19 April 2017
Mistletoe is a common problem. We are asked, on occasion, about what can be done to control it.
The bottom line is that there is no practical chemical control available currently. The best option is pruning back the mistletoe, and then wrapping it in black plastic for a year.
These are excellent resources:
New methods for control of leafy mistletoe (phoradendron spp.) on landscape trees
New Methods for Mistletoe Control
Considerations when using ethephon for suppressing dwarf and leafy mistletoe infestations in ornamental landscapes
Although this is early 1990s research, it appears to be the basis for current control methods. Here is a cut and paste of the conclusions of the first paper:
“In conclusion, we found that 10% ethephon applied to mistletoe stubs can be used effectively for mistletoe control in landscape trees. Ethephon appears to be a cost effective, environmentally safe, easy to use and inconspicuous method for mistletoe control. The 10% ethephon treatment would be appropriate on high value landscape trees, or on large scaffolds in combination with pruning of smaller limbs. Black plastic wrapping, while effective, has some possible drawbacks in terms of bark health. Apparently the effectiveness of pruning paint was similar to that of black plastic wrap. More research is needed to confirm the promising preliminary results with pruning paint.”
The chemical they are talking about is a plant growth regulator, Ethephon.
A search, on 19 April 2017, of the California Department of Pesticide Regulation’s site for chemicals approved for mistletoe control shows only one approved material: ACTIVE (03/24/10)NUFARM ETHEPHON 2 PLANT GROWTH REGULATOR ( 228- 660-AA )
It is a category one material, however, a DANGER label. See http://fs1.agrian.com/pdfs/Ethephon_2_Label5.pdf
Florel (https://www.harrells.com/resources/exports/file?n=FLOREL&t=label) has the same active ingredient, ethephon, and a CAUTION label, but is not labeled for mistletoe, and that is likely because it contains only 3.9 percent, versus the 10 percent used in the research. They used Florel Pro in that 1991 research, but Florel Pro is not listed in the CDPR database.
Here is the UC recommendation: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7437.html
But it is an older publication, as Florel is not currently approved for the use.
This article is on track: http://homeguides.sfgate.com/home-remedy-kill-mistletoe-trees-76951.html
Branch removal, pruning back the mistletoe, and then the use of the black plastic wrap may be the better option, as you won’t have the chemical hazard, and related regulatory hassles, to deal with.