Today, we are discussing Weed Management in Agriculture, Farming, and Gardening.
Weed Definition in Agriculture/Farming/Gardening:
A Great Britain farmer Jethro Tull was the First person who has defined the term weed in 1731.
Weeds are the plants, which grow where they are not wanted (Jethro Tull, 1731) Weeds can be referred to as plants out of place. Weeds compete with crops for water, soil nutrients, light, and space & thus reduce crop yields.
Weeds typically generate large numbers of seeds, assisting their spread. They are often excellent at surviving and reproducing in disturbed environments and are regularly the first species to colonize and dominate in these conditions. A weed can be an exotic species or a native species that colonize & persists in an ecosystem in which it did not previously exist. Weeds can inhabit all environments; from our towns and cities through to our oceans, deserts & alpine areas.
Weed Management and its importance
It is the process of minimizing the weed population and their growth below the level of economic injury to the crop with minimum environmental pollution.
Weeds can be managed by adopting any suitable method of weed control & if needed by combining two or more methods of weed control.
Importance of Weed Management:
The three important weed management goals in order of importance are as follows: 1. Maximize herbicide action of all herbicides at all times; 2. Eliminate weed seed making (zero seed rain on plants prior to flowering); and 3. Perform diverse weed management (use all tools in the toolbox, not just herbicides & especially a single herbicide). If these three goals are met for each individual field of a farming operation, then the chance to select for herbicide-resistant weeds is very minimal.
The total annual loss of agricultural make various due various parts of India is as below
- Weeds: 45%
- Insects: 30%
- Diseases: 20%
- Other pests (Rats, wild animals)
A recent estimation shows that weeds cause an annual loss of Rs. 1980 crores to Indian Agricultural which is more than the combined losses caused by insects, pests & disease. Weeds compete with crop plants for the plant for plant nutrients, soil moisture, space & sunlight. Weeds are hardy and vigorous in expansion habit.
Advantages of Weeds:
- Some lawn and garden weeds bring nutrients and water up from deep in the soil and down from the air, and subsequently make them available to microbes & plants.
- Some weeds break up the hardpans and compaction and manage erosion.
- Weeds Check Wind, Water, and Soil Erosion:
Weeds growing on desert lands, wastelands & sloppy fields lower wind and water erosion and help for protection of the environment.
- Weeds Add Organic Matter and Nutrients to the Soil:
Weeds add about 5 to 15 tones of green matter per hectare depending upon weed species & their growth.
Nutrient contents of several weeds are given below:
Gokhru – 3 to 3.5 % N
Bavachi – 3 to 3.5 % N
Leguminous weeds – 1.5 to 6 % N.
- Some of the Weeds are used as Leafy Vegetables:
- Tandulaja (Amaranthus Polygamus).
- Math (Amaranthus viridis).
- Kunjru (Digera arvensis).
- Ghol (Portulaca spp).
- Pathari (Lactuca runcinata).
- Some of the Weeds have Medicinal Value:
- i) Gumma (Leuclas aspera) Used in snake bite
- ii) Oil of Piwals dhotra – Useful against skin disease.
iii) Maka (Eclipta erecta) – Against cough & as hair oil.
- Some of the Weeds Serves as Ornamental and Hedge Plants:
Ghaneri (Lantana camara) and Cactus – Used as ornamental & hedge plants.
Ghol (Portulaca spp) – For beautiful flowers.
- Certain Weeds have Nematicidal Properties (Control of Nematodes):
Crotalaria spp; Calotropis spp, Parthenium etc. when incorporated into the soil help for manage of nematodes.
- Weeds can be used for Paper Pulp, Bio-gas, and Manufacture of Edible Proteins.
- Some of the Weeds are used for Religious Purpose E. g Hariali, Aghada, Maka etc.
Classification of Weeds in Weed Management:
The weeds with related morphological characters, life cycle, requirements of soil, water, climatic condition, etc are grouped together as a class or category. Therefore the classification of weeds is useful for adopting weed management methods for a particular group of weeds instead of against an individual weed species. It is always economically and practically feasible to manage the group of weeds as compared to control the individual weed species.
