Weed Survey and Mapping

Systematic (Complete) Survey

Systematic, complete, or basic survey — a full-scale survey of all agricultural lands of an enterprise in order to obtain the most complete information on species composition, abundance, and distribution of weeds. During a systematic survey, information is also collected on non-agricultural lands of adjacent territories as foci of weed spread.

A systematic survey is a labor-intensive process, so it is carried out annually or periodically (once every 2–3 years). The time should be chosen so as to cover most fully the entire floristic composition and quantitative abundance of weeds on the surveyed land. For cereal crops, the optimal survey time is at the full heading stage; in other crops of solid sowing, 2–3 weeks before harvest; in row crop sowings, the middle of the growing season; in perennial grasses, the beginning of flowering of legumes; on non-agricultural lands, full flowering of plants of the Brassicaceae family.

Operational Survey

Operational survey — a survey of a specific field or agricultural land before the start of weed control operations. It is carried out at the following crop growth stages:

• spring cereals — at the beginning of full tillering;
• winter cereals — at the end of autumn vegetation and in spring after regrowth;
• grain legumes — at a height of up to 8 cm;
• fiber flax — at the fir-tree stage (height 3–10 cm);
• row crops — before inter-row cultivation;
• perennial grasses — before tillering of grasses or at the beginning of regrowth of the legume component;
• on clean fallows — at mass emergence of weeds.

An operational survey makes it possible to clarify the species composition, quantitative abundance, and growth stages of weed vegetation in a specific field. The data obtained are used to adjust the areas to be treated, the timing and methods of treatment, the type and application rate of herbicides, etc.

Methods of Surveying Field Weed Infestation

The unit of survey is a field (or plot) occupied by one crop and uniform in relief, fertility, and applied agricultural practices. A route is first planned, consisting of: for a relatively compact field shape, several parallel passes along the field; for a narrow or irregularly shaped field, one zigzag pass. Along the entire route, weed survey points—stations—are marked, located at equal distances from each other and, relative to the adjacent pass, in a checkerboard pattern. If the area of the surveyed plot is up to 50 ha, 10 survey points are chosen; from 50 to 100 ha, 15 points; in fields over 100 ha, for each additional 50 ha, the number of survey points is increased by one.

At the selected survey points, the weed infestation of the plot is determined by the visual or quantitative-weight method.

The visual survey method consists in walking around the field along its boundaries and diagonals and carefully visually examining it for weed infestation. The assessment is carried out on a four-point scale: 1 point — weeds occur in the crops singly; 2 points — there are few weeds in the crops, but they already occur not singly; 3 points — there are many weeds in the crops, but they do not quantitatively predominate over the crop plants; 4 points — weeds quantitatively predominate over the crop plants.

The quantitative-weight method consists in counting the number of weeds and determining their fresh and dry mass. In fields and lands, at equal intervals along the longest diagonal, plots measuring 50×50 cm (0.25 m²) are established. Within each plot, the number of weeds of each species is counted separately. When surveying plots up to 50 ha, it is sufficient to conduct studies at 10 points; from 51 to 100 ha, at 15 points; and in fields over 100 ha, at 20 points. The degree of infestation is determined in points: 1 point — up to 10 weeds per 1 m²; 2 points — from 10 to 20 weeds per 1 m²; 3 points — from 20 to 30 weeds per 1 m²; 4 points — from 30 to 40 weeds per 1 m²; 5 points — more than 40 weeds per 1 m². The results of weed counts at each survey point are entered into survey records. The quantitative-weight method gives more accurate estimates of field infestation.

Processing of Results and Mapping

After the survey is completed, the results are processed, including calculation of:

• the average number of weeds for each species;
• the average number of all weeds per 1 m²;
• the average number of weeds of each species per 1 m².

For weed mapping, schematic maps of agricultural land areas or a contour map of the area are used, onto which survey data are plotted using accepted conventional symbols. The map is compiled once every 8–10 years, but preferably over the rotation of a crop rotation.

For convenience when compiling the map, the following recommendations can be used. On the map, circles or other convenient figures 2–4 cm in size are drawn within the field boundaries, into which the crop name and the year of the survey are written. The circle is divided into sectors proportional to the abundance of each species. In the sectors, all main weed species, including quarantine and poisonous ones, are entered with initial letters or shading, in descending order of their average abundance per 1 m². Places infested with quarantine weeds are marked, for example, with a red cross, and those with poisonous weeds, with blue. Below the map, an explanation of the conventional symbols is provided.

The weed infestation map of lands is supplemented with tables indicating the complete list of species composition and quantitative abundance (plants/m²) of weeds for each field or plot. To analyze infestation dynamics, the same map is used when plotting survey data in subsequent years.

The weed infestation map is the main document in developing a set of agricultural practices, compiling transition tables for crop rotations, and other aspects of agricultural production. It is the scientific basis for developing measures to suppress, destroy, and reduce the harmfulness of weed vegetation.

List of Sources

• Bazdyrev G. I., Loshakov V. G., Puponin A. I. et al. (2000). Agriculture. Textbook for universities. Moscow: Kolos Publishing House.
• Niklyaev V. S. (2000). Fundamentals of Agricultural Production Technology. Agriculture and Crop Production. Moscow: Bylina.