An overview of mistletoes on hardwoods in California Katy Mallams USDA Forest Service Forest Health Protection Central Point, Oregon
An overview of mistletoes on hardwoods in Californiacaforestpestcouncil.org/wp-content/uploads/2011/03/Katy-Mallams.pdf• Parasites on hardwoods and conifers • Require living host
An overview of mistletoes on hardwoods in California
Katy MallamsUSDA Forest Service
Forest Health ProtectionCentral Point, Oregon
Mistletoes
• Green, flowering, perennial plants• Parasites on hardwoods and conifers• Require living host• Seeds possess a viscid layer
Leafy mistletoes• leaves contain chlorophyll• primarily water parasites• plants in large clusters
P. Mistretta
Presenter
Presentation Notes
If you live or work in CA, aware Plants, green… As parasites, mtos require living..… All mtos have seeds with sticky coating, helps adhere to host Leafy mtos have… Easy to ID see round, oblong clusters of plants in trees
Species Common name
Phoradendron villosum Oak mistletoe
Phoradendron macrophyllum Big-leaf mistletoe
Phoradendron californicum Desert mistletoe
Viscum album European mistletoe
Mistletoe species on hardwoods in California
Presenter
Presentation Notes
4 species of mto on hardwoods in CA Pv ---, PM --- are the 2 that are significant pests, of concern to landowners, managers Also Pc, Va
Phoradendron villosum, oak mistletoe
Jepson Manual On-line
Hosts: Primarily oaks, occasionally other hardwoods, native and introduced
ID: oval leaves with dense short hairs
J. DiTomaso
P. Zambino
Presenter
Presentation Notes
Common mto of oak savannah and woodlands in Sierra foothills, coast range, Klamath mountains Hosts primarily oaks, occasionally on native and introduced ornamentals Most common other native hosts are bay and manzanita No oak mistletoe in San Joaquin valley
Phoradendron macrophyllum, big-leaf mistletoe
Jepson Manual On-line
Hosts:
Many native and introduced hardwoods, including black walnut, buckeye, Modesto ash, cottonwood, locust, maple, sycamore, willow, fruit and nut trees.Common in riparian areasNot on oaks
Bonterra
Consulting
R. Mathiasen
ID:
smooth oval leaves
Presenter
Presentation Notes
Does occur in SJ Valley Can be damaging pest on landscape trees and in orchards Also common on native hardwoods esp. in riparian areas Does not infect oaks In San Joaquin valley this is only mistletoe on hardwoods In coast range, Sierra foothills, Sacramento valley, range overlaps with oak mistletoe Can often distinguish by identifying host
Phoradendron californicum, desert mistletoe
Jepson Manual On-line
Hosts:
Primarily Pea family including acacia, palo verde, ironwood, mesquite. Also creosote bush, jojoba
ID: scale-like leaves, reddish-green, in drooping clusters
R. Mathiasen
R. Mathiasen
Presenter
Presentation Notes
In wildland settings not generally considered significant pest
Viscum album, European mistletoe
Jepson Manual On-line
Only within ±
5 mile radius of Sebastopol
Hosts:
Many native and introduced hardwoods, including apple, black locust, cottonwood, maple, willow
Not on oaks
ID:
long narrow leaves on long thin stems
J. DiTomaso
Presenter
Presentation Notes
Introduced in Sebastopol about 1900, probably deliberately, Luther Burbank? Wide host range, native and introduced, fruit trees Not on oaks So far slow spread – lack of continuous hosts once outside infested area If introduced elsewhere, esp urban, ag areas, could become a problem due to wide host range
Leafy Mistletoe Biology
• Separate male and female plants
• Female flowers produce berries
• Birds ingest berries, spread seeds
• Seeds adhere to branches
Presenter
Presentation Notes
Like other mtos, leafy mto plants male or female Berries produced on female plants Seeds spread by birds -- birds eat berries, seeds pass through digestive system Deposited on where birds roosting Leafy mistletoe prevalent where birds like to roost – tops of large open-grown trees
Development of infection
• Specialized structure penetrates host bark
• Root-like structure develops in host tissue
• Aerial shoots develop
Presenter
Presentation Notes
If seed lands on suitable host germinates, penetrates bark Root-like structure develops first Integrated with host xylem absorbs water, minerals Aerial shoots sprout – leaves produce carbos, later flowers produced
Important component of woodland and desert ecosystems
• Berries eaten by birds
