Maintaining roses

ROSES bring colour, scent and brightness to the summer garden, but appeal to pests as much as to us. Inevitably, the weather can bring heartache as well as joy and there’s nothing we can do about it. When a rose bud is on the point of bursting out and then rots, all you can do is fight back a tear.

But it might partly be our fault if a rose develops powdery mildew during a warm sunny spell in summer. The fungus causes white pustules on leaves, with ascospores forming beneath a white coating. The disease is disfiguring and, though damaging, is rarely fatal. Stressed plants are more at risk than healthy vigorous ones, so we can hardly blame the weather if we’re not growing our roses properly in the first place.

Start by choosing one of the many modern varieties that have been bred with some resistance to the fungus. But they too need a helping hand. They require moist, fairly fertile soil. Mulches pay dividends, retaining moisture and encouraging good soil structure.

But don’t mollycoddle your roses with lashings of nitrogenous feed as this artificially stimulates leaf growth, partly inhibits flowering and also weakens the plants, making them even more attractive to pests as well as diseases such as powdery mildew. Instead, increase a leaf’s natural resilience by spraying with liquid seaweed every week.

Pests such as greenfly, scale insects and sawfly attack a plant when it’s down. Greenfly consume plant sap and excrete sugary honeydew which develop a black coating that you might confuse with blackspot. Brown scale insects produce similar symptoms on stems. A curled leaf may be harbouring a sawfly grub which it will shortly consume. Reduce this risk by looking out for it and removing the pest. Easier said than done, I know, but eagle eyes work wonders.

Best of all, manage the garden to encourage a build-up of natural predators to control these pests: lacewing and hoverfly larvae, tiny parasitic wasps and small birds, like tits. Even dread wasps are doing a brilliant job just now, with each hoovering up as many as 100 greenfly a day for the larvae in their bykes, or nests. Only later in the season, with their real job done, do they indulge in sweet goodies. I confess in my longestablished organic garden, my