Tolerance of Grindelia chiloensis (Asteraceae) to pre- and postemergence herbicides

Abstract

Several species of Grindelia (Asteraceae) are known to produce diterpene resin acids with potential uses in the naval stores industry. In recent years, the focus has changed from G. camporum to Grindelia chiloensis as the main candidate for domestication, because of its significantly higher resin content. Most agronomic technology developed for G. camporum has been adapted to G. chiloensis, although weed competition continues to be a problem during establishment, resulting in reductions in plant stands. The objective of this work was to evaluate pre- and postemergence herbicides for weed control in irrigated stands of G. chiloensis. Two greenhouse and field experiments were conducted to evaluate the effect of commercially available broad-spectrum herbicides on biomass production and resin content. Only Dual 8E, Karmex 80DF, AAtrex, and Caparol 4L at intermediate to low doses can be used safely as preemergent herbicides. Once the stand has been established, either by direct seeding or by clone transplanting, pendimenthalin, linuron, propaquazifop, haloxifop- R-methyl, or fluazifop- p-butyl, can be used, because, biomass accumulation was not affected by these herbicides. MCPA when applied at the six to ten leaf stage caused severe damage and plant mortality. Resin content ranged between 22 to 25% (dry weight basis) and no differences were present between the treated and control plants.