Creeping bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua) putting greens are difficult to manage without fungicides. Earlier research showed that two commonly used fungicides, iprodione and azoxystrobin, are liable to leaching when used on sand-based root zones. At least in part, this may be due to the development of hydrophobic spots causing water to percolate in fingers instead of uniformly through the root zone.
The objective of this project was to study the effect of organic amendment and surfactant on turfgrass quality, hydrophobicity and fungicide leaching. An experiment was conducted from May 2006 till May 2007 on a three year old green seeded to creeping bentgrass ‘Penn A-4’ in the field lysimeter facility at Bioforsk Landvik, Norway. The experimental plan included two root zone compositions (straight sand (SS) vs. the same sand amended with 2.3 % (w/w) garden compost (‘Green Mix’ (GM)); two surfactant treatments (no surfactant vs. ‘Primer 604’, 19 L ha-1 applied at monthly intervals from May to September 2006); and two fungicides (‘Rovral 750’ (iprodione 1.5 kg a.i. ha-1) vs. ‘Amistar Duo’ (azoxystrobin + propiconazole, 600 + 375 g a.i. ha-1) sprayed in June, July and October 2006) in factorial combination. Turfgrass quality and disease occurrence, infiltration of water vs. ethanol, water droplet penetration time, and spatial variability in soil water content was determined at regular intervals. Fungicides in leaching water were analyzed 2 to 3 weeks after each application and in spring 2007.
Application of ‘Primer 604’ reduced dry spots and improved turfgrass quality during summer, especially on SS plots. The improvement was associated with increased water infiltration rates and a reduction in the spatial variability in soil water content at 4-10 cm depth, suggesting that hydrophobicity extended deeper in the profile than the 14-19 mm thatch/mat layer. However, ‘Primer 604’ also increased snow mould (Microdochioum nivale and Typhula spp.) in spring 2007, probably because of a significant increase in the mean soil water content in the thatch–mat layer. Leaching of fungicides from GM root zones was always negligible, but regular use of ‘Primer 604’ reduced the total leaching of iprodione, azoxystrobin, and propiconazole from SS root zones by 60, 63, and 80 %, respectively. In conclusion, ‘Primer 604’ offers many benefits on SS root zones, but there is also a need for surfactants that retain less water in the thatch/mat layer.
Head of Research
Norwegian Institute for Bioeconomy (NIBIO), Department for Urban Greening and Environmental Technology, Turfgrass Research Group, Landvik, Reddalsveien 215, 4886 Grimstad, Norway.