All about potatoes.pdf - Vegetableipmasia.org

10.
MAJOR POTATO DISEASES
Management
Bacterial wilt cannot be controlled with fungicides, and bactericides are seldom
available to farmers and generally very expensive. Management principles for
bacterial wilt are as follows:
• Remove sources of disease from the field by:
o Planting potatoes in soils free from bacterial wilt.
o Using healthy seed not infected with bacterial wilt.
o Rotating potato crops with other non-solanaceous crops. Good practice is to
rotate potatoes with corn or sweetpotato. In fields with serious infections, it is
best to plant non-host plants for more than 2 years, as agents of bacterial wilt
can survive in the ground without host for that amount of time.
o Removing infected plant debris before planting and clearing weeds away
before planting, while plants are growing and at harvesting time.
o Using composted organic fertilizer not infected with bacterial wilt.
o On heavily infested soils, apply brassica residue based biofumigants.
• Inhibit the development and spread of bacterial wilt in the field by:
o Putting dolomitic lime on the soil around infected plants as this increases soil
pH, creating a less favorable environment for the pathogen..
o Carefully managing irrigation in the field by digging channels that allow water to
flow freely from the field. Bacterial wilt will spread rapidly in flooded fields. Also
when watering the field, try to make sure water does not flow over the surface
of the field.
o Using water not contaminated with bacterial wilt to irrigate the crop.
o Cleaning the field by destroying (burning or burying) plants and tubers infected
with bacterial wilt throughout the whole season.
o Cleaning farming tools after use.
Observation methodology
You can begin making field observations for bacterial wilt at 35 DAP by looking at
symptoms on affected plants. Identifying an infection as bacterial wilt can be done by
using the following methods:
• Testing plants with vascular flow test – This will determine whether plants with
symptoms of wilting are infected by bacterial (and not fungal) wilt. Cut 2-3 cm
lengths off stems at the base of plants showing signs of infection. Suspend these
pieces vertically in water and leave for a while. If the plant is infected with bacterial
wilt, milky threads of bacterial ooze will flow from the stem pieces into the water.
• Testing tubers – Cut a sample tuber near its base, leave it for a few minutes, or
squeeze it. If it is infected with bacterial wilt, it will exude a thick white fluid.
• Testing soil with bioassay test – Three-week old tomato seedlings grown on BWfree
substrate and several soil samples suspected of infection are used for testing.
Put the soil samples in pots and water them with clean water. Plant five tomato
seedlings in each pot, and tend them for one or two months. Make observations
by looking at symptoms that appear on each of the plants in the pots. When wilting
appears, test the plants with vascular flow tests. Wilting plants that exude a milky
flow in the vascular flow test are proof that their pots contain infected soil. You can
also do this test to determine if manure contains bacterial wilt.
10.1.2 Blackleg or soft rot
Blackleg or soft rot is a widespread disease caused by the bacterium Erwinia spp.,
which affects stems and tubers particularly in warm and humid regions.
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ALL ABOUT POTATOES