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Agrotechnical methods of weed control

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Agrotechnical methods of weed control – weed control measures based on the use of technical means and methods of soil treatment.

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

Agrotechnical methods of weed control include:

  • seed provocation to germination;
  • mechanical and physical elimination;
  • depletion;
  • smothering;
  • drying;
  • freezing, etc.

In the system of tillage agrotechnical methods are subdivided into:

  • in the system of main tillage;
  • in the system of pre-sowing tillage;
  • in the care of crops;
  • in the post-harvesting period.

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

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

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Agrotechnical control methods

Provoking seeds to germinate

Seed provocation to germination is a technique that allows creating favorable conditions for rapid and simultaneous germination and emergence of weeds with their subsequent elimination.

It consists in surface treatment of the soil, its compaction and moistening in the warm period of the year.

It is used on fields with high weed infestation.

Mechanical elimination

Mechanical eradication – cutting or pulling weeds by hand or with tillage implements.

It is used on weedy fields with all kinds of weeds.

The technique is effective in the systems of the main, pre-sowing tillage and in the maintenance of crops.

Physical elimination

Physical elimination is the elimination of weeds and their reproductive organs under the influence of physical factors: fire, flooding of fields and areas with water, exposure to electric or electromagnetic fields, etc.

Depletion

The depletion technique includes regular pruning of vegetative organs of weeds in order to deplete the stock of nutrients spent on the growth of new shoots, subject to further elimination.

It is used in the fields and areas clogged with perennial and biennial weeds.

The method is most effective in controlling root-shoot weeds in the system of fallow tillage.

Smothering

Smothering technique consists in crushing underground breeding organs of perennial weeds with tillage implements at the main depth of their occurrence and subsequent deep plowing of cuttings into the soil.

It is used in winter tillage systems on the fields clogged with perennial rhizomatous weeds.

Drying

Drying of shredded rhizomes and vegetative organs of weeds under the action of sunlight during tillage in dry and hot weather.

Freezing

The technique of freezing consists in extraction of underground parts of perennial weeds to the soil surface during deep plowing in late autumn, which lose their viability when frosts come.

It is effective mainly in areas with little snowy frosty winters.

Tillage system

Depending on the method of tillage there are three systems of tillage:

  • mouldboard;
  • non-mouldboard (including flat-cut);
  • combined.

When switching to regular non-mouldboard tillage, for example, on eroded and erosion-prone soils, the weed infestation of certain crops increases due to the accumulation of the bulk of weeds in the upper soil layer and deterioration of the nutrient regime, which naturally leads to a drop in yields. Barley, winter wheat and perennial grasses are particularly sensitive to this.

The seed stock decreases to a lesser extent in the case of moldboard tillage, as their deep embedding creates a conservation effect for a long period. In subsequent tillage, being in the upper layers, they successfully give sprouts.

Application of agrotechnical methods of weed control in tillage systems

In the system of basic tillage

The autumn mouldboard tillage is the main measure in the arsenal of agrotechnical methods of weed control, the first method of which is harvest-disking.

Disking

Disking allows to eliminate low-growing weeds that occur in grain crops and, as a rule, persist during harvesting, as well as to activate the growth processes of the seeds that have been crumbled during the year.

According to the data of the Research Institute of Agriculture of the South-East, the seeds of pinchwort (Amaranthus), bristlewort (Setaria), barnyard grass (Echinochloa crus-galli) and other stubble weeds collected before the disking and put on germination, did not give rise in the laboratory conditions, while collected after disking with disc tools, germinated by 67-92%.

Soil moisture has a significant impact on the effectiveness of disking to induce seed germination. Moisture deficit leads to delay of germination. With sufficient moisture the disking ensures germination of 30-40% of weed seeds at the depth of the polydisk tiller.

The depth and timing, as well as the means of disking are selected depending on soil conditions, the species composition of weeds and the degree of weed infestation.

Timing. Earlier timing increases the efficiency of disking. Studies of the Russian Flax Research Institute showed that the disking conducted on August 20 resulted in the germination of 2,400 weeds per m2, while the disking conducted in late September resulted in only 16 weeds per m2. In addition, delaying disking gives the weeds remaining after harvesting an opportunity to become inseminated and replenish the seed bank.

