Bacterial soft rot is commonly caused by Erwinia carotovora subsp. carotovora (synonym for Pectobacterium carotovorum subsp. carotovorum)or E. chrysanthemi (synonym for Dickeya chrysanthemi). The bacterial soft rot pathogens have very broad host ranges and can attack many vegetables including carrot, potato, cabbage, and lettuce. Infection generally requires a wound caused by heavy, wind-driven rain, hail, insects, or cut necks at harvest. Splashing water, aerosols, contaminated equipment and workers, and insects spread soft rot bacteria. Bacterial soft rot pathogens are commonly found in and easily disseminated by irrigation water. Erwinia spp. survive between onion crops in soil, crop debris, and pathogenically on other crops.
Bacterial soft rot symptoms often appear as a soft, watery rot of individual scales that may advance and rot the entire bulb. A foul-smelling viscous fluid oozes from the neck when infected bulbs are squeezed. In the field, the youngest leaves or the entire foliage of affected plants appear bleached and wilted. Yield losses can be significant in the field and storage.
No biological control strategies have been developed for bacterial soft rot.
Practice a three-year or longer rotation to nonhosts such as small grains. Avoid reuse of irrigation tail water and overhead irrigation. Prevent bruising and wounding of plants and bulbs during field operations, harvest, and handling. Control onion maggots and other insects that can vector soft rot bacteria. Sever all roots during lifting to promote rapid drying of foliage and necks before topping. Cure bulbs with abundant ambient air until necks are completely dry before storing bulbs at 32 to 36ºF and 70% or less relative humidity.
Copper bactericides provide some bacterial control in Colorado when applied before disease is observed. Sprays should be initiated two weeks before bulb initiation, and continued on a 5 to 10 day spray interval depending on weather conditions. Apply in a sufficient volume of water to ensure thorough coverage. Include a low rate of a non-ionic surfactant to further improve coverage.
Copper tolerant strains of the pathogens are common in the U.S. Tank mixing copper bactericides with a low rate of an EBDC fungicide such as maneb is essential for effective disease suppression. Tank-mixing coppers with zinc or iron can also enhance their activity.
Product List for Bacterial Leaf Blights; these may reduce Soft Rot:
|
Pesticide |
Product per Acre |
Application Frequency |
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 78.9 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 |
|
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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. |
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Categories: Onion, Disease, Bacterial Soft Rot
Date: 04/01/2007