Needle Damage Development in Norway Spruce Seedlings as Affected by Humidity, Temperature, and Gray Mold: A Preliminary Study

Botrytis cinerea inoculation on 3- and 6-month-old Norway spruce seedlings was tested in combinations of temperature (15 and 25°C) and relative humidity (50 and 80%) in a growth chamber. Occurrence of needle damage was examined 11 days after the inoculation. Damage occurred more on inoculated than on control seedlings. Needle damage tended to occur proportionally more on the older seedlings and concentrating more on the tops of the shoot in the younger seedlings. The higher temperature suggested slightly more damage occurrence than the lower temperature did. The relative humidity did not appear to correlate with the damage outbreak. Surface wetness tended to increase the damage occurrence but so did also the vapour pressure deficit. At the lower relative humidity, the seedlings had to be irrigated more frequently, which increased the surface wetness. Thus, the results suggest that any irrigation method or other condition control that can provide low surface wetness on seedlings decreases needle damage by B. cinerea in forest nurseries.