CARROT & PARSNIP
MOTLEY DWARF VIRUS - The central leaves show a distinct yellowing, and the outer leaves take on a red tinge. The virus is spread by the carrot-willow aphid. Growth is reduced, and the yield is dramatically cut down. No treatment is available, and the only prevention is to keep young carrots free from aphids by spraying with a pesticide (such as permethrin, heptenophos or pirimicarb), or to grow a more hardy variety (hence we've gone back to AUTUMN KING variety)
CARROT FLY - The tell tale sign are red leaves that wilt in sunny weather. At later stages, the leaves take on a yellow tinge. This pest attacks mainly carrots, but will also go for parsnips and celeriac. Seedlings are killed, and mature roots are riddled with holes, and eventually rot. Attacks are worst in dry soil. No treatment is available once an attack has started. Try to grow carrots well away from tall plants, and sow thinly, ensuring all thinnings are destroyed. If carrot fly are a known problem in your area, lift the early crops no later than mid August, and delay the main crop sowing until late July-early August. Then lift them as soon as they are big enough.