Using energy requirements to compare the suitability of alternative methods for broadcast and site-specific weed control

Abstract

The widespread use of herbicides in cropping systems has led to the evolution of resistance in major weeds. The resultant loss of herbicide efficacy is compounded by a lack of new herbicide sites of action, driving demand for alternative weed control technologies. While there are many alternative methods for control, identifying the most appropriate method to pursue for commercial development has been hampered by the inability to compare techniques in a fair and equitable manner. Given that all currently available and alternative weed control methods share an intrinsic energy consumption, the aim of this review was to compare methods based on energy consumption. Energy consumption was compared for chemical, mechanical, and thermal weed control technologies when applied as broadcast (whole-field) and site-specific treatments. Tillage systems, such as flex-tine harrow (4.2 to 5.5 MJ ha−1), sweep cultivator (13 to 14 MJ ha−1), and rotary hoe (12 to 17 MJ ha−1) consumed the least energy of broadcast weed control treatments. Thermal-based approaches, including flaming (1,008 to 4,334 MJ ha−1) and infrared (2,000 to 3,887 MJ ha−1), are more appropriate for use in conservation cropping systems; however, their energy requirements are 100- to 1,000-fold greater than those of tillage treatments. The site-specific application of weed control treatments to control 2-leaf-stage broadleaf weeds at a density of 5 plants m−2 reduced energy consumption of herbicidal, thermal, and mechanical treatments by 97%, 99%, and 97%, respectively. Significantly, this site-specific approach resulted in similar energy requirements for current and alternative technologies (e.g., electrocution [15 to 19 MJ ha−1], laser pyrolysis [15 to 249 MJ ha−1], hoeing [17 MJ ha−1], and herbicides [15 MJ ha−1]). Using similar energy sources, a standardized energy comparison provides an opportunity for estimation of weed control costs, suggesting site-specific weed management is critical in the economically realistic implementation of alternative technologies.

A Review of Non-Chemical Management of Couch Grass (Elymus repens)

“…However, even reasonably objective effects can be difficult to compare. For example, Coleman et al, [166] found that many mechanical treatments use less energy than glyphosate per pass because of the energy needed to produce glyphosate. However, they could only estimate glyphosate energy consumption based on one old study since this information is considered a trade secret.…”

“…This means that after a successful application, glyphosate will often not need to be applied as frequently as the tillage strategies, which may have to be applied annually or biennially. By some estimates, tillage treatments against annual weeds can have a lower overall energy cost than glyphosate [166], but for perennials like E. repens this is likely to be offset by the increased number and frequency of operations that are needed for control. One of the major arguments against tillage has been that it increases the risk of nutrient leaching and erosion, especially if conducted during periods of heavy rainfall, which is often the case in autumn.…”

“…Van Evert [110] suggested that one way to make selective cutting an efficient control method of R. obtusifolius was to design a robot that would perform weekly cuttings. Such targeted spot-applications are also a way to make other defoliation methods more resource efficient [166] and a way to perform non-selective treatments without damaging or killing the crop. Compared to R. obtusifolius, a grass such as E. repens is far more difficult to distinguish in grasslands, but targeted applications are likely to be possible in other crops.…”

“…The main non-chemical control method for E. repens is still tillage as other non-chemical control methods either use too much energy unless spot-applied [166], or they are too ineffective against E. repens. Tillage also has a high efficacy against E. repens, is effective against many weed species, but requires many passes/treatments to be effective against E. repens and other perennial weeds.…”

Tillage based, site-specific weed control for conservation cropping systems

“…The ability to directly target individual weeds provides the opportunity for the introduction and use of alternate weed-control technologies. One reason for the lack of development of these technologies is the unacceptably high energy (and hence, cost) requirements for effective weed control (Coleman et al 2019). The research of Coleman et al (2019), however, highlighted that the site-specific weed control approach that, due to the substantial energy and cost savings, creates the opportunity to develop alternative, nonchemical weed-control technologies for large-scale crop production systems.…”