A scale of grades for evaluation of herbicide weed control efficiency

Abstract

The present work aims to describe a proposal of scale of grades for analysis of herbicide efficiency to make results of researches closer to the technical reality. The proposed scale of grades is based on a 5-percentage point scale (5-PPS), i.e., the weed control grade 1 is 0% to 4%, grade 2 is 5% to 9%, and so on up to 20 (95% to 99%) and 21 (100% weed control). This scale was based on three factors. The first considers the decreases in the coefficient of variation and standard deviation in statistical analyses, which improve the precision of results, when compared to a 20-percentage point scale (20-PPS), and the detection of significant differences between means that are not detected in the 20-PPS. The second factor is based on the comparison of the described symptomatologic analysis that attributes 5 grades that are, analogically, a 20-PPS. The proposed scale improves the statistical and agronomical evaluations. Therefore, the proposed methodology is better in differentiating results of weed control efficiency in field evaluations. The third factor considers improvements in the interpretation of results of herbicide efficiency, enabling the use of higher grades in the scale for studies on resistance to herbicides by indicating the selection pressure. It is concluded that the use of the proposed grading scale reduces the coefficient of variation and results in a better interpretation of the technical reality of the effects of herbicides.