By Bhabesh Dutta, Ph.D.
Diseases of onion can be difficult to distinguish. But the more familiar you are with the symptoms, the easier they become to recognize.
Below are five photos of diseases of onion, along with some key information about each. Can you identify the disease?
- The symptoms of this disease, the color of a ripe banana, are mainly due to a toxin produced by an ice-nucleating bacterium, and remission of symptoms frequently occurs under higher temperatures. This disease has only been reported from Georgia and prevalent during the cooler months of January and February.
- Bacteria causing this post-harvest disease produce a vinegary odor, primarily rot outer scales of the bulb and survive in the soil. This disease is prevalent in all onion growing regions of the U.S., and management is primarily based on crop rotation and copper-based spray.
- This disease is caused by a distinctively yellow, gram-negative, aerobic bacterium that is primarily seed-borne. Initial symptoms are small, chlorotic spots or lens-shaped lesions with water-soaked margins. Lesions enlarge into long chlorotic streaks and large greasy, water-soaked areas. Severe infection can result in reduced bulb size.
- This disease is characterized by a variety of symptoms with one of the most distinctive being a collapse of leaf tissue displaying protruding veins and dark green, almost black discoloration. It causes a soft rot in the bulb, which is fluorescent under UV light. The disease is favored by cool and wet conditions. The primary source of inoculum for this disease is weeds.
- This bacterial disease derives its name from the location where symptoms occur on the leaves and in the bulb. The bacterium can survive on weeds, in seed and plant debris, and can be transmitted by thrips.
Answers:
1. Yellow bud of onion
2. Sour skin of onion
3. Xanthomonas leaf blight or bacterial blight of onion
4. Bacterial streak and bulb rot of onion
5. Center rot of onion
This material is provided courtesy of Bhabesh Dutta, Ph.D., Assistant Professor and Extension Vegetable Disease Specialist at University of Georgia.
