Soil treatment for plant disease control by K. M. Golam Dastogeer
STUDY OF SOIL TREATAMENT FOR PLANT DISEASE CONTROLSoil treatmentIt is the process by which soils are treated with soil treating chemicals by mixing soil up to a depth of 10-15cm front tile soil surface of by any physical or biological agents to prevent germinating seeds and theseedlings from the attack of soil-borne pathogens.ObjectivesThe objective of soil treatment is the differential destruction of soil-borne phylopathogenic fungi, bacteriaand nematodes to prevent germination failure of seeds and infection of seedlings without disturbing thenatural 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 treatmentThe above mentioned methods are not practiced in our country but the following practices are commonlyused 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 methodsi) Soil drenching ii) Furrow application iii) Broadcast iv) Fumigation v) Ball placementC. Biological methodThe 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 beforeor after plants emerge. Certain quantity of fungicide suspension is applied with a sprinkler per unit area sothat the fungicide in general reaches a depth of a least10-15 cm. This method is followed for controlling
damping off, root rots, or any kind of infections at the ground level.2. Furrow applicationFungicides are applied either as dusts, granules or with water to the furrow at the time of planting followingthis 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. Thismethod is suitable for the crops planted in furrows such as potato arid sugarcane.3. BroadcastNon-volatile fungicides are mixed with soil or fertilizers and broadcast on the soil surface. Dust, powdery orgranular fungicides are generally applied by this method. Light ploughing or harrowing is applied to mix thechemical in sufficient depth after broadcasting. In this method involves consumption of greater quantity offungicides than other methods and is applicable where suitable implement/equipments for properapplication of fungicides are rot available.4. FumigationSoil fumigation, is usually done to control soil-borne fungi and plant parasitic nematodes. The chemicalsused for this purpose are usually volatile and on corning in contact with soil moisture releases gases whichdiffuse in the soil and kill the larvae of the nematodes and fungi. Some impervious cover, like thinpolythene sheet, which confines the gas to the soil for a limited period of time is required. Application ofthese highly toxic volatile substances is recommended some days or weeks before actual planting of thecrop. This method is usually restricted to small areas and high value crops. Since the diffusion is restrictedto certain distance the chemicals are injected into soil at regular distance (12-15 inches) all over the fieldand the depth of application is kept at 6-9 inches.Some soil treating chemicalsA. 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 chemicalsi) Copper fungicides ii) ZnO iii) PCNB iv) Dithio carbamate v) salt of Ca etc, vi) cheshunt compound.Types of soil treating chemicals
Soil treating chemicals are of types depending on their chemical naturea. 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 afteremergence e.g. Copper fungicides, Organomercurials, Dithiocarbamates, PCNB, nemagon etc.Soil treatment with formation solutionGenerally soil can be treated with 3-5% formalin solution. There is a thumb rule of application of formalini.e. one gallon of formalin (40% HCHO) added in 50 gallon of water to prepare 50 gallon of spray solutionsfor 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 bedSmall sized seed beds (4 x 2.5 m Z) were prepared on the surface of the soil at equal distance. Then thechemical was applied / drenched on the soil surface and mixed with soil properly. It was then compressedby hand press and covered by a polythene paper for 48 hours. Then the polythene sheet was turned outand spading the soil. The soils were then loosed and exposed to the environment for the removal of toxicbases. After 7 days, the seed beds are ready for sowing seeds.2. Treatment of pot soilFor experimental purpose in the laboratory soil was collected from the field. The clods were broken andstables were removed. Then the soil was spread on a brown paper and the approximate volume of the soilwas determined by measuring tape. Then, 500 ml of 4-5% formalin solution was mixed with cft soiluniformly. Finally the soil was kept in the pot and was covered with a plastic sheet for 48 hrs to retain thegases within the soil. After 7 days, the treated soil will be ready for use.