Soil treatment for plant disease control-A lecture note for L-4, S-1 students of Bangladesh Agricultural University, Department of Plant Pathology.

1. STUDY OF SOIL TREATAMENT FOR PLANT DISEASE CONTROL
Soil treatment
It is the process by which soils are treated with soil treating chemicals by mixing soil up to a depth of 10-15
cm front tile soil surface of by any physical or biological agents to prevent germinating seeds and the
seedlings from the attack of soil-borne pathogens.
Objectives
The objective of soil treatment is the differential destruction of soil-borne phylopathogenic fungi, bacteria
and nematodes to prevent germination failure of seeds and infection of' seedlings without disturbing the
natural balance necessary for biological activities in the soil.
Methods of soil treatment:
A. Physical methods
i) Heat treatment
ii) Hot water treatment
iii) Vapor treatment
iv) Electrical heat treatment
The above mentioned methods are not practiced in our country but the following practices are commonly
used by our farmers:
- Exposing soil to the summer heat by ploughing to reduce the soil- born inocula.
- Burning crop residues alter harve5tin- the crops to heat the soil surface for killing the
pathogens.
- Covering the soil with polythene sheet in small scale in the nursery to kill the pathogens.
For experimental purpose, sometimes soil is being treated by autoclaving.
B. Chemical methods
i) Soil drenching ii) Furrow application iii) Broadcast iv) Fumigation v) Ball placement
C. Biological method
The chemical methods that are practiced in our country are as follows:
Soil drenching:
Fungicides are made up with water at the definite concentration and applied to the soil surface either before
or after plants emerge. Certain quantity of fungicide suspension is applied with a sprinkler per unit area so
that the fungicide in general reaches a depth of a least10-15 cm. This method is followed for controlling

2. damping off, root rots, or any kind of infections at the ground level.
2. Furrow application
Fungicides are applied either as dusts, granules or with water to the furrow at the time of planting following
this method. This method requires less quantity of fungicides per hectare than the broadcast method.
Special equipment must be required for such application since manual application is never uniform. This
method is suitable for the crops planted in furrows such as potato arid sugarcane.
3. Broadcast
Non-volatile fungicides are mixed with soil or fertilizers and broadcast on the soil surface. Dust, powdery or
granular fungicides are generally applied by this method. Light ploughing or harrowing is applied to mix the
chemical in sufficient depth after broadcasting. In this method involves consumption of' greater quantity of
fungicides than other methods and is applicable where suitable implement/equipments for proper
application of fungicides are rot available.
4. Fumigation
Soil fumigation, is usually done to control soil-borne fungi and plant parasitic nematodes. The chemicals
used for this purpose are usually volatile and on corning in contact with soil moisture releases gases which
diffuse in the soil and kill the larvae of' the nematodes and fungi. Some impervious cover, like thin
polythene sheet, which confines the gas to the soil for a limited period of time is required. Application of
these highly toxic volatile substances is recommended some days or weeks before actual planting of the
crop. This method is usually restricted to small areas and high value crops. Since the diffusion is restricted
to certain distance the chemicals are injected into soil at regular distance (12-15 inches) all over the field
and the depth of application is kept at 6-9 inches.
Some soil treating chemicals
A. Volatile chemicals:
1. Chloropicrin @ 1 gallon/1000 square feet area
2. Methyl bromide u 2 (luid 03/square feet of land
3. Vapona @ 1 quart/ 100 square feet of land
4. Formaldehyde @ 1 gallon of 40% HCHO per cft.
B. Non-volatile chemicals
i) Copper fungicides ii) ZnO iii) PCNB iv) Dithio carbamate v) salt of Ca etc, vi) cheshunt compound.
Types of soil treating chemicals

3. Soil treating chemicals are of types depending on their chemical nature
a. Pre-emergence chemical: There are chemicals which are phytotoxic and can be used as pre-
emergence drenches e.g. Formaldehyde, Methyl bromide (MB), Chloropicrin, Vapam, Ehylene dibromide
(EDI3), D-D (Dichloropropane-Dichloropropane).
b. Post-emergence chemicals: There chemicals which are less phytotoxic and can be used after
emergence e.g. Copper fungicides, Organomercurials, Dithiocarbamates, PCNB, nemagon etc.
Soil treatment with formation solution
Generally soil can be treated with 3-5% formalin solution. There is a thumb rule of application of formalin
i.e. one gallon of formalin (40% HCHO) added in 50 gallon of water to prepare 50 gallon of spray solutions
for 100 cft soil up to a depth of 1 5 cm. It can be used for pot experiment or in the nursery.
Treatment of small seed bed
Small sized seed beds (4 x 2.5 m Z) were prepared on the surface of the soil at equal distance. Then the
chemical was applied / drenched on the soil surface and mixed with soil properly. It was then compressed
by hand press and covered by a polythene paper for 48 hours. Then the polythene sheet was turned out
and spading the soil. The soils were then loosed and exposed to the environment for the removal of toxic
bases. After 7 days, the seed beds are ready for sowing seeds.
2. Treatment of pot soil
For experimental purpose in the laboratory soil was collected from the field. The clods were broken and
stables were removed. Then the soil was spread on a brown paper and the approximate volume of the soil
was determined by measuring tape. Then, 500 ml of 4-5% formalin solution was mixed with cft soil
uniformly. Finally the soil was kept in the pot and was covered with a plastic sheet for 48 hrs to retain the
gases within the soil. After 7 days, the treated soil will be ready for use.