There were several queries about roses in this week’s postbag. It seems blackspot has made an early appearance.
This annoying disease has already defoliated some roses, but this can be overcome if drastic action is taken.
If you find roses without any leaves, cut the stems to about a foot, pick up all the dead leaves and apply Vitax Q4 fertiliser.
Fork this into the topsoil and water. Now give each rose a teaspoonful of Epsom salts. In a fortnight new growth will form and the leaves will be free of blackspot.
To control diseases roses need to be sprayed every fortnight with a fungicide. Trouble is, this is a nuisance and we tend to put it off. This is understandable as there are so many things to do at this time of year. But determination is essential.
Pests and diseases become immune to the chemicals in the products we buy. Overcome this by using a selection of different sprays.
The best idea is to use a different fungicide once a fortnight, throughout the summer.
Blackfly, greenfly and aphids are also rampant this year, not only on roses but also on broad and runner beans. Everyone at the allotment is complaining.
Why are there so many and how do they breed so quickly? You spot one or two and a week later plants are smothered. Here’s the explanation.
In the autumn the pests mate and the females lay eggs low down on the stems of roses or at the base of perennial weeds. During a warm spell in spring, the eggs hatch. All the baby aphids are females and in a few days, every female starts laying nine young ones every day for three weeks. Imagine all those aphids produced from just one egg. But hang on, there were dozens of eggs laid in the autumn so by midsummer there could be as many as 20,000 aphids and, you are thinking, that is true and they are all on my runner beans and roses!
There are a few natural predators such as ladybirds, lacewings and blue tits, but an insecticide may be considered. Derris has been withdrawn but pyrethrum, made from chrysanthemum flowers, is environmentally-friendly.
You’ll find it labelled as PY at good garden centes. They always have it in stock at Keydell Nurseries, Horndean.
Please read the instructions on the pack before buying. Always spray late in the evening when the sun has gone off the plants. At that time bees and hoverflies have will have gone from the garden and only the pests and disease will be controlled.
Try my grandpa’s method. He used bits of soap dissolved in hot water and sprayed the pests when the sun had gone.
These days we can buy liquid soap flakes. Use one capful in two gallons of water and spray when the sun has gone. Don’t use washing up liquid. This is a detergent and may damage the leaves. If applied too strongly it will kill the plants as well as the blackfly.
TIP OF THE WEEK
Gladioli corms are available at half-price at several garden centres. Plant them now and they will bloom in October.
Plant them in groups of five. Planted this way they give a good colour impact in autumn.