The greatest effect of disking is achieved when it is carried out simultaneously with or immediately after harvesting.

In the Non-Black Soil Zone due to the short post-harvesting period, the disking should be carried out in a short time.

Depth of disking. Effectiveness of the reception depends on the depth of cultivation which is determined by the degree of infestation, moisture and granulometric composition of the soil, the presence of post-harvest residues, and ranges from 6-8 to 10-14 cm.

Methods of disking. In the central, western and southern regions of the Non-Black Soil Zone of Russia double disking is widely used: the first is done by disk topsoil to a depth of 6-8 cm, the second – with polydisk tiller or disk tiller harrows to a depth of 12-14 cm. In combination with plowing this method allows to reduce the weediness by 80-90%, which is especially effective in vegetable growing after early harvesting crops.

Disking down to the depth of 10-12 cm weaken the growth of perennial root-shoots weeds (Canada thistle (Cirsium arvense), perennial sow thistle (Sonchus arvensis), bitterling pink (Rhaponticum repens), field bindweed (Convolvulus arvensis), etc.). In 2-3 weeks after sprouting, plowing to a depth of the arable layer by plows with coulters is carried out. This method allows to reduce the infestation of perennial weeds by 70-75%.

To control rhizomatous weeds (couch grass (Elytrigia repens), pigweed (Cynodon), coltsfoot (Tussilago), field horsetail (Equisetum arvense)), the disking is done immediately after harvesting to a depth of 10-12 cm in two or three trails along and across. In 10-15 days, cuttings of rhizomes and shoots are plowed with plows with skimmers to the depth of the arable layer. Non-observance of this technology or delay in its application can increase the infestation of the field, especially with couch grass (Elytrigia repens).

Choice of tools. Polydisk tiller are less productive than disk topsoil or disk tiller (heavy disc harrows).

Plowing

Deep plowing, carried out after disking, during the mass regrowth of most weeds well destroys them, which allows to reduce the weed infestation of the fields in 4 times compared with autumn tillage without disking. Plowing underway plow with skimmer, held after stubble disking, moves 55-70% of the seeds from the upper layers in the soil to a depth of 8-16 cm, where they germinate, but are below the limit of appearance, ie do not give rise and die.

The use of alternation of deep plowing with ordinary or shallow plowing reduces the clogging of the soil by 35-40%.

The effectiveness of plowing depends on the depth of tillage and the timing of its implementation.

Timing. If the plowing is delayed with deep tillage, weeds (especially perennial) have time to develop a powerful root system and accumulate a stock of plastic substances, which makes it difficult to control them in subsequent periods.

Methods of plowing. In the areas of the Non-Black Soil Zone, the Volga region and the North Caucasus – a highly effective method in the system of cultivation to control weeds is plowing two-tier plow, which performs complete wrapping of the arable layer, the best quality plowing and deeper penetration of the seeds. This method increases the effectiveness of organic fertilizers in 2-2,4 times and significantly reduces the weediness of crops.

Half fallow tillage, that is surface treatment of the soil after plowing, creates favorable conditions for the development of weeds in the fall, which do not have time to develop, die in the first frost or frost in winter. Plowing with three times of cultivation in half-fallow cultivation can be replaced by three discing, which is also effective in the fight against harmful weeds, including creeping couch grass (Elytrigia repens).

In the system of soil protective main tillage

The introduction of soil-protective tillage technologies on eroded and potentially erosion-prone soils in modern farming has led to changes in the species composition of weed vegetation. Agrophytocenoses of such soils are very different from plain soils: the number of weeds increases down the slope, perennial weeds prevail in the lower part of the relief.

Weed infestation increases by 60-80% with prolonged use of flat-cut and minimum tillage. If in the systems of main tillage based on plowing, annual weeds predominate, mainly spring weeds, in surface tillage – rhizomatous and root-shoots.

With non-plow tillage the stock of viable seeds in deep layers loses germination over time. Therefore, in this system of tillage the main task in weed control to ensure the purity of the upper layer of 0-10 cm. This is achieved by periodic surface treatments in the summer and autumn period.

