Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.

sap

Aphids are sap-sucking true bugs. They range in size from 1 to 7mm (¼in or less) long. Some aphids are known as greenfly or blackfly, but there are species that are yellow, pink, white or mottled. There are more than 500 aphid species in Britain. Some feed on only one or two plant species, but others can be found on a wide range of plant hosts. Many have lifecycles that involve more than one host plant. Almost any plant can be a host to aphids, including ornamentals, vegetables, fruits, greenhouse plants and houseplants. More information on aphids. 

The presence of rose root aphids is usually only detected when bands of the shiny black 1-2mm long eggs are found at the base of rose stems in the winter months. The female aphids which are brown, are sometimes found above ground in late summer and autumn when they lay eggs. The aphids feed on rose roots but appear to cause little damage. They are often associated with ants, colonies of the aphid sometimes form on the base of stems, ants often cover these above ground colonies in a column of soil.

Rose root aphid, although not uncommon, is somewhat irregular in its occurrence. A plant can be heavily laden  with eggs in one year and then in the following year there is no sign of eggs.

If it were not for the habit of laying eggs on the stems it is likely that this insect would go usually unnoticed, since it seems to have little impact on the plant's growth and so management interventions are usually unnecessary and it should be accepted as part of the biodiversity supported by roses.

Non-pesticide control

• This aphid can normally be tolerated and even welcomed as part of the biodiversity roses can support
• Aphids provide food for a wide range of other animals. Encourage aphid predators in the garden, such as ladybirds, ground beetles, hoverflies, parasitoid wasps and earwigs. Be aware that in spring aphid populations often build up before natural enemies are active in sufficient numbers and then give good control
• If causing concern eggs can be destroyed when found. On some roses, such as bush types, it is  possible to reduce the number of overwintering eggs during winter pruning

Pesticide control

Pesticide control for this aphid is not necessary as it does not usually affect the vigour of roses. None of the insecticides available to home gardeners will kill eggs and they will be ineffective against the aphids feeding on roots. 

The rose root aphid, Maculolachnus submacula spends much of the year below soil level where it feeds by sucking sap from rose roots. During the autumn, females emerge from the soil and climb a few cm up the stems before depositing their eggs. These eggs hatch during March. Although the small, dark brown aphids may linger for a while on the stems, it is not long before they move down into the soil.

Although not uncommon the rose root aphid is somewhat irregular in its occurrence. A plant can have many eggs in one year and then in the following year there is no sign of eggs. As with many other root-feeding aphids this species is closely associated with ants when it is in its root-feeding phase. It is possible that if a nearby ant nest dies out or moves elsewhere then the fortunes of the aphids will also decline.