A Fungus Falsely Accused?
G. G. Nearing, Ramsey, N.J.
Among the imaginary diseases of rhododendrons, it may be possible to list the shoestring fungus or honey mushroom, Armillaria mellea. I have read repeatedly that this fungus will kill living rhododendron plants, but have never seen one so killed, and have reason to believe that the notion is unfounded. I have read also that the same fungus kills oak trees, and have myself even repeated the statement as fact. Yet now I doubt its truth.
If I saw a vulture eating a deer, and told you that the vulture had killed the deer, you would laugh at me. Everybody knows that the vulture lives on carrion, and does not kill. The fungus Armillaria mellea is a fungous vulture, eating dead wood, and while there is a possibility that it may sometimes kill living trees as claimed, I do not believe that this fact has ever been properly established. It is more probable that foresters have jumped to conclusions, and claimed that the vulture killed the deer.
My rhododendrons are grown in beds shaded by oaks, Quercus palustris, Q. velutina and Q. coccinea. Before the beds were built, these trees had been thinned, and when a stump stood where the edge of a bed would come, it was not dug out, but left there to form part of the edge of the bed. Two of these stumps produce large crops of the honey mushroom, Armillaria mellea, every season, and they are gathered for food. The "shoestrings," rhizomorphs, of this fungus, long, elastic, black cords grow all through the beds. Often when digging a rhododendron, I pull these rhizomorphs out of the root ball, for they are very strong, and if mishandled, might break the ball.
The cutting-grown rhododendrons in these beds are exceptionally thrifty, and less than one-half of one per cent have died. In nearly every one of these few cases the cause of death was obvious, and it was not Armillaria mellea. In fact, 1 suspect this fungus of actually benefiting my plants. Some fungi are known to form mycorhizal associations with the roots of rhododendrons. I had a remarkable demonstration of this in the case of the black puffball, Scleroderma bovista, which will be found growing plentifully around the roots of R. maximum in its native bogs, and is hardly separable from the even more common S. vulgare. Appearing in a propagating frame, it caused five-fold to ten-fold increase in root promotion, accompanied by marked increase in top growth. I have no proof that Armillaria mellae produces such beneficial effects, but general observations over a period of years lead me to consider that it probably does.
I am sure that the fungus has not injured my plants, and suspect that it has benefited them. How then did the idea of its being fatal to rhododendrons originate? I do not know, but have a strong suspicion. The men who have advocated and still advocate the use of deadly chemicals as fertilizers, need some way of explaining the deaths which follow. No doubt after the plants have died, this fungus lives on the dead wood, and in due time puts out its telltale mushrooms. "See," says the chemical poisoner, "the vulture killed the deer." And with that he diverts suspicion from his own evil part in the slaughter.