We were once inundated with armyworms, they multiply so fast! I still have no idea how they got into our fields but they quickly made it their home and they were very destructive to the soil and fed on most of our plants. We always maintained we'd have organic crops, and we lasted this way (with a lot of hard work) for about four years. When the armyworms came in, it highlighted a whole lot of other issues we had, including soil borne diseases. That explained the browning leaves!
After this debacle, we had to fumigate. As it turns out, it wasn't all that bad. I think we'd got so wrapped up in myths around fumigation that we were very misguided. If you're still having issues with armyworms, I recommend calling in a fumigation service. And if you're worried about it, like I was, this article should settle your fears https://www.leicesters.co.nz/soil-fumigant-myths/
