Hi James,
Our Expert, David Williams, has responded with the following answer:
I assume that you are considering the ground cover spray as a way of controlling Woolly Aphid.  Confidor sprayed on the ground around the base of the tree should not affect the Aphelinus mali wasp unless it is active on the ground cover when you spray or feeds on nectar from the plants.  Spraying confidor onto ground cover plants will not do much by way of controlling wooly aphid. Confidor is usually applied for wooly aphid control as a “butt drench” where the chemical is applied around the lower part of the trunk butt and it seeps down to the roots where most of the over-wintering wooly aphids will be hiding. The wasp only parasitizes the wooly colonies on the aerial part of the tree and not the underground parts.  The wasp would normally not emerge until late October- November so doing the soil/butt drench before the aphid crawlers start working their way up the trunk in spring should not impact on the wasp.