Fatores que influenciam a tecnologia de aplicação de herbicidas: cobertura do alvo

Want to learn more about weeds? Access the Agro Weeds Combo course: https://hotmart.com/product/combo-pla... Target coverage can be calculated using the formula: C = 15(VRK2)/AD Where: C = coverage (% of area); V = applied volume (L/ha); R = recovery rate (% of applied volume captured by the target); K = droplet spreading factor; A = existing vegetation surface area per hectare; D = droplet diameter. In high-volume applications, high coverage is achieved even with large droplets, however, the probability of losses due to runoff increases. The increase in the recovery rate (R) is obtained by using droplet sizes that are more efficiently collected by the air. Electrically charged droplets induce an opposite electrical charge on the leaf surface and are electrostatically attracted, significantly increasing the recovery rate by the leaves. Increasing the droplet spreading factor (K) can be achieved by adding surfactants, which reduce surface tension, allowing for better droplet spreading. Increasing the leaf area implies reduced coverage if other factors remain constant. In large leaf areas, it is recommended to increase the spray volume to obtain good coverage, in the case of contact herbicide application. Droplet size is also a very important factor; smaller droplets provide greater coverage, but also have a shorter lifespan and greater drift potential. Thus, the ideal droplet size depends on environmental conditions (wind, relative humidity, and temperature) and the desired coverage, and will be defined as that which is small enough to produce good coverage and large enough to cause less loss due to drift and evaporation. On the other hand, the desired coverage depends on the type of herbicide to be applied: systemic or contact. To increase the number of droplets, they must be finer or smaller. To numerically express the size and uniformity of droplets, four basic parameters are used: Volume Median Diameter (VMD); Numerical Median Diameter (NMD); Dispersion Coefficient (r); Dispersion Amplitude (Span). Volume Median Diameter (VMD) is the median of the droplet volume. It is the droplet volume that divides the sprayed volume into two equal halves. Numerical Median Diameter (NMD) is the median of the number of droplets. It is the diameter that divides the number of droplets into two equal portions. Dispersion Coefficient (r) refers to the ratio between VMD and NMD. The dispersion coefficient expresses the uniformity of the droplet set. Dispersion Amplitude (Span) is another way to express droplet uniformity. Thus, the smaller the amplitude value (closer to zero), the more uniform the droplet set is in the sample. One of the most dominant factors that can drastically influence the efficiency of a herbicide or any other agricultural pesticide is the spray distribution. The main factors affecting the distribution of the sprayed solution are: Spray nozzles; Boom; Pressure losses; Clogged filters; Piping problems influencing liquid turbulence; Environmental conditions; Sprayer speed and resulting turbulence. Spray nozzles: type, pressure, spacing, spray angle, deviation angle, spray profile quality, wear, clogging, and flow rate. Full cone jet nozzles produce the largest droplets, followed by flat fan nozzles and hollow cone jet nozzles. Nozzles with higher flow rates at the same working pressure produce larger droplets. An increase in pressure will reduce the size, while a reduction in pressure will increase the droplet size. Nozzles with the same flow rate, at the same pressure, but with larger angles, produce smaller droplets. Boom height (a boom height above the recommended height promotes drift, and below it does not allow for uniformity in the deposition pattern, resulting in areas with excess droplets and others with a lack thereof) and boom stability (vertical movement - tilt and lateral movement - yaw). References used in class: Aspects of the biology and management of weeds / organized by Patricia Andrea Monquero – São Carlos: RiMa Editora, 2014. 430 p. Weed Science: studies on weeds / Arthur Arrobas Martins Barroso (Organizer); Afonso Takao Murata (Organizer). -- Jaboticabal: Fábrica da Palavra, 2021.