Home » Arable farming » Methods of weed control

Methods of weed control

Methods of weed control – a scientifically sound set of measures aimed at the destruction of weeds and prevention of their spread, including agrotechnical and biological techniques, chemical means.

In agriculture there is a large number of methods of weed control, differing in essence, economic costs, labor intensity, biological and economic efficiency.

Scuffing (stubbling)
Scuffing (stubbling) - one of the agricultural methods of weed control

Navigation

Classification of methods of weed control

The classification of weed control methods is based on the ability of weeds to spread and how they are killed and suppressed.

They are distinguished:

  1. Preventive measures:
    • quarantine;
    • organizational.
  2. Extermination measures:
    • agrotechnical;
    • biological;
    • chemical;
    • special;
    • complex.

Planning of weed control measures is based on data on species composition, biological and ecological characteristics, as well as the state of weed plants (seedlings, mature plants, fruits, seeds, rhizomes, rootstocks, etc.), the degree of weed infestation of lands.

All control measures are part of the farming system and are carried out in accordance with the general plan of agronomic measures, which include: crop rotation rotation, tillage technology and fertilizer system, sowing and harvesting dates, etc.

Preventive measures

Preventive measures are measures aimed at identifying, localizing and destroying weed outbreaks and pathways.

Preventive measures include:

  1. Quarantine;
  2. Organizational:
    • cleaning seed, transport and machinery, forage, containers from weed seeds;
    • chopping or steaming fodder contaminated with weed seeds before feeding to livestock;
    • proper storage and application of manure to ensure destruction of weed seeds;
    • eradication of weed vegetation prior to flowering on adjacent territories: uncultivated lots, roadsides and irrigation canals, field shelter belts, wastelands, etc;
    • cleaning of irrigation water;
    • timely technological harvesting of agricultural products, etc.

Provision of optimal conditions for growth and development of cultivated plants, method of sowing also belong to preventive measures of weed control.

Quarantine measures

Quarantine measures are phytosanitary control of plant seeds imported from abroad (external quarantine) or moved within the country (internal control), carried out by quarantine services on a national scale. The objective of quarantine measures is to prevent the importation of weed seeds that are not present in the country and to prevent the spread of dangerous weeds within the country.

Quarantine weeds spread by the same routes as other weeds, but due to their high danger, the control of their importation and spreading is stricter. 

Detection of an outbreak of a quarantine weed in a farm requires all available measures for its complete eradication, including mechanical (burning) and chemical means.

In order to prevent the spread of quarantine weeds, regulations should be followed:

  • cleaning and storage of infested agricultural products shall be done in separate facilities;
  • it is prohibited to export seed material outside the farm without a certificate of the State Veterinary and Phytosanitary Inspectorate;
  • it is forbidden to place the seed plots in the places where centers of quarantine weed are marked;
  • it is allowed to use the wastes after cleaning only in steamed or milled form, the wastes unsuitable for fodder purposes shall be burnt (with drawing up an act);
  • straw and hay contaminated with seeds of quarantine weeds may be used only on the farm where they were received;
  • organic fertilizers may be used only in the decomposed state and kept in separate piles;
  • strict control of cleanliness of granaries, machinery, equipment, containers, etc.

There are outbreaks of common, field (Cuscuta campestris), flax (Cuscuta epilinum), and clover dodder (Cuscuta epithymum) in various regions of Russia. Alfalfa, flax, clover, potatoes, legumes, and beets are considered susceptible to these quarantine weeds, while wheat, oats, barley, corn, cereals, and perennial grasses are considered resistant. In fields with Dodder outbreaks, return of susceptible crops to their former location in rotation is determined by seed viability: for field dodder and common dodder (Cuscuta campestris), at least 6 years; for flax dodder (Cuscuta epilinum), 2 years; for clover dodder (Cuscuta epithymum), 12 years.

Organizational measures

Organizational measures are techniques, methods or types of work aimed at improving the phytosanitary condition of agricultural land in an enterprise or farm. They include reclamation, cultural and technical, general economic activities aimed at preventing the spread and reducing the infestation of soil and crops.

Measures to reduce the clogging of organic fertilizers

Manure storage and usage. Seeds and fruits of weed plants do not lose viability after passing the digestive tract of animals and accumulate in manure. When manure is stored, seed viability is significantly reduced, but it is not lost completely even at high temperatures. Organic fertilizers have a stimulating effect on the germination of old seeds that are in deep rest.

Studies of All-Russian Research Institute of Fodder named after V.R. Williams show that the content of viable seeds in 1 ton of manure is from 43 to 56 thousand, in chicken manure – 120-412 thousand, in slimy and hard fractions of pig manure – almost a million, in peat – from 10 to 37 thousand seeds. Germination of seeds isolated from peat and manure reaches 25-84%.

