Symptoms

Orange-brown pustules develop on the undersides of leaves. These can often go unnoticed and the disease has taken quite a hold by the time the pustules appear on the upper leaf surface and are noticed.

Cause

A fungus which produces spores that need a moist environment to germinate, so most bad infections are in damper places.

Harm

Badly affected plants can be so weakened they are unable to withstand winter frosts.

Treatment

• Organic - remove and burn all infected leaves. Grow resistant varieties.

• Chemical - spray with a systemic fungicide at the first signs of an attack.