By Dr Vinod B Shimpale shimpaleyahoo com 1

By Dr. Vinod B. Shimpale shimpale@yahoo. com 1

Paper-IV: Plant diseases and weeds Unit-IV: Plant quarantine and weeds A) B) Ø Ø Ø 2 Plant quarantine: Domestic and International Weeds: Classification, Life cycle, Dissemination, Association of weeds with certain crops. Physical, Chemical and Biological Method of control, Herbicides and their Classification.

What is weed? A Great Britain farmer Jethro Tull was the First person who have defined weed in 1731. ‘A weed is plant growing where it is not desired’ OR A weed is a plant growing out of its place. OR Any plant not sown in the field by the farmer is out of place and is called weed. OR 3 A plant grown at wrong place at a wrong time is referred as weed.

Weed Management and Its Important Weed Management: It is the process of keeping or minimizing the weed population and their growth below the level of economic injury to the crop with minimum environment pollution. Weeds can be managed by adopting any suitable method of weed control and if needed by combining two or more methods of weed control. Importance of Weed Management: The total annual loss of agricultural produce various due various parts in India is as below: 1) Weeds: 45% 2) Insects: 30% 3) Diseases: 20% 4) other pests (Rats, wild animals) 4 A recent estimate shows that weeds cause annual loss of Rs. 1980 crores to Indian Agricultural which is more than combined losses caused by insects, pests and disease.

v CLASSIFICATION OF WEEDS There are over 30, 000 species of weeds round the world. Out of these about 18, 000 are known to cause serious losses. In the list of world’s worst weeds nutsadge (Cyperus rotundus) ranks first and hariali (Cynodon dactylon) second position. The weeds with similar morphological characters, life cycle, requirements of soil, water, climatic condition etc are grouped together as a class or category. Therefore classification of weeds is helpful for adopting weed management methods for particular group of weeds instead of against an individual weed species. It is always economical and practically feasible to manage the group of weeds as compared to manage the individual weed species. 5

WEED CLASSIFICATION On the basis of ONTOGEN Y 1. Annual 2. Biannual & 3. Perennial 6 ECOLOGICA MORPHOLOGY L ADAPTATIO 1. Dicot & Parasitic NS 2. Monoco 1. Total- Stem & Root t 2. Partial- Stem & Root

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PARTIAL PARASITIC 6

Total Parasitic 6

v CROP ASSOCIATED WEED q Some weeds remain associated with certain crops. Crop microclimate also plays role towards species-wise weed distribution and overall abundance, growth and competition of weeds. q Usually in crop field, annual weeds create major competition because of their quick multiplication through seeds from soil and initial rapid growth and vigour. q Although a good pre-emergence herbicide can take care of them to a great extent, periodicity of their germination by virtue of variable dormancy in their seeds many time nullifies this measure and additional control measures are required to be followed. 1. Weeds associated with Rabbi Crops: Some weeds are associated with Rabbi crops, in such type weeds weed germinates during winter season. The common examples are Convolvulus arevensis, Aristolochia bracteata etc. associated with rabbi crop like Jawar. 2. Weeds associated with Kharif crops: Some weeds are only associated 6 with Kharif crops e. g. Euphorbia geniculata etc.

3. Crop bound weeds: Crop-bound, which do not produce their own food by themselves and therefore, necessarily parasitize partially or wholly a crop for their food and survival e. g. Cuscuta sp, Orobanche sp, Striga sp, Loranthus etc. • They remain dependent upon crops and other wild hosts for food. • Crop rotation can be of immense use against them. • They take away food from the host-roots and do not have any other source of gathering food. Therefore, they are also called “obligate root-parasite. ” For example, Orobanche sp on tobacco, tomato. 4. Specific Crop-associated weeds: which remain associated with certain crops like crop-bound weeds but do not parasitize the crop plants. • Crop-bound weeds and crop-associated weeds are recognized separately although both of them are crop-specific and may be trapped by a single crop rotation. • Crop-associated weeds are not parasitic like crop-bound weeds, but there are certain reasons why they remain associated with certain crops, e. g. for specific microclimate requirement, weeds mimicking with crops

