Has eelworm invaded the overwintering onions?

You know how it is when it seems something might be amiss with a crop but you hang on in the hope that it was just a silly mistake and it will all blow over as soon as the weather improves. Some hope! We try to celebrate life’s rich tapestry as best we can but when push comes to shove a bit of ruthlessness is called for. These onions, (Autumn Champion, grown from sets), looked fine until a few weeks ago and then, just when they should have taken off, they began to show signs that something was wrong.  We had been careful because we previously lost a crop of leeks to allium leaf miner, and so they were covered with fine insect mesh from winter onwards. However, facts are facts and these onions looked sick.  It’s sometimes difficult for a non expert to diagnose these pests and diseases, but the effect on the leaves was very like leaf miner.  So that gave three possibilities – allium leaf miner, onion fly and eelworm. According to the books it’s a bit early for leaf miner, the mesh should have seen off the onion fly as well and so that left eelworm as the prime suspect. Whatever it was, the remedy was much the same – dig them up and burn them and then don’t grow alliums on the plot for three years.  The RHS rather loftily suggest that the ground should be left fallow, but our allotment doesn’t stretch into the blue remembered hills, and we can’t afford to leave a whole bed empty so we’ll probably try to kill any remaining eggs, cysts or pupae with the flame gun and then observe the rotation carefully.

It’s always sad to lose a crop, but we have the spring planted onions which appear to be OK, and the leeks, garlic and shallots are all alright too, so in a break in the rain and for fear of going stir crazy we went up and did the deed.  As we were pulling them out I examined them carefully to see if any further light could be shed on the problem, and most of the post mortems showed no signs of maggots or pupae, supporting the eelworm hypothesis.  However I did find a couple of plants with 2mm brown pupae that looked very like allium leaf miner – so it was an open verdict. Much as I hate any green material going off the allotment, I’m afraid this lot went straight to the tip. Just for reference or any further ideas I’m including a photo of the pupa and another plant.  Please don’t take this as a sign I know that much about plant pathology, I’m only one page ahead in the textbook!