• Nectar, pollen food for insects
• Leaves eaten by deer, elk in winter
• Decay resulting from infection provides habitat
Ecological RoleD. Shaw
Bird photos: P. LaTourrette
Impacts of mistletoe infection
• Sufficient water = tolerance• Dieback of branches common• Drought exacerbates effects• Greatest impact on old, heavily infected trees• Entry court for decay fungi
D. Shaw P. Zambino
Presenter
Presentation Notes
Mistletoe not harmless Continue to transpire when tree shuts down during dry periods If trees have enough water OK Old heavily infected trees seriously weakened, may die Blue oak and buckeye 2 native species especially prone to damage in dry years Decay fungi enter through cracks in bark created by mistletoe, eventual failure large branches, even stems Can cause enough breakage to destroy crowns of old trees A factor in significant decline of entire stands of oaks in Sierra foothills
Management in developed settings
Issues• High-value trees• Tree vigor and survival• Hazard due to failure of stems and branches
Management Options•Remove mistletoe shoots physically or chemically•Prune small infected branches•Remove branches with significant decay over a target•Remove declining or severely decayed trees•Plant resistant species
Presenter
Presentation Notes
In developed settings each tree has value, expect vigor, survival Have to be concerned about hazards due to failure Range of treatments from minimal to drastic Removing shoots does not affect “roots” of mistletoe inside branch – will usually grow back
Pruning
For lightly infected trees
Combine with shoot removal
Excessive pruning may destroy tree structure and vigor
Pruning wounds an entry court for decay fungi
Re-infection likely
P. Zambino
Presenter
Presentation Notes
Can combine pruning with removing plants from large branches and stems Don’t have to remove every plant to get a benefit Effect of mistletoe will be reduced for several years – tree may regain vigor Proper pruning technique is important -- don’t want to remove many large branches, destroy structure, harm tree more than mto -- large pruning wounds entry courts As long as still attractive to birds, probably re-infected – monitor, retreat
Chemicals to control mistletoe•ethephon (Florel™)•glyphosate
Wrapping •used to prevent sprouting•black plastic, duct tape, etc
Presenter
Presentation Notes
Chemicals -- Ethephon a growth regulator, can used to control mto on deciduous trees while trees are leafless causes shoots to drop off, mistletoe still alive inside branch, often re-sprouts, amount varies by species Glyphosate an herbicide – can kill mistletoe used in orchards while trees are dormant – results on landscape trees variable – deformity of tree leaves – uptake of chemical by trees Some swear by wrapping branches after mistletoe plants removed to prevent sprouting -- Black plastic, duct tape, weed cloth -- on at least one year Results variable – reports of heat damage and habitat for insects, swear by to worthless After any treatments, inspect trees every 3-5 years for regrowth and/or new infections
Management in forests and woodlands
Issues• Stand vigor and survival• Ecosystem function• Expense
Management Options
•Favor resistant species in mixed stands•Underburning?•Regeneration
Presenter
Presentation Notes
In woodlands more concerned with vigor, survival of stand as a whole Rarely possible to treat individual trees Possibilities for treating severely infected declining stands Favor resistant in mixed species stands Underburning may be tool Some work in S. CA with coast live oak – branches often re-sprout if killed – could remove low mto this way Since most mto in tops, not sure if effective Big problem many stands, esp oaks are old, little regen Infections typically take many years to develop Trees healthy a long time Increasing population of young trees may be the best way to lessen impact of mto at stand level
J. Pscheidt
Presenter
Presentation Notes
Mistletoes just one of challenges facing hardwoods in CA especially oaks Can be a significant factor in decline of older trees Result in physical hazards Can be managed to reduce negative impacts
Pete Angwin, USFS Forest Health Protection, Redding
Larry Costello, UC Cooperative Extension
Bruce Hagen, CalFIRE, Retired
Ted Swiecki, Phytosphere
Research
Paul Zambino, USFS Forest Health Protection, San Bernadino
