Plantwise Factsheets for Farmers
Neem to support control of late blight in potato
Recognize the problem
is a fungus-like mould disease in potato that spreads fast in cool and humid weather.
Infected plants have necrotic areas on their leaves which wilt, bend
downwards, become weak and eventually die. Look for white cotton-like
surfaces on root necks after rains. Inside tubers, late blight causes
reddish-brown lesions or spots that have an unpleasant smell.
can cause complete field destruction. The disease spreads through leftover
plant residues from the previous crop. Affected plants and residues should be
buried deeply outside the field. Late blight is also spread by planting
infected tubers or by splashing during overhead irrigation. The most powerful
tool is the use of resistant varieties such as Avalance, or at least
moderately resistant varieties such as Kennebec, Sebago, and Allegany. Direct
control measures are difficult and often too late. Neem sprays have some protective
anti-fungal properties but will not help if most of the potato plants are
already infected. Neem trees naturally grow in Zambia, but commercial neem
products (Azadirachtin) can be bought from agro-input dealers.
Fresh leaves are collected
from neem trees that usually grow in your neighbourhood
- To grow your own neem
trees, seeds can be sourced from ZARI research stations such as Mt. Makulu
and Nanga, Zambia
- Pound the fresh neem
leaves in a mortar
- Soak 1kg crushed leaves in
5 litres of water for 24 hours. Mix well.
- Remove the crushed soaked
leaves from the water and squeeze to let the extract drain back into the
- The extracted solution is
sieved using a sieve or mutton cloth to get a clear solution for use in the
- Dilute the concentrated neem
solution with water in a 2:1 ratio
- Liquid soap (10 ml / 20
litres) is added to the solution to make the extract stick to the potato
The extract is applied
to the leaves to completely cover the plants using a sprayer or a broom. Spray
every 7 to 10 days if weather is wet and cool, but maximum three times.
The recommendations in this factsheet are relevant to:
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