by Marie-Claude Boileau | 30 January 2019
Published in Turfgrass Society Research Journal 12: 713-719
Pesticide restrictions in Ontario, Canada have prompted research into weed control strategies for establishment of turfgrass areas in conjunction with overseeding programs. A greenhouse study and three field studies were conducted to determine if corn gluten meal (GM) or hydrolyzed corn gluten meal (HGM) could be used to reduce weed populations for establishment of Kentucky bluegrass, fine fescue and perennial ryegrass turf, and for overseeding with perennial ryegrass. In all studies the herbicide Bensulide was added as a positive control treatment. In the greenhouse GM was shown to decrease survival of all weed seedlings (white clover, black medic, dandelion, and prostrate knotweed). Prostrate knotweed was the only weed with reduced germination and survival in pots treated with HGM. Kentucky bluegrass and perennial ryegrass establishment were negatively impacted by Bensulide although there was no impact on grass establishment for GM and HGM, except for the 60% lower survival rate of Kentucky bluegrass seeded one week after treatment with GM. In grass establishment field trials the GM and the HGM did not negatively impact the establishment of Kentucky bluegrass, fine fescue, and perennial ryegrass turf. A significant reduction in weed establishment was observed in the fine fescue establishment as long as the seeding occurred between 2 weeks before to 4 weeks after application. However, there were high weed populations in all plots. GM reduced white clover establishment when it was overseeded into an existing turfgrass stand. The results show that while there is limited efficacy of either GM or HGM to reduce weeds during the establishment of turfgrasses, GM may reduce invasion of weeds into existing turfgrass stands.
by equipewp | 30 January 2019
Published in TPN 56(2): 43-49. The hydrous status of seeds and pollen can now be characterized more precisely than moisture content through the measurement of water activity (aw). This new technique, now available to managers of genetic resources banks, offers the advantage of being fast, easy to use and, above all, nondestructive. (…)
by Audrey Verreault | 30 January 2019
Published in Landscape Ecology 29: 111-126. https://doi.org/10.1007/s10980-013-9966-x
Recurrent and synchronous spruce budworm (SBW) outbreaks have important impacts in boreal and sub-boreal forest ecosystems of North America. This study examines the early phase of an outbreak that was developing across a 268,000 km2 area over a period of 9 years (2003–2011). The territory was subdivided in 225 km2 cells, and the relative influence of forest composition, elevation, forest age, average degree-days and soil drainage were examined during three development phases of the outbreak: initial epicenter location, relatively longdistance spread (cell-to-cell expansion), and expansion inside individual cells (within-cell expansion). The results indicate that elevation is the most determinant variable for initial epicenter location. Other variables that were identified as important for outbreak development by previous studies, such as forest composition and average degree-days, were not so important during this phase. However, forest composition and average degree-days were important factors during the cell-to-cell and within-cell expansion phases. Separating outbreak development in distinct phases also allowed to integrate phase-specific spatial and temporal covariates that were highly significant in the models, such as distance from previous year defoliations during the cell-to-cell expansion phase, and the proportion of defoliated stands during the preceding year for the within-cell expansion phase. Overall, this study provides limited evidence that patterns of SBW outbreak expansion could be altered by reducing host tree species abundance in the forest [mainly balsam fir (Abies balsamea) in this region]. More generally, this study suggests that the influence of environmental variables on SBW outbreak development is clearly phase-dependent, and that this landscape-level, process-based approach could be useful to forecast insect outbreak development in forest ecosystems.
by Claire Morin | 30 January 2019
Published in Canadian Journal of Forest Research 43: 66-77
Along with climate, multiple global or large-scale change agents shape forest ecosystem health. We present a case study where we attempted to elucidate the driving factors causing decline symptoms in white spruce (Picea glauca (Moench) Voss) in young spruce–fir boreal stands. Tree defoliation rate in the studied areas was related to the foliage discoloration intensity of the 2-year old needles and the decreasing stem basal area increment from 1997 to 2008. The onset of this growth decline in 1997 coincided with the occurrence of extremes for four climatic indices. The foliage of affected trees was deficient in K. The relationship between tree decline and K deficiency was tested through a diagnostic fertilization trial using a two-level factorial combination of N, K, and Mg. The trial indicated that K was the single limiting nutrient among the three tested elements. A single K addition increased stem basal area by 43% on average after 11 years. It is hypothesized that the poor K status of trees can be attributed to a series of natural and anthropogenic disturbances along with past forest management activities. Climate change in the region since the last decades also may have contributed to exacerbate K deficiency in such forest ecosystems.
by Audrey Verreault | 30 January 2019
Published in Vadose Zone Journal 13(3). https://doi.org/10.2136/vzj2013.05.0081
Seedlings are rejected every year in forest nurseries because of insufficient root development and root plug cohesion. Adequate substrate bulk density and aeration properties are of critical importance for root growth and water and nutrient uptake. The quality norms for nursery substrates, based in part on the ratio of coarse to fine particle sizes, have recently been questioned with respect to substrate performance. We conducted experiments in 2008 and 2009 under commercial nursery conditions to determine the effects of substrate physicochemical properties on seedling growth and nutrition. Seedlings were grown in 13 different substrates composed of coarse and fine peat particles (threshold size: 0.5 mm), perlite, and vermiculite, covering a broad range of physical properties with adequate available water and various coarse/fine particle ratios and aeration properties. Substrate properties had significant effects on growth parameters in both years. Seedling growth was affected by water stress in 2008 and low gas diffusivity in 2009. This study emphasizes the importance of management on substrate performance, indicating that short periods of moderate water stress (matric potential lower than −10 kPa) may hinder seedling growth. It also suggests that when irrigated substrates are maintained within the 0 to −5 kPa matric potential range, gas diffusivity should not be lower than 0.003 to 0.005 cm2 s cm−2 s−1, in agreement with the modeled O2 profiles in root plugs. Hence, when designing and using substrates at the nursery scale, more attention should be paid to aeration properties after potting and to the management rather than to the coarse/fine particle ratio.
