Picão-preto: uma planta daninha especial em solos tropicais

Abstract

RESUMO -Bidens pilosa está presente em praticamente todo o território brasileiro, além de vários outros habitats tropicais. Entre as características presentes na planta, a abundante e longa produção de propágulos, o fotoblastismo preferencial, o uso eficiente da água, a elevada extração e utilização de nutrientes, bem como características morfofisiológicas específicas, conferem vantagem na competição com as principais culturas anuais e perenes. Devido à plasticidade e flexibilidade adaptativa de B. pilosa e às interações de suas características na determinação da competitividade desse vegetal, torna-se difícil identificar aquelas que realmente se associam com elevada capacidade competitiva e que possuam maior expressividade. Dentro da espécie ocorrem biótipos resistentes a determinados herbicidas, o que dificulta seu controle nas áreas agrícolas. O uso de outros métodos de manejo também possui entraves, devido à ampla variação do fluxo de disseminação, germinação e emergência de propágulos e, ainda, às associações benéficas dessa espécie com microrganismos presentes no solo. Embora seja dotada de características que a tornam infestante agressiva nas áreas agrícolas, este trabalho reporta alguns mecanismos que podem ser usados para o manejo integrado da espécie. Além disso, B. pilosa apresenta propriedades medicinais, sendo necessário o aprofundamento científico para usufruto de seus benefícios.Palavras-chave: Asteraceae, Bidens pilosa, Manejo Integrado de Plantas Daninhas, polimorfismo germinativo, resistência a herbicidas.ABSTRACT -Bidens pilosa occurs in practically all the Brazilian territory, besides several other tropical habitats. This plant's most advantageous aspects in the competition with major annual and perennial cultivars are its abundant and long propagule production, preferential photo-blastism, water use efficiency, high nutrient extraction and use, and morphophysiological characteristics. Due to B. pilosas plasticity and adaptative flexibility, as well as interaction of the characteristics determining its competitiveness, it is difficult to identify those which are associated with higher competitive capacity and expressiveness. This species presents biotypes resistant to some herbicides, rendering its control difficult in agricultural areas. The use of other management methods is also difficult, due to the wide variation in the flow of propagule dissemination, germination and emergence, as well as the beneficial association of this weed with microorganisms present in the soil. Although this plant has aggressive infesting characteristics, this work has reported some mechanisms that can be used for its integrated management. B. pilosa also presents medical properties, with extensive scientific studies being necessary in order to obtain benefits.

Microbial activity of soil cultivated with corn in association with weeds under different fertility management systems

“…This finding can partly explain why this species can be established in different edaphic conditions, provide greater competitive ability, and be able to exude the amount of C sufficient to sustain high MB. According to Santos and Cury (2011), B. pilosa has a high potential for nutrient accumulation, and regulation of attraction and/or repulsion of microorganisms; this is probably due to the characteristic of roots exuding a variety of compounds, which make the rhizosphere a highly regulated environment that is adapted to environmental changes. In general, the ratio of corn and weed depends on the species involved and soil fertility management.…”

Comparison of Experimental Methods to Assess the Competitive Ability of Weed Species

“…Crops have been improved and selected to respond to higher levels of factors such as the availability of nutrients and water, and its lack causes more damage to crops compared to weeds [8] (Figure 2). Another study did not find any correlation between the dry mass of different soybean genotypes and their productivity, although this relationship is usually significant when considering the same plant genotype, being more accurate when dry mass is assessed closer to harvest [9]. …”

“…The Genus Bidens infests several crops, being highlighted Bidens pilosa with worldwide occurrence, being also very aggressive and efficient in the extraction of water from soil [9].…”

Reproduction of Pratylenchus zeae on Weeds

“…The release of allelochemicals produced by the weeds and their role as hosts for diseases and pests, among them nematodes, make the cultivation practices much more difficult and lead to reduced yields (Santos and Cury, 2011). Different species of weeds have been recognized as host plants for Pratylenchus spp.…”