Associated Problems and Pests in Growing Onions

If you have planted onion sets, then you shouldn’t worry too much about pests and diseases associated with onions.  If you started from seeds, that’s a different story.  An experienced gardener would know what to do.  But if you’re a newbie, you might lose your harvest if you do not know what your enemies are.

Onions Root Maggots

These small, white worms just a third of an inch long affect the bulbs of the onion.  Adult maggots have a brown or grayish color with wings and they burrow in the soil right into the onion bulbs.  They proliferate especially during wet years.

To control these vermins, you can spray the onion leaves with malathion.  You can also use diazinon.  However, make sure to check for proper pesticide use with your county agent.

Pink Root

Like the name says, this condition affects the roots of onions.  You would know your onions have pink when their roots take on a pinkish hue that slowly turns to purple.  If you let it go on, it could mean a greatly reduced harvest because onion plants can die of this.

To control pink root, make sure you start your onion-planting in soil sterilized with vapam, especially if the problem is acute.  Also remember to rotate crops to get rid of problems such as pink root.  Fumigation will also help.

Neck Rot

Another problem associated with onions is neck rot.  How would you know your onions are suffering from this problem?  You would notice the neck of your onion – that area right between the bulb and the foliage – turn yellow.
Gray molds would appear between the scales of the bulb.  This often happens right before harvest time.

To control neck rot, avoid injuring the bulbs and using too much nitrogen fertilizer.

Sour Skin


A disease that affects onion bulbs, it is characterized by the yellow-brown color of the onion’s inner scales.  It would also become slimy to the touch and would begin to rot.  However the exterior of the bulb including its core will remain firm.


To control sour skin, do not use overhead sprinklers on your onions.  Harvest them the moment they reach maturity and dry them quickly.

One Response to “Associated Problems and Pests in Growing Onions”

  1. Daryl Bye says:

    We planted onion sets 2months ago (we live in the Algarve). The onions have grown well, however, the onion bulb is very small with the onion neck about the same diameter. We appear to have what I call straight up and down onions that do not become any larger in diameter at the root (onion) end. The onions to look at appear very healthy and green but we are concerned that we don’t have any real onions at the business end. Any advice would be very welcome.