Manure and peat without measures aimed at reducing weed infestation is a potential danger of soil infestation with seeds of weeds, which can lead to an increase in the infestation of crops by 10 times or more. Even high agricultural practices with proper manure preparation and storage do not eliminate the growth of weeds.

The greatest efficiency in sterilization of manure from weed seeds is achieved with the “hot” method of storage. As a result of active microbiological processes its composting temperature increases to 60-70 ° C, which causes the death of weed seeds. The technology of heat treatment of chicken manure by 90-100% reduces the viability of seeds.

Weed seed germination is directly dependent on the degree of decomposition of manure: the more decomposed manure, the lower the number of viable seeds. Research data show that 1 kg of fresh manure contains 297 germinating seeds, the decomposed manure contains 22 seeds and 1 kg of fermented manure contains 4 seeds.

Stubble residues. When using the technology of leaving chopped straw and chaff as organic fertilizer during harvesting it is necessary to consider the possibility of spreading with it the seeds of weeds, especially hard-to-grind and immature (Tripleurospermum inodorum), lamb’s-quarters (Chenopodium album), Apera spica-venti, Sonchus and others. Timely harvesting in a short time by direct harvester method allows to reduce shattering of seeds and soil contamination, while the separate way of harvesting has no this advantage.

Leaving high stubble after grain harvesting creates favorable conditions for the development of weeds, especially low-growing plants.

The chopper and silage harvesters allow, together with the green mass, to harvest the main part of the seeds and fruits of weeds for silage or green fodder, where the seeds lose their germination.

Cleaning of seed

Cleaning of seed material is a technological process of separating weed seeds from seeds of cultivated plants based on the difference of their physical and mechanical (size, weight) and aerodynamic properties.

The permissible content of weed seeds in the seed material is regulated by regulatory documents (GOSTs). For seeds of major crops (wheat, oats, barley, buckwheat, etc.) admissible impurity per 1 kg: for the first class – 5 pieces, the second – 20 and the third – 70 pieces.

The viability of weed seeds is preserved for 3-10 years or more when stored in granaries.

Cleaning methods of seeds are divided into:

  • preliminary (primary) – removal of easily separable, large and small impurities;
  • main – deeper cleaning of seed material from weed seeds remaining after preliminary cleaning;
  • special – cleaning of the seed material from hardly separable weed seeds, for example, seeds of perennial grasses received from clogged seed plots. The data of the Russian Research Institute of Fodder named after V.R. Williams show that even when performing agrotechnical methods of control, 1 kg of perennial grass seeds included up to 20 thousand and more weed seeds.

Grain-cleaning aggregates and flow lines are used for seed cleaning. Sorting machines are used to obtain seeds of different classes. There are the following cleaning methods: hydroseparation, influence of electric or electromagnetic field, pneumogravitational units.

In addition to seed purification, it is important to grow seed material in low-weed areas. Seeds of some weeds are difficult to separate from vegetable plants, especially from the genus cabbage and umbrella plants. Therefore, the weed infestation of seed fields of vegetable crops is not allowed.

Creeping couch grass (Elytrigia repens), awnless bromegrass (Bromus inermis), meadow fescue (Festuca pratensis), pasture ryegrass (Lolium perenne) are typical weeds of perennial grass crops, their seeds are not separable on modern seed-cleaning machines. Therefore, weed infestation of seed plots is also not allowed.

Measures to reduce weed infestation in irrigation

One of the ways of spreading weed seeds is hydrochoric, i.e. through water, including irrigation systems and water sources.

In 1 m3 of irrigation water can contain from 2 to 6 thousand weed seeds. Under the irrigation norm of 600 m3/ha, 120-360 seeds per 1 m2 are brought, including those which have not been previously noted in the field. In the period of floods, seed inflow is also high.

Under irrigated farming system, a set of measures combining agrotechnical, biological and chemical methods of control should be provided, as well as additional: cleaning of irrigation water, mowing before weeds bloom on canals and their cleaning from silt containing seeds and vegetative parts of weeds.

Treatment of irrigation water involves the use of sumps, shields, panel skimming, etc.

The combination of irrigation, causing emergence of mass sprouts of weeds (provocative irrigation), with subsequent methods of their elimination is an effective method of control under conditions of irrigated lands. The optimum time for extermination measures is the period of germination and emergence of seedlings before the beginning of steady growth of weeds. High rates and early timing of irrigation contribute to the growth of more weeds, which increases the effectiveness of control measures.

Pre-sowing tillage, especially for late crops, as well as pre-seeding and post-seeding harrowing, inter-row treatment and hilling are mandatory methods of weed control in irrigated agriculture.

