I am having a problem with root maggots in my garden. They have all but destroyed my cabbage and brussels sprouts. They also have infested my onions. I cut a small potato in half, and skewered each half on a stick. I then buried the potato halves in different parts of my garden. After 3 days, I pulled the potato halves up and examined them. I found one root maggot on one half and 3 root maggots on the other. The potato halves were buried too deep for a fly to lay eggs. Unless the potatoes carried fly eggs, the maggots must have hatched from eggs in my soil. Did I till-in fly eggs that overwintered near the surface? Did the fly eggs come with the composted horse manure that I tilled into my soil?
What Is the Source of Root Maggots in My Garden
Certified GKH Gardening Expert
Yes, the eggs likely overewintered in the soil. Here is more information that should help with their control: https://www.gardeningknowhow.com/plant-problems/pests/insects/root-maggots.htm