Hot foam: Evaluation of a new, non-chemical weed control option in perennial crops

Hot foam applications represent a new, smart concept in the field of thermal weed control. The aim of this study was to evaluate the efficacy of hot foam and other weed control methods in two olive groves in southern Greece (Pyrgos and Kalamata). The experiment was laid out in a randomized complete block design (RCBD) with six treatments and three replicates. Treatments were applied in the areas between trees, in the row and included mowing with a disc-flail mower, mulching with pruning residues (2.65 kg m(-2)), glyphosate (at 1,440 g a.e. ha(-1)), hot foam (13.33 L m(-2)), pelargonic acid (at 1,088 g a.i. ha(-1); twice), and an untreated control. Two experimental runs were conducted at each site using the same treatment list. Malva parviflora L. and Sinapis arvensis L. were the predominant weeds in Pyrgos, while Urtica urens L., Galium aparine L., and Parietaria officinalis L. dominated in Kalamata. Site-experimental runs and treatments significantly affected NDVI and weed biomass ( P -Value <= 0.001). Hot foam reduced weed biomass by up to 81, 88, 90, and 96% compared to mulching, mowing, pelargonic acid, and the untreated control, respectively. This treatment also reduced M. parviflora biomass by 75- 88 and 92-93% compared to mowing and pelargonic acid, respectively, in Pyrgos and P. officinalis biomass by more than 80% in Kalamata compared to the above treatments. In all site-experimental runs, hot foam and glyphosate resulted in the lowest NDVI and weed biomass. The overall performance of hot foam was comparable to glyphosate, suggesting that this method is an environmentally friendly and effective, alternative method to control weeds in olive groves. Further research is required to optimize the use of hot foam for weed control in more perennial crops and under different soil and climatic conditions.