To exterminate the most vicious weeds, special control methods are used: deep and semi-steam tillage, selection of competitive crops, allocation of “ameliorative” fields in crop rotation, use of environmentally safe herbicides.

Harvesting

Seeds of weeds, whose growing season ends at the same time as the crop, fall with the main mass into the combine hopper. The direct harvester method of cereal crop harvesting reduces the falling off of seeds and fruits. Harvesters are also equipped with seed catchers.

Leaving high stubble and uncut areas, by creating favorable growth conditions, allows low-growing weeds to continue their vegetation.

Timely harvesting of haulm leaves and silage crops allows collecting the un-falling off part of the weed seeds together with the green mass.

Running parts of harvesting and tractor machinery and tillage implements should be cleaned of the adhered soil, stuck seeds and rhizomes. It is also necessary to pay attention to cleaning of vehicles involved in transportation of agricultural products.

Fodder preparation

Weed seeds and fruits in fodder (silage, hay, haylage, haylage, straw, forage, etc. ), retain viability for a long time: in haylage and chopped hay throughout the storage period; in silage, despite the formation of acetic acid, destructive to the seeds – up to 30 days for the thyrene (Amaranthus), pickleweed (Galeopsis), white marigold (Chenopodium album) and from 3 to 18 months – for chicken millet (Echinochloa crus-galli), thistle (Cirsium), field creeper (Convolvulus arvensis), Melilotus. 

Steaming of grain fodder is one of the methods of destroying weed seeds that cannot be got rid of by grinding.

Combined feed and forage grains can contain quite large amounts of weed seeds. Given that the feed may be imported from different countries or areas of the country, it represents a potential threat to the spread of weeds, including quarantine weeds. The use of feed containing large quantities of weed seeds requires measures to reduce their viability, including the use of herbicides.

Litter manure and solid fractions containing seeds of weeds must be treated with herbicides with 20-26% higher application rate after they are spread in the field. The application technique in this case is similar to herbicide application in pre-sowing treatment or on vegetative crops, after which the organic fertilizer is embedded in the soil.

Elimination of weeds on non-agricultural areas and other measures

Non-agricultural plots and surrounding areas are potential weed hotspots. Timely mowing and application of herbicides can prevent the spread.

Field protection forest strips, especially in steppe and forest-steppe zones, largely protect agricultural land from the spread of weed seeds. 

Extermination measures

Extermination measures are measures of weed control aimed at destroying both the weeds themselves and their reproductive organs.

Extermination measures are divided into the following control methods:

  • agrotechnical;
  • biological;
  • chemical;
  • special;
  • an integrated system of measures.

Agrotechnical methods

Main article: Methods of weed control: Agrotechnical methods

Agrotechnical control methods are extermination measures based on the use of technical means and methods of soil treatment. It is the main method of weed control.

The advantage of agrotechnical methods of control is their economic efficiency relative to other methods and means and combination with soil treatment measures.

Agrotechnical methods include:

  • seed provocation to germination;
  • mechanical and physical elimination;
  • depletion;
  • asphyxiation;
  • desiccation;
  • freezing etc.

Rational and timely application of agrotechnical methods allows reducing the weed infestation of crops by 50-60%, increasing the competitiveness of cultivated plants by creating favorable living conditions, suppressing pathogens of diseases and pests. The main role among agro-technical methods is given to the main tillage.

Biological methods

Main article: Methods of weed control: Biological methods

Biological control methods are control measures based on the targeted use of various living organisms (bacteria, viruses, fungi, insects, fish, birds, rodents, plants) for the selective destruction of weeds. The action of biological methods is manifested at the level of agrophytocenosis. 

The advantage of the biological method is a long-term effect with relatively small primary costs. The disadvantages of biological methods are the narrow selectivity of action and the potential danger to other beneficial species created by organisms introduced into the agrophytocenosis.

Biological methods of weed control include the use of:

  • biological agents;
  • competitive relationships between species;
  • allelopathy;
  • crop rotation and other agricultural practices.

The latter belong to biological methods due to the fact that the features of crop rotation and the use of such agricultural practices as liming, seeding rates and fertilizer system have a direct impact on the competitiveness of plants. In Western farming practice, they are allocated to separate cultural methods of weed control.

Chemical methods

Main article: Methods of weed control: Chemical methods

Chemical control methods are extermination measures based on the use of chemical means of weed control (herbicides).

The advantages of the chemical method are high efficiency, relative ease of technical application, selectivity of action. The disadvantages are high economic costs, negative impact on the environment, the danger of use for human health and product quality, especially in conditions of unskilled use.

