Resistance of Picea abies to Ips typographus: Tree Response to Monthly Inoculations with Ophiostoma polonicum, a Beetle Transmitted Blue-stain Fungus

Fifty pole stage trees were inoculated with O. polonicum at monthly intervals between May and September. Most infection, measured as the area of sapwood blue-stained, occurred in July and least in May and September. The difference between July, August and September might be explained by the effect of temperature on fungal growth, but in May and June the trees had a higher resistance than expected. Tree resistance was correlated with resinosis. Tree variables not correlated with resistance were DBH, annual ring width, periodic growth, vigor index, or phloem carbohydrate concentration.