Rainstorm effects on the biocontrol efficacy of the decay fungus Chondrostereum purpureum against birch sprouting in boreal forests

Abstract

In forest regeneration areas, alongside roads and railways, under electric power lines and above gas pipe lines, there is a need for regular sprout control. A biocontrol method against broadleaved sprouting with formulations including the decay fungus Chondrostereum purpureum (Pers. Ex Fr.) Pouzar has been shown to be effective. Yet, heavy rain during spreading of this fungal inoculum on freshly cut stumps may affect the efficacy of the treatment, i.e., stump mortality during the following years. Thus, we performed an experiment where freshly cut birch stump surfaces (Betula pendula Roth and Betula pubescens Ehrh.) were treated with fungal inoculum under heavy irrigation and without it. Furthermore, two different adjuvants which aimed to fix the fungal inoculum to freshly cut stumps during irrigation and to protect against solar radiation were tested. Our results revealed that the artificial rainstorm treatment caused a delay in the efficacy of C. purpureum, but after three growing seasons, there was no significant difference in the mortality of birch stumps treated under irrigation or without it (stump mortalities 74 and 86%, respectively). Adjuvants did not improve the efficacy in stumps treated under irrigation nor in those treated without irrigation. Key Points • Heavy rain delayed the sprout control efficacy of a fungus Chondrostereum purpureum. • Final efficacy of formulations was the same in wet and dry conditions. • No additional adjuvants are needed to improve formulations.

Role and function of Chondrostereum purpureum in biocontrol of trees

“…Usually, the desired tree saplings must compete with naturally grown tree species for growing space, solar radiation, water and nutrients, and therefore, unwanted saplings are removed to promote the growth of more valuable cultivated trees (Huuskonen and Hynynen 2006 ; Huuskonen et al 2020 ; Wagner et al 2006 ). However, unwanted trees are often hardwoods that can sprout efficiently from stumps (Becker et al 2005 ; Hamberg et al 2020 ; Jobidon 1998 ; Lygis et al 2012 ; Mallik et al 2002 ; Wall 1990 ), and therefore additional pre-commercial thinning (PCT) operations are usually needed (Äijälä et al 2019 ; Thiffault and Roy 2011 ).…”

“…Pouzar, that can be utilized as a biological control agent due to its efficient ability at preventing sprouting, potentially even as efficiently as chemicals (Becker et al 2005 ; Bellgard et al 2014 ; Harper et al 1999 ; Jobidon 1998 ; Lygis et al 2012 ). Consequently, the use of this fungal species as a biocontrol agent against weed hardwoods has been investigated in the Netherlands, Belgium, Lithuania, Finland, Canada, and New Zealand (Becker et al 2005 ; Bellgard et al 2014 ; de Jong 2000 ; Dumas et al 1997 ; Hamberg et al 2015 , 2018 , 2020 ; Lygis et al 2012 ; Roy et al 2010 ; Spiers and Hopcroft 1988 ; van den Meersschaut and Lust 1997 ; Vartiamäki et al 2008a ). In this mini-review, the role and function of C. purpureum in biocontrol of trees is described.…”

“…sinuata 2.2 90 c! 11 Harper et al 1999 Paper birch Betula papyrifera 5.4 99 c 56 Jobidon 1998 Silver birch Betula pendula 3.5 (1–12) 100 b 20 Lygis et al 2012 Silver and downy birch Betula pendula and B. pubescens 3.5 92 b 57 Vartiamäki et al 2008a 3.0 (2.1–4.4) 96 c 60 Vartiamäki et al 2009a 1.1 78 c 9 Hamberg et al 2015 1.4 86 c 17 Hamberg et al 2020 11.2 (1.0–30.8) 97 b 56 Hamberg and Hantula 2018 Largetooth and trembling aspen Populus grandidentata and P. tremuloides 5–60 37 a-b 12 Dumas et al 1997 Poplar Populus euramericana 40–60 100 b 15 de Jong 2000 European aspen Populus tremula 1.9 77 d 52 Hamberg et al 2014 1.2 78 c 47 Hamberg and Hantula 2016 3.5 (1–12) 100 ...…”

“…fil.) with stump mortalities of 80–100% after the treatment (Becker et al 2005 ; Hamberg and Hantula 2018 ; Hamberg et al 2015 , 2020 ; Jobidon 1998 ; Lygis et al 2012 ; Scheepens and Hoogerbrugge 1989 ), but promising results have been achieved also for aspen ( Populus tremula L., P. tremuloides Michx.) (Hamberg and Hantula 2016 ; Hamberg et al 2014 ; Harper et al 1999 ; Lygis et al 2012 ).…”

“…In a large stump, there is more space for a higher number of fungal fragments to colonize it and cause stump decay, leading to mortality sooner than in smaller stumps. When birch ( Betula pendula and B. pubescens ) saplings 0.5–6.0 cm in stump diameter were cut and treated with C. purpureum inoculum, larger stumps died faster than smaller stumps (Hamberg and Hantula 2020 ; Hamberg et al 2020 ). However, when the diameter of experimentally treated stumps ranged from 0.6 to 30.0 cm, the results showed that the smallest and largest stumps were most susceptible to the fungal treatment, with trees ca.…”