Abstract

MOLINA-FREANER, Francisco; ESPINOSA-GARCIA, Francisco  and  SARUKHAN-KERMEZ, José. Weed population dynamics in a rain-fed maize field from the Valley of Mexico. Agrociencia [online]. 2008, vol.42, n.6, pp.655-667. ISSN 2521-9766.

Maize has a highly diverse weed flora in Mesoamerica, with a high proportion of native weed species. The long agricultural history of maize in Mesoamerica has imposed selection regimes that adapted native weeds to maize farming systems. These native weeds are expected to exhibit stable or increasing populations under traditional maize culture where herbicides are not used. In this paper, we study the population dynamics of major weeds occurring in a rain-fed maize field in the Valley of México. Eighteen species were recorded in the seed bank that showed a seasonal variation from 24 169 to 135 770 viable seeds m^-2. The four most abundant species represented 93% of the total seed bank and exhibited contrasting patterns of emergence that represented 2.2 to 3.1% of the initial seed bank. The first cohort was eliminated by mechanical cultivation while the second exhibited greater survivorship and fecundity than those emerging later. Weed species exhibited a wide spectrum of variation in finite rates of population increase (0.6-9.17): populations of Lopezia racemosa (λ=7.02), Galinsoga parviflora (λ=9.17) and Salvia tiliifolia (λ=1.81) exhibited values greater than one while Acalypha indica var. mexicana showed values less than one (λ=0.60). We argue that variation in population increase is associated with emergence patterns and with the maize monoculture and maize-alfalfa rotation system.

Keywords : Acalypha indica; Galinsoga parviflora; Lopezia racemosa; seed bank; traditional farming systems; weed demography.

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