How to control maggots in carrots and onions?

Is there something special, that need to be done to the soil, before planting carrots and onions.? And what do you use, to get rid of that problem during the growing season?

Onion maggot control

The adult of the onion maggot is a small fly about half the size of a housefly. The female fly lays her eggs at ground level on the base of the stalk of the emerging onion early in the spring. The egg hatches into the maggot, which is the destructive stage. The maggot burrows into the onion bulb which causes the plant to become flabby and begin to yellow. Small onion bulbs may become completely mined out by maggot feeding. In large bulbs the maggots eat out cavities which contribute to later rotting in storage.

Onion maggot control should be applied at planting time. An in-furrow application of Dursban Lawn and Garden Insect Control is an effective onion maggot control technique. A second lay-by treatment can be applied later in the season to protect larger bulbs that are left to mature for dry winter onions. For an organic method of control, sprinkle diatomaceous earth around transplants which you want to protect. The fine fossilized shell material has microscopic sharp edges that pierce soft bodies and causes them to dehydrate. Apply after a light rain for better effectiveness.

I am wondering if the diatomaceous earth treatment would work against carrrot weevils

For organic control methods, I understand diatomaceous earth works well against onion maggots, you should rotate the crop regularly and you can also use row covers to prevent the flies from laying their eggs in the onions.
For carrot maggots, I use grub nematode control, I spread it while the carrots are still young. You can also use yellow sticky traps placed near the carrot patch to attract the flies.

I've used nematodes for carrots...kind of pricey and not sure I got my money's worth.

Why do you think you didn't get your money's worth? I've used the nematode control will good results. I rotate my crops every year and I do try to pay attention to what's going on around the patch. I always inter plant with marigold, but keep them at a distance from the carrots I've treated.

Thanks, for the info, Paul and doccat, nice to know where that little dreaded creature comes from. They're not very appetizing. I'm not sure I can find nematodes here, but I know we can find the diatomaceous earth .
I had read marigold will keeps some insect away, but why not plant them near carrots?

Well, marigolds produce pyrethrins which kill nematodes. So if I'm using nematodes to deal with the maggots I don't want to kill off the beneficials. :) I've found over time, the flies are becoming less and less of a problem. As we work on improving the soil. We're going to try the Bokashi microbe mixture both on the soil and in our compost. It should increase not only the microbial activity but also increase the number of earthworms "working" the soil. It's all good. :) I should tell you I use only organic methods and have done so off and on for the last 25 years. I've got good soil, we've worked hard at that, but what I've read in the soil and composting threads have lead me to believe we can make it even better. We started with good old VA red clay, now I have black loam. ;)

Good to know about the marigold. Never heard of Bokashi microbe mixture. I try to good as organic as possible too.

Indy, you were expecting using "nuclear" results. I'll bet you had fewer channels than before, more production?
Check the soil and composting threads for more information on Bokashi, burn.

There are carrot cultivars with varying resistance to the carrot fly, Flyaway and ResistaFly spring to mind but there are 20 odd cultivars with varying degrees of resistance.

Most of mine were Kuroda.

Haven't been on this veg forum before, Will check out the Bokashi, thanks.

I hope I don't have the problem.