Weed flora and dormant‐season cover crops have no effects on arbuscular mycorrhizae of grapevine

Abstract

Baumgartner K, Fujiyoshi P, Smith R & Bettiga L (2010). Weed flora and dormant‐season cover crops have no effects on arbuscular mycorrhizae of grapevine. Weed Research50, 456–466.SummaryWe tested the hypothesis that arbuscular mycorrhizal fungal (AMF) diversity and colonisation of grapevine increase with increasing frequency and diversity of mycorrhizal hosts on the vineyard floor. The vineyard floor cover was manipulated by cover cropping (rye, triticale) inter‐rows, and implementing weed control treatments in intra‐row areas. Weed control treatments were the standard practice of pre‐emergence applications of oxyfluorfen or simazine, and alternatives of post‐emergence applications of glyphosate or oxyfluorfen, and cultivation. Grapevine mycorrhizal colonisation and frequency, diversity and richness of mycorrhizal weeds were examined for 3 years, after which AMF diversity was evaluated using PCR. Canonical correspondence analyses showed that weed control, but not cover crops, affected weed composition; cultivation and post‐emergence treatments were dominated by mycorrhizal weeds (Sonchus oleraceus and Conyza canadensis respectively), pre‐emergence treatments were dominated by non‐mycorrhizal Cyperus esculentus. Weed frequency varied among treatments; cultivation was less effective than both herbicide treatments in the first year, and both cultivation and post‐emergence herbicide were least effective in the last year. Therefore, the alternative weed control methods may not be as effective as the pre‐emergence herbicide. Weed control had a significant interaction with year on frequency, diversity and richness of mycorrhizal weeds, none of which correlated with grapevine mycorrhizal colonisation. Our finding of no effect of weed control on grapevine mycorrhizae, despite significant effects on weeds, provide no support our hypothesis, but rather suggest that mycorrhizal hosts on the vineyard floor have no influence on grapevine mycorrhizae.