I promised to set up a topic with a title and appropriate searchable key words explaining the situations where liquid copper fungicide and be used to prevent wood rotting fungi that can weaken and/or destroy trees. I have seen many, many trees weakened or destroyed by wood rotting fungi that entered through large pruning cuts and/or wounds to tree trunks. Most of not all of these trees could have been "saved" if the wood rotting fungi could have been kept out.
I experimented with some other fungicides. None worked except for the liquid copper fungicide. Some fungicides break down rather quickly, but liquid copper fungicide depends on the copper itself as the anti-fungal agent, and this copper is rather stable and does not break down, so it can remain active for a long period of time.
I have been using liquid copper fungicide for about 22 years on something close to 100 trees. I have used it mostly on some very large "pruning" cuts, some of which have required many years-some over 20 yearsÂto re-grow wood over the exposed wood, yet none have become infected with fungal rot. In fact, the exposed wood is still hard and fresh, without any softening after as many as 22 years. I have used this mostly on white pine, red pine, and Norway spruce, but also on a number of other kinds of trees, including red oak, ash, red maple, and sugar maple.
When and where should liquid copper fungicide be used? There are two common situations where it can be used on exposed wood to prevent fungal rot. The first is large pruning cuts. Most smaller pruning cuts to remove dead limbs or living limbs that need to be cut off for one reason or another have little risk of infection. On most healthy trees, pruning cuts less than three inches in diameter will not need any treatment, unless the tree is of a susceptible species like red maple, AND fairly slow growing. On trees like pines, spruces, white oaks, and some others, pruning cuts can be 4 or 5 inches in diameter, and in some situations even more, and if the tree is growing reasonably fast, there is little risk. But as the cuts get larger, the risk of infection increases. There is no way to quantify this risk-Âno rule about the size of pruning cut that should be treated, but I think a risk that I can imagine could be more than one percent would make treatment advisable. I will treat almost any pruning cut more than two or three inches in diameter, except on pines and spruces, because I donÂt want to take any risk whatsoever.
The other situation where treatment is advisable is injuries to the trunk of trees that result in some loss of bark and exposure of bare wood. These can become infected more easily than pruning cutsÂthere is no branch collar, which often can act as a barrier to the entrance of fungal infections. If the tree cannot close these kinds of wounds very quickly, the risk of infection is high. Especially dangerous are wounds that have some vertical length. Narrow (less than two inches) horizontal wounds that are not more than 3 or 4 inches wide are less likely to become infected. But these should be treated anywayÂthis risk of infection in these wounds is less, but still significant, and these should be treated, especially if the tree is really special.
Here is how to use liquid copper fungicide. Mix two or three parts liquid copper fungicide as it comes out of the bottle with one part water. This is much more concentrated than recommended for the regular "on-the-label"uses. Then it should be painted on with a paint brush. Use one good liberal coat so it soaks into the surface of the wood. More is not advisable. If it is for a recent injury, or a recent pruning cut of a live limb, the area should be left to dry for several months. If the sapwood is still "green," it will not absorb the fungicide. It should be used on dry wood.
It should be reapplied every year to make sure the protection is maintained. For areas of the trunk where the bark has died and/or been knocked off, it is especially important to refresh the treatment. For pruning cutsÂ-cuts across the grain of the woodÂafter about four years of annual refreshing, perhaps refreshing every other year is OK. I have not done experiments to determine just how often reapplication must be done. I am sure it would vary, depending on the kind of wood and its ability to absorb and hold the fungicide. My recommendations for annual refreshing will guarantee effectivenessÂ-at least my doing this has without fail kept out fungal infections for, as of now, 22 years.
Do not let excessive amounts soak down into the trunk of a tree. If there is any kind of area where this fungicide can collect and soak into the wood, you must be careful that this does not happen. There is some mild toxicity to the living sapwood of at least some kinds of trees. There is no benefit to having this soak deeply into the wood in any quantityÂit is a surface treatment to prevent the entrance of fungi.
This liquid copper fungicide, as far as I know, cannot be used to eliminate an established fungal infection. If wood has begun to rot, to become soft, it is too late to use this treatment. This treatment is not to be used in any hollow trunks or put into any cavities in any tree. It is likely to do more harm than good in these places.
It also cannot be used to prevent fungal infections in any wound that goes down under ground level, such as some lightning strikes. If the bottom of the wound cannot be treated and is exposed to the soil, the infection will start there and move upward and infect the main part of the wound.
What is liquid copper fungicide? Where can I get it? I have used two brands that I bought in garden shops. The one I used the most was one by Dragon. I am not sure it is still available. Another I used is by Bonide. Both of these have a water soluble form of copper. There are, I think, other brands, and some of these can be bought on-line. The key is that the copper must be in some water soluble form. Some fungicides, such as Bordeaux mixture contain copper, but it is not in a water soluble form and will not work for this purpose.
I encourage anyone reading this with the resources to do so, to do scientifically controlled experiments to help verify for all that this works. I want no citation for my idea to use this, and desire no credit what-so-ever. I just want to see trees saved. This idea is free and in the public domain.
--Spruce
sprucemanOriginal Author