All signs
Soft clusters on growing tips and leaf undersides; sticky honeydew; curling leaves; sooty mould follows. Early warning: ants running up plant stems in spring almost always means a colony is already present. Heavy persistent infestations can also indicate over-nitrogen feeding: high-N sap is more attractive to aphids.
Organic control
Blast with a strong hose; soap spray on leaf undersides; cut off and bin infested tips; place a piece of sweet fruit (watermelon, melon) nearby to draw ants away while you treat: ants protect aphid colonies and removing them makes treatment more effective.
Spray
Soap spray (2 tsp dish soap + 1 litre water).
