Russian wheat aphid can't be eradicated

A toxic pest that's been found in South Australian cereal crops cannot be eradicated, agricultural authorities say.

The Russian wheat aphid, which poses a major threat to the state's $1.6 billion grain industry, has been found at a number of sites in SA's mid-north - the first time it has been reported in Australia.

State and federal agricultural bodies have conceded they're unable to eradicate the pest and will focus on early detection and management.