What is the problem?
According to the United States Forrest Service, dwarf mistletoe is a parasite that steals water and nutrients from coniferous pine trees and significantly weakens them resulting in reduced growth, loss of vigor, and increased mortality rate. While dwarf mistletoe typically will not directly kill its host, combined with other issues such as drought and bark beetle, dwarf mistletoe will make the trees much more likely to die prematurely. Per John at Truckee Meadows Fire Protection, a tree that is heavily infested with the dwarf mistletoe is much less likely to be able to fend off bark beetle and poses a significant fire hazard in its weakened state.
It is important to understand how the mistletoe spreads to fully understand the problem. Mistletoe has a 1 to 2-year life cycle that slowly grows on branches (occasionally trunks) until pods become fully mature and filled with fluid that eventually bursts at a very high rate of speed when enough pressure is built up. The seeds from these explosions can spread as far as the tree is high and combined with wind, this could potentially be hundreds of feet. In addition, birds can land on the seeds, get them in their feathers, and then travel and spread the seed to other trees.
The most important fact to understanding the problem is that trees that are left unpruned, will continue to infect non-infected trees around them particularly younger trees below them creating a vicious cycle ultimately killing all the coniferous trees in the area.
More Information from the United States Forest Service: https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev2_025738.pdf
What can be done to fix the problem?
The U.S. Forestry indicates that trees infected with dwarf mistletoe can live a long healthy life if the mistletoe is pruned out. Studies have been conducted that show even trees that are heavily infested (up to 70%) can live healthy lives if the mistletoe is pruned below the crown. New growth at the top of the crown will remain uninfected for the remaining life of the tree since the seeds typically spread downwards due to gravity (so long as there are no trees surrounding it with mistletoe higher than the new growth).
Even trees with over 70% infestation can potentially be saved if pruning is done to remove large witches’ brooms, enabling the tree to increase vigor due to a reduction in the parasite.
If the heavily infested trees cannot be saved they must be removed to prevent further spread, particularly on the edges of the property, at a minimum, to create a buffer zone.
In addition to saving the trees from dying, pruning will prevent spread to other surrounding trees.
Pruning should be done from mid-October (when temperatures go down) to early April (before temperatures go up). If pruning is done outside of that time frame, there is a risk the tree could be weakened and more susceptible to bark beetle attacks.
- Spraying with Florel
Florel is a growth regulator that can be sprayed directly to dwarf mistletoe to kill and prevent the seeds from maturing. It will not completely remove the mistletoe from the infected area, but it will help to prevent spread. I’ve used it on some smaller younger trees, to avoid having to prune them and further injure and weaken the tree. I have had great success so far with this method.
This is the product I used: https://www.montereylawngarden.com/product/floral-brand-growth-regulator/
- Reducing Vegetation Underneath Canopy
Manzanita and other brush should be removed below the infected trees to reduce brush competition and give the remaining trees further opportunity to grow.
- Removing Competing Trees
Areas with lots of trees that are only a few feet apart should be evaluated for removal. Trees that are clearly smaller and not receiving enough sunlight will not thrive and are stealing water and nutrients from the larger surrounding trees. By removing the smaller trees, the larger trees will thrive more.
More information about managing dwarf mistletoe can be found here: https://www.srs.fs.usda.gov/pubs/27287
Helpful Resources with Contact Information
- John at Truckee Meadows Fire Protection – 775 427 5655
- John was very helpful in evaluating my lot for mistletoe and bark beetle and providing additional information on how to protect our trees. I’d also recommend following up with him about the potential for the FEMA grant to prune the trees.
- Michelle Roberts at Nevada Division of Forestry – 775 309 7958
- Michelle was very helpful in evaluating my lot and gave me recommendations for removing specific trees that would help with the overall health of the other trees.
- Owner referenced contractor-Marx at Northern Nevada Tree Experts LLC. – 775 360 6209.
- Marx comes highly recommended from several other neighbors, They have a boom truck which makes it easier and faster for him to get the job done. They were easily the cheapest of all the quotes I got, and his team did a professional high-quality job.