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What is it?
Onion maggots are of the hylemya antiqua species and cause onion plants to grow slowly, become weak and eventually die off. Maggot infested onion bulbs are often hard to discern, so unless you treat plants effectively, you may plant infected onion bulbs the following growing season and have your onion plants once again infested by onion maggots. These maggot larvae are one of the most dangerous and persistent pests to onion plants.
What does it look like?
Hylemya antiqua species onion maggots tend to by fat white maggots which grow to be approximately 1/3 inch long. Usually if you see them it is because you have sliced open an onion bulb. Onion maggots burrow in through the onion skin to the center of the onion bulb. It is there that they feed. Your onion plants may show signs of onion maggot infestation if you notice burrow holes in them, or if the onion plants start to slow growth. Often the plants will turn yellow and begin to wilt. If this occurs they will eventually die as they are being weakened from the inside. Once an onion plant has been infested with onion maggots of the hylemya antiqua species they must be discarded and destroyed.
How does it manifest?
Onion maggots prefer cool, wet weather and it is under weather conditions like this that onion maggot infestations can become severe. Onion maggots over winter as pupae in the soil, on fallen plant debris that was not cleared away after the harvest, and inside onion bulbs. In the spring when winter thaw begins, onion maggots commence feeding and emerge as adults. Adult onion maggots tend to be brownish or greyish in color. Adult onion maggots lay their eggs at the bases of onion plants in small clustered groups. These groups of eggs then hatch and the onion maggots burrow quickly into the soil where they then burrow into the onion bulbs themselves and begin feeding. Once they are done feeding, they pupate in the soil, bulbs or plant debris and emerge to start the cycle of reproduction once again. Typically a garden can be plagued by up to three generations of onion maggots attacking the onion plants each year. Often an unthought of source of onion maggots are those maggots which have over wintered in onion bulbs in storage, only to emerge and affect new plant growth in the spring.
What can you do about it?
Once you find damaged or onion maggot infested onion plants you will need to destroy and discard all infected onions. Be sure that you carefully clear and destroy all fallen plant debris from the garden around your onion plants after harvesting the crop. Prior to planting onion plants you can treat the soil where you intend to plant with an insecticide containing diazinon or chlorypirifos, which will help to reduce infestations. Additionally, always be sure to check onion bulbs for any burrow holes prior to planting them in the soil of the garden.
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