Yield Losses of Maize (Zea Mays Subspp.) Due to Teosinte in Northeastern Spain

A new grass weed was reported in 2014 in Spain invading irrigated maize fields, some decades after its appearance in France. In both cases genetic analysis confirmed the relationship with the annual teosinte Zea mays ssp. mexicana but revealed also admixture from maize. No herbicide control of this weed is possible in maize fields due to the crop-weed similarity. Visual observations suggest a high competitive ability of teosinte, although no other experimental data is available. In this research, the effect of teosinte on maize yield at five different densities was studied for three years (2016–18) in on-farm field trials growing maize on an infested plot in northeastern Spain (Huesca, Spain). The most notable results are that a) maximum teosinte density at maize harvest was 15 to 20 plants m −2 ; higher initial density diminished naturally and b) a decreasing linear relationship of yield and maize cobs was found for increasing teosinte density. A 50% yield reduction occurred with 10, 13, and 15 teosinte plants m −2 and 100% yield loss with twice the number of teosinte plants, depending on the year. The teosinte biomasses causing 50% yield loss were 8, 5, and 3.5 t ha −1 ; twice the amount of biomass led to 100% yield loss. Although most teosinte plants emerged some days after the maize, the weed was able to develop and grow perfectly, even surpassing the crop in height. The results demonstrate the importance of maintaining teosinte density as low as possible in maize to avoid yield decreases.