- Posted By: Jaime Adler
- Written by: Douglas McCreary and Jeannette Warnert
Many blue oak trees in California foothills might be more accurately described as “silver oaks” this year. From a distance, they shimmer with a silvery halo. On closer inspection the outermost leaves are coated with a white to gray powdery fuzz.
The cause, according to Doug McCreary of the Integrated Hardwood Range Management Program at UC Berkeley, is powdery mildew. Powdery mildew, a group of fungi that causes a white, flour-like growth on the surface of leaves, is common on roses, begonias, grapes and many other ornamental plants and agricultural crops.
“People have called us worried that the affected trees may be showing signs of SOD, but this is clearly not the cause. SOD symptoms are far different, blue oak is not a SOD host and SOD is restricted to coastal forests,” McCreary said.
McCreary assures oak lovers that powdery mildew rarely kills the majestic trees. Even small seedlings that have all of their leaves severely infected usually survive and recover.
“Powdery mildew makes it more difficult for the affected leaves to photosynthesize and produce food, and if it’s severe enough, it can also result in the leaves distorting, curling up, dying and falling to the ground,” McCreary said. “But most affected trees will simply grow a new crop of leaves later in the summer or the following spring. And if weather conditions return to a more normal pattern next year, with little or no rainfall after March, it is unlikely that powdery mildew would continue to be severe or widespread.”
Some people may be inclined to treat affected trees with fungicides. However, these treatments are most effective when the symptoms first appear, which occurred weeks or months ago. It is also generally not recommended to treat trees in wildland settings. There are too many trees to treat and the potential environmental risks of applying fungicides across a large landscape can outweigh the benefits. Above all, McCreary said, don’t panic and cut down the trees, even if all their leaves fall off.
“The trees are still very much alive,” McCreary said. “Losing their foliage is just the oak’s way of dealing with an unwanted pest. By this time next year they should again be leafed out without that silver covering currently observable.”
The unusually wet March and April is at least partially responsible for the higher-than-normal incidence of powdery mildew in blue oaks, he said. Increased incidence of powdery mildew has also been reported on California black oaks and coast live oaks on the coast.
“Powdery mildew doesn’t need rainfall, but it is favored by warm conditions, high humidity and low light and it loves young, succulent foliage,” McCreary said. “Because California was blessed with above average rainfall this past spring, there has been – and continues to be – considerably more moisture in the soil. Under these conditions, oak trees will grow a ‘second flush’ of leaves, usually in May or early June, that is very susceptible to powdery mildew.”
To Register Click Here by June 24th!
When: Thursday, June 30, 2011 9:00am-2:30pm. Please register by Friday, June 24th.
Where: Avenales Ranch Road, Pozo, CA 93453, San Luis Obispo County . We will meet at the American Canyon Forest Service Campground
Who: Anyone interested in research, education, management and conservation of oak woodland ecosystems. This includes landowners and managers, consulting range managers and registered professional foresters, community and conservation groups, land trusts and policy makers.
What: Agenda for the day
9:00 am - Arrive for coffee and registration
10:00 am - Brief Introduction to Avenales Ranch
10:15 am - Oak woodland management concerns
10:30 am - Oak regeneration, seeding, stump-sprouting
11:15 am - Oak thinning, measuring, management
12:00 pm - Lunch*
12:45 pm - Forest production and management
1:15 pm - Wildlife in Oak woodlands
1:45 pm -Sycamore regeneration study
2:15 pm - Alternative Review Program
2:30 pm - Adjourn
*Please remember to bring your own bag lunch.
In addition, appropriate clothing and footwear are recommended. There will be some off-trail hiking.
Please register by June 24th by Clicking Here!
For more detailed information, including directions, please Click Here! Please note: you do not need to be an Oak Webinar participant to attend this field trip.
