The main objective of the project "Healthy spruce transplants for forest regeneration" (FriskGran) was to reduce the losses in forest nurseries during production and storage. To get an overview of the causes and range of losses, we conducted a survey through the systematic collection of samples from five nurseries. We found that, on average, the loss during the production was 25%. Of this, 56% was caused by lack of germination or death of plants during the production phase, while 44% was plants discarded due to poor quality prior to cold storage. We found that up to 60 % could be discarded due to damage by fungal pathogens. Grey mould, caused by the fungus Botrytis, was an important disease, but we also found other pathogens such as Phoma, Phomopsis and Alternaria. In some cases, damage appeared to be caused by a complex of fungal pathogens rather than one single species. Moreover, in many cases we considered the damage to be caused by a combination of climate and fungal pathogens. In addition to the loss prior to cold storage, fungi also caused losses during storage, were Botrytis was the most important causal agent of disease.
Grey mould is undoubtedly an important disease in forest nurseries, and fungicides are applied repeatedly to protect the plants during the growing season. We therefore examined Botrytis-isolates from forest nurseries for fungicide resistance. Of 46 tested isolates, 67% were resistant to one or more fungicides. Tiophanate methyl was the fungicide with the most widespread resistance, and 59% of the isolates were resistant to this fungicide. For pyraclostrobin (only 11 isolates tested), fenhexamid, pyrimethanil, iprodione and fludioxonil, 45, 33, 25, 4 and 0% of the isolates were resistant, respectively. Many isolates were multi-resistant; eight isolates were resistant to two, one was resistant to three, and four isolates were resistant to four fungicides. Knowledge of fungicide resistance in Botrytis is now considered when choosing disease control strategies in forest nurseries.
To keep inoculum pressures as low as possible in forest nurseries, it is important to remove discarded plants and plant residues from the production areas. Routines related to this were in general satisfying in all the forest nurseries that participated in the project, but weeds in and around production areas and in the greenhouses, as well as damaged spruce plants that wilted during the production phase were inoculum sources for Botrytis. A survey showed that the Botrytis sporulated on senescing plant parts (flowers, flower stems, leaves) of several weed species. An important finding was that weeds also hosted fungicide resistant Botrytis strains. Three isolates from weeds in two nurseries were resistant to three to four different fungicides. This shows how resistant populations of Botrytis can survive on alternative host plants in forest nurseries and its surroundings to infect new spruce transplants.
To achieve the best possible control of grey mould, trials were carried out to find the most important infection period during the growing season. We found that the spruce plants were most susceptible in May and June. This is earlier than the forest nurseries usually start to apply fungicides, and we therefore recommended to spray against Botrytis earlier in the season. It became clear during the project period that there was a potential for technical improvements related to fungicide application, and tests of nozzles, travel speeds, and spray pressures were conducted to optimize fungicide efficacy.
The project has led to practical advice and recommendations on disease management to the forest nurseries. It has also revealed disease management challenges that need attention to improve IPM in forest nurseries.
FriskGran har som overordnet mål å halvere tapet av granplanter fra norske skogplanteskoler ved hjelp av integrerte planteverntiltak (IPV) mot soppsjukdommer. Særlig er gråskimmel en viktig skadegjører, ikke bare under dyrkingen, men også under lagring og transport. Det plantes årlig ut om lag 25 millioner skogplanter i Norge, hvorav mer enn 90 % er vanlig gran. For å sikre overlevelse og god etablering må granplanter til utplanting være frie for sjukdommer. Dette forutsetter en effektiv sjukdomsbekjempel se i produksjonen, men det vil også sikre en økonomisk gevinst for skogplanteskolene og gjøre dem mer robuste i et konkurransemarked. I FriskGran vil vi kartlegge omfanget av planteavgang på grunn av sjukdommer i noen planteskoler. Fordi flere soppmidler har vært brukt relativt hyppig over mange år, er det en fare for at gråskimmel og andre sopper har utviklet resistens mot disse midlene. Siden gråskimmel er viktigst, vil isolater av denne soppen bli samlet inn fra frasorterte planter og testet for resis tens. Av hensyn til resistensfaren må bruken av soppmidler gjennom sesongen trolig reduseres, og sprøyteforsøk vil derfor bli gjennomført i utvalgte skogplanteskoler. Ikke-kjemiske kulturtiltak vil ha stort fokus i FriskGran og vil forsøkes sammen med nye sprøytestrategier. Potensielle smittekilder i skogplanteskolene vil bli undersøkt, og tiltak vil bli satt i gang for å redusere spredning fra smittekildene. Rutiner i forhold til dyrking, lagring og transport av planter skal gjennomgås grundig for å avde kke muligheter for å gjøre forholdene under oppal mindre gunstige for soppangrep. På bakgrunn av resultatene fra FriskGran vil det utarbeides en IPV-strategi for sjukdomsbekjempelse.
FoU-teamet i FriskGran har lang erfaring med næringsrettet forskning og formidling, og resultater fra prosjektet skal formidles gjennom hele prosjektperioden til næringen.