Root and butt rot, caused by Heterobasidion annosum, the worst decay-disease in coniferous forests
Heterobasidion annosum, the root and butt rot fungus infecting Norway spruce and Scots pine, causes butt rot in spruce and resinosis in pine. H. annosum occurs in trees of all ages, but it is most common in sawlog size trees. Butt rot can be seen as rotting of the stem in spruce. In pine the fungus causes resin to collect in the roots with the consequence that the trees fall or die where they stand.
Root and butt rot impairs forest health and causes forest owners and industry losses as wood quality reduces. Rot-damaged wood is not acceptable as sawn timber; instead, it is used as raw material for chemical pulp or in energy generation. An important aspect in the fight to control H. annosum is to reduce the damage already in infected areas and also to prevent the spread of the fungus to new areas.
Root and butt rot in spruce caused by Heterobasidion annosum.
How Heterobasidion annosum spreads
The fungus causing root and butt rot spreads via air-borne spores, which are abundant in the forest during the summer period. Having landed on freshly cut stumps, the spores germinate and start producing hyphae which penetrate into the stump and the root system. Moreover, the annosus rot fungus is able to spread from infected trees into healthy trees via roots and from infected stumps into seedlings on the regeneration site.
The fungus Phlebiopsis gigantea in Rotstop populates freshly-cut stump surfaces and prevents the butt rot fungus from infecting stumps. Unlike chemical stump-treatment substances, Rotstop also prevents the spread of butt rot fungus through tree roots.
Rotstop stump treatment recommendations
Stump treatment is required during that time of the year when the air temperature is favourable to the spread of the root rot fungus. The time to use Rotstop is when the average diurnal temperature is over +5ºC. Stump treatment should be done on all mineral soil sites as per the following recommendation.
In Norway spruce stands
in which the proportion of spruce exceeds 50% of the stand volume:
– Always in conjunction with thinning
– In final felling of spruce unless there is a change of tree species when renewing the stand
In Scots pine stands
in which conifers make up over 50% of the stand volume:
– Always in conjunction with first thinning of pine
– Always in conjunction with final felling of pineIn conjunction with thinning of tree stands established on former agricultural landIn slightly damaged stands.
Stump treatment is not required
– In deciduous trees
– Tending of young stands when the average stand dbh is less than 10 cmIn final fellings when there is a change in tree species to deciduous trees and when the area felled does not border on coniferous stands.
– On peatland forest sites
Here’s how to do the Rotstop treatment
– Treat the stumps at felling or within 3 hours from felling
– When applying the treatment manually, use a backpack sprayer or a spray bottle and spray a layer of the suspension about 1 mm thick evenly over the stump surface
– Average in mechanized treatment is 2 litres of prepared Rotstop suspension per sq. metre of stump surface
Treatment in mechanized harvesting
– Application through the sawbar or by a sprayer
– A 25 gram bag of Rotstop is sufficient for an area yielding between 40-80 cubic metres of harvested timber
– A 100 gram bag of Rotstop is sufficient for an area yielding between 150-300 cubic metres of harvested timber
– The equipment used in spreading needs to be cleaned at least once a week
How to prepare a Rotstop suspension
– Cut off a corner of the bag and pour 0.3 litres of water into a 25 gram bag or 0.6 litres of water into a 100 gram bag. Use clean cold or lukewarm water
– Fold the cut corner over and shake the contents carefully until the powder and water have formed an even suspension
– Mix the suspension into more water (1 litre per 1 gram of powder) e.g. the contents of a 25 gram bag into 25 litres of water
– Rinse the bag and add to the suspension
– Dissolve a Blue Stump Marker tablet into the suspension (1 tablet/25-100 litres of suspension) to help monitoring the evenness of spreading. The tablet dissolves entirely in about 15 minutes.
– Use the suspension within 24 hours
Personal protective equipment
Use the following protective equipment when handling Rotstop:
– overalls and protective footwear
– rubber or plastic gloves
– head covering
– when preparing the suspension use respirator equipped with P2 dust filter