This year I have had terrible trouble with my Swiss chard, blotches all over the leaves which makes them look very unhealthy and distinctly unappetising. At first I thought the leaves had scorched, which can happen if the sun gets on them after you have watered. The water droplets act like a magnifying glass which concentrates the heat of the sun causing the leaves to scorch. That theory went out the window as I have some chard planted where the morning sun can’t reach them and they were watered after sunset.
Then I thought it might be slug or snail damage but there were no slime trails anywhere so unless they can transport themselves Star Trek style that was not the answer either.
I did wonder if it could be leaf miner but they were blotches rather than the normal tell-tale trails. Then I came across a website, British Leafminers that proudly informed me that there are over 400 different types of leaf miner which target different plants, deep joy. Sure enough there is a chard leaf miner, there is a huge list of plants that have their own leaf miners but you will need to know what the botanical name of what you are looking for is called. If you think you have leaf miners on your pumpkins you would have to look for ‘Cucurbita’ for example, if you don’t know the botanical name put the common name into Google or Wikipedia.
Leaf miner damage is normally easy to spot, it looks like someone has been doodling on you plant leaves with off-white tippex, almost like a maze. As in the photo I took of a weed on the left. They are in fact the larvae of moths and flies, the female makes a tiny nick in the surface of the leaf and lays an egg in it. When it hatches into a larvae it meanders around between the top and bottom of the leaf feeding as it travels.
When they are ready to turn into another moth or fly it can make a cone out of the leaf while it pupates. The only way to get rid of them is to remove any affected leaves and burn or put in the dust bin, do not put them in the compost or leave them laying around in the garden. There is no chemical quick fix.
The only way I know to prevent it is to cover the plants with fine netting. If you know of something else that will deter them please let us know.