Correct volume of spray applications

The reduction in application volume meets the agricultural sector's desires for greater operational performance of sprayers with efficiency in the application of phytosanitary products, economy and sustainability, but requires greater understanding and use of the principles of Phytosanitary Product Application Technology to ensure the efficiency of operation.

Grain producing regions in Brazil maintain 56% of their cultivated areas under Direct Planting (PD). This system recommends minimum soil cultivation associated with the formation of straw by cover crops. Therefore, before implantation and establishment of the subsequent crop, it is important to efficiently desiccate cover plants or spontaneous vegetation so that this does not become a problem during the establishment or during the cycle of the successor crop. In this context, glyphosate has been the herbicide most used in applications.

The success of desiccation is related not only to high-tech sprayers, but also to the appropriate recommendation of spray tips, application volume and knowledge of the characteristics of the herbicide and the vegetation cover to be controlled. However, justified by the market pressure exerted on the agricultural production chain, practices in the application of herbicides are observed in the field that are not based on the principles of Phytosanitary Product Application Technology.

Currently, due to the lack of machines in relation to the size of cultivated areas in Brazil and skilled labor, reducing the application volume is one of the alternatives found by grain producers to maximize the use of sprayers, especially self-propelled ones that have high acquisition cost. Thus, by increasing operational capacity (ha/h) by reducing application volume (L/ha), operational costs are reduced. However, application volumes and droplet sizes can influence the application efficiency and the effectiveness of controlling vegetation covers.

Recent research with systemic herbicide (glyphosate) in the southwest of the state of Goiás (UFG-Regional Jataí) found that the reduced spray volume (50L/ha) using very thick drops with air induction was efficient in controlling brachiaria. With the use of fine drops, reducing the application volume may result in a loss of efficiency in depositing the active ingredient and, consequently, a reduction in the control of vegetation cover (Almeida, 2014).

The association of the herbicides glyphosate (systemic) and saflufenacil (with restricted translocation) with a spray volume of 50L/ha efficiently controlled fleabane plants up to 40 centimeters in height. Although, volumes of 150L/ha and 200L/ha provided lower percentages of plants with regrowth with both droplet sizes (fine and extremely coarse) in plants with heights above 40 centimeters. In this case, it is worth noting that saflufenacil is recommended for plants up to 40cm. However, remember that many weed species have staggered germination. Thus, the spray volume, when spraying herbicides with restricted translocation, could be a bias in the efficiency of application and control of plants (effectiveness) in emergency moments when drying is necessary to sow the crop (Almeida, 2014).

When dealing with desiccation of areas with spontaneous vegetation (weeds) with different architectures, reducing the application volume will result in a reduction in droplet coverage in the lower thirds. Thus, when applying herbicides with restricted translocation (contact herbicide) or with apoplastic/acropetal translocation (via xylem), it is possible to use air-assisted spray bars or double flat jet nozzles to increase coverage in the thirds lower. Therefore, maintaining sufficient coverage prevents the incidence of resprouting plants (Almeida, 2014).

In liquid applications, when there are favorable humidity, temperature and wind conditions, smaller droplets will provide greater target coverage. On the other hand, in adverse conditions, such fine drops or even medium droplets will be subject to drift and evaporation, resulting in losses of the applied solution and reduced application efficiency. Furthermore, they can expose operators to syrup and the risk of poisoning and worsen the problem of environmental pollution (Ferreira, 2009). According to international organizations such as the FAO (Food and Agriculture Organization of the United Nations), the limiting meteorological conditions for spraying are a minimum relative humidity of 55%, wind speed of 3,2km/h to 9,6km/h and temperature below 30ºC (Ferreira, 2009). However, in regions such as the Central-West of Brazil (Cerrado Biome) the meteorological conditions encountered during daytime periods (morning and afternoon) will normally be outside the limits suggested by FAO for an application with lower risk of losses (Almeida et al.

When using reduced spray volumes, concerns about unfavorable atmospheric conditions increase, as minimal losses due to drift in this situation can result in insufficient deposition of the active ingredient on the plants to be dried.

However, glyphosate can be applied in alternative periods (dawn and night) without solar radiation, as during these periods favorable atmospheric conditions for application normally prevail (temperature, relative humidity and wind speed), with possibly smaller losses of action potential. of herbicide (Almeida, 2014). It is worth noting that molecules that inhibit the action of Protox or PPO, even when applied efficiently at night, have reduced control effectiveness. This probably occurs due to the reduction in the amount of free radicals produced in the cytoplasm of cells, in the period without solar radiation. This hypothesis is evidenced when comparing daytime (morning and afternoon) and nighttime applications of saflufenacil to horseweed plants (Ferro, 2015).

In nighttime applications, in addition to a possible reduction in effectiveness due to possible metabolization of the molecule by the plant to be dried, there is another factor to be considered, the wetness of the plants. This phenomenon occurs due to the condensation of water on the leaves (dew). Finally, the wetting of plants by dew may result in two forms of product loss, one by dilution, to the point of hindering penetration into the leaf and consequently its absorption, and the other by runoff. In this case, using reduced spray volumes may reduce the potential for such losses to occur in nighttime applications, due to the increase in product concentration in the spray when reducing the application volume for the same product dosage.

The reduction in application volume meets the agricultural sector's desires for greater operational performance of sprayers with efficiency in the application of phytosanitary products, savings and sustainability. However, the importance of understanding and using the principles of Phytosanitary Product Application Technology and advancing basic issues such as maintenance, adjustment and calibration of sprayers is highlighted. Therefore, for progress and sustainability in agricultural production to occur and be maintained, the transfer of information through frequent human resources training is essential.

Application technology 

In everyday life in the field, one can remember and apply the concept of Application Technology in phytosanitary treatment through four questions:

1. Who wants to control (- target, - biology)?

2. Where is it (- plant organography, - behavior)?

3. What to apply (product has proven effectiveness)?

4. How to apply efficiently (Application via liquid: - physical-chemical characteristics of the products and syrups; - morphology and anatomy of the surface where the drops are intended to be deposited, - with a thin or thick drop, - what is the volume of syrup)?

Thus, it is clear that before applying phytosanitary products there is a demand for knowledge of the situation of the production system as a whole.

Optimal application volume

Regarding questions about the ideal application volume (L/ha), it is worth noting that there is no exact recommendation on which one to use and, before choosing, we suggest answering four basic questions:

1. What is the size of the surface to cover?

2. What is the maximum volume that the plant can retain?

3. What volume is necessary to control the phytosanitary problem?

4. How should the drops be distributed in the areas so that the target receives a sufficient deposit in quantity and quality (uniformity of coverage) of the phytosanitary product? (Ferreira 2014).

 

Dieimisson Paulo Almeida, Marcelo da Costa Ferreira, Nedta/Unesp; Paulo César Timossi, LPD/UFG; Henrique Borges Neves Campos, Lapda/Unesp

Article published in issue 167 of Cultivar Máquinas.