Amaranthus palmeri expands in Portugal

The plant Amaranthus palmeri has been identified in Portugal. Technicians from the National Institute of Agricultural and Veterinary Research (INIAV) and the Beja School of Agriculture detected populations in cornfields in the Tomar region, in the west of the country. According to reports, this is the second year they have found it in the region. There are also reports of its presence in Ribatejo, Coruche, and Sobralinho.

The species belongs to the Amaranthaceae family. It grows quickly, reaching up to three meters in height and producing over 600 seeds per plant. It has a high adaptability, preferring regions with hot summers. It develops rapidly when light, high temperatures, water, and nutrients are available. It is highly competitive in spring-summer crops such as corn, tomatoes, and sunflowers.

The plant is dioecious, with male and female flowers on distinct individuals. It has rhomboid-ovate leaves, a petiole longer than the blade, a purple coloration at the base of the seedling, and a waxy sheen on the stem. The inflorescences are spikes or panicles, and the female flowers have spiny bracts. Germination is favored by light.

Specimens found in Spain have already shown resistance to nine different herbicide modes of action, including substances such as glyphosate, nicosulfuron, terbuthylazine, and mesotrione. Resistance in Portuguese specimens has not yet been confirmed, but the species' high genetic variability increases the risk.

Experts recommend continuous monitoring of plots, early identification, and the adoption of integrated protection strategies. Cultural methods include deep tillage (minimum 20 cm), dense cover crops in the fall/winter, increased planting density, and rigorous sanitation of agricultural machinery. Harvesting should begin in uninfested plots, with cleaning between plots.