• . This basic knowledge about weeds is highly necessary for suggesting herbicides or other weed control measures as applicable. • Specific micro-climate requirement: Some weeds for their higher growth and survival, require shady, cool and moist habitat and therefore, they associate themselves where such situation available. Coronopus didymus is associated with lucerne for the same reason. • Weed mimicry with crops: In natural system, some plants made-up in various forms to maintain their survival and continue existence. In crop fields too, some weeds mimic with crop plants in various forms to establish their existence and perpetuation with crops. Weeds may mimic with crops in the following four ways. a) Vegetative/phenotypic mimicry: Some weeds have similar morphology (leaf, stem) as that of the associated crop plant and therefore, it is difficult to identify and separate out them from crop plants until inflorescence occurred. It is called “vegetative/ phenotypic mimicry”. As a result, they remain unweeded even by trained farmers and are harvested along with crops. For example, Oryza sativa mimics with Oryza longistaminata; a weeds Echinochloa colona in rice, Avena fatua and Phalaris minor in wheat.

b) Seed mimicry: These weeds have seeds similar in shape, size and even to some extent by weight to that of some crop seeds called “seed mimicry”. For example, seeds of Argemone mexicana, resemble with mustard seeds, Avena fatua seeds resemble cultivated oat seeds. They are also called “satellite weeds. ” c) Chronological mimicry: These weeds have similar height and ripening time with associated crop plant is referred “chronological mimicry”. For example, Phalaris minor has almost similar maturity time with wheat crops and as a result, they are harvested along with crop and contaminate wheat grains. d) Biochemical mimicry: A crop plant is normally tolerant to a herbicide selective to it. A weed associated with the crop although controlled by it may develop resistance to that herbicide through biochemical and physiological modifications on continuous exposure to it in course of time and behaves like the tolerant crop. As a result, that weed may remain associated with the crop as long as that herbicide or herbicide with similar mode of action continues to be applied in that crop. This is biochemical mimicry. This means that the weed which was earlier susceptible now mimicking the crop plants through biochemical means.

v. WEED CONTROL

FOR SUCCESSFUL CONTROL Habits of weed plants Life cycle of the weed Dispersal of seeds PRINCIPLES OF WEED MANAGEMENT Susceptibilities Methods of reproduction 16 Resistance to adverse conditions without losing viability Dormancy period

PRINCIPLES OF WEED CONTROL Habits of weed plants: A xerophytes weed blooming under dry & arid conditions will die if fields are flooded with water. Life cycle of the weed: Annuals & biennials can be controlled effectively if the land is cultivated before seedling stage of weeds. Perennials require deep ploughing to dig out rhizomes, bulbs, etc. or vegetative part by which they propagate. Susceptibilities: Some weeds are susceptible to certain chemicals while others are not. e. g. : Dicots are susceptible to 2, 4 -D while monocots are not, hence 2, 4 -D is used to control broad leaved weeds in monocot crops. Dormancy period: While controlling weeds, dormancy period is to be considered as they have long dormancy period.

Resistance to adverse conditions without losing viability: Some weed seeds have hard seed coats which enable them to remain for a long time without losing their viability, hence they should be controlled before seed formation. Methods of reproduction: Weeds propagate either by seeds, vegetative parts or by both. Seeded weeds should be removed or smothered before seed formation. Vegetative propagated weeds should be exposed to sun heat to dry & die like rhizome, bulbs, solons, etc. by deep ploughing. Frequent cultivation leads to destroy green leaves & thereby exhaust the food reserves & starve the plants may have to be restored too. In weeds propagated by both mechanical & chemical methods may have to be followed. Dispersal of seeds: Weeds can be controlled or kept in check if the ways in which different weed seeds disseminate are known and counter measures are undertaken.

PREVENTIVE MEASURES In this, the weeds are prevented from its multiplication, introduction & nipped off the buds. It consists of: 1) Use clean seed, 2) Use well decomposed FYM/Compost, 3) Cut the weeds before seeding, 4) Remove weed growth or keep irrigation & drainage channels clean or free from seeds, 5) Avoid use of sand or soil from weed infested areas to clean or cultivated areas, 6) Avoid allowing cattle to move from weed infested areas to clean or cultivated areas, 7) Clean all the farm implements & machinery properly after their use in infested areas & before using in clean areas.

WEED CONTROL METHODS Cultural methods Biological methods Ploughing Bacterial Hoeing Fungi Hand weeding Insects Field sanitation Crop rotation Mulching Crop cover Chemical methods

CULTURAL METHODS These measures are followed to remove or to arrest the weed growth & further multiplication. It includes: Plugging It practices before cultivation of crops. It is of two types: Simple & Deep plugging. Simple plugging kills only aerial parts of weeds while deep plugging kills whole plant part, it is effective to control perennial weeds.