Under moderate climatic conditions with a coefficient of moisture of 1-0.55, on eroded and erosion-prone soils, use flat-cutting and surface treatments. During harvesting of crops on such fields, straw or green manure is scattered with subsequent embedding them into the soil. Straw mulch is incorporated by harrows (BIG-3, BM1P-15, UNS-5,7[1]Russian nomenclature.) to a depth of 8 cm. Sideral crops, for example, sweet clover – with heavy disc harrows (БДТ-7) in 1-2 trails. If weeds grow again – in 15-20 days additional processing with harrows (BMSh-15 and BDT-7). This method allows to destroy the weeds remaining in the stubble.

In bare and seeded fallow processing systems

The greatest effect of weed control is observed in the treatment systems of bare fallow and seeded fallow.

As a rule, the most weedy fields are allocated for bare fallow.

Treatment technology of bare fallow should be soil-protective. It includes:

  • harvest-disking;
  • autumn plowing with a plow with a skimmer;
  • from the spring of the following year – the system of spring-summer care.

Herbicides may be used instead of mechanical treatments.

Depending on the type of weed infestation, the method of disking is chosen:

  • if there are abundant perennial weeds, a single disking to a depth of 5-7 cm is carried out;
  • in the presence of root-shoot weeds – double stubble loosening with hoeing machines, disc harrows or flat-cut cultivators to a depth of 6-8 and 10-14 cm;
  • for rhizomatous plants – double longitudinal-transverse disking at a depth of 10-12-14 cm.

In spring, seeds lifted to the upper soil layers during autumn plowing massively germinate on the surface of the fallow field. Polydisk tiller are most effective for weeds killing at the depth of 6-8 to 8-14 cm. Small weeds are killed, and perennial weeds are strongly depleted.

In the system of weed control on bare and seeded fallows the features of winter and wintering weeds – the most dangerous for winter crops – should be taken into account. The fallow system does not provide complete cleaning of fields from these weeds.

In the system of pre-sowing tillage

Weed control measures in the system of pre-sowing tillage are subdivided:

Efficiency depends on intensity of germination and appearance of shoots. 

Increased depth of cultivation in the system of pre-sowing treatment significantly affects the weed infestation of fields by perennial weeds, due to good germination and aeration of the soil.

The cultivation to the depth of the arable layer by conventional cultivators is not carried out, but chisel-cultivators or chisel ploughs are used. In addition to the destruction of weeds, this method eliminates the consequences of soil compaction from the passage of machinery, tractors and combines.

To accelerate the emergence of small-seeded crops (vegetables, flax, millet, perennial grasses) spend presowing tillage, which contributes to a more uniform seeding and accelerates emergence, as well as enhances the germination of weeds.

In the system of pre-sowing tillage it is advisable to use combined units, which contributes to improving the environmental conditions of growth and development of crops, as well as reducing weed infestation and the number of passes of the technique. Additional labor costs are reduced by 1.4-2.0 times, the productivity, respectively, increases by 1.6-2.2 times.

For sowing winter crops

Optimal conditions for germination of the seeds of winter and wintering crops are formed at a soil temperature of about 20 ° C and humidity of at least 20-25%.

For sowing spring crops

Only 20% of weeds germinate before sowing of early spring crops, another 20 to 70% germinate after sowing, and the rest germinate throughout the season until frost. Depending on the prevailing weather conditions, the intensity may increase or decrease.

For late sowing crops

The greatest effect of control measures is achieved in pre-sowing treatment for late crops because most of early spring weeds (lamb’s-quarters (Chenopodium album), Galeopsis, Polygonum, wild radish (Raphanus raphanistrum), wild mustard (Sinapis arvensis) and others) have germinated by the time of sowing and can be easily eliminated by harrowing followed by cultivation.

If the fields are heavily infested with perennial, rhizomatous and root-shoot weeds, the treatment in spring begins with cultivation to a depth of 14-16 cm. As weeds grow, the second and, if necessary, the third layered cultivation is carried out to the depth of seed sowing. Such method leads to depletion of root system of perennial weeds.

