Seasonal susceptibility of boreal plants: red raspberry phenology as a bioindicator of optimum within-season timing of glyphosate applications

Abstract

In Canada, forest managers operating under public licenses are under pressure from the public to cease using herbicides or at minimum reduce the quantity of active ingredient applied in the environment. Lacking in their decision-making toolbox is information about biological cues that could help optimize herbicide performance. In 1990, two rates of the herbicide glyphosate, 1.1 and 1.7 kg acid equivalent (a.e.) ha -1 , were applied bi-weekly between July 21 and September 25 using a backpack sprayer to release jack pine (Pinus banksiana Lamb.) seedlings from red raspberry (Rubus idaeus L. var. strigosus (Michx.) Maxim.) competition. On average, the higher application rate reduced raspberry cover by at least 6% more than the lower rate (p < 0.01). Control of raspberry was poor with the earliest application, peaked with mid-to latesummer applications, and decreased with late-season applications. Peak jack pine performance, as measured by stem volume index, followed a mid-August application at the low rate. Earlier applications resulted in substantial herbicide injury and later applications were not as effective at reducing raspberry competition. The optimum timing for jack pine performance corresponded with the period between the beginning of raspberry's floricane senescence (i.e., end of full flowering) and the initiation of primocane senescence (i.e., fruit maturation). Seedlings released in mid-August maintained a growth advantage over other seedlings from the fifth through to the tenth year of this study. Discerning forest managers may choose to use phenological cues from the target species, such as red raspberry, as a bioindicator of glyphosate efficacy.Key words: forest vegetation management, herbicides, herbicide efficacy, phenology, Pinus banksiana, Vision ® , glyphosate, Rubus idaeus RÉSUMÉ An Canada, les aménagistes forestiers en fonction sur les terres forestières publiques subissent des pressions de la part du public pour mettre un terme à l'utilisation d'herbicide ou au moins de réduire la quantité d'agent actif déversé dans l'environnement. Cependant l'information sur les signaux biologiques qui pourrait aider à optimiser la performance des herbicides est absente de leur coffre d'outils d'aide à la décision. En 1990, deux taux de l'herbicide glyphosate, 1,1 et 1,7 kg d'agent actif ha-1, ont été appliqués aux deux semaines entre le 21 juillet et le 25 septembre au moyen d'un pulvérisa-teur individuel dans le but de dégager des semis de pin gris (Pinus banksiana Lamb.) de la compétition exercée par le framboisier (Rubus idaeus L. var. strigosus (Michx.) Maxim.). En moyenne, le taux d'application le plus élevé a réduit la compétition des framboisiers de 6 % de plus que le taux inférieur (p < 0.01). Le contrôle des framboisiers a été faible lors de l'application la plus hâtive, a culminé lors des applications de la mi-et de la fin de l'été et a diminué pour ce qui est des applications de fin de saison. La performance dominante du pin gris, telle que mesurée par l'indice de volume de la tige, s'est...

Ecology and Traits of Plant Species that Compete with Boreal and Temperate Forest Conifers: An Overview of Available Information and its Use in Forest Management in Canada

“…With such a short life span, annuals and biennials rarely constitute a serious obstacle to conifer regeneration. They may, however, reduce height growth of and occasionally even smother (through snow load) small conifer seedlings (Bell et al 1998). Perennials (trees, shrubs, and herbs that live for more than two years) may create greater competition through rapid spring growth from overwintered roots and shoots or rapid recovery following a disturbance.…”

“…Regional forest ecosystem classification (FEC) information linked to plants species, e.g., Klinka et al (1989) and Beaudry et al (1999Beaudry et al ( , 2003 provide information for British Columbia, and Sims et al (1990), Bell (1991), and Bentley and Pinto (1994) provide that for Ontario. Combined with some knowledge of plant resource requirements, resource managers can use this information to develop site-specific silvicultural practices to promote or retard the growth of selected species.…”

“…Autecology guides published in Canada (i.e., Haeussler and Coates 1986, Bell 1991, Louter et al 1993, Bentley and Pinto 1994, Jobidon 1995 provide information about species' nomenclature, growth habit, reproduction, phenology, ecophysiology, and response to disturbance.…”

“…Trait databases are increasingly used by the scientific community to model ecosystem responses to a variety of human-induced changes (e.g., see recent papers in the journals Ecology, Nature, and Science). They may also be useful in applied science (e.g., Aubin et al 2008), as well as for assessing risk and developing silviculture guides (e.g., Bell et al 1998).…”

“…stinging nettle Coding: x = yes, * = possible, some evidence Sources: Anderson (2001), Arnup et al (1995), Bell (1991), Bentley and Pinto (1994), Buse andBell (1992), Campbell et al (2003), Coladonato (1994), Gibson (1961, Harris (1990), Howard (1993), Louter et al (1993, Mallik (1993), Matthews (1992), Ramovs and Roberts (2005), Steinberg (2001), Thiffault et al (2004), Tirmenstein (1999), Tollefson (2007), Trindle and Flessner (2003), Uchytil (1989), Walkup (1991), Zouhar (2001) escape, or resist human-caused disturbance will ultimately depend on the traits it has developed to respond to various natural disturbances such as fire, browsing, insects, and disease (Bell et al 1998). Additional considerations for resource managers include the temporal nature of competition-its likeliness to persistand the ability of individual species to pre-empt resources.…”