some people and books say you can intercrop carrots and onions so that cancel out each others fly menaces, but if you look on a crop rotation, carrots are roots and onions come under the same umbrella as legumes and 'others', so its awkward, but I tend not to plant them together.
Lat year, being clever, I tried to remember to plant successionally, so on each row of carrots, I planted half the row with carrots and the other half with parsnips, then a week later, did another row etc. Only problem was, although I had more carrots than I did before, I only got about a dozen prasnips growing on an 8ft square piece of ground!!!!! lol