Hoeing Ø Hoeing is done by hoe. Ø It practices mostly after cultivation of crop. Hoeing is helpful for stirring of soil but do not remove the weeds from the rows of crop. Ø It also increases the aeration in the soil. Ø By this practices only annual and biannual weeds get controlled, in case of perennial weeds only aerial growth get arrested and underground part remains as it is.

Hand weeding It practices by physical removal or uprooting of the weed by hand or by using hand weeding tool like khurapi or sickle etc. Advantages: Special technical skills are not required. It helps to control all types of weeds like annual, biannual or perennial. Disadvantage: it requires high labor inputs. It is time consuming method.

Field sanitation Filed sanitation means cleaning of fields after harvesting of crops. In this method all weeds uprooted and collected at one place and after sun drying they burned. Advantages: It helps for complete destruction of weed. Disadvantage: This practiced after harvesting of

CROP ROTATIONCrop rotation helps It also increases the soil fertility. Also check the rate of soil infecting fungi. to break the life cycle of a weed. Some weeds have ability to grow in specific or on specific crops. E. g. Striga grows on bajara or sugar cane but if the species crop is not available in the field the life cycle of Striga weed get

MULCHING Mulching means to cover the soil. It has two types: a) Straw mulching and b) Paper mulching It prevents light transmission and eliminate photosynthe sis ultimately growth of weeds get suppressed and seed production rate get minimized.

Crop cover “One who establish first/early, will suppress other. ” Therefore, the cultural practices are so managed that the crop plants should establish early and grow faster ahead of the weeds. These are the crops which have ability to grow fast and cover the more area. The weeds present below the crops do not show healthy growth due to insufficient sunlight. .

BIOLOGICAL METHODS It includes the use of living organisms for suppressing or controlling the weeds. Plant, animal or micro organisms may be used for destruction of weeds. These are called as bioagents which feed on only the weeds and not on crop plants. e. g. Prickly pear or Nagphana weed in South India was controlled by Conchineal insects (Dactlopius tomentosus). In Australia (Hawaii Islands) several kinds of moths were used to control Lantana camara which eats the flowers & fruits. This method is very efficient & economical provided right type of predators, parasites or pathogens which even under starvation conditions will not feed upon cultivated crops are found out & introduced.

Fungi The fungi used to control weed is called mycoherbicide. Production of mycoherbicide The fungus that attacks on weed on large proportion is isolated from infected weeds species. It is cultured on suitable nutrient medium and fungal spores isolated and these isolated spores spray again on weed.

species Puccinia chondrillina juncea Cercospora rodamanii crassipes Cercospora lantenae camera Chondrilla Eicchornia Lantana Puccinia chondrilina 1. Mycoherbicides are very chief. 2. They are usually more specific in action. 3. They do not persist for long time without their proper host. 4. They do not give residual effect.

Insect s Ø Some insects are used to kill the weeds. Ø When killing insect are released to the field they attach on the weed and also multiply their numbers till the complete destruction of weed. Ø After destruction population of these insects get reduced due to lack of food material because they feeds on very specific host plants. SOME EXAMPLES Control Eicchornia crassipes: It is free floating weed found in water bodies, the weevils Neochetia alchnarniae and N. brunchi are used to control water hyacinth.

Parthenium hysterophorus : It has been controled by releasing Mexican beetle (Zygograma bicolorata) into the field. This beetle feeds on all parts of plants and also breed very fastly (within 30 -35 days) , as a result of growth population of this weed get

Bacterial Some bacteria are used to control some weeds Such bacteria especially attack on underground part like root, stolon, tuber as well as above ground parts like stem and leaf. Some bactria species secretes toxic chemicals which absorbed by weed and causes death to weed plant. Bacteria causes diseases to weeds, like dampping off, root rot, seedling blight etc. Agrobacterium sp. Are used to control some of weeds.

ADVANTAGES OF BIOLOGICAL CONTROL 1) Biological control is eco-friendly since it does not lead to environmental pollution. 2) It is economical in the long run, although initially monetary investment is high. 3) Classical biological control does not need to introduce insects/bio-agents repeatedly in every year or every crop season and therefore, relatively permanent and longer lasting. 4) It preserves bio-diversity since weed control by biological means/agents is not achieved to the level of 100%. 5) It is effective in areas inaccessible to man. That weed wherever found even in dense forest, high mountains, is likely to be controlled particularly by insect bio-agents.

