HPIPM:Onion Pantoea Leaf Blight Center Rot
Author: Howard F. Schwartz and Michael E. Bartolo
Identification and Life Cycle
Pantoea leaf blight and center rot is caused by the bacterium Pantoea ananatis. The disease has been reported from Colorado, Georgia, and several other onion producing regions of the world. Infection occurs when bacteria are deposited in or on leaves by wind, water splashing, or thrips. The disease is favored by moderate to warm temperatures and rainfall at bulb initiation, and continuing through bulb development. P. ananatis can survive between onion crops epiphytically on weeds, on contaminated seed, and perhaps as a pathogen of melons.
Plant Response and Damage
Center rot can be a devastating disease when weather conditions favor the pathogen. Disease symptoms begin as necrotic, bleached areas on young leaves that typically wilt. An irregular border between healthy and infected tissue is often apparent. This leaf blighting continues and the pathogen progresses downward into the bulb, causing a soft rot. Affected bulbs have a pale yellow to yellow-orange decay and breakdown of one or more of the inner bulb scales. Secondary bacteria can also invade the bulb, causing a more watery decay and breakdown of the entire bulb. However, the center rot pathogen alone can cause a breakdown of the entire bulb interior. Under disease favorable conditions, yield losses may approach 100%.
No biological control strategies have been developed for Pantoea leaf blight and center rot.
Plant seed free from the center rot pathogen. Eliminate weeds, volunteer onion, and cull piles that may be a source of P. ananatis. Deeply bury crop residues after harvest to reduce pathogen survival. Avoid reuse of irrigation water and overhead irrigation. Disease tends to be more severe with furrow rather than drip irrigation. Avoid excess nitrogen, especially after bulb initiation and storm damage. Practice a three-year or longer crop rotation to non-hosts such as small grains. Avoid working in fields when the foliage is wet, which can easily spread bacteria throughout the field. Plant wider rows in the direction of prevailing winds to increase air movement in the crop canopy and decrease periods of leaf wetness. Varieties vary in their reaction to center rot, and highly susceptible varieties should be avoided. Thrips and onion maggots are known to transmit the center rot pathogen, and should be controlled. Harvest and store onions only after thorough curing in the field and packaging shed. Avoid wounding or bruising bulbs during harvest and storing operations. Store bulbs at 32 to 36ºF with a relative humidity of 70% or less.
Copper bactericides provide some disease control in Colorado under low to moderate disease pressure when applied before disease is observed. Sprays should be initiated two weeks before bulb initiation, and continued on a 5 to 7 day spray interval depending on weather conditions. Ensure thorough coverage by applying in a sufficient volume of water with a low rate of a non-ionic surfactant. Disease forecast models have been developed in Colorado that may improve spray timing and effectiveness.
Copper tolerant strains of the pathogen are common in the U.S. Tank mixing copper bactericides with a low rate of an EBDC fungicide such as maneb is essential for suppression of these strains. Tank-mixing coppers with zinc or iron also may enhance their activity.
Product List for Other Onion Bacterial Blights, these may provided some control of Pantoea Leaf Blight and Center Rot:
|Pesticide||Product per Acre||Application Frequency (days)||Remarks|
|Copper-based Fungicides—not all formulation listed|
|Champ DP||1.33 lb||7-10 days|
|Cuprofix||2.5-6 lb||7-10 days||Can be phytotoxic|
|Cuprofix MZ||5-7.25 lb||3-7 days||Maximum of 78 pounds per season; 7 day PHI|
|Kocide 2000||1.5 lb||7-10 days||Can be phytotoxic to leaves|
|Kocide 3000||0.75 lb||7-10 days||Can be phytotoxic to leaves|
|ManKocide||2.5||3-7 days||Maximum of 160 pounds per season; 7 day PHI|
|Nordox||2-4 lb||7-10 days|
|NuCop 50WP||2.0 lb||7-10 days|
|Top Cop with S||2-3 qt||7-10 days|
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.