An Overview of Advanced Weed Management Technologies for Orchards

It is a complex task where multiple weed species at a time, non-uniform germination patterns and rapid growth, herbicide resistance, and weather conditions can pose significant challenges. While reemerging and new technologies and strategies can offer effective solutions, their implementation can be costly. Farmers face a pressing need to manage weeds while minimizing herbicide use. The consequences of poor weed management cannot be ignored: weeds can compete with crops for resources, leading to reduced yields and crop quality. Therefore, exploring innovative approaches like precision chemical and mechanical weeding systems is crucial to ensure optimal weed management and overall long-term orchard health.

Conventional Weed Management

Conventional weed management has long relied on herbicides for weed control. However, negative public perception and side effects of herbicide use (e.g., herbicide drift, illegal herbicide residue in the crop) have called for alternative approaches. Research into the efficacy of conventional weed management techniques has shown that while these methods can reduce weed growth in the short term, they can negatively affect soil health and biodiversity. Overreliance on simplified herbicide programs can lead to the evolution of herbicide resistance, increasing weed management costs.

Advancement in Weed Management Techniques

The future of weed management looks promising as reemerging and new and sustainable solutions are being developed. Several emerging technologies offer farmers more efficient ways to manage weeds. Mechanical weeder, thermal weeder, laser weeder, flame weeder, and electrical weeder are some of these techniques. These methods can potentially be more cost-effective and environmentally friendly than conventional weed management techniques. In addition, non-chemical control tools reduce the likelihood of herbicide resistance evolution.

Mechanical weed control includes using primary and secondary implements to help reduce the rate and spread of certain weeds, kill emerged weed seedlings, and bury weed seeds below the germination zone. These implements include finger hoes, rotary hoes, and chain-link harrow weeders dragged over the field (Figure 1). These implements displace small seedling weeds and expose them to wind and sun-drying effects. Finger hoe weeder and rotary hoe implements are the best mechanical implements for controlling weeds in orchards.

Thermal weed control is a highly effective method that involves the use of heat to eliminate weeds. There are several effective methods for thermal treatment, including hot water (or steaming), flaming, and lasers. These methods offer a comprehensive solution for controlling weeds.

• Hot water or steam weed control involves using heat to kill weeds. The Weedtechnics Satusteam product, SW2100, is an example of an effective weed management tool (Figure 2A). It is suitable for use in orchards and can provide custom trailer options with the Weedtechnics Orchard Head and hydraulic arms for continuous delivery from a vehicle-mounted applicator head. The SW2100 can operate with single or dual rowtech heads and an orchard head up to 4 feet wide. The Orchard Head can move in any direction necessary to treat orchard rows effectively. The greatest limitation of this technology is the need for large quantities of water and fuel to generate the heat and the limited speed by which the treatment is applied.
• Flame weed control involves directing a controlled stream of propane gas and fire toward the weeds in the tree row, causing them to wilt and die. The flames are typically mounted on a frame that can be towed behind a tractor, allowing for efficient and precise application. While flame weeders are commonly used in corn farming, they can be applied to various crops, including tree fruits. Their efficacy depends on weed species and size, with annual broadleaf weeds being easier to control than grasses in general.
• Laser weed control is another promising method for weed treatment. This approach is gaining popularity due to its precision and environmental friendliness. Although several trials have been carried out in vegetable production fields using laser weeders, there is scarce information on trials in orchards. Unlike flame weeders, which can cause damage to the crop, laser weeders can selectively target weeds while leaving other desirable plants unharmed.

Electrical weed control is another promising technology that involves passing an electric current through a weed. Weeds resist the electrical current, generating heat, causing them to wither and die. Although electrical weeding has been around since the late 19th century, interest has been regained in optimizing its use in various cropping systems. Figure 3 depicts a RootWave electrical weeder attached to a tractor's PTO via a three-hitch point. In orchards, this electrical weeder operates along tree rows against the trees to remove weeds under the trees. The technology is an effective and sustainable alternative to conventional herbicides. Its efficacy relies on various factors such as the plant species, architecture, morphology, root system size, soil texture, and soil moisture.

Targeted Chemical weed control is a technology that only sprays on weeds. For example, WEED-IT uses plant detection technology that applies chemicals only to the target instead of spraying bare ground. Algorithms are used to distinguish between an actual plant or soil with just a fraction of the fluorescence response. The WEED-IT sensors with blue LED lighting can detect anything containing chlorophyll. These intelligent sensors sample the ground 40,000 times per second, searching for living plant matter up to 15mph. The WEED-IT system measures the ground speed and adjusts application timing so the target is within the spray pattern. WEED-IT Quadro uses one WEED-IT detection sensor with four spray nozzles, and each nozzle accounts for 25 cm (10 inches) of the entire spray boom width (Figure 4). The extra small zones with improved optics ensure the system never misses weeds.

While the technologies for mechanical weed control mentioned above offer exciting opportunities for weed management, it is essential to acknowledge that each weed management technique has its own limitations. For instance, flame weeding may be unsafe to use in dry or windy conditions due to fire risk. Laser treatment may be limited due to equipment maintenance requirements and its suitability for certain weed species. Similarly, electrical weeders may be impractical for more extensive areas or areas infested with perennial or older weeds. Despite these limitations, these methods offer an eco-friendly and sustainable alternative to conventional herbicides and be part of an integrated weed management program. It should also be noted that mechanical weed control typically requires multiple treatments for prolonged and satisfactory weed control because of the non-uniform germination patterns of the various weed species. One significant barrier hindering the widespread adoption of the aforementioned technologies is the substantial initial investment required to acquire the necessary equipment.

Robotic Weed Management Systems

The future of weed management looks promising with the emergence of robotic systems. These systems are expected to revolutionize weed management by providing unprecedented precision and efficiency. Robotic weed removal systems can perform self-guidance, weed detection, mapping, and control, all while ensuring the surrounding crops remain untouched. Several companies are currently developing autonomous solutions for mechanical weeding to minimize the use of herbicides and reduce their impact on the environment, such as Naio Technologies (Figure 5A) and Vitibot (Figure 5B). Both are mostly used for vineyards at this stage.

There are a few robotic spraying systems that can be used for weed management in orchards. One is GUSS Automation's latest product, the Herbicide GUSS (Figure 6A), which incorporates LIDAR (Light Detection and Ranging) to navigate the sprayer in the tree row. With nine weed detection sensors, it can detect and spot-spray weeds on the orchard floor. Another one is the XAG R150 unmanned ground vehicle (UGV) with spray settings (Figure 6B), which includes two main sections: a self-driving unit that uses RTK-GPS navigation to autonomously follow a pre-planned path from a smartphone app and a spray unit for precise application. It is designed with the ability to adjust its vertical pitch angle to a maximum of 200°, which can be used for spray herbicides when the angle range is set to target the orchard floor under tree rows (need to validate).                      

Conclusion

Precision weed management is becoming increasingly promising with advancements in weed detection and the adoption of robotic technologies. Spraying only weeds is expected to dramatically minimize the usage of herbicides for weed management in orchards. In the long term, implementing advanced precision weed management systems not only ensures crop yield and quality but also maintains the sustainability of the agricultural industry by reducing production costs and environmental impact.