Growing roses - rose diseases


by Adam Pasco

Are your roses martyrs to disease? Are their leaves covered with black spots or a white overcoat of powdery mildew?


Rose blackspot on rose leavesAre your roses martyrs to disease? Are their leaves covered with black spots or a white overcoat of powdery mildew? Well, I'll come clean and put my hand up on both counts. Much depends on the time of year and whether it's wet or dry - but, most years, even some varieties that claim to be disease resistant can show signs of disease.

I wish I'd thought more carefully before buying eight standard 'Bonica' roses a few years ago. By mid-summer, the older leaves have usually developed orange rust pustules on yellowing leaves. Rose rust doesn't kill roses, but it does take the edge off an otherwise glorious display.

And this is where I'm pulled in two opposing directions. Do I maintain health and vigour, and spray regularly with fungicides to keep my roses disease-free, or leave alone and put up with some infection? I'm not one of the old school, who sprays regularly, regardless of season just to create a perfect display. I garden with the absolute minimum use of artificial chemicals, probably like most people today I would think.

Chemicals cost money, are time consuming to apply, and must be used carefully and sensitively. If my roses can flourish without them then so much the better in my book.

When buying roses, it's a good idea to choose varieties which have been bred to resist disease, but some of us inherit old varieties, or just grow roses we fall in love with for their colour or fragrance, without considering their health status.

If that sounds like you then you have a choice: leave things to chance, or pick up the pressure sprayer. Today I fall into the former category, but a devastating disease year may persuade me that preventive action would be better in future. And this means using a suitable rose fungicide regularly from early in the year to prevent disease. Once blackspot, mildew and rust symptoms are present it's really too late to start spraying. As a rule of thumb, prevention is better than cure.



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Gardeners' World Web User 30/05/2011 at 09:54

Even on a drizzly day like today I go out in the garden and inspect my roses and take off and dispose of any leaves with blackspot on. I've never needed to spray in this garden for the 47 years I have been growing roses. My "Albertine","Queen Elizabeth, the Queen Mother", "Matisse", "Iceberg" and Bourbon roses are making a splendid, fragrant display as well as the ramblers I do not know the name of as they were in the garden when I came. But my favourites are the early ones, "Canary Bird" and the Banksian rose which never seem to have any disease.

Gardeners' World Web User 31/05/2011 at 10:18

On one of my rose bushes, white foam-like stuff appears. It will wash away when I water the bush, but will reappear somewhere else on the bush the following day. Can anyone tell me what this may be, and what I should do, if anything? Thank-you. The rosebush otherwise looks really healthy and it is at present flowering more than it has done in previous years.

Gardeners' World Web User 31/05/2011 at 11:12

This is called cuckoo spit, lijemc, and , apart from being a little unsightly, will not harm your rose. Inside each froth you will find a tiny nymph which is immature. The adults live on the bush but do no harm. You are doing the right thing by washing the spit away.

Gardeners' World Web User 31/05/2011 at 14:54

Reply to lijemc: Yes, happymarion is right. The tiny green nymph inside the cuckoo spit is the immature stage of an insect called the froghopper – getting its name because the adult jumps away like a frog if you try and touch it. Some people call this white froth 'spittle-bug'. This insect doesn't really do any harm, although any insect feeding on plant sap can introduce virus disease. You can simply rub them away between your fingers, or blast off with a jet of soapy water. A hedge of lavender near my home is covered with them, but within a month them will have gone.

Gardeners' World Web User 31/05/2011 at 14:56

Check this link to a BBC information site for more details about Cuckoo Spit and Froghoppers: http://www.bbc.co.uk/dna/h2g2/A812828

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