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The presence of large numbers of shiny black rose root aphid eggs on rose stems can cause concern, however the activities of the root feeding insects rarely damage plants.
Rose root aphid (Maculolachnus submacula>) on Rose (Rosa sp.)
Aphids, also known as greenfly and blackfly, are sap-sucking insects. There are several species that occur on roses in Britain. The small brown rose root aphid feeds during the summer months on rose roots and occasionally on stems close to the soil surface. Rose root aphid overwinters as shiny black eggs which can cover areas of rose stems.
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 and 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 infested 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 control is usually unnecessary.
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 are will also 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 be heavily infested with 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.
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