Questions? Email Rick Standiford: firstname.lastname@example.org
Pictures from one of our field trips to the Sierra Foothills Research and Extension Center:
- Posted By: Jaime Adler
- Written by: Bill Tietje and Royce Larsen, UC Cooperative Extension
California residents who want to plant an oak tree or two on their property, often find it challenging, given our climate with irregular winter rains and no summer rainfall, to keep the newly-planted trees green and growing. A devise that has come onto the market recently is dubbed the “Groasis Waterboxx”. According to the website (Groasis.com) the Waterboxx has proven effective at “self-watering” new plantings, even in a truly desert climate.
Recently, we started a trial to test the Waterboxx by planting some oak seedlings and elderberry plants in a remote area. The Waterboxx is a round plastic “box” that fits around the tree trunk. The inward-slanting corrugated top cools during the night and channels condensed dew and heavy fog that collects on the top to the base of the tree. The Waterboxx also provides some protection for the newly planted tree and reduces the evaporation of water from the soil around the base of the tree, important additional benefits for new plantings. Once the tree is established, the Waterboxx can be removed and reused for another plant. Placing a collar around a tree that collects moisture and at the same time provides some protection can be a big incentive and a boost to getting that tree started.
As you can understand, the Waterboxx can be a big help as an alternative to carrying water to distant areas or setting up a drip system. For more information about the Waterboxx, contact your local UC Cooperative Extension Office or go to the Groasis Waterboxx website: Groasis.com. On the website you will notice that the inventor of the Waterboxx is providing users the opportunity to provide information on the growth and survival of their plantings. You may want to check it out.
A special offer for you!
Oaks in the Urban Landscape: Selection, Care, and Preservation
Written by: Larry Costello, UCCE; Bruce Hagen, CAL FIRE;
Katherine Jones, Author
On Sale NOW through MAY 31st on the ANR Catalog
This publication offers a comprehensive look at the management of oaks in urban areas. As development moves into oak woodland areas, more and more oaks are becoming “urban” oaks.
Oaks are highly valued in urban areas for their aesthetic, environmental, economic and cultural benefits. However, significant impacts to the health and structural stability of oaks have resulted from urban encroachment. Changes in environment, incompatible cultural practices, and pest problems can all lead to the early demise of our stately oaks.
Using this book you’ll learn how to effectively manage and protect oaks in urban areas – existing oaks as well as the planting of new oaks. Three key areas are addressed: selection, care, and preservation. You’ll learn how cultural practices, pest management, risk management, preservation during development, and genetic diversity can all play a role in preserving urban oaks.
Arborists, urban foresters, landscape architects, planners and designers, golf course superintendents, academics, and Master Gardeners alike will find this to be an invaluable reference guide.
Working together we can help assure that oaks will be a robust and integral component of the urban landscape for years to come.
Health, Growth, Aging and Decline
Roots and Soils
Biotic and Abiotic Disorders
Structural Failures, Defects, and Risk Assessment
Oak Preservation during Development
Ordinances for Tree Protection
Using Genomic Tools to Manage Healthy North
American Oak Populations
Symposium and Workshop
June 24, 2011, Davis, CA 1-5 PM
Venue: Alpha Gamma Rho Room, Buehler Alumni and Visitor Center, UC
Victoria Sork, University of California, Los Angeles. Genomics as a
conservation tool for oak management
Susan Frankel, USDA- Forest Service, Pacific Southwest Research Station.
Overview of current threats to Oaks in the West
Richard Dodd, University of California, Berkeley. Potential use of
genomic tools for hybridization studies of oaks
Jessica Wright, USDA-Forest Service, Pacific Southwest Research Station.
Using transcriptomics to study oak pathogens
Sally Aitken, University of British Columbia. Using genomics to
understand forest responses to climate change.
Panel Discussion with resource managers from State, Federal, and Non-governmental organizations
No registration fee, but please RSVP by June 1, 2011.
A no-host picnic dinner will follow the discussion.
Organized by the North American Oak Genomics Working Group in collaboration
with the Conifer Translational Genomics Network and the International Symposium on Genomics-Based Breeding in Forest Trees