Factors affecting glyphosate activity in Imperata cylindrica (L.) Beauv. and Cyperus rotundus L. II: effect of shade

Abstract

Summary: Imperata cylindrica and Cyperus rotundus were grown under three different light regimes; unshaded, 50% shade, and 75% shade and no shade plus 75% shade before and after spraying, (temporary shade) in a heated greenhouse. Six weeks after the start of the experimenis, glyphosate was applied to the plants at 0·2, 0·4 and 0·8 kg/ha (for Imperata) or 0·3, 0·6 and 1·2 kg/ha (for Cyperus). Glyphosate toxicity was enhanced as shade increased. In Imperata, all shade regimes at all rates of glyphosate eaused greater damage to the plants than the unshaded regime. The reduction in shoot dry weight, rhizome dry weight and total carbohydrate content of Imperate rhizotties at 75% continuous and temporary shaiie conditions, with the lowest rate of glyphosate, was almost twice as much as the reduction in the same features m the unshaded plants caused by the highest rate of glyphosate. In Cyperus. glyphosate at the intermediate and highest rates decreased the shoot dry weight at 75% continuous shade by 79% and 98% respectively. Plants in 50% shade were significantly affected only at the highest rate of glyphosate. Sprouting ability of the tubers al 75% continuous shade was inhibited when the tubers were replanted for recovery. Enhanced toxicity of glyphosate in reduced light intensity was attributed to the morphological changes in the nature of the leaves caused by shade.

Shade-based control of Imperata cylindrica: tree fallows and cover crops

“…The susceptibility of Imperata to herbicides is also greater in plants grown under shade, as reported for the herbicides dalapon (Sukartaamadja and Siregar, 1971) and glyphosphate (Moosavi-Nia and Dore, 1979). This is due to the depletion of carbohydrates in roots and rhizomes in plants grown under shade.…”

“…In an experiment using unshaded, 50% and 75% shade, Moosavi-Nia and Dore (1979) found reductions in shoot dry weight, rhizome dry weight and total carbohydrate content of Imperata rhizomes of plants grown in shade. They also reported significant reductions in rhizome and tuber-bulb production compared with plants grown in normal daylight.…”

Manejo de tiririca e trapoeraba com glyphosate em ambientes sombreados

“…Com o sombreamento, ocorrem alterações na morfologia e na estrutura foliar, como a expansão do limbo foliar, ocasionada pela turgidez e alongamento das células desse órgão, e a diminuição na deposição de ceras epicuticulares (Magalhães, 1967;Moosavinia & Dore, 1979;Lima Jr. et al, 2006;Gondim et al, 2008;Gobbi et al, 2009). Essas mudanças são relacionadas à maior interceptação e absorção foliar de herbicidas aplicados em pós-emergência.…”

“…As plantas cultivadas a pleno sol foram mais eficientes na translocação e distribuição dos carboidratos para suas estruturas de reserva, quando comparadas às de sombra, aumentando a produção total de tubérculos (Tabela 3). Em média, a produção de tubérculos em plantas a pleno sol foi 16,1 e 29,5% superior à de 30 e 50% de sombra, corroborando Moosavinia & Dore (1979), que observaram redução no número de tubérculos em plantas sombreadas, quando comparadas às de pleno sol.…”

“…As doses superiores a 810 g ha -1 de glyphosate foram responsáveis por valores acima de 93% no controle dos tubérculos de tiririca cultivados a 30 e 50% de sombra. Moosavinia & Dore (1979) obtiveram resultados semelhantes em plantas de tiririca manejada com diferentes níveis de sombreamento e doses de glyphosate; com o aumento do estresse luminoso, ocorre diminuição significativa dos tubérculos viáveis.…”