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Accounting and mapping of weeds

Accounting of weed plants – systematic detailed accounting of weed infestation on agricultural lands, taking into account floristic and quantitative composition of weed vegetation, their distribution, landscape features and agroclimatic conditions, applied agricultural practices, etc.

Weed mapping – visual presentation of the account of weed plants in a farm, enterprise or area.

The purpose of accounting and mapping of weeds is to develop a targeted, rational and cost-effective program of weed control, to plan preventive and control measures. 

Data collection is based on information obtained in the process of field survey directly on the ground. A distinction is made between systematic and operational surveys.

Field survey
Field survey

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Systematic (solid) survey

Systematic, solid or basic survey is a full-scale survey of all agricultural land of the enterprise in order to obtain the most complete information on the species composition, number and distribution of weeds. The systematic survey also collects information on non-agricultural land of adjacent areas (machine yard, fuel depot, technical workshops, grain streams, cattle farms, power line alienation area, etc.) as foci of weed distribution.

Systematic survey is a labor-intensive process, so it is carried out annually or periodically (once in 2-3 years). The time should be chosen so as to cover the entire floristic composition and quantitative abundance of weeds on the surveyed land. For grain crops the optimal time of survey is in the phase of complete earing, in other continuous crops – 2-3 weeks before harvesting, in row crops – the middle of the vegetation period, in perennial grasses – the beginning of legume flowering, in non-agricultural lands – complete flowering of plants of cruciferous family.

Operational survey

Operational survey is a survey of a particular field or agricultural land before the start of weed control activities. It is performed in the following growth phases of crops:

  • spring cereals – at the beginning of full tillering;
  • winter cereals – at the end of the fall vegetation and in spring after regrowth
  • leguminous crops – at the height of up to 8 cm;
  • fiber flax – in herringbone phase (3-10 cm in height);
  • row crops – before inter-row tillage;
  • perennial grasses – before tillering of cereals or at the beginning of legume regrowth;
  • on clean fallows – at mass emergence of weeds.

Operational survey allows specifying species composition, quantitative abundance and growth phases of weeds in a particular field. The data obtained are used to adjust the areas to be treated, timing and methods of treatment, type and rate of herbicide consumption, etc.

Methods of accounting for the weed infestation of fields

A field (or an area) occupied by one crop, homogeneous in relief, applied agricultural technology and fertility, is taken as a unit of survey. Beforehand, the route of movement is outlined, consisting of several parallel passes along the field for relatively compact form of the field; for narrow or irregular form of the field – one zigzag pass. Along the entire route the weed counting stations are marked, which are located at an equal distance from each other, and relative to the neighboring passages – in a staggered manner. If the area surveyed is up to 50 hectares, 10 accounting locations are selected, from 50 to 100 hectares – 15 locations, in the fields over 100 hectares – for every additional 50 hectares the number of accounting locations increases by one.

In certain places of the account the infestation of the plot is determined by visual or quantitative weight method.

The visual method of counting consists in walking around the field borders and diagonals and a thorough visual inspection for weed infestation. The assessment is carried out on a four-point scale: 1 point – single weed plants are found in the crops; 2 points – weeds in the crops are few, but are no longer found singularly; 3 points – weeds in the crops are many, but quantitatively do not dominate the cultivated plants; 4 points – weeds quantitatively dominate the cultivated plants.

Quantitative weight method consists in counting the number of weeds and determining their wet and dry weight. Plots of 50×50 cm (0.25 m2) are determined on fields and grounds at equal intervals along the largest diagonal. Within this area, the number of weeds of each species is counted separately. When surveying an area of up to 50 ha, it is sufficient to survey 10 points, from 51 to 100 ha – 15 points, and in fields over 100 ha – 20 points. The degree of weed infestation is determined by points: 1 point – up to 10 weeds per 1 m2; 2 points – 10 to 20 weeds per 1 m2; 3 points – 20 to 30 weeds per 1 m2; 4 points – 30 to 40 weeds per 1 m2; 5 points – more than 40 weeds per 1 m2. The results of counting weeds for each place of accounting are recorded in the record sheets. Quantitative weight method gives more accurate estimates of weed infestation of fields.

Results processing and mapping

After completing the survey, the results are processed, including the calculation:

The average number of weeds of each species;
the average number of all weeds per m2;
the average number of weeds of each species, attributable to 1 m2.

Schematic maps of agricultural land areas or a contour map of the area on which the accounting data are marked with conventional symbols are used for mapping of weeds. The map can be drawn up once in 8-10 years, but it is better to choose the period equal to the rotation period of the crop rotation.

For convenience, the following recommendations can be used when making a map. On the map you must draw circles or other convenient figures 2-4 cm in size within the boundaries of the field, in which the name of the crop and the year of the survey are recorded. The circle is divided into sectors proportional to the numbers of each species. All major weed species, including quarantine and noxious ones, are recorded in the sectors using initial letters or shading, in the order of decreasing their average number per 1 m2. Places infested by quarantine weeds are marked, for example, with a red cross, and poisonous plants – with a blue cross. The legend of the symbols is given below the map.

The map of weed infestation is supplemented with tables indicating the full list of species composition and quantitative abundance (pcs/m2) of weeds for each field or plot. In order to analyze the dynamics of weed infestation, the same map is used in the application of accounting data in subsequent years.

Weed infestation map is the main document in the development of a set of agricultural practices, compilation of transitional tables of crop rotations and other aspects of agricultural production. It is a scientific basis for the development of measures to suppress, destroy and reduce the harmfulness of weeds.  

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. Edited by V.S. Niklyaev. — Moscow: Bylina, 2000. — 555 с.