Onion Troubleshooting Guide
• Pink Root: Symptoms include onions that are underdeveloped and that have discolored roots. The roots often start to rot and have a pinkish tone. This disease is caused by a fungus in the soil. The fungus is usually brought home on young plants so make sure to inspect all onion sets and seedlings for evidence of discoloration on the roots. Look for onions certified against pink root. PRR indicates pink root resistance. Rotate your crops frequently to avoid problems with this and other soil borne diseases.
• Rot: This problem occurs when onions rot quickly when placed in storage. Improper removal of the onion neck can expose your crop to fungal diseases growing in the soil. Make sure to remove the tops when they are completely dry. Letting the tops of the onions dry out completely after cutting will also help to prevent this problem. Do not store your onions too close together after harvest. You can also use a natural fungicide in the soil to prevent rot and other soil borne diseases.
• Purple Blotch. The symptoms of this fungal disease are a purplish discoloration on the leaves. This disease is not spread from the soil. It most often affects plants during extended periods of high moisture levels and it spreads from plant to plant through the air. This disease can cause stunted bulb growth and bulb rot when the plants are harvested and stored. Try an organic fungicide to counteract this problem.
• Tip die off: Symptoms of this fungal disease include browning tips which begin to rot and die off. Pink root causes similar symptoms. Alternaria is the fungus often responsible for this problem. You can deal with Tip die off by asking your nursery for resistant varieties. Also check to see the soil conditions and your watering frequency. A well draining soil is important to prevent this disease.
• Thrips: Thrips are a common insect that attack onion plants. Symptoms of thrips include graying leaves and the presence of tiny yellow to dark colored insects. Try out a natural or organic insecticide to kill off thrips and other insects.
• Root Maggots: Problems with root maggots often occur above 40 degrees north latitude. Root maggots cause rotting at the base of the onion. Beneficial nematodes are useful for controlling this problem. Please see this website from a professional extension agent for more information on root maggots.
• Bent, Broken Onions: If the leaves of onions are accidentally bent over or crushed before the onion bulbs are properly formed, the bulbs may cease to grow. This will cause problems with storage. While you can still use these onions, they will not be of the best quality and are definitely not recommended for selling.
• Bolting: Bolting occurs when your onions send up flower stalks. This is often caused by rapid changes in temperature. The change in temperature is a signal to the plant to go to seed, thus the onions begins to send up a flower stalk. If you see flower stalks emerging from your onions, harvest them immediately. Unfortunately, onion bulbs will not grow any larger once they bolt. Another problem is that the flower stalk comes from the center of the onion bulb. Therefore, you should eat these onions quickly as they do not store well after bolting. Pick the proper onion variety for your area and you should avoid most problems with bolting.