I have had little or no insect damage to common onions over nine years or so. Without insecticides.

Have you had a serious problem or are you speculating?

For the past couple of years, I haven't even bothered trying to grow common onions because of the onion maggots. The thrips I can probably overlook since they generally only bother the onion greens while the onion maggots destroy the bulbs as they start to swell.

Before a couple of years ago, I had been trying to grow onions for several years in small trial beds (approx 5'x10'), trying different varieties and different methods to prevent bug damage. The best crop I got, which was over 50% damaged, was grown under a row cover and was sprayed about once a week. I only have this problem with common onions and shallots. I can grow leeks, garlic, ramps, egyptian onions, potato onions, and chives with basically no bug problems whatsoever.

I've been told that a large percentage of onion maggots have built up a resistance to insecticides, so I figure that it's not really worth it to spray. I've also been told that my problem may be due to the fact that I live near a lot of water. Within half a mile, there is a large wetland, a lake, a river, and a brook. All that water is quite nice for growing vegetables, but maybe not onions.

-Nick

Wow. I've never heard of such a problem on small-scale gardening. Are you using fields that were agricultural recently? Is there large-scale commercial onion growing nearby? Both seem rather unlikely in ME, I guess.

I can't imagine what wetlands would have to do with it, unless your ground is heavy and wet as a consequence. In which case, one would expect problems with other crops as well.

How about a trial plot with very different soil? A raised bed of sand mixed with compost, for instance.

The use of beneficial nematodes has allowed a 99% maggot free onion crop. While expensive they only need be applied every 2 or 3 years. They also allow growing spring turnips and radishes as well as setting brocolli w/o tarpaper squares.