Cultural plant disease control by Malek_h88

Cultural plant disease control :Cultural plant disease control

Cultural measures are mainly preventive Modify the environment that it becomes unfavourable for the pathogen development

The cheapest of all control measures

I. Preparation of planting material Resistant varieties .1 For pathogens, resistant to chemicals

Necessary to overcome the effects of the development of new races of pathogens

Certified seed .2 All of the major plant pathogens can be transmitted by seed or propagating material Certified material provide safeguard to growers Cleaning of seed .3 Many inactive or dormant structures of fungi are mixed with the seed Pathogens may be present in the dust accompanying the seed For cleaning use 5 per cent salt solution and after dry seeds

Heat treatment of seeds .4 Against pathogens either on the surface of seeds or inside them Such diseases are known as seed-borne (late blight of potato, smut of rice and (wheat, viruses

The pathogen of smut disease remains in the seed and shows its impact when the plant starts fruiting Hot water treatment (seeds are dipped in hot water for a limited time) and hot

air treatment

Proper drying and storage of seeds .5 If the seeds are not dried properly before storage they loose their germination capacity and also have several types of plant pathogen in them The fungus, causing downy mildew present in the seed when it is fresh, but when the seeds are thoroughly dried the fungus present in it dies Prolonged storage of seed also helps in eliminating several pathogens (If the storage of cotton seeds infected with anthracnose or wilt pathogen is prolonged (for two years, pathogen present inside the seed will die

Vegetatively propagated material .6 小ontaminated tools Tissue culture techniques may be necessary to obtain disease-free planting material (viruses and some fungi do not reach the apical meristems of their hosts until late in the development of the disease, so pathogen-free meristems can be tissue-cultured and used for vegetative propagation

II. Mixed cropping Mixed cropping The number of host plants is reduced, the disease cannot spread due to mixture of plants The roots of other plants may be a barrier for the movement of pathogens in the soil

The secondary crop plants may release some toxic substances from their roots which may suppress the growth of the pathogens attacking the main crop (sorghum plant roots exudates hydrogen cyanide which is toxic to Fusarium (udam that causes wilt Proper selection of crops for the mixed cropping can make soil environment unfavourable for pathogens. Growing cotton with kidney bean can control

.root rot of cotton by changing soil environment III. Destruction of crop residues Crop residues Crop residues-are suitable substrates for many pathogens, that is why burning and removal of postharvest crop residues are important cultural control If crop residues are buried, some potential pathogens may be either killed or inhibited in their development (many fungus require a food source near the (surface of the soil- verticillium wilt Fungal pathogens such as Sclerotinia and Claviceps (produce sclerotia ) can be controlled by burying surface soil Crop residues Burning the stubble of harvested cereal crops reduce the inoculum of Sclerotium oryzae (stem rot), Cercosportum gramineum and Pseudocercosporella spp Burning potato leaves after harvest reduces inoculum of Alternaria solani

((early blight Burning a l0 cm of the soil surface destroys nematodes (Burning of citrus trees infected with citrus canker (Xanthomonas citri Crop residues

Weeds are the alternate host of many pathogens (they carry over the pathogen

(from one season to another Alternate hosts are very important for many rust fungi (some rusts cannot

(complete their life cycles in the absence of alternate hosts

IV. Crop rotation Crop rotation Intervals between susceptible crops must be longer than the known survival period of pathogens Rotations are effective in controllingPyrenophora tritici-repentis, various Colletotrichum and Phoma spp, some pathogenic bacteria Less likely to be effective in controlling Pythium, Aphanomyces, Fusartum, Sclerotinia which can survive for long periods in the soil

V. Tillage Tillage Predispose pathogens to antagonistic effects of the microbiota Reduces populations of weeds Buries plant pathogens from the top soil into deeper layers of the soil where they cause less or no disease Influence nutrient release mechanisms of the crop (healthy plants are more ( resistant Reduce inoculum because of desiccation by the sun -

VI. Fallowing :Fallowing is of three types Dry fallowing - the field is kept dry for one season to kill the pathogen by starvation Wet fallowing - frequent irrigation is given during the fallow period (for some weeks); pathogen germinate in the soil which later dies due to lack of host plant Flood fallowing - pathogens die due to lack of oxygen

VII. Adjustment of sowing time Reduces the infection period of a pathogen to meet the susceptible stage of the host plant to the minimum Changing the date of sowing so that the susceptible stage of plant growth does not coincide with the environments highly favorable for the pathogen

VIII. Crop density Generally as the density of a crop increases, the incidence of disease also increases Plant densities can be manipulated by varying sowing or planting rates - increased rates may compensate for expected crop losses from pathogens IX. Intercropping Is more common for smaller farms The incidence of disease is often less in mixed plantings than in monocultures - propagules of pathogens can not successfully move from one host to another

X. Mulching Conserve soil moisture and organic matter and reduce soil Spread of soil-borne diseases can be reduced - layer of mulch on the soil surface prevent contact of bacterial and fungal propagules with leaves, flowers or fruits

XI.Flooding The primary purpose of flooding is to control weeds It also reduces the number of fungal propagules, insects and nematodes in the soil

May influence both the level of initial inoculum and the rate of diseases spread (flooding diseased cotton 'trash' for up to six weeks reduced the incidence of (bacterial leaf blight (Xanthomonas campestris pv. malvacearum Control nematodes

XII. lrrigation Irrigation can increase disease development Propagules of pathogens after drought begin to grow (dangerous in in areas where it is possible to grow two susceptible crops in the same field in one (year Irrigation water may contain propagules of pathogens which it carries from one place to another Free moisture remains on leaf surfaces (the longer leaf wetness periods (increase fungal spores germination Irrigation can reduce disease development Rewetting soil encourages the activity of micro-organisms that destroy sclerotia Can reduce or inactivate airborne inoculum by washing it out of the atmosphere

XIII. Fertilizers Fertilizers can decrease disease development Applications of zinc reduce the incidence of maize downy mildew Sulphur fertilization inhibits the occurrence of cercospora leaf spot Copper applications reduce take-all in wheat Nitrogenous fertilizers indirectly affect the spread of disease by modiffing crop environments - reduction in the incidence of Rhizoctonia solani following nitrogen fertilization is thought to result from stimulation of certain soil microorganisms which compete for nutrients Fertilizers can increase disease development -

Heavy applications of nitrogenous fertilizers increase in infection by obligate

parasites such as the powdery and downy mildews and rusts Phosphorus fertilizers (Reduce the incidence of potato scab (Streptomyces scabies Increase the incidence of cucumber mosaic virus in spinach

Potassium Inhibit the development of fungi ( Fusarium oxysporum ), bacteria (Corynebacterium insidiosum and Xanthomonas spp.), various viruses and nematode Reduce some of the disadvantages of nitrogen applications Reduce infection by wound parasites such as Botrytis

Increase resistance to frost injury

Calcium Effect on the composition of the cell walls of the host - make cell walls more resistant to penetration by facultative pathogens such as Rhizoctonia, Sclerotium, Botrytis and Fusarium High levels of calcium in soils can raise their pH and eliminate pathogens such as Plasmodiophora brassicae which are favoured by acid soils

XIV.Trap (or catch) and decoy crops The pathogens infect the crop which must be destroyed before the life cycles of the pathogens are complete Decoy crops stimulate the hatching of nematode eggs Ryegrass (Lolium spp.) reduces the incidence of clubroot of crucifers

(Plasmodiophora brassicae) in infested soil Weed thornapple (Datura stramonium) reduces the incidence of powdery scab (of potatoes (Spongospora subterranea