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Common bacterial blight in beans

Xanthomonas axonopodis var. phaseoli
  • Plant certified seed of disease resistant varieties from IITA
  • In high rainfall areas, plant in mid-January to avoid disease outbreaks.
  • Do not save and re-use seeds from previously infected fields as they carry over the disease.
  • Avoid movement through the field when plants are wet to prevent blight spread.
  • Remove re-grown beans after harvest because they are potential sources for the bacterial disease.
  • Plough after harvest to burry debris and encourage decomposition (note that, once the field is infected, the disease also survives in the soil)
  • Rotate with non-leguminous crops for at least 2-3 years to break the cycle of the disease.
  • Start checking two weeks after seedling emergence and weekly until pods form.
  • Check for signs of small water-soaked dark spots on underside of leaves and pods shortly after seedling emergence.
  • Check for narrow lemon-yellow ring around small necrotic lesion on both leaves and pods. Act when more than 4 rings on 5 to 10 out of 50 plants are found
  • Prevention is the most effective control measure for the bacterial blight disease. There are no known green direct control measures that can completely control bacterial diseases
  • There are no other pesticides than copper, which can be used against bacterial plant diseases. Thus, do not buy and spray fungicides as they will not work.
  • When using a pesticide, always wear protective clothing. Follow the instructions on the product label, such as dosage, timing of application, pre-harvest interval, max number of sprays, restricted re-entry interval. Do not empty into drains.
  • WHO class II pesticides might not be allowed in local IPM schemes.
  • Always consult recent list of registered pesticides (ZEMA).
  • Spray with Copper-based compounds such as copper oxychloride (COPPER OXYCHLORIDE 850g/l; CUPROZIN 35 WP; and others). This can help to some extent to manage bacterial blight, but it cannot completely control the disease. It is a multi-side action bactericide. Usually applied at 40 – 80 mg per 20 litre knapsack sprayer (2.4kg/ha), but double-check product label. Never spray more than 6 kg copper per ha per year !
  • WHO toxicity class II (moderately hazardous) but very toxic to aquatic organisms so don’t spray near water source. Pre-harvest interval (p.h.i.) 1 week; restricted re-entry interval (r.e.i.) 1 day after spray. When used too much, copper(II)-ions can accumulate in soil and water. It can burn leaves. Do not use during fruit set.
AUTHOR(S): Malumo Judith (Zambia Agricultural Research Institute, P/bag 7 Chilanga),Tel.: +260 977403035, email, Matthews Matimelo (ZARI), Henry Mgomba (MAL), Andor Kiss (NVI, SZIE)

PRODUCED BY: Plantwise

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