Weed control also requires technique, effectiveness, and efficiency

Weed control also requires technique, effectiveness, and efficiency

By Raul Osorio – Director at Peulla Asesorias y Servicios SPA

The negative effects of weeds on crops include competition for production factors (light, water, nutrients) and/or allelopathy (interaction of organic substances secreted by plants at the root level). The competition exerted by weeds on fruit species for production factors will be greater in newly established plantations or young orchards.

An optimal weed control strategy in cherry trees should initially consider prevention and eradication, followed by weed management, which should be incorporated into all cultural practices (manual and mechanical methods), physical, biological, and chemical methods aimed at reducing their incidence and minimizing the damage that weeds can cause in agricultural operations.

Chemical control offers effective and timely weed control, often being more cost-effective compared to other control methods. Of course, herbicides are excellent tools that must be used appropriately, taking care of the environment, and avoiding potential phytotoxicity problems that improper use may cause. (For reference, see in Spanish: https://smartcherry.cl/noticias/control-integrado-de-malezas-en-cerezos/).

In industrialized countries, herbicides are applied to 85-100% of all major crops. Finney (1988) predicted that the need for intensified agriculture, as a result of high population growth, will increase the use of herbicides. When used judiciously within an integrated weed management system, herbicides are safe for farmers and pose minimal risk to the environment (Source: Food and Agriculture Organization of the United Nations https://www.fao.org/3/t1147s/t1147s0e.htm)

Herbicides can be applied to foliage or soil. Those applied to foliage that only affect the treated part are described as contact herbicides, while those that move from the treated foliage to a target site elsewhere in the plant are called systemic herbicides. Soil-applied herbicides, which generally affect weed germination, need to persist for some time to be effective and are called residual herbicides. Some residual herbicides have contact action and affect the emerging roots and stems, while others enter the root and underground parts of the plant and translocate to their target site.

Preemergence treatments are always carried out before weed emergence. Post-emergence treatments are applied after the crop and (usually) the weeds have emerged.

Two of the most important factors determining spray effectiveness are the range or spectrum of droplet sizes and target coverage by the spray.

Small droplets provide very good coverage and adhere well to surfaces that are difficult to wet, such as waxy grass leaves, but they are prone to drift and evaporate quickly, especially at low relative humidity. Larger droplets tend to bounce and detach from “hard-to-wet” surfaces, but in this case, drift and evaporation are less of a problem. To achieve good coverage of these diverse targets, a wide range or spectrum of droplet sizes is preferred, and the correct selection of spray nozzles generally fulfills this requirement (Source: Food and Agriculture Organization of the United Nations https://www.fao.org/3/t1147s/t1147s0e.htm).

Herbicide Application Equipment in Fruit Farming

There are several types of equipment used in fruit farming for herbicide applications. Among them are backpack sprayers, hydropneumatic application bars (suspended or trailed), application motorcycles with bars and electric pumps, among others.

Nozzles for herbicide application

The functions of a nozzle are to divide the liquid into droplets, form the spray pattern, and control the flow or discharge rate of the liquid. The most commonly used nozzles for weed control are fan nozzles. Within this category, the most common types are flat fan nozzles with an application angle of 110° or 90° (tips) and “mirrored” nozzles that can generate an application angle ranging from 130° to 160°.

Within both types of nozzles, there are options with air injection (anti-drift effect) and without air injection. There are various brands available on the market, and it is recommended to invest in those that guarantee manufacturing components and technical qualities, such as the recommended flow rate according to the working pressure.

In general, for applications with spray bars, it is recommended to space the nozzles between 50 to 60 cm apart on the application bar, with a recommended application height of 50 to 60 cm.

The quality of the spray, or the range of droplet sizes, becomes finer as the size of the orifice in the fan nozzle is reduced, and the nozzle angle and application pressure increase. Conversely, the spray quality becomes coarser as the orifice diameter is increased, and the nozzle angle and application pressure are reduced.

The quality of the application, similar to foliar applications, depends on three components described in Figure 1.

Figure 1. Responsibility of factors in achieving effective control through application.

  1. Choosing a good herbicide product (active ingredient and effective formulation) with sufficient backing, a reasonable cost for the intended purpose, ideally with low environmental impact, and always considering the recommended dosage range.
  2. Using agrochemical products in a timely manner based on the developmental stages of the crop and the target weeds.
  3. Lastly, using application equipment that is always well-maintained, clean, and properly calibrated to perform applications within a wide range of water volumes or application rates.

Herbicide applications can be conducted at different travel speeds, depending on various factors. However, it is always recommended to choose the highest possible transit speed in orchards based on the topography and available equipment. Application speed ranges (provided as reference) can vary widely, from 3.6 km/h (for backpack sprayers) to 5.5 km/h for suspended hydraulic sprayers with spray bars or motorcycles with electric pumps and spray bars.

Do we apply to 100% of the surface or a proportion of it?

We can perform weed control on the entire surface of a hectare or only a proportion of it (more common recommendation) by leaving a central strip of vegetation cover in the middle of the rows, which is generally 50% of the surface.

Regardless of the chosen weed control and vegetation cover management approach, herbicide doses are expressed in doses per hectare (kg or L).

The recommended water volumes for applications vary and depend on the type of herbicide being used. As examples, some recommendations suggest volumes between 100 and up to 300 L/ha.

If we consider applying to 50% of the surface (over the row) and the commercial product recommendation is 2 L/ha with an application volume of 100 L/ha, we would need to use only 1 L on one physical hectare and a volume of 50 L for wetting.

The example above may seem common sense, but improper use or overdosing of certain herbicides occurs because the calculated, purchased, and applied doses are the “total” doses per hectare.

Continuing with the example and considering an orchard with a row spacing of 4 meters, to apply to 100% of the surface (label recommendation) with a spray bar equipped with nozzles spaced 50 cm apart, we would need 8 nozzles to cover the row width.

The arrangement of the nozzles should include an overlapping pattern between their spray fans, as described in the following diagram:

[Diagram showing nozzle arrangement]

If we consider an application speed of 5.5 km/h, the time available for application within the crop (excluding turns) is 27.27 minutes.

The nozzles that can be chosen for this recommendation are AVI 11001 Orange with a pressure of 4 bars (flow rate of 0.46 L/minute). Total number of nozzles: 8.

To cover only 50% of the surface, we can simply “eliminate” 4 of them (the central ones) and leave 2 at each end of the herbicide bar.

It is always recommended to maintain an application height of 50 to 60 cm (maximum) to achieve the desired spray width and uniform deposition.

Timely and effective weed control will always be part of the profitability of cherry and other fruit crops. Do not neglect it.

To develop efficient and effective application management plans, it is necessary to have equipment that has been previously diagnosed in all its components, repaired, critical elements replaced, undergo annual and periodic maintenance, ensure ongoing cleanliness, and have highly trained personnel to carry out applications that will translate into the success of our crop at harvest time with minimal impact on the environment and people.


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