Hot foam weeding evaluation
Weeds are probably one of the main problems that have always affected agriculture productivity, causing yield decreases that, in the worst cases, can wipe out production. The weed control, during recent decades, have been based on chemical methods, often sharing the advantages of economical convenience and simplicity of application, enhanced by the effectiveness of chemical herbicide treatments. Chemical herbicides, within the category of plant protection products, can lead to serious environmental issues. For example, they can lead to imbalances in natural ecosystems by causing permanent damages on some living organisms. Therefore, the need to move the agriculture sector towards sustainable production processes also involves weed management. The Task 3.4 of CONSERWA project is aimed at introducing “eco-friendly” agronomic technologies or practices as alternative and agroecological weed management approach.
The most innovative weed-killing alternative, under evaluation in this Task of the Conserwa project, is based on the employment of a machine designed by an Italian company, which produces hot foam (Figure 1), that is able to denature irreversibly plant tissues. The potential of this innovation lies in applying relatively low temperatures, in the range of 60-80 °C, and keeping them close to the weed plants for few minutes, enough to “boil” the plants.
The effectiveness of the treatment is closely related to the weed species and their morphology. One of the adjustments that can be made on the machine, in fact, regards the speed of the machine's fan, which affects the volume of the foam layer on the soil. A thin layer of foam allows the temperature to be kept concentrated on the soil; vice versa, a more voluminous layer of foam is more diluted but the temperature is distributed in a larger amount of foam. Another important setting that affects the treatment efficacy is the forward speed of the tractor; this last aspect naturally affects the amount of foam that is distributed on the soil unit area.
Leviers testés
- Facteurs: Type of weeding and presence of plant cover
- Modalités: 4 (Glyphosate, hot foam, acetic acid and mechanical weeding)
- Répétitions: 3 per site
Contacts
Testing grounds
The experimental trial is realized in the experimental farm of the University of Bologna, in two locations: Cadriano, where conventional farming is applied (Figure 2), and Ozzano dell'Emilia, where organic farming is applied. The experimental trial started in 2023 and it will end in 2026.
The experimental trial aimed to evaluate alternative treatments to glyphosate and mechanical tillage, in conventional and organic farming, respectively, both in the presence and absence of a cover crop, intercropped with the main crop. In the two main plots of the experimental scheme, in fact, a cover crop consisting of a mixture of Sinapis alba L., Vicia sativa L. and Trifolium incarnatum L. had been sown, with the aim of keeping the soil covered and competing with winter weeds.
Protocol
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The experimental trial aimed to evaluate alternative treatments to glyphosate and mechanical tillage, in conventional and organic farming, respectively, both in the presence and absence of a cover crop, intercropped with the main crop. In the two main plots of the experimental scheme, in fact, a cover crop consisting of a mixture of Sinapis alba L., Vicia sativa L. and Trifolium incarnatum L. had been sown, with the aim of keeping the soil covered and competing with winter weeds.
The cover crop was mulched and the residues superficially buried in March (Figure 4), with the same machine through which the bare soil was tilled.
During the following month, the weed seeds throughout the experimental field germinated and new plants emerged. After this time, experimental treatments were applied, in order to terminate the weeds before the summer crops plantation: maize and soybean in the conventional farm, chickpea in the organic farm. Within each main plot, with winter cover crop precession and bare soil, respectively, treatments were realized by randomizing them across the experimental area, with 3 replications for each treatment.
For each plot, soil samples were taken before treatments to characterize the weed seeds bank prior to the experimental trial and realize soil microbiome analysis, in order to define any consequences of the treatments on the soil microorganisms.
The treatments were carried out on April 17, 2024, during the M12 project meeting, so that all participants could see how the hot foam machine works and interact with the manufacturer (Figure 5).
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Both alternative treatments (hot foam and acetic acid) and control treatments (mechanical soil tillage in the organic farm and glyphosate application in the conventional farm) were evaluated in terms of weeding efficacy, following field survey protocols (Deliverable D2.2). The first field survey was carried out immediately before treatment, by identifying each weed species within 3 survey areas for each plot, each 1 m2 surface.
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The following parameters were monitored for each identified weed species: number of weed plants and phenological stage (Figure 6).
