Comparison among different available strategies for weed control in maize

Weed competition can cause severe yield reduction in maize cultivation. Since the sixties the large availability of different herbicides has allowed maize growers to reach appreciable increase in the yield per hectare. At present different strategies based both on chemical and mechanical control can be adopted to control weed infestation. The aim of the study was to compare different weed control strategies currently available in terms of type (chemical, mechanical or a combination of both) that fulfill the requirements of the Directive 2009/128/EC and the guidelines contained in the National Action Plans adopted by the European member states. The study was conducted in 2014 at Turano Lodigiano, Lombardy region, North-west of Italy on a field of about 6000 m2, with 90 plots of 28 m2 each. Plots were completely randomized with three replications for each strategy and several untreated plots. Five weed control strategies were compared: chemical pre-emergence (PRE), chemical post-emergence (POST), chemical pre+post emergence (PRE+POST), mechanical control (MECH), and chemical and mechanical control (CHEM+MEC). In particular, nine different mixtures of herbicides were applied in PRE, 5 mixtures in PRE+POST and 5 in POST. In MECH, weed control was based on a combination of spring-tooth harrowing and ridging, in CHEM+MECH, 4 herbicide applications were combined with ridging. The effects on weed infestation were assessed on key weeds (Abuthilon theophrasti, Amaranthus retroflexus, Chenopodium album, Echinochloa crus-galli, Panicum dichotomiflorum, Poa annua, Portulaca oleracea, Setaria viridis and Solanum nigrum) by measuring plant density (plants/m2), ground cover (\%) and by visually evaluating overall efficacy on a percentage base. Crop yield was also determined for all tested treatments. Untreated plots showed a severe and homogeneous infestation (97.56 plants/m2). Highest weed densities were assessed in MECH (36.00 plants/m2), POST (29.33 plants/m2), PRE (16.07 plants/m2) and CHEM+MECH (9.89 plants/m2). Maximum weed cover values were observed in MECH (46.67\%), POST (34.38\%) and PRE (9.66\%). The visual efficacy of weed control in the different strategies compared was generally close to 100\%. A negligible lack of efficacy was observed in PRE strategies for the formulation containing isoxaflutole (50 g L-1) and thiencarbazone-methyl (20 g L-1) at 2 L/ha field rate and in POST for the formulation containing terbuthylazine (16.94 g L-1), S-metolachlor (28.23 g L-1) and mesotrione (3.39 g L-1) at 4 L/ha. The grain yield was remarkably high (18.5 t/ha on average) without significant differences between strategies, with the exception of untreated plots (0.53 t/ha) and MECH (3.67 t/ha). Overall, the chemical control showed a high efficacy towards most of the weeds. The lack of efficacy seen for MECH strategies was mainly due to the incomplete action of the spring-tooth harrowing intervention.