Here is an article on an approach to carry out limited protection of our elm trees but is only suitable for non-diseased prime specimens as it has to be repeated every year.
History of Dutch Trig®
Dutch Trig® is a preventative vaccination for elms developed by the University of Amsterdam at the end of the 1980’s. In the Netherlands the need for this biological vaccine for elm trees to prevent Dutch elm disease was, and is very high because of the ban on use of chemicals on street and park trees.
What is Dutch Trig®?
Dutch Trig® is a non-chemical, non-toxic, biological control agent, or vaccine. The vaccine consists of a suspension of spores of a very specific strain of the fungus Verticillium, (not genetically modified), in distilled water. This spore suspension is injected in the elm in spring.
Where does Dutch Trig® come from?
The Verticillium albo-atrum used in Dutch Trig® was originally isolated from a potato field in the Netherlands. Verticillium itself is a natural soil borne fungus occurring all over the world, of which several species are capable of infecting many species of herbaceous and some woody plant species through damaged roots. Normally, natural strains of Verticillium(of both dahliae and albo-atrum species) infect the xylem tissue and cause wilting symptoms.
How does it work?
The strain of Verticillium albo-atrum used in Dutch Trig® is a natural hyaline (or white) variant of the natural strain. This specific hyaline strain of Verticillium has lost so much of its pathogenic capabilities that it no longer is able to cause wilting symptoms on trees any more. The strain has still a little of its original pathogenicity left, which is just enough to induce an immune response in the elm after injection. Dutch Trig® can be seen as a catalyst, which induces an immune response in a healthy elm tree that will protect it against Dutch elm disease during one growing season. This is called induced resistance. After injection, with its defence mechanisms up and running throughout the growing season, the elm is able to successfully fend off Dutch elm disease infections later in the growing season.
In practice, it can be compared with an influenza vaccination. Dutch Trig® does not make healthy elms sick, but prepares them for any onslaught of Ophiostoma novo-ulmi carried by elm bark beetle. Because elm trees grow a new outer layer of sapwood on the trunk and branches every year, which is separated from the growth of previous years (heartwood), the treatment has to be repeated annually.
Where does the vaccine go?
Dutch Trig’s mode of action is based on inducing natural resistance in healthy elms. This means that there is no relation or direct interaction between the Dutch Trig® and the Dutch elm disease fungus. Dutch Trig® does not produce any phytotoxins in the elm to fend of the Dutch elm disease infection, nor does it “grow all throughout the trees xylem tissue where otherwise Ophiostoma would grow”. The vaccine does not “travel” to the elms branches, roots, or leafs.
In fact, after injection, Dutch Trig® stays within a circle of 4 inches around the point of injection in the trunk, and within two to three weeks after injection, the elm has removed all the injected Verticillium from its xylem tissue. Two weeks after injection, Dutch Trig® can no longer be re-isolated from the injected tree.
The vaccine has no curative properties. Vaccinating elm trees which already have Dutch elm disease is of no use. Injecting disease trees can be compared to vaccinating humans after they already have fallen ill, which is of no use because the body will already be at work trying to get the disease out.
Is Dutch Trig® harmful?
Dutch Trig® is safe for humans and animals, because Verticillium is not a human or an animal pathogen and because the vaccine has no chemical or toxic substances. Dutch Trig® is safe for trees too: Dutch Trig® has been injected in several tree species (amongst which Verticillium susceptible species such as maple) to check in the vaccine would induce any wilting. None of the injected species showed any signs of wilting after injection (for species injected see list below).
Does the vaccine have any side effects on treated trees?
Wilting of trunk suckersDutch Trig® does not have any significant side effects on the treated trees. The only one visible side effect of the Dutch Trig® injection so far has been noted on a few trees in the US, showing wilting of specific suckers low on the trunk of the elm, above the site of injection. The wilted trunk suckers would sprout new leaves later in the growing season.