Correct use of application technology

The correct use of application technology, knowing the target to be controlled, the action of the product used and the appropriate adjustment and calibration of the sprayer, allows treatments with a volume close to the ideal. Thus, the activity becomes more sustainable, with lower economic and environmental costs and more effective.

Phytosanitary problems are common when intensive agriculture is practiced in places with a tropical climate, as is the case in most of Brazil. The manifestation of diseases, insects becoming pests and weeds competing with crops, at different phenological stages, can compromise, in whole or in part, the expected production and, consequently, the farmer's investments and profits.

The control of phytosanitary problems is mostly done with the use of products applied in liquid form and distributed, using spray equipment, in the location where the problem is found. Phytosanitary products are sold in containers containing the concentrated active ingredient, which implies the need for its dilution in some other substance that serves as a vehicle and facilitates the homogeneous distribution of the product in the area.

In Brazil, the vehicle used in sprayer tanks is almost exclusively represented by water, as it is a universal solvent, exists in sufficient quantity and has a relatively low cost. The more diluted the product is in water, the greater the volume of syrup sprayed so that the recommended amount of the active ingredient is distributed per area.

Large volumes of water mixed with products are a defense argument for farmers and operators who carry out applications, who believe that the success of the application depends on how wet the plant foliage or the soil is. However, there are several studies pointing out that the application volume is not responsible for controlling the phytosanitary problem and that excessive wetting during spraying promotes losses through runoff and drift.

Good phytosanitary control must promote the application of the correct amount of the product's active ingredient to the desired target, using no more than a sufficient volume of vehicle so that there is a homogeneous distribution in the area, avoiding greater losses to the soil and through drift.

To avoid errors in the dosage of the product and the ideal volume of application, the producer must first pay attention to the correct adjustment and calibration of the sprayer. Once we have determined the spraying speed and the direction of the sprayer in the area to be treated, we choose the application volume.

Treatments carried out on tree crops must consider the width of the canopy and the number of leaves. Citrus consultants have considered an optimal application volume corresponding to 100ml/m² of canopy of each plant, in order to adapt the spraying to the size of the plant and the spacing in the area. Other parameters can be used for other tree crops, shrubs such as coffee and herbaceous crops such as soybeans, peanuts, beans, etc., so that the volume can be chosen with discretion. Work in progress shows equality or even improvement in the quality of spraying on citrus, through the analysis of the spray deposit, using reduced volumes (Box).

The visual way of evaluating whether the application volume is correct is still the most adopted in the field and can be done through the use of sensitive paper strips fixed to different parts of the plant. This paper is easily found in phytosanitary products stores, it is yellow in color and changes to blue when in contact with the sprayed drops, which shows the producer whether the volume of syrup is reaching the plants correctly. If syrup runs off the leaves or the sensitive papers turn completely blue, this indicates that the volume applied may be higher than necessary. Furthermore, the papers also report with some confidence the number of drops per cm² of leaf area, as long as they are not completely blue.

The control of diseases and some pests such as mites and leafminers requires that a number of between 50 and 70 drops with a diameter of 100µm to 200µm reach each cm² of the foliage to be treated, when using products that act through contact action. For products with systemic action on the plant, the recommended quantity of drops with a diameter between 200µm and 300µm is 30 to 40 per cm².

Knowing the target is essential to know whether the treatment requires more or less volume applied. Disease control, for example, requires greater leaf coverage compared to insect and weed control, so that the target, represented by the pathogen, is reached with the product. This is due to the fact that, often, even if the recommendation includes the use of small drops (100µm to 200µm), the application may require larger diameter drops due to unfavorable weather conditions at the time of application. Such conditions are temperature above 30ºC, relative humidity below 55% and wind speed above 10km/h.

The use of adjuvants with anti-evaporant action, such as mineral or vegetable oil, as long as it is in the appropriate concentration, can reduce the risk of drift in unfavorable weather conditions, allowing the use of smaller drops, in addition to facilitating their spreading, resulting in greater coverage of plant surface. With this, there is the possibility of considerably reducing the volume of sprayed solution.

In the case of weed control, post-emergence applications with contact action products require a larger application volume compared to control using systemic action products, as the latter is capable of translocating through plant tissues. .

Pre-emergence weed control allows the application of a few thick drops per cm² of soil, as the action and distribution of the product will occur after the occurrence of rain. This way, the volume sprayed is smaller when compared to post-emergence applications.

However, there are phytosanitary products on the market that do not inform the ideal dose to be used per area, instead, they inform their quantity per volume of water. This last information is unnecessary and confuses the operator when adjusting and preparing the syrup in the sprayer tank.

To increase or decrease the volume applied without compromising the quality of the spraying, we must maintain the quantity of the phytosanitary product in the area and change the spray tip. The tips must produce the same adequate range of droplet sizes, however, with a smaller or larger nominal flow rate, without working pressure above or below the ideal range indicated in the manufacturer's table.

Choosing the correct application volume to distribute the product to the target allows the operational performance of the treatment to be greater, taking into account refueling stops. The greater the volume, the more stops to refuel, which results in more time spent spraying and higher operating costs.

High applied volumes also burden the operation, considering that a significant part of the phytosanitary product can reach non-target locations, resulting in low-efficiency control and a high risk of environmental contamination, in addition to reduced operational performance.

The correct use of application technology through knowledge of the target to be controlled, the action of the phytosanitary product used and thorough adjustment and calibration of the sprayer allows the treatment to be carried out with a volume close to the ideal. In this way, the activity becomes more sustainable, with lower economic and environmental costs, ensuring effective control through the phytosanitary products used.

Comparison of spray deposit (µL/cm2 of leaf) in citrus by changing spray tips

A. Spray deposit per application volume reduced by almost half compared to the conventional volume used on the property, using TXA8002 tips.

B. Conventional volume tank of 1.200L/ha with TXA8003 tips. In both settings, the sprayer was equipped with 20 nozzles in total (ten on each side) for each flow and maintained a speed of 5,14km/h.

Partial results of the doctoral thesis in progress by Sergio Tadeu Decaro Junior (Unesp/FCAV – Campus de Jaboticabal-SP).

Sergio Tadeu Decaro Junior, Marcelo da Costa Ferreira, Unesp

Article published in issue 150 of Cultivar Máquinas.