The fight against root rot is an ever-ongoing project. One way to fight it is to treat the stumps with the fungus Phlebiopsis gigantea. It doesn’t cure the trees from root rot, but it prevents the spreading of it. The method became common in Sweden in the 90s. However, recent research shows it isn’t as efficient as we thought.
Stump treatment against root rot
It’s mainly Norwegian spruce that must be treated against root rot, and it’s done in Sweden in thinning when the average daytime temperature is over + 5 degrees centigrade. To achieve a good result, the stumps must be 100 percent covered. However, the requirements from the suppliers of fungus and the forestry companies are between 85 – 95 percent.
The most common method to treat the stumps with Phlebiopsis gigantea is to spray it on the stump through holes in the saw bar when felling trees. I wrote about this a couple of years ago. The fungus is in Sweden named Rotstop and the company Interagro is the supplier of it to Swedish forestry. 
Does it work?
According to a recently published article, the results in practice are lower than the requirements. Of the 394 analyzed stumps in the study, sampled across 15 sites, only 19 percent were fully covered (100 percent coverage). 46 percent of the stumps had a coverage of 85 – 99 percent, and 35 percent of the treated stumps had less than 85 percent coverage.
Of the 394 stumps, 178 (46 percent) were infected by root rot (Heterobasidion). The percentage of infected stumps did not differ between the coverage rates; Less than 85 percent of coverage had 45 percent infected stumps. More than 85 percent coverage had 46 percent infected. Of the stumps with full coverage 45 percent were infected.
Obviously not(?)
To summarize only one of five stumps was completely covered. On one-third of the stumps, the coverage was below the lowest requirement of 85 percent, leaving 46 percent of approved stumps (according to the lowest Swedish requirement which also is the RotStop supplier’s recommendation).
“We know for sure that Rotstop prevents root rot,” says Mimmi Blomquist, a researcher at the Swedish University of Agricultural Sciences, SLU, and continues. “It requires the right handling all the way up to spraying the stump. There is obviously more to be done in practical forestry concerning methods, education of machine operators, and technology. It’s an important issue for forestry. Provided it is a functioning treatment, there are good reasons to do it both in thinning and on clear-cuts.”
For example, the Rotstop must be kept cool to be effective. To keep the fungus cool all the way to the stump could be difficult in the forest. Furthermore, there could be problems with the technology. The settings must be right and the right number of holes in the bar must be open to achieve a good result. 
Many contractors and harvester operators see this treatment only as extra trouble for them. Something they must do without getting paid for it.
A new saw bar – part of the solution?
There is a lot to do before we reach a satisfying result in the treatment against root rot. A couple of years ago I followed up on Rotstop treatment and met with many harvester operators in connection with it. My experience is that two main problems prevent good results.
First, the settings. Very few of the harvesters I visited had the right settings in the control system. Some operators didn’t even know they could make settings.
Secondly, the saw bar. To get an even distribution of the fungus over the stump, the right number of holes for a certain diameter must be punched or drilled open. The problem here was that the operators used the same bar for thin trees as for thicker ones. With the same number of open holes. “Do we have to get a new bar every time we switch from thin to thick forest?” was a common question. After all, saw bars for harvesters are quite expensive.
As for the saw bars, a possible solution to that problem turned up at the Swedish Forestry Expo in June this year. Iggesund Forest presented a new saw bar with a track to distribute the fungus instead of holes. 
Maybe this, in combination with a cooler, could be the solution.
Sources: Skogsforum, SLU, Wikipedia, Science Direct
