How to tackle black spot on your roses

Dahlias - one of the boldest plants you can grow .

GARDENING: Brian Kidd is planning for summer with dahlias

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There have been quite a few queries regarding roses in my postbag and I notice that black spot has made an early appearance.

I’ve never known it to strike so early in the year, but this is because of the excessive amount of rain we had in April.

This annoying disease has defoliated some roses already, but this can be overcome if drastic action is taken.

If you find some of your roses have lost all their leaves, cut the stems down to about a foot, pick up all the dead leaves and apply some Vitax Q4 fertiliser. Fork this into the top of the soil, then give each rose a teaspoonful of Epsom salts.

In about two weeks, new growths will form and the leaves will be dark green and free of the blackspot.

To keep control of diseases, the roses need to be sprayed every fortnight with a fungicide. The trouble is that this job is a nuisance and we tend to put it off.

But determination is essential. It is a fact that pests and diseases become immune to the chemicals in the products we buy, but we can overcome this problem by using a selection of different sprays.

I have a method that will work if the products are used every two weeks. The programme is used by professional rose growers and council parks departments.

Week one: Spray the roses and the soil with Roseclear 3.

Week three: Spray the roses and the soil with Bordeaux mixture. It is a powder and has to be added to water.

Week five: Spray the roses and the soil with Multirose – this will kill pests as well as diseases.

Week seven: Go back to Roseclear 3 and repeat this programme all through the summer and you will be free of diseases.

Blackfly and greenfly (also called aphids) are rampant this year as well, not only on roses but on broad beans and runner beans too.

Why are there so many and how do they breed so quickly? Just one or two are spotted but, a week later, the plants are completely smothered.

Well, during the autumn the pests mate and the females lay eggs low down on the stems of the roses or at the base of perennial weeds.

During a warm spell in spring, the eggs hatch out and all the baby aphids are females. Within a few days, every female starts laying nine live young ones every day for about three weeks.

After a few days, the baby ones do the same. Imagine all the aphids produced from just one egg, but there were dozens of eggs laid in the autumn so by midsummer there could be as many as 20,000 aphids on your runner beans and roses.

There are quite a few natural predators such as ladybirds, lacewing flies and blue tits, but an insecticide may be considered. I suggest you try Pyrethrum, made from chrysanthemum flowers.