DISADVANTAGES OF BIOLOGICAL CONTROL 1. It requires high initial cost. 2. Screening and identification of bio-agents if not proper, they may damage the economic crops. For example, Zygogramma bicolorata (Mexican beetle) meant for control of Parthenium hysterophorus, but it feeds also on sunflower. 3. Biological control has limited use in a crop field, which usually witnesses a composite culture of weeds. It is in most cases weed-specific and the weed is managed at a lower density. 4. It is slow in action initially. Release/introduction of bio-agent and its subsequent establishment in the field and multiplication to build up the desired level of population for causing significant damage to weed take time and therefore, the process of control of weed goes slow initially.

5. The bio-agents employed feed on mainly foliage (not the whole plant or all plant parts). Certain bio-agents (namely insects), of course, eat up flowers, fruits and seeds of the weeds. Biological control, therefore, cannot be of much help towards weed eradication. 6. The biological control warrants the use of other pesticides such as insecticide, fungicide in the crop, which may kill the bio-agents or hamper its activity. 7. The span of activity of bio-agent in most cases is small/narrow, whereas weeds may grow all through the year. For example, Parthenium hysterophorus grows all through the year, but Zygogramma bicolorata, the bio-agent is active only during rainy season for a period of 2 -3 months starting from July. It goes for wintering during cold season.

CHEMICAL METHODS The chemicals used for weed control & which suppress or destroy the growth of weeds, called as herbicide. These either help in killing the weeds or in inhibiting their growth. e. g. 2, 4 -D, Atrazine, Glyphosate etc. This is very effective in certain cases and has a great scope. The chemicals are cheap, efficient & easily available. 28

v HERBICIDES The chemicals used for killing the weeds or inhibiting growth of weeds are called herbicides (Weedicides). 1. Chemical method of weed control is very effective in certain cases and have great scope. 2. The herbicides are cheap, efficient and easily available.

CLASSIFICAION OF HERBICIDES 1. On the basis of type Herbicide classification 3. On the basis of formulations 2. On the basis of applications

Based on type 1. Selective Herbicides: The chemicals which kills or retards the growth of some plants with little or no injury to other plants. 2. Non-Selective Herbicides: These chemicals are toxic to all the plants or kill all kinds of vegetation. 3. Contact Herbicides: A herbicides which kills only those plants or retards the growth of those plants which comes in direct contact. 4. Translocated Herbicides: The herbicides which are absorbed by the one part of the plants and exert a toxic action to other parts. These are also known as systemic herbicides. These absorbed chemicals upset the plant growth and metabolic processes. 5. Soil Fumigants: They usually function as a vapour or gas that diffuse through the soil and have relatively short life in the soil. 6. Soil Sterilants: Any chemical which prevent the growth of green plants when present in the soil is considered as soil Sterilants.

Based on time of application Pre-Planting /Pre-sowing Pre-emergence Post-emergence The herbicides which are applied before a crop is planted are called pre-planting herbicides. The herbicides is usually incorporated into the soil. e. g. Paraquat, Basalin. The Pre-Emergence herbicides is most effective when applied before the emergence of crop and weeds or the term may also refer to herbicides use after weed has emerged or established but before crop emerge e. g. Simazine, Atrazine. These herbicides are most effective applied after the emergence of crop and weeds. e. g. 2, 4 -D, Dicamba ( Banvel) etc.

Based on Basis of formulation i) Wettable Powder (WP) : made soluble or receptive to moisture, as by the addition of the a chemical agent e. g. Atrine, 2, 4 -D, Sodium salt, Diuron ii) Liquid Water Soluble (Concentrates) (WSC): e. g Diaquat, Paraquat, Bromacil. iii) Water Soluble Powder: e. g 2, 4 -D, Sodium Salt. iv) Granule: Butachlor, Bromacil, Calcium cynamide, ester salt, Nitrofen. v) Dusts: e. g. 2, 4 -D, Ester salt. vi) Emulsifiable Concentrates (EC): e. g. Propanil, Alachlor, Barban, Eptam. vii) Pellet: e. g. Arsenic Compounds. 33

Check the herbicide container, its manufacturing and expiry Use the required and recommended dosage Wear required safety dress Keep the herbicide away from the children Read the instruction before use Stir the herbicide with water properly

Care should be taken that the herbicide does not spill over Show the herbicide container and the information booklet the doctor Dispose the empty container Take precautionary measures

THANK YOU FOR YOUR ATTENTION! 45