There should be as much time as possible between the first and second cultivation to allow more weeds to germinate. Immediately after the first cultivation, when the top layer has dried out, it is effective to roll to create optimal conditions for seed germination, especially on soils with poor moisture retention. Thanks to this method, weeds sprout 4-6 earlier, and their number is 2-3 times higher.

Corn, millet, and buckwheat are cultivated two to three times before sowing, which destroys weeds and increases crop yield by 10-15%.

When caring for crops

The basic techniques of tillage for crop care include the basic techniques:

  • rolling;
  • harrowing;
  • inter-row loosening;
  • hilling-up.

The timing of techniques is determined by the state of cultivated and weed plants, when weeds are most sensitive to mechanical influences, and the decrease in yield from possible damage to crops is minimal.

The greatest harm to spring crops in the Non-Chernozem zone of Russia is caused by weeds growing in the spring and summer, and perennials, and winter crops – by winter and overwintering weeds that sprouted in autumn. Optimal germination conditions for the latter are created immediately after sowing, when cloudy days with precipitation and relatively favorable temperatures occur.

Rolling

In the pre-emergent harrowing, packing is carried out, provoking to germination of weed seeds by creating favorable conditions with their subsequent elimination. The effectiveness of the technique depends on the granulometric composition, moisture and ripeness of the soil, and the weight of rollers. On heavy soils and overwatered rolling may show a negative result.

Harrowing

After sowing large seeds to a depth of at least 5-6 cm, harrowing is carried out in the pre-emergence period. The efficiency of harrowing is 80-90% of weed seedlings and sprouts killed, in the autumn period – 70-95%. Tilling is carried out at a depth in such a way as to leave no less than 0,5-0,8 cm between harrow tines and seedlings of cultivated plants.

In order to reduce damage to cultivated plants harrowing is carried out across the rows or at an angle at a speed of no more than 4 km/h in the hot season, when plants have weakened turgor.

Harrowing of winter crops. To improve agrophysical properties when the soil is heavily compacted and swamped, as well as to control weeds, harrowing is advisable in spring. The best results are achieved by harrowing the dried up soil in winter crops when it is easily loosened. In clogged crops, where winter crops were exposed to bulging, instead of harrowing apply rolling.

Early harrowing of winter crops is not recommended because of the physical immaturity of the soil, as well as harrowing of parched soil.

Harrowing of spring crops. Spring crops are characterized by early spring, root-shoot and rhizomatous weeds. Due to the formation of crust, moisture evaporation increases and soil aeration deteriorates, which negatively affects germination and leads to thinning of seedlings. Therefore, 4-5 days after sowing pre-emergence harrowing is carried out.

Harrowing for small-seeded crops (vegetable, millet, flax, perennial grasses), as a rule, is not carried out because of the strong damage to seedlings.

Harrowing of crops with late sowing period. Harrowing is most effective for row crops – potatoes, corn and vegetables.

Inter-row harrowing well destroys weeds in row-spacing and partly in rows. The number of treatments depends on the degree of weed infestation and culture. Treatment depth starts with 5-7 cm and increases with the following treatments on 2-3 cm. When the height of cultivated plants 30-40 cm loosening of row spacing is carried out to a depth of 14 cm.

Corn crops due to the unevenness of its germination are harrowed in 2-3 terms, 3-4 days before sprouting: on loose soils – with light tooth or reticulated harrows; with slight compaction – medium, with strong – heavy harrows. To reduce damage to plants harrowing in the phase of two or three leaves is advisable to use medium tooth or light harrows. Repeat the harrowing in the phase of 4-5 leaves. In years with a long cold spring period, when corn growth is slow and weeds are well-rooted, the fourth harrowing is carried out. Harrowing the corn crops can kill 90-95% of the weeds and increase yields by 20-25%.

Potatoes also have their own characteristics. Because of the long pre-emergence period of 20-30 days in good weather conditions, crops can become overgrown with weeds. Therefore, weed control and loosening the soil in the pre-emergence period and during care of the crops contributes to an increase in yields by 20%.

