Written by Justin Tornatore, ISA Certified Arborist | TIMBERx
Abstract
Those reddish, leafless clumps hanging in Tucson's mesquites, palo verdes, ironwoods, and acacias are desert mistletoe (Phoradendron californicum), a native parasitic plant that lives on desert legume trees across the Southwest [1]. Homeowners usually want to know two things: will it kill the tree, and how do you get rid of it? According to University of Arizona Cooperative Extension, true mistletoes cause a slow decline over many years and it "usually takes many years" for an infection to kill a mature tree [1]. Heavy infestations, however, can cause significant decline, and the added weight can break branches [2]. Removing the visible shoots is the only practical control, but it doesn't kill the infection living inside the wood [1][2]. This article explains how mistletoe works, what the extension research says about its impact, and how to manage it without doing more harm than the parasite itself.
Background: How Mistletoe Actually Works
Mistletoe is a hemiparasite. It has green stems and makes some of its own food through photosynthesis, but it depends on its host for water, mineral nutrients, and carbohydrates [1]. I like to picture it as a straw pushed into the tree's plumbing. The mistletoe drinks from the same xylem stream the tree uses to move water from roots to leaves.
Desert mistletoe has leaves reduced to tiny, inconspicuous scales and reddish stems, and its clumps can grow very large, especially in palo verde [1]. Like other true mistletoes, individual plants are either male or female, and only the females produce berries [1].
The bird connection. Mistletoe doesn't spread on the wind. Birds eat or carry the sticky berries and deposit the seeds onto branches. When a seed germinates, it penetrates the host directly and develops inside the branch for about two years before any shoots appear outside [1]. Since birds prefer to perch high in taller, mature trees, young and small trees are seldom infected [1].
What the Research Shows
Mistletoe is slow, not sudden. UA's True Mistletoes publication describes true mistletoes as "not aggressive pathogens," noting that it "can take decades for mature, infested trees to die" [1]. The vigor of the mistletoe is usually tied to the vigor of its host [1].
But it adds up. In desert landscapes, UA's urban tree publication notes that while mistletoe "generally does not kill a tree, it can cause significant decline over time." If it isn't pruned out, its weight can become great enough to break the branch [2]. Heavily infected trees are also probably more susceptible to other stresses and to insects [1]. In a desert where drought and heat already strain trees, that extra competition for water matters.
Removing the shoots doesn't cure the infection. Breaking off or cutting the aerial shoots every two to three years reduces competition with the host and keeps the mistletoe from producing seed, but it doesn't eradicate the infection living inside the wood [1]. Products containing ethephon (ethylene) can make shoots drop, but they also leave the internal infection alive [1].
Cutting the branch is more thorough, when it's appropriate. For infections on smaller limbs, UA recommends cutting at least one foot below the infection site, or preferably back to the nearest crotch [1]. For infections on the main stem or trunk, periodic shoot removal is the only option. For trees with heavy infestations that have persisted for several years, removing the tree may be the only remedy [1].
It's part of the desert ecosystem. Mistletoe berries mature in winter and are an important winter food source for many bird species, and mistletoe clumps make attractive nesting sites [1]. UA notes that for lightly infested trees, removal is largely an aesthetic decision [2].
Field Observations
In the field, mistletoe problems usually come in two flavors. The first is a healthy tree carrying a few clumps. In that case, I'd generally recommend periodic shoot removal and leaving the birds their winter food. The second is a tree so loaded that whole sections of the canopy are more mistletoe than tree. That one needs a real plan, and sometimes an honest conversation about the tree's future.
A common mistake is chasing mistletoe with the saw. When every infected branch gets cut back hard in one visit, a tree can lose far more canopy than it can afford. That puts it under the same stress that lets mistletoe and borers take hold in the first place. In my palo verde article I recommended removing mistletoe by scraping or cutting the stems rather than taking out whole branches. That approach still fits most trunk and scaffold-limb infections. On small, expendable limbs, cutting a foot or more below the infection is the more thorough fix [1]. As with any pruning, the 25% ceiling still applies [3].
Practical Recommendations
- Identify what you have. Reddish, leafless, scale-leaved clumps on mesquite, palo verde, ironwood, or acacia are almost certainly desert mistletoe [1]. They're often easiest to spot when deciduous hosts like mesquite drop their leaves.
- Decide on the goal. For a light infestation on a healthy tree, removal is optional [2]. For heavy infestations, the goal is to reduce the load and stop seed production [1].
- Remove shoots every two to three years on trunks and major limbs, where cutting the branch isn't an option [1].
- Cut small infected limbs back a foot or more below the infection, or to the nearest crotch [1], following correct pruning cuts at the branch collar.
- Stay under 25% of the canopy per session [3]. Spread heavy cleanups over multiple seasons.
- Remove shoots before berries ripen where you can. Repeated shoot removal keeps the mistletoe from producing seed [1].
- Keep the host healthy. Deep, appropriate irrigation and good structural care help a tree tolerate its passengers, since heavily infected trees are more vulnerable to other stresses [1].
- Think long term. UA suggests planting young trees, especially non-host species, near older infested trees before those trees decline [1]. Neighborhood-wide cleanup can help, but it only works with broad cooperation [1].
Key Takeaways
- Desert mistletoe is a native hemiparasite of mesquite, palo verde, ironwood, and acacia, spread by birds [1].
- It rarely kills a tree quickly, but heavy infestations cause significant decline and can break branches [1][2].
- Shoot removal controls spread but doesn't cure the infection. Cutting infected limbs a foot or more below the clump is more thorough [1].
- Never over-prune to chase mistletoe. A stressed tree is a better host, not a worse one.
Happy planting (and pruning), friends!
Talk to an Arborist
Is mistletoe taking over a mesquite or palo verde? Text Justin at (520) 451-8790 (texting is preferred over calling) or email Justin@TimberxTrees.com. TIMBERx is a veteran-owned tree care company led by Justin Tornatore, ISA Certified Arborist, serving Tucson, Oro Valley, Marana, Vail, Sahuarita, Green Valley, and Benson.
References
- Olsen, M. W. (2003; revised 2011). True Mistletoes (AZ1308). University of Arizona Cooperative Extension. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1308.pdf
- Schuch, U., & Kelly, J. (2012). Mesquite and Palo Verde Trees for the Urban Landscape (AZ1429). University of Arizona Cooperative Extension. https://extension.arizona.edu/publication/mesquite-and-palo-verde-trees-urban-landscape
- Larson, P., Vance, L., & North, D. (2025). July Monthly Gardening Guide for Pima County. University of Arizona Cooperative Extension. https://www.extension.arizona.edu/publication/july-monthly-gardening-guide-pima-county
