Halo blight is caused by the bacterium Pseudomonas syringae pv. phaseolicola. The pathogen can be found on the leaves of many plants, but only causes disease on a few hosts in the High Plains region. Infection occurs when bacterial cells are deposited onto leaves by splashing water, aerosols, or from contaminated seed, and multiply to form large populations. The bacteria gain entry into plants through natural openings and wounds. Infection occurs most readily during cool (less than 80ºF), wet weather, especially hard, wind-driven rains. Bacteria are disseminated within and among fields by splashing water, aerosols, and on contaminated equipment and workers. The pathogen survives between susceptible hosts in and on weeds, infested crop debris and contaminated seed.
Halo blight symptoms first appear as small water-soaked spots on leaflets. In a dry climate, this infected tissue dies and is tan-colored. A broad yellow-green halo develops around the spots. This broad halo helps distinguish halo blight from common bacterial blight which exhibits a narrow, lemon-yellow border around leaf lesions. Presence of the halo is absent under high temperatures. Systemic infection causes younger leaflets to curve and exhibit considerable yellowing on these leaves with no apparent dead spots or distinct halos. Halo blight symptoms on pods begin as water-soaked circular spots or water-soaked streaks on the pod suture. The bacterial ooze in the center of the spots appears light cream or silver colored. Early pod infection causes shriveled seeds. Stem girdling and joint rot occur above the cotyledonary node of plants grown from infected seed. The disease is most damaging during cool, wet weather, and can reduce both seed yield and quality
No biological control strategies have been commercialized for halo blight.
Plant certified seed of recommended varieties less susceptible to halo blight. Avoid overhead irrigation and reuse of irrigation water where possible. Avoid working in fields when plants are wet. Promptly and thoroughly incorporate infested bean debris into the soil after harvest, and rotate beans with non-host crops such as small grains for at least two years. Practice strict sanitation of weeds and volunteer beans early in the following season.
Antibiotic seed treatment and preventative bactericide applications can reduce spread of the halo spot pathogen, but chemical controls are most effective when integrated with sound cultural practices.
Product List for Halo Blight:
Pesticide |
Rate per Acre |
Application Frequency |
Remarks |
|
Copper fungicides: not all formulations listed |
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|
Basicop |
32-64 oz |
7-10 |
- |
|
Champ DP |
0.66-2.0 lb |
7-14 days |
Apply preventatively beginning when plants are 6”in height |
|
Copper Count N# |
64-96 fl oz |
5-10 |
- |
|
Cuprofix Disperss |
1.5-3.5 lb |
7-14 days |
Apply preventatively beginning when plants are 6”in height |
|
Kocide 2000 |
0.75-2.25 lb |
7-14 days |
Apply preventatively beginning when plants are 6”in height |
|
Kocide 3000 |
0.5-1.25 lb |
7-14 days |
Apply preventatively beginning when plants are 6”in height |
|
Nu Cop 50 WP |
1-3 lb |
7-14 days |
Apply preventatively beginning when plants are 6”in height |
|
Top Cop+S |
64 fl oz (37.1) |
- |
1 day PHI |
|
Tri Basic Copper# |
32-48 fl oz |
7-10 |
Maximum of 6 times |
|
Streptomycin: not all formulations listed |
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|
Agri-Strep 500 |
13 oz (6.6) |
- |
Slurry seed treatment (50,000 ppm) |
|
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: Dry Bean, Disease, Halo Blight
Date: 04/01/2007