Disease management cost accounts for over 45% of the total production cost. In pepper ( which include bell pepper “Hoho-bell pepper and pili pili-hot pepper”) farming as in any other farming enterprise, understanding common bacterial diseases will help the farmer equip with necessary less costly disease prevention skills as well as increase his production.
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Bacterial Canker
Causal Agent:
Clavibacter michiganensis subsp. michiganensis
Symptoms:
- Symptoms of bacterial canker in pepper include leaf and fruit spots and, less frequently, systemic wilt.
- In localized infections, symptoms first appear as small blisters or raised white spots on leaves and stems. Later, the centres of the leaf spots become brown and necrotic and develop a white halo.
- Stem lesions often develop a crusty appearance and elongate to form cankers. Symptoms on fruit first appear as very small, round, slightly raised spots.
- These spots gradually increase in size and may develop a brown centre and a white halo. When these are numerous, spots merge and take on a crusty appearance. In systemic infections, a gradual wilting occurs followed by plant death.
Conditions for Disease Development
- The bacterium enters the plant via wounds and stomata. Clavibacter may be seed-borne and may infest the seed externally or under the seed coat.
- High relative humidity and daytime temperatures between 25° and 30° C (77° and 86° F) generally favour the disease.
- Dense plant populations and overhead irrigation also provide an ideal environment to spread the bacterium. Insects, tools and human contact may also aid the spread.
Control
- Sow only tested seed and certified transplants. Do not transplant peppers into the ground used for tomatoes during the previous season.
- Clean cultivation equipment before entering a new field, avoid entering fields when foliage is wet and incorporate plant debris immediately after harvest to help reduce losses.
- Never harvest fruit from symptomatic plants. Rogue all symptomatic and adjacent plants. Rotate to a non-host for a minimum of three years if the disease is found in a field.
Bacterial wilt
Causal Agent:
Ralstonia solanacearum (synonym = Burkholderia solanacearum, Pseudomonas solanacearum)
Distribution:
Worldwide in the tropics, semi-tropics and some temperate regions
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Symptoms:
- In tropical and subtropical regions, affected plants may wilt and die within days of infection. Leaves may appear healthy or only slightly yellow prior to plant death.
- Under temperate conditions, infected plants develop slower, progressive wilt in which leaves turn yellow.
- The lower stems of affected plants develop dark, vascular browning that often extends into the cortical and pith tissues.
- When stems of symptomatic plants are cut and placed in water, milky-white streams of bacteria flow from cut ends.
Conditions for Disease Development
- Ralstonia solanacearum is soilborne and can survive for long periods in the soil on roots and debris.
- The bacterium infects roots through wounds caused by nematode feeding, transplanting and cultivation.
- High temperatures and high soil moisture generally favour the disease. Bacteria is spread in irrigation water, diseased transplants and in soil moved with cultivation equipment.
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Control:
- When possible, avoid land with a history of Bacterial Wilt.
- Commercial pepper and eggplant varieties with intermediate resistance to Bacterial Wilt are available. Resistant rootstocks are also available.
- A soil pH between 5.5 and 7.0, good soil drainage and raised beds to help alleviate disease pressure. Rotate to non-host crops in order to lower the population of bacteria in the soil.
Bacterial Spot
Causal Agent:
Xanthomonas euvesicatoria (synonym: Xanthomonas campestris pv. vesicatoria) X. vesicatoria, X. gardneri
Distribution:
Worldwide in warm, humid areas
Symptoms:
- Symptoms develop on leaves, stems and fruit of sweet pepper and are less severe in hot pepper.They first appear on leaf undersurfaces as small, irregular, water-soaked areas.
- Later, lesions enlarge, turn dark-brown to black with a pale tan centre and may develop a thin, yellow halo.
- Generally, lesions on upper leaf surfaces are slightly sunken, and those on lower leaf surfaces are slightly raised.
- Leaves that are severely infected often turn chlorotic and appear ragged.
- Defoliation occurs under heavy disease pressure.
- Stem lesions appear as narrow, light-brown, longitudinally raised cankers.
- Fruit spots begin as water-soaked areas that later turn necrotic. These spots are rough in appearance and crack as they develop.
Conditions for Disease Development:
- Xanthomonas is seed-borne on the seed surface and within the seed.
- Infected seeds and transplants moved over long distances can be the initial source of inoculum for epidemics.
- The bacterium also survives in crop debris, volunteer plants and in solanaceous weeds.
- High relative humidity and heavy dew formation on leaves, together with warm weather, favour infection and development of Bacterial Spot.
- The bacterium is readily water-splashed from infected transplants or debris to healthy plants.
- Fruit are infected through growth cracks, abrasions, insect punctures and other wounds. Secondary fruit rots often develop around Bacterial Spot lesions during damp weather.
Control:
- Use only tested and treated seed and certified transplants.
- Once present, the disease is difficult to control. Commercial varieties with one or more genes for resistance to X. campestris pv. vesicatoria are available.
- Copper-based sprays can help reduce the rate of disease development.
- Clean cultivation equipment before entering a new field, avoid entering fields when foliage is wet and incorporate plant debris immediately after harvest to help reduce losses due to Bacterial Spot.
- Rotation to non-host crops and controlling weeds and volunteer plants are good preventive practices. When the disease is present, avoid overhead irrigation.
Bacterial stem & peduncle canker (soft rot)
Causal Agent:
Pectobacterium carotovora, P. atrosepticum, Dickeya chrysanthemi
Distribution:
Worldwide
Symptoms:
- This disease affects pepper stems and fruit.
- Internal discolouration appears on the stem, followed by hollowing out of the pith and wilting.
- As lesions expand along the stem, branches break. Foliar chlorosis and necrosis may also develop.
- Symptoms of post-harvest decay start as sunken, water-soaked areas around the edge of wounds or on the stem end next to the peduncle.
- These areas may be light or dark and become soft as they rapidly expand. Often, the epidermis splits open, releasing watery, macerated tissue.
Conditions for Disease Development:
- Soft rot bacteria are common inhabitants of soils.
- Under warm, humid conditions, infection through wounds or cut stems occurs.
- Splashing rain and irrigation water spread bacteria to foliage and fruit.
Control:
- In greenhouse operations, provide adequate air circulation to help reduce relative humidity.
- Avoid injuries to plants during the growing season and on fruit during harvest.
- Improved sanitation in the field and in packing houses is effective in reducing losses.
- All harvesting equipment, the packing line and packing boxes should be sanitized frequently.
- Dump tank water and packing line washers should maintain a minimum available chlorine concentration of 150 ppm at a pH of 6.0 to 7.5.
- Wet fruit should be dried promptly before packing and then cooled quickly to below 10° C (50° F).
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Reference: Seminis disease guides
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