on the leaf, it germinates and sends its little root system through the cell wall into the sap stream below and it spreads.
If you can thicken the cell walls, when the spore lands and the root system germinates - it gets halfway and then fizzles out, resulting in less black spot.
But how do you thicken that cell wall?
It's easy - Experts have found using sulphate of potash and giving about 100 to 150 grams per bush about four times a year should result in a good reduction of black spot.
Plants are no different to people - the better fed they are, the more likely they are to resist disease.
That’s also true with roses and black spot - so that means give your roses a good feed every six to eight weeks through the growing season with an organically based rose fertiliser.
You will still need to be vigilant and spray to contain the remaining spores and reduce chances of outbreaks. Depending on your preferences and time -there are a number of safe, organic spray options as well as copper based fungicides to choose from.
Nutrition and spraying will control most black spot but from time to time some bushes will be chronically affected. The only thing to do is to rip these out so they don’t infect any of the others.
Remember, garden hygiene is of vital importance.
Go round on a regular basis and pick off any black spot affected leaves, put them in a plastic bag and tie the top tightly.
Then leave it out in the sun to cook and that will kill the spores. Don't put them in the compost heap, instead put them in the bin.
When you control black spot, you can have some beautiful roses.