There are totally 30,000 species of weeds around the world. Out of these about 18,000 species are known to cause serious losses. In the list of world’s worst weeds nutsedge (Cyperus rotundus) ranks first & hariali (Cynodon dactylon) second position.
- Classification according to the anatomy of weeds:
Depending upon their rotation, weeds can be classified as
- Annual Weeds
- Biennials weeds
- Perennials weeds
- Annual weeds:
Annual weeds normally complete their life cycle in one season. Annual weeds can be either
- Summer annuals
- Kharif annuals e.g. foxtail
- Winter annual e.g. lambs quarter
- Biennial weeds:
Biennial weeds complete their life cycle in two years in the first year they remain vegetative, and in the second year, they make flowers and set seeds. E.g. Daucus, Carota, Nulicaulis, etc.
iii. Perennial weeds:
Perennial weeds produce for three or more years. E.g. Shallow rooted perennials – Bermuda grass, Quack grass. Deep-rooted perennials – Johnson grass
- Classification according to an origin of weeds:
Several weeds in India originated in some other part of the world. For e.g. Convolvulus sp –Eurasia, cyperus –Euphorbia,-Europe, Lantana –Africa.
- Classification according to soil:
Of the several variables of soil, soil pH is implicated frequently with the distribution of weed species. Weeds, such as red sorrel, corn sporry & bracken tend to comminute with weed flora on saline and alkali soils.
- Classification according to the nature of the stem:
Based on the development of bark tissues on their stems & branches, weeds are classified as a woody, semi-woody and herbaceous species.
(a) Woody weeds: Weeds include shrubs and under shrubs & are collectively called brush weeds e.g. Lantana camera, Prosopis juliflora.
(b) Semi-woody weeds: e.g. Croton sparsiflorus.
(c) Herbaceous weeds: Weeds have green, succulent stems and are of more regular occurrence around us e.g. Amaranthus viridis.
- Obligate Weeds:
Weeds which grow or happen primarily in a cultivated field where the land is distributed frequently. E.g Chandvel (Convolvulus arvensis).
- Noxious Weeds:
The weeds which are undesirable, troublesome and not easy to manage are called noxious weeds E.g Nutgrass, Hariali, Parthenium, Striga, Orobanche, Water hyacinth etc.
- Objectionable Weeds:
Weeds which generate seeds that are difficult to separate once mixed with crop seeds are called objectionable weeds. E. g the mixture of Argemone Mexicana or Pivala Dhotra seeds with mustard.
- Industrials Weeds:
Weeds invading areas around buildings, highway, railway lines, fence rows, electric & telephone pole bases etc are called industrial weeds. E .g Parthenium, Reshimkata, Katemath, etc.
- Poisonous Weeds:
E.g. Parthenium, Datura, Poison, ivy (Rhus sp), etc.
- Based on morphology:
Based on the morphology of the plant, the weeds are classified into three categories. This is the main widely used classification by the weed scientists.
(a) Grasses: All the weeds which come under the family Poaceae are called as grasses which are normally having long narrow spiny leaves. The examples are Echinocloa colonum, Cynodon dactylon.
(b) Sedges: The weeds go to the family Cyperaceae come under this group. The leaves are generally from the base having modified stem with or without tubers. The examples are Cyperus rotundus, Fimbrystylis miliaceae.
(c) Broad-leaved weeds: This is the main group of weeds. All dicotyledon weeds are wide leaved weeds. The examples are Flavaria australacica, Digera arvensis, and Tridax procumbens.
Weed Biology, Weed Ecology, and Weed Hardiness:
Read: Cover Crops Advantages.
Weed biology is an integrated knowledge with the mean of reduces the negative effects of weeds and promoting positive characteristics in the agroecosystem. It includes the biology and ecology of individual weed species & weed communities.
Weed ecology is the connection of weeds to their environment. It is concerned with the effect of climatic, soil and biotic factors on the distribution, prevalence, competing for ability, behavior & survival of weeds.
It is the ability of the weed to withstand climatic, edaphic, & biotic stresses.
Persistence of Weeds:
Factors affecting persistence
Climatic factors of the persistence of weeds:
Climate can effect variations in cuticle development, vegetative growth, vigor, competitiveness, etc. Climate thus has profound produce on the persistence of weeds which can adapt to a wide variety of climates. The important climatic factors are light, temperature, rainfall, wind & humidity.
