Mistletoe Matthew Thorn and Dr
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MISSISSIPPI FORESTRY COMMISSION Forest Health Technical Bulletin #80 December, 2016 Mistletoe Matthew Thorn and Dr. John J. Riggins It’s that time of year again…holiday parties surrounded by family, friends, and food…and the ever present sprig of mistletoe hanging above it all. But other than helping folks spread good tidings and cheer, what is mistletoe? Perhaps you’ve also noticed it in the canopies of Figure 1: Oak Mistletoe from Mississippi hardwood trees, particularly Photo credit: Charles Bryson; USDA Forest Service after the leaves fall in autumn and winter. These softwoods⁵. All mistletoes some mistletoe species such highly visible bushy green are parasites on their hosts, as Phoradendron leucarpum bunches in our trees can depending on them for all of attacking at least fifty genera have an effect on tree their water and nutrients and of trees²,⁴,⁵. health, although usually varying amounts of minor. photosynthetic products¹-⁵. Identification Mistletoes are most easily What is mistletoe? Distribution and Hosts recognized after host leaves Mistletoes are parasitic Leafy mistletoes parasitize a have dropped because plants that grow on the wide variety of hardwood mistletoes are evergreen. outside of other plants, hosts, and occur During summer, it can be including both hardwood and predominantly in the difficult to see them among conifer trees⁴. Mistletoes southeastern U.S. extending all of the other greenery on from two genera are native into southern New Mexico, the tree. Identifying to North America, both in Arizona, and coastal mistletoe to the species level the family Viscaceae⁴,⁵. California⁴. The southwest can be difficult, usually Phoradendron (Figure 1) and northeast are home to requiring both the flower contains the leafy mistletoes the dwarf mistletoes, which and fruit2,5. Although, and infects primarily use trees in the families knowing the range and host hardwoods, while Pinaceae and Cupressaceae species can simplify the Arceuthobium (Figure 2) as hosts². The host specificity process²,⁵. The most contains the dwarf among both types of commonly seen mistletoe in mistletoes that are found on mistletoe varies greatly, with Mississippi is the oak 1 can be serval years²,⁴. The fruit produced by leafy mistletoes is used by a wide variety of birds and some mammals, who disperse the sticky seeds onto other host plants⁴. Dwarf mistletoes rely on the forcible ejection of their seed from the parent plant for dispersal²,⁴. Mistletoes produced by dwarf mistletoe are favored nesting sites for many birds, and having mistletoes in a forest contributes to a greater bird diversity¹,⁴. Figure 2: Pinyon dwarf mistletoe on singleleaf pinyon Mistletoes also help to create patchiness in a stand, Photo credit: Brytten Steed; USDA Forest Service helping to kill older susceptible trees and pruning mistletoe (Phoradendron tops in heavily infected trees branches of others, creating leucarpum)5. It is also the are also indicators⁴. habitats for many animals most widely distributed and plants and driving forest mistletoe and occurs across Ecology of Mistletoes succession¹,⁴. much of the eastern U.S.5. All mistletoes are dependent on their host tree for water, Leafy mistletoes have Management of Mistletoes nutrients, and varying obvious leaves that remain The management of amounts of green year round, while mistletoes varies widely carbohydrates ¹-⁵. They steal dwarf mistletoes have leaves depending on objectives. If these resources by tapping reduced to scales with the forest is managed for , , into the host’s vascular reddish or orange stems² ⁴ ⁵. wildlife, then mistletoes can system using their parasitic Mistletoe damage is most be considered beneficial, but roots, also called haustoria⁴. easily recognized by seeing in timber production or Once attached to the host, the bushy mistletoe itself on urban forestry situations the mistletoe will grow the tree, but hypertrophy they are generally shoots and leaves²,⁴. The (brank or trunk swelling), considered pests⁴. Mistletoes time between haustoria branch dieback, and dead can persist for years inside development and the the branches of its host appearance of aerial shoots 2 without any aerial shoots or remaining stub is wrapped 4. Mathiasen, R. L., Nickrent, D. L., Shaw, D. C., & Watson, D. M. leaves visible, only to emerge tightly with black plastic or (2008). Mistletoes: pathology, years later, making control sprayed with pruning paint, systematics, ecology, and difficult³,⁴. Leafy mistletoes either of which can kill the management. Plant Disease, are generally less damaging parasite³. In forest stands, 92(7), 988-1006. 5. Scharpf, R. F., & Hawksworth, F. G. than dwarf mistletoes, but controlled burns can also (1974). Mistletoes on hardwoods still reduce tree vigor and help to control mistletoe in the United States. U.S.D.A., heavily infested trees populations by reducing the Forest Service. become more susceptible to mistletoe seedbank⁴. For additional information , other stressors⁴ ⁵. Dwarf Sprayed herbicidal contact: mistletoes cause billions of treatments can kill mistletoe, dollars of damage every year but extreme care must be Mississippi Forestry to timber stands in the taken to not also harm the Commission Local Office , southwest and northeast² ⁴. tree. Contact a certified or The mortality they can cause arborist or your county means that it is almost forester for further Randy Chapin always advised to remove information on specific Forest Health Coordinator them from commercial herbicides, etc. Southwest District Forester stands⁴. Control of P.O. Box 749 mistletoes usually consists of References: 515 County Farm Lane NE pruning the branches that 1. Bennetts, R. E., White, G. C., Brookhaven, Mississippi 39602- Hawksworth, F. G., & Severs, S. E. 0749 are infected with mistletoe in (1996). The influence of dwarf Office: (601) 833-6621 order to ensure complete mistletoe on bird communities in Email: removal of the pest³-⁵. Colorado ponderosa pine forests. Ecological Applications, [email protected] Branches must be pruned 899-909. several feet inside (closer to 2. Hawksworth, F. G., & Wiens, D. Dr. John J. Riggins the trunk) of the visible (1972). Biology and classification Associate Professor of Forest of dwarf mistletoes mistletoe plant, because any (Arceuthobium). US Forest Entomology haustoria left behind can re- Service. Box 9775 Mississippi State, MS sprout. The mistletoe itself 3. Lichter, J. M., Reid, M. S., & Berry, A. 39762 can also be cut off the M. (1991). New methods for [email protected] control of leafy mistletoe du branch, but most of the time (Phoradendron spp.) on landscape it will grow back unless the trees. Journal of Office: 662-325-2984 Arboriculture, 17(5), 127-130. 3 .