Along with the improvement of herbicides, weeds over time develop resistance to chemical means, which in the long run can create great environmental problems. In addition, the general trend of reducing economic costs in agricultural production makes chemical methods of weed control less promising than biological methods.

Special methods

Special control methods – extermination measures used to destroy especially malevolent and quarantine weeds.

Malevolent weeds – weeds that can displace cultivated plants when spreading, leading to complete loss of crops, are found everywhere.

The group of the most malevolent weeds includes:

  • non-propagating shoots (Canada thistle (Cirsium arvense), perennial sow thistle (Sonchus arvensis), tartar lettuce (Lactuca tatarica), Johnsongrass (Sorghum halepense));
  • weeds of irrigated agriculture;
  • rhizomatous (couch grass (Elytrigia repens), pigweed (Cynodon), clubroot (Bolboschoenus), marsh hedgenettle (Stachys palustris)).

The maximum effect of special control measures is achieved by using mechanical method and fallow tillage. Tillage depth should be up to 30 cm, sometimes half-planted (semi-trenching) to 40-45 cm, combined with discing with a heavy disc harrow 12-14 cm and cultivator-ploughshare to a depth of 25 cm. Mechanical treatment is carried out in conjunction with herbicide treatment – picloram, dicamba, dialenom, atrazine and glyphosate in combination with herbicides of 2,4-D group.

In the system of complex weed control measures, considerable attention is paid to special measures to control harmful and quarantine weeds.

Complete eradication of malevolent and quarantine weeds is possible when using in crop rotations or individual links of deep tillage in combination with the use of selective herbicides. On non-agricultural areas it is acceptable to use herbicides in higher doses.

Small pockets and in clumps, destruction of malevolent and quarantine weeds is carried out by manual weeding with selection of rhizomes and subsequent incineration.

Fire methods

Fire methods of weed control are extermination measures based on short-term exposure to high temperatures on weed seedlings.

It is not effective against rhizomatous and root-shooting weeds, such as perennial sow thistle (Sonchus arvensis), because their root system, which lies at some depth in the soil, is not accessible to the effects of fire.

An integrated system of measures to control

Integrated system of measures is a set of agrotechnical, chemical, biological, environmental and other measures aimed at regulating the number of weeds to the level of economic threshold of harmfulness and built on scientific and practical principles.

An integrated system of measures should be based on a scientifically justified combination of crop rotations and tillage, herbicides and plant growth stimulants, fertilizer system, etc.

It acquires special importance in systems of minimum tillage where weediness of crops decreases by 2.5 times and weed seed bank by 1.5-2 times. Also in areas prone to water and wind erosion, where the use of herbicides allows reducing the number of soil treatments that intensify erosion.

In modern farming systems integrated weed control measures are part of an integrated system of pest control. It is most effective in combination of all control methods at maximum yield. Use of the complex of measures in the best world experience made it possible to achieve the yield of grain crops of 5-6 t/ha while maintaining the stability and sustainability of farming regardless of agroclimatic conditions.

Development of a comprehensive system of measures is carried out simultaneously with the construction of crop rotations and the design of tillage technologies.

The effectiveness of a comprehensive system of measures, as well as individual techniques of weed control, can be assessed only after a long and thorough study of the results of practical application, since the positive and negative effects are sometimes manifested over several years, especially if weediness is considered as a biological factor of fertility.

A combination of agrotechnical and biological control methods is used to control persistent perennial weeds. The essence of the combination is the systematic pruning of weed shoots in a fallow field with subsequent suppression of the remaining viable plants by winter crop stalks. The combination of mechanical removal followed by biological suppression is used in the cultivation of row crops. By efficiency such method in crops is close to the effect of a clean steam.

Table. Influence of complex application of chemicals on the yield of winter wheat[1]Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. - M.: Publishing house "Kolos", 2000. - 551 p.

Option of experience
Yield, t/ha
Yield increase, t/ha
Check
4.07
-
N180P90K40 (background)
4.88
0.81
Background + herbicide
5.96
1.89
Background + herbicide + growth promoter
6.42
2.39
Background + herbicide + growth promoter + fungicide
8.02
3.92

Studies of the Moscow Agricultural Academy for the Moscow region on barley and oat crops showed that the combined use of fertilizers, herbicides, and plant protection agents increases the grain yield to 5.66-6.05 t/ha.

Sources

Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. – Moscow: Publishing House “Kolos”, 2000. – 551 с.

Fundamentals of Agricultural Production Technology. Farming and crop production. Ed. by V.S. Niklyaev. – Moscow: “Bylina”, 2000. – 555 с.

Fundamentals of agronomy: textbook / Y.V. Evtefeev, G.M. Kazantsev. – M.: FORUM, 2013. – 368 p.: ill.