Occasionally something disgusting happens in the garden. When it does, even the bravest gardeners step back with a shudder. Right now – late May – spinach is getting nailed by leafminers. 
This tiny fly overwinters in the soil as pupa; once spring arrives they molt to the adult stage and emerge, looking for love. Females then lay masses of white eggs on the underside of spinach leaves (usually the older leaves).
At hatching, larvae tunnel into the leaves, munching their way under protection of the top and lower surfaces of the leaf. There can be several generations per year until the heat of mid-summer.
Sounds harmless, doesn’t it? Here’s the catch – those cute little larvae are maggots. 
Now, I like maggots; they’re misunderstood and often maligned. But these fellows are in my food and because they’re tunneling between the leaf layers, their frass (a nice way of saying ‘droppings’) stays in the tunnel with them.
Eeeewwww.
Before giving up on the spinach bed, nip this in the bud by scouting the leaves, looking for the egg masses. When you find them, crush them. If your leaves are already infested, pick, remove, and destroy them. Don’t make the mistake of thinking that picking the leaves and composting them will help – the maggots will continue to develop in the leaf regardless of whether it is on the plant or off.
Gardening after five 