Effectiveness of mechanical weed control on Italian flint varieties of maize

Weed control is one of the most important practices for a satisfying crop performance. In organic farming, weeds are mainly controlled by using mechanical methods, which may result in incomplete crop selectivity. Maize is one of the crops for which mechanical weed control is commonly applied. To assess weed control efficacy and the possible crop injuries caused by mechanical interventions (harrowing, hoeing and ridging), a field experiment was carried out in 2013-2014 on traditional flint Italian varieties of maize (Marano, Ottofile, Pignoletto, Nostrano and the hybrid Maranello) suited for organic food production. The study included the following treatments: weed control with a spring tine harrow + hoeing and ridging (STH), manual weed removal all season long (MWR), spring tine harrowing + manual weed removal (STH + MWR) and an untreated check (CHK). In the 2 years, the experiment was carried out in two similar fields in which 60 plots (6 x 10 m) were arranged in a RCBD with three replications. Weed control efficacy was assessed by determining weed density, weed species composition and weed cover after each mechanical intervention in the STH and CHK plots. Weed diversity indices were also calculated at the final assessment. The possible crop injuries caused by mechanical means were assessed by determining maize plant height, number of leaves, and plant density after each mechanical intervention. At maturity, maize yield and other yield-related traits (1000-seed weight, hectolitre weight, and grain moisture) were determined. The results showed that the mechanical treatments lowered the weed infestation, without changing weed species dominance and slightly lowering species richness; even though they were not able to completely control the weeds. In both years, the final weed density in STH plots was of about 50 plantsm(-2). Better weed control was obtained when weeds were at early growth stages and with a repeated number of harrowing. Mechanical weeding did not cause significant injury in terms of plant height nor density; however, for Marano and Maranello, a delay in the crop cycle was observed as shown by the lower number of leaves in STH compared with MWR. Yield ranged from 0.3 t ha(-1) for Marano CHK to 10.4 t ha(-1) for the hybrid Maranello in MWR + STH. Yield and yield-related traits were not affected by mechanical weeding.