Harrowing of potato crops in 6-8 days after planting with net and light harrows destroys the main mass of mostly annual and biennial weeds. The efficiency of late harrowing decreases: harrowing in 6 days destroys 80% of weeds, and in 12 days – only 20-30% due to development of a strong root system. In 7-10 days the second harrowing is carried out, then the third. During the growing season carry out at least 2-3 treatments.

Post-sowing treatment of fodder beets includes:

  • pre-emergent harrowing with mesh or seed harrows and 5-7 days after sowing, destroying up to 60% of weed sprouts and seedlings;
  • post-emergent harrowing before the formation of the first pair of true leaves, consisting of 4-5 longitudinal loosening between the rows;
  • mechanized thinning of crops – loosening of row spacing by a cultivator equipped with razor hoes;
  • thinning by cultivator with harrowing by bunches, longitudinal-transverse inter-row tillage.

The depth of tillage depends on soil conditions and weediness of crops and is usually for the first – 7-8 cm, the second – 8-10, the third – 10-12, the fourth – 12-14 cm.

For other row crops, the technology of crop care for weed control is similar.

The choice of the type of harrow. The type of harrow (rotary, tooth, reticulate, etc.) is determined by the depth of seeding, pressure on the soil, the type and friability of the soil, the system of cultivation. The longer the period of seedlings emergence and the larger the seeds, the more often weeds are controlled by pre-harrowing.

Mesh harrows are used when weed seedlings are detected and to destroy the crust. Tooth harrows are not always effective, usually due to soil conditions: insufficient physical ripeness, overwatering of heavy soil. Rotary hoes are effective in years when winter crops are affected by snow mold.

To control weeds in the protection zones (in the rows), weeding harrows with spring or rigid teeth, aggregated with cultivators, and rotary-ring harrows or rotary discs are used.

Weeds 35-40 cm in height in rows and nests are eliminated by burying with disc harrows with simultaneous inter-row cultivation. At an angle of attack of 25-30°, movement speed up to 8 km/h and a depth of 6-7 cm up to 90% extermination of annual weeds up to 8-10 cm is achieved.

In the post-harvest period

Agrotechnical methods in the post-harvest period are interrelated with extermination measures carried out in the system of basic tillage, and also include disking, cultivation and plowing.

The depth, timing and types of disking tools are determined by soil and climatic conditions, the degree of weed infestation and the species composition of weeds.

In areas with a short growing season in the Non-Chernozem zone, early autumn plowing followed 2-3 weeks later by discing or cultivation is effective against weeds.

Additional surface tillage after the main autumn plowing according to the type of half-fallow gives a positive result in the fight against invasive rhizomatous and root-shoot weeds, especially couch grass (Elytrigia repens). It consists of tillage by cultivators with resilient tooths in combination with harrows to a depth of more than 10 cm.

The system of improved fall-plowed land consists of two or three disc tilling, depending on the culture at a depth of 6-7 or 8-10 cm and the subsequent plowing to a depth of 20-22 or 25-27 cm. Conservation of moisture and acceleration of weeds germination is provided by timely harvest-disking and subsequent disking. Thus, the number of weeds per 1 m2 in spring wheat crops when disking was carried out simultaneously with disking of preceding winter crops was 35 plants, and when disking was delayed by 10 days – 54. Delay with disking for 30 days increased weed infestation by 3 times.

To control perennial weeds such as Canada thistle (Cirsium arvense), perennial sow thistle (Sonchus arvensis), field bindweed (Convolvulus arvensis) and others, a system of layering has proven effective. It consists of successively deepening several shallow tillings, which provoke multiple regrowth that weakens the weeds, followed by deep plowing. On eroded soils deep plowing is replaced by deep non-moldboard loosening.

Agrotechnical methods of control in the post-harvest period is advisable to combine with the use of herbicides. Field experiments and production practice show that 80-90% of weeds are killed when treating the leaf surface of regrowth weeds.

This technique includes disking, herbicide treatment and deep plowing. 2,4-D herbicides in doses up to 2-3 kg per 1 ha are used for spraying. The greatest effect, especially in relation to perennial weeds, is achieved at air temperatures no lower than 12-14°С. Lower temperatures reduce herbicide penetration to the root system, which reduces efficiency.

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.