The information collected in the pre-treatment survey (T0) were necessary to define the efficacy of the treatments as the percentage of plant tissue dried or dead, 7 days (T1) and one month (T2) after the treatment. In both surveys, efficacy were considered as the percentage of plant tissues completely dried by the treatment and those partially compromised. The two post treatment surveys are essential to understand the immediate effect of the treatment and the effect in the medium-long term, depending on the ability of the weed plants to recover from the damage obtained.
Results
Preliminary results after one year - Weed analysis
Considering the results obtained from the weed surveys, in the maize crop cultivated in the conventional farm of Cadriano (BO), the hot foam treatment registered higher efficacy rates, in combination with the preceding cover crop, showing the best efficacy compared to the other alternative treatments tested, but with unsatisfactory values, comparing it to the glyphosate treatment (Figure 7).
Regarding the efficacy in relation to each individual weed species, the highest efficacy was recorded for Polygonum aviculare L. and Stellaria media L., with significantly lower values for the other weeds species detected in the plots, as shown in the figure below (Figure 8).
Considering soybean crop, cultivated in the experimental farm of Cadriano, the results recall what has been observed in maize crop. The hot foam treatment shows higher efficacy when it is preceded by the cover crop, with efficacy on weeds decreasing from T1 to T2 (Figure 9).
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Considering specific weeding efficacy on the different weed species, the hot foam treatment registered good results on Papaver rhoeas L., maintaining positive effects at T2 as well, while registering low efficacy on the other weeds species, as shown in the following figure (Figure 10).
Considering chickpea crop, grown under organic farming system in Ozzano dell'Emilia farm (BO), the effects of hot foam treatment are similar to what has been observed for maize crop, under conventional farming: the efficacy of hot foam showed the best results in combination with cover crop, preceding the main crop. Although the hot foam treatment had an acceptable success in weed termination rate, the results were not comparable to the control, which in this experiment is represented by mechanical tillage (Figure 11).
Regarding efficacy for each individual weed species, the field used for the experimental trials respect organic farming management; consequently, the weed species are different from those observed previously for maize and soybean crops. In this experiment, Medicago sativa L. and Veronica spp. L. were more susceptible to hot foam treatment (Figure 12).
Preliminary results after one year – Crops analysis
The yields obtained after maize harvest showed that hot foam led to significantly lower productivity than the other experimental treatments. Hot foam treatment was not able to reach a sufficiently long effect, in order to allow the maize to compete with the weeds, lowering the plant cover of the maize above the ground. Competition with the weeds, which affected plant growth, probably led to stress conditions for the plants, that affected the productivity of maize crop (Figure 13).
Due to low efficacy of hot foam and the consequent excessive weed-crop competition during the soybean growing cycle, combined with excessive abiotic stresses for this crop, no grain production was obtained during the first growing season of soybean.
Considering the environmental stresses experienced during 2024, in 2025 chickpea crop will be cultivated also in Cadriano farm, as legume crop, trying to cultivate a more resilient crop to climatic stresses.
Considering organically grown chickpea, on the other hand, the production results of the hot foam treatment plots were comparable both in terms of yield and seed size with the other treatments, and this evidence was confirmed also by the chickpea's ability to compete with weed plants (Figure 14).
Preliminary results after the first year of experimentation with hot foam machinery
The variability in results between the two farms underscores the complexity of implementing innovative weed control solutions across different agricultural systems. In the conventional system, hot foam and acetic acid treatments lacked sufficient efficacy to control aggressive weed growth. This is likely due to suboptimal application timing and dosage. Additionally, the absence of cover crops may have exacerbated weed proliferation in these plots.
In the organic site, however, the integration of cover crops significantly enhanced weed suppression. The combination of natural weed control techniques with rotational cropping appears particularly effective in promoting crop health. These results highlight the potential of integrating innovative and traditional methods within organic systems, to achieve superior outcomes.
Conclusion
The first-year trials offer valuable insights into the strengths and limitations of hot foam technology. While the method demonstrated interesting perspectives, particularly in organic systems, significant optimization is required to ensure its efficacy and scalability in conventional farming. Cover cropping emerged as a vital tool for enhancing weed management, across both farming systems. The next years of research will focus on refining application protocols for hot foam and acetic acid.
