Weed management in apple trees

The occurrence of weeds causes economic losses in the most diverse agricultural activities in all growing regions. Weeds are considered to be all species that occur spontaneously in a place of human activity and are causing interference to this activity. Weeds are known as inço, bush, invasive plant, weedy plant, weed, spontaneous plant, ruderal plant and others. Therefore, they are present in all environments as long as there is a space or areas of bare ground with minimum conditions for survival.

Management aims to provide an environment favorable to the crop and unfavorable to weeds. In this context, it is necessary to adopt control and management strategies to reduce interference in the crops of interest.

control methods

• Preventive control: consists of the use of practices and care to prevent or avoid the introduction, establishment and dissemination of certain weed species in orchards and thus eliminate or minimize future problems.

• Cultural control: use of practices aimed at benefiting the crop and disadvantaging weeds, reducing or inhibiting their development, such as defining the management system for the implementation and use of cover crops.

• Mechanical control: reduction of the growth or elimination of weeds by mechanical cutting or pulling with the use of implements that can be manual, motorized backpack or brush cutter attached to the tractor or other forms.

• Physical control: uses practices to prevent the germination or growth of weeds, such as organic soil cover or plastic material, electricity, among others.

• Biological control: control by natural enemies, such as fungi, bacteria, viruses, insects, birds and other beings, or by products of their metabolism, which reduce the population of weeds or by allelopathy.

• Chemical control: use of chemical products with herbicidal action capable of killing target weed plants or inhibiting seed germination or growth, or even killing some types of plants (selectivity) without causing injury to apple plants.

• Integrated control: consists of the combination of two or more control methods aimed at managing weeds.

Integrated management

Integrated management can be conceptualized as the set of soil and cultural management practices that negatively interfere with the establishment and competition of weeds with apple trees, and can be carried out by preventive, mechanical, chemical or biological means, considering the environmental conditions prevailing in the orchard.

Perennial crops such as apple trees are very suitable for integrated management in the expectation of medium and long-term planning, aiming at control efficiency, facilitating management, providing high productivity and economic return. The methods to be used need to consider the weed species present, the structure of the property, the characteristics of the orchard area and the costs involved.

Integrated management is used in apple orchards in southern Brazil where mechanical mowing (mechanical method) is carried out between the orchard rows and herbicides are applied (chemical method) on both sides of the planting row, which may or may not be associated with other methods. Although the vast majority of orchards adopt integrated management, many small and medium-sized producers only use the mechanical method with periodic mowing between the rows and under the plants in the planting rows.

In practice, no control measure should be used in a single and isolated way, as they are definitely not sustainable in the long term. Efficient management needs to integrate different control methods, which must be chosen depending on the conditions of each orchard. The continuous use of the same method will favor the selection of certain weed species, and in this dynamic the selected species will predominate in the area.

Management in orchards

The age of the orchards needs to be considered when interfering with weeds.

• Newly established or newly formed orchards: In new orchards, competition with weeds is critical and can reduce the growth and development of new plants, delay the beginning of the productive age, reduce initial production and cause difficulties in carrying out cultural treatments.

• Adult orchards or in production: In adult orchards or in production, weeds practically do not interfere with productivity through competition, especially on vigorous rootstocks. However, control is necessary, as uncontrolled and excessively growing weeds impair the effectiveness of treatments in phytosanitary operations, fertilization, thinning and harvesting, with losses in productivity and fruit quality.

Weed species

Knowledge and characteristics of the main weed species present in orchards is important, especially those that are difficult to control, which will guide decisions about which measures to adopt.

The main species present in apple orchards, especially in higher altitude regions, are: ryegrass (Annual ryegrass), white clover (trifolium repens), black walleye (bidens pilosa), white walleye (Galinsoga parviflora), woolly grass (Holcus lanatus), yellow-flowered nutsedge (Hypoxis decumbens), crabgrass (Digitaria horizontalis), marmalade grass (Urochloa plantaginea), turnip (Raphanus the radish), guanxuma (Sida rhombifolia), labaça (Rumex obtusifolius), viola string (Ipomoea spp.), quicuio grass (pennisetum clandestinum), crow's foot grass (Eleusine indica), horseweed (Conyza spp.) and other less important ones.

Registered herbicides

Herbicides are chemical substances that interfere with the biochemical and physiological processes of weeds, causing death and/or preventing development, and may be capable of selecting certain species for control. In the table below, you can see some products registered for use in apple cultivation.

Herbicides are effective under certain application conditions specified in the leaflet.

If possible, perform a single application of the same action mechanism per harvest.

Check the dose to be used considering the main weeds in the orchard.

Prevent the herbicide from coming into contact with the apple tree leaves. Caution increases with excessively growing (tall) weeds.

Use 100 to 450 L/ha of syrup. Each herbicide has a recommended spray volume.

Pressure: 20 to 40 pounds per inch. Regular for producing medium, thick or very thick drops in herbicide applications.

Nozzle or tips: fan type with flat jet or similar, 11002, 8002, 11003 or similar.

Avoid applying herbicides to weeds in advanced vegetative development. The younger the weed plants, the greater their sensitivity to herbicides.

Always use clean water when preparing spray mixtures.

Do not apply during dry periods, avoid the hottest times of the day or before rain.

The application of herbicides with pre-emergence action must be carried out 10 to 20 days after eliminating vegetation with full-action herbicides (glyphosate, glufosinate ammonium or others).

In orchards with the presence of ryegrass or horseweed resistant to glyphosate, it must be associated with other herbicides to control these species.

In newly established orchards, the apple tree is more sensitive, so be more careful with drift.

It is important that the application equipment is well adjusted for uniform distribution of the mixture.

Always work using personal protective equipment (PPE).

Herbicide resistance

The use of herbicides is a fundamental technology in the management and control of weeds in agriculture, which must be preserved in view of the increasing cases of resistance observed in several species of weeds around the world. Many cases have also been reported in Brazil and the southern region close to apple growing areas. Currently, the presence of ryegrass and horseweed with resistance to glyphosate is known in apple orchards.

As a preventive measure, it is important to follow the technical recommendation for the use of herbicides reported in the product leaflets to avoid new cases of resistance, such as using the same product or mechanism of action only once per harvest, observing products, doses, species to be controlled and the recommended application technology. To control ryegrass and horseweed resistant to glyphosate, it is necessary to manage with a combination of herbicides and other methods.

By Zilmar da Silva Souza (Epagri) and Marcelo Goulart Souza (Udesc)

Article published in issue 145 of Revista Cultivar Hortaliças e Frutas