Light intensity, quality, and duration are important in influencing the germination, growth, reproduction & distribution of weeds. Photoperiod governs the seed setting and maturation and on the evolution of different ecotypes within a weed species. Tolerance to shading is the main adaptation that enables weeds to persist.
The temperature of the atmosphere and soil affect the latitudinal & longitudinal distribution of weeds. Soil temperature affects seed germination and dormancy, which is a main survival mechanism of weeds.
Rainfall has a significant effect on weed persistence & distribution. More rainfall or less rainfall determines reproduction and survival.
Wind is a principal part of the dissemination of weeds.
Soil factors of Persistence of Weeds:
Soil factors are soil, water, aeration, temperature, pH and fertility level & cropping system. Some weed species are normally alkali plants, known as basophilic (pH 8.5) which can grow well in alkali soils and those grow in acidic soil is called as Acidophiles.
The distribution of weed species depends upon conditions of the soil is:
For example, 1. Moist Soil Condition: Kena (commelina spp), Maka etc.
- Water Logged Soils: Typha, Cyperus
- Light Soils: Cock’s comb, Piwala dhotra, Euphobia hirta (dudhi), Aghada etc.
- Heavy soils: Hariali, kunda.
- Basophiles: Weeds growing on alkali soils (pH 7.4 to 8.5) E.g Alkali grass, Quack grass.
- Acedophiles: Weeds increasing on acidic soils (pH 4.5 to 6.5) E.g Hariali, Digitaria spp.
- Neutrophiles: Weeds growing on neutral soils (6.5 to 7.4)
Several weed species develop on neutral soils. Several weed species of the Compositae family develop well in saline soils. A shift in soil pH, towards the acid side due to continuous use of Ammonium sulphate as a nitrogen source can cause a shift in the weed spectrum.
Many weeds can develop well in soils of low fertility level, however; can adjust well to soils of high fertility also. Weeds have adapted to moist soil, drought condition etc.
Biotic Factors of Persistence of Weeds:
Plants, animals, birds, insect, and disease-causing organisms are the biotic factors that modify the growth of weeds and seed production in a variety of ways that affects weed persistence directly & indirectly. Weeds produce a large number of seeds has dormancy & viability for a longer period and also have disagreeable taste and odor. All these characteristics of weeds enable them to survive even under the different effects of biotic factors.
Principles of Weed Control in Weed Management:
Prevent weeds from contaminating an area. As much as possible, this preventive measure is the main effective means of weed control.
- Making sure new weed seeds are not carried in contaminated crop seeds, feed, and machinery.
- Preventing weed from generating seeds
- Preventing the extent of perennial weeds that reproduce vegetatively.
These measures can greatly decrease weed problems.
This is the process of limiting weed infestation & minimizing competition with crops. When weeds are limited they have minimal effect on crop growth & yield. However, this principle is useful when the problem of weed exists. It is not prevented.
It is the complete elimination or destruction of all live plant parts & seeds of a weed infestation from an area. Practically, it is not feasible to eradicate the weeds as it is long term & a very expensive method.
Methods of Weed Control in Weed Management
Controlling weeds in forage crop production can involve a wide range of techniques. Nevertheless, virtually all weed control methods can be classified into one or more of the five main categories. The five general categories of weed control are:
- Preventative Weed Control
- Cultural Weed Control
- Mechanical Weed Control
- Biological Weed Control
- Chemical Weed Control
Preventative weed control:
Preventative weed control refers to any control process that aims to prevent weeds from being established in a cultivated crop, a pasture, or a greenhouse.
The following different measures are adopted for preventing further introduction & spread of weeds for missing weed population.
- Use clean seed that is free from weed seeds for sowing function.
- Use well-decomposed compost and F.Y.M. During the decomposition much heat is generated & most of the weed seeds lose their viability. Avoid addition matures weeds to manure pits.
- Destroy the weeds before the formation of flowers for avoiding seedling & the further spread of weeds.
- Remove weed growth: The cropped area, bunds irrigation channels, public places, etc. should be kept clean or free of weeds.
- Do not permit the livestock to go from weed infested area to clean areas.
- Avoid feeding animals with fodder & other material containing weed seeds.
