- 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.”
- Author: Jaime Adler
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: standifo@berkeley.edu
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.
- Posted By: Jaime Adler
- Written by: Adina Merenlender, CE Specialist
California’s hardwoods have so many virtues it is difficult to count them all. Only recently scientists have come to appreciate the influence that living hardwoods exert on stream channel shape as the key to providing good habitat for all aquatic species, including salmon in coastal California streams. It is well known that wood in streams provides habitat for a broad range of fresh water species and can influence the shape of the stream channel and important ecosystem processes, such as moving sediment and nutrient cycling. Wood also provides important habitat for fish by creating pools, providing shade and hiding places from predators, protection from high flows, food and shelter for invertebrates, woodjams that store spawning gravels and organic matter, and facilitates riparian plant regeneration. Wood is considered one of the most important habitat components for anadromous salmonids and with salmon on the decline it is important we ensure the presence of wood in California’s coastal streams.
Previously, scientists attributed all of these qualities to large pieces of dead wood from species that rot slowly such as the infamous California redwoods. But this begs the question: What is happening in streams lined by hardwoods such as California bay laurel, live oaks, alders, and willows commonly found in our mediterranean-climate woodlands? Field research conducted by Dr. Jeff Opperman, UC Berkeley alumnus now working for The Nature Conservancy, in 20 stream reaches in the northern parts of the San Francisco bay area, documents that living hardwoods are playing an essential role in California’s hardwood dominated streams by providing permanent structure that interacts with stream flow and gravel movement to create essential aquatic habitat for salmon and other native species (Figure 1).
Figure 1. Extracted from OPPERMAN, J. J. and A. M. MERENLENDER. 2007 Living trees provide stable large wood in streams. Earth Surface Processes and Landforms 32:1229-1238 (a) A red willow (Salix laevigata) that has fallen into Wildcat Creek (Aladmeda County, CA) but remains rooted and living (photo taken looking upstream).The lower arrow indicates sprouts growing from the lower branch of the willow. The upper arrow indicates a branch that has reoriented to become the primary source of photosynthesis for the fallen tree. A channel-spanning wood jam has accumulated upstream of this willow, which has contributed to the formation of the pool in the lower left portion of the picture. (b) The shaded areas denote all the wood that is still living within this wood jam.
As you can imagine trees that fall or grow over the stream and remain rooted and alive are more stable over time and and can withstand sizeable storms. After falling into the stream, hardwoods can often sprout new branches or bend into new shapes that result in vertical branches to capture more light for photosynthesis. A live tree spanning a creek with leaves on vertical branches creates significant shade and captures additional wood and organic material all to the benefit of the fish living below (Figure 1). These persistent hardwoods provide important in-stream structure in streams with riparian corridors that lack large conifers. In fact, in the 20 streams Jeff studied living hardwoods were the key piece of wood within a wood jam, the primary mechanism by which wood in?uences channel morphology, and had greater influence on channel morphology than larger pieces of dead wood found. Only 74% of the wood jams without live wood persisted to allow for scowering and pool formation in the stream over 1-2 years while 98% with living wood as a key piece remained in place for longer. Wood jams that span the entire channel provide the greatest influence over stream morphology and create complex habitat that maintains cooler safer waters for fish. Out of all the channel-spanning jams measured by Jeff, 44% had a living hardwood as key piece (Figure 2).
Figure 2. Extracted from OPPERMAN, J. J. and A. M. MERENLENDER. 2007 Living trees provide stable large wood in streams. Earth Surface Processes and Landforms 32:1229-1238 The proportion of all wood jams with a live key piece (shaded), dead key piece (white) or no key piece (black), based on channel position of the wood jam.
Clearly, California hardwoods are a necessary component within California’s fresh water aquatic ecosystems because they contribute to ?sh habitat by creating and maintaining wood jams, forming pools, and providing cover. Unfortunately, wood in streams is often removed by landowners, in some cases to protect property, but in other cases because of the desire for a clean stream or for easily accessible firewood. To stress the importance of maintaining wood in streams for fish habitat I, along with Jeff, and David Lewis a UCCE Watershed Management Advisor for Sonoma County, wrote a free publication for landowners titled “Maintaining wood in streams: A vital action for fish conservation.” Please click here to access the publication and learn more about this topic: http://ucanr.org/freepubs/docs/8157.pdf.
- Posted By: Jaime Adler
- Written by: Douglas D. McCreary
For almost a century there has been concern that blue oak (Quercus douglasii Hook. & Arn.), a California endemic, is not regenerating adequately in portions of its range. For the last 20 years, there have been concerted efforts to develop successful procedures for artificially regenerating this species so that it can be planted in areas where natural regeneration is unsuccessful, or in areas where it once grew but has been lost. These efforts have been successful in identifying procedures that will work, but unfortunately, such procedures often require intensive management and are costly. Since 80% of the oak woodlands in California are privately owned and the principal activity is livestock grazing, many large woodland owners and managers have marginal incomes and are reluctant to spend a great deal to regenerate oak trees.
An alternative, but untested, approach is to use naturally regenerating oak seedlings and take measures to promote their advancement to the sapling stage. This could be critical since research has demonstrated that the bottleneck for successful regeneration is often getting seedlings to grow into saplings. If successful, using natural seedlings could result in considerable savings because no effort or cost would be expended to collect acorns, or to grow and plant seedlings. An additional advantage would be that only genetically adapted plant material would be used, alleviating concerns about using “offsite” planting stock. Because of these economic, ecologic, and low input (i.e., less work) advantages, the development of techniques to advance natural regeneration holds great promise for being adopted and implemented by landowners.
To test this strategy, a study was initiated in 2007 at six field sites in the range of blue oak throughout the state. At each site, 144 naturally occurring blue oak seedlings were identified. Half of these were under the canopy of onsite trees and half were in the open. In addition, treatments included protecting seedlings with tree shelters and controlling weeds. When the plots were established, the height of each seedling was recorded. Yearly assessments of survival and height growth have been made every fall since establishment to evaluate the efficacy of the treatments.
After three years, seedlings in treeshelters have consistently grown taller than unprotected seedlings. In addition, the survival of those receiving an annual weed treatment has been significantly higher than those not receiving it. These results suggest that utilizing existing natural seedlings could contribute to increased blue oak regeneration at lower cost, thus improving the chances that this important species can be managed sustainably and conserved for future generations.