- Farm implements and machinery must be properly cleaned before moving from a weed infested area to clean areas.
- Inspect seed, necessary stocks for the presence of weed seeds, rhizomes, weed seedlings etc.
Cultural weed control:
Cultural weed control refers to any method that involves maintaining field conditions such that weeds are less likely to become established and increase in number. Examples of cultural weed control would be to crop rotation, avoiding overgrazing of pastures, and maintaining good soil fertility.
Mechanical or Physical methods of weed control:
This includes the use of hand tools, implements & machinery operated either with the help of manpower, or machine power for control of weeds. These are costly & time-consuming methods. However, these methods cause damage to the environment.
i) Dredging and Chaining:
- Dredging & chaining methods are used to control aquatic weeds.
- Removing of weeds along with their roots and rhizomes with the help of mechanical force is known as dredging.
- The floating aquatic weeds are removed by the method chaining.
- A heavy chain is pulled over the water bodies to collect the weeds.
Digging method is useful for controlling perennial weeds like nut grass, hariali etc. Digging is useful for removing the underground propagation parts of weeds from the deeper layer of soil digging, hand collection. It is not economical in large areas as it is the costly & time-consuming method.
iii) Hand Pulling or Hand Weeding:
Pulling the weeds by hand or hand weeding with the help of weeding hook is the oldest & most effective methods for control of weeds. Weeds can be simply uprooted after good soaking irrigation. Weeding should be done before the flowering stage of weeds for avoiding seedling & the further spread of weeds.
It is one of the practical processes of destroying weeds of all categories.
a) Deep Ploughing:
Weeds are buried deep in the soil & also exposed to the heat of the sun by deep ploughing. Many annual weeds can be controlled by deep ploughing and exposing the field to the heat of the sun.
Caring for cutting and burying of weeds. Harrowing with blade harrow is very efficient in destroying newly germinated weeds before sowing of the crop.
Intercultural with different types of mechanical weeders is useful to control weeds in between rows of the crop.
v) Mowing and Sickling:
This process is used in lands, pastures, gardens, and roadsides. The implement mower is applied for cutting weeds. It does not destroy the weeds completely but prevents seed production by cutting rising parts. Cutting above ground parts of weed with the sickle is called sickling & it prevents seed information.
Flooding helps in controlling weeds like Kans. This grows luxuriantly in heavy ill-drained soils through rainy seasons. The weeds get submerged under water & are smothered.
The burning method is adopted to destroy weeds in non-cropped areas like wastelands roadsides, railway lines, bunds, etc. The flame throwers & steam boxes are used for burning weeds in advanced countries. The flame must be so adjusted that causing only wilting but not charring of weeds. The heat kills the living cells by coagulating the protoplasm & inactivating enzymes.
This method is to cut off light & avoid all top growth of weeds. The organic mulches such as plant residues that is Stubbles, rice hulls, sugarcane trash, etc are spread in between crop rows @ 5 tonnes/ha & thickness about 10 to 15 cm. The inorganic mulches such as black or white polythene sheet are spread in between crop rows. However, it is expensive & used for high-value crops only. The black polythene is effective for controlling weeds.
ix) Summer Fallow:
This process is widely practiced in dry farming areas. The land is ploughed after harvest of Rabi crop & left without any crop in a summer season. The underground parts of the perennial weeds are exposed to strong sunlight & destroyed.
Biological Control of Weeds:
It is also known as classical biological control.
- Bioagent like insects, pathogen & other animals is used to control weeds.
- Insect and pathogens infest weeds & they either reduce growth or kill weeds.
- Biological control method can decrease weeds, but it is not possible to eradicate weeds.
The philosophy behind the biological weed control is that in nature the growth of many weeds remains limited due to biotic stresses from their natural enemies, largely the insect pests and diseases. Therefore, the bio-agent which is specific to a particular host weed can be used for control of the weed.
Chemical Control of Weeds:
Chemical weed control refers to any technique that involves the purpose of a chemical (herbicide) to weeds or soil to control the germination or growth of the weed species. Chemical control of weeds is a very large industry & there are scores of examples of chemical weed control products. Examples of chemicals used to control weeds in forages are bromoxynil and paraquat.
Read: Custard Apple Cultivation.