Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Help Desk Response: Thank you for emailing the photos of the spots on your blueberry leaves. While we are unable to specifically identify the disease with certainty, it is highly likely that the spots are caused by a type of Anthracnose leaf spot fungus.
This and most other fungus diseases thrive in cool wet weather such as we have had this past year. The Anthracnose fungus has been identified on blueberries by researchers at the University of Oregon. The University of California recommends a number of measures that can be undertaken to control fungus. In general, it is recommended that you select resistant varieties and planting should be in the full sun. Other recommended practices for reducing fungal diseases include the following:
- Prune diseased growth as it appears.
- Provide drip irrigation if possible, otherwise irrigate in the early morning using mini-sprinklers.
- Avoid over fertilizing.
- Prune in the winter to increase air circulation.
- Once you have cleaned up diseased material from the plant and soil, place a generous amount (3 inches deep) of mulch on the soil below the plant canopy. This will help trap fungal spores so they don't splash up and re-infect the plant.
Hopefully implementing these practices and the onset of dryer, hotter weather will reduce the spread and minimize damage caused by the fungus.
There are also a number of additional recommendations for how to plant blueberries in a manner that will increase the plant health and resistance to stressors including diseases. These include:
- Select a variety bred to do well in California soil and known to do well in hot areas. These include Emerald, Jewel and Star.
- Plant in acidic (pH of 4.5-5.5), well-drained soil.
Blueberries belong to the Ericaceae family, which also includes other acid-loving plants such as azalea and rhododendrons . These plants need higher acidity to uptake needed nutrients. Contra Costa soils are generally slightly acidic to moderately alkaline. You can test your soil pH using a kit purchased from your local nursery. If you need to increase acidity, amend the soil six months prior to planting with 6-12 lbs. of aluminum sulfate per 100 square feet of garden. This will increase acidity by one pH unit (from 6 to 5). Another option is to plant them in raised beds (8-18 inches high by 3-4 feet wide) or a large pot. This allows you to more easily manage the soil pH and drainage. - Plant in a location where there is minimal frost and wind.
- Add mulch, which is usually slightly acidic and releases beneficial elements gradually and supports beneficial microbial organisms. Liquid fertilizers can be too strong. If using, apply four weeks after planting with a 10-10-10 mixture and reduce the amount recommended on the label. If using organic fertilizer apply one pound of blood, feather, or fish meal for each plant.
- Irrigate to maintain moist but not wet soil as blueberry roots are vulnerable to root rot.
- Hand weed to avoid damaging fragile surface roots.
If you would like additional information about blueberry varieties and growing tips, you can find it at: http://ucanr.edu/sites/gardenweb/berries/blueberries/
In addition, the UC Master Gardener Program of Contra Costa County is holding a program on Successfully Growing Blueberries at "Our Garden" on May 17th from 9am to noon. The main program will be presented at 10am by Kathy Echols, long-time DVC horticulture instructor. Our Garden is located in Walnut Creek at the corner of N. Wiget Lane and Shadelands Drive.
Thank you for contacting our UC Master Gardener Program. Please feel free to re-contact us with further questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (NPH)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
/span>Advice for the Home Gardener from theHelp Desk of the
UC Master Gardener Program of Contra Costa County
Help Desk Response: Thank you for contacting the UC Master Gardener Program's Help Desk with your question. Winter cold hours needed for various fruiting plants and trees are defined as “chill hours”. Chill hours are monitored by UC Davis at 4 sites in the County at El Cerrito, Moraga, Concord, and Brentwood (see map right).
Blueberry bushes need a minimum number of chill hours by variety each winter to enhance their fruiting. Chill hours are defined as hours less than 45°F but above 32°F. If a blueberry bush doesn't experience enough chill hours in the winter, the flower buds might not open at all in spring, or they might open unevenly. In either case, fruit production will be reduced.
We have found the best resource for calculating chill hours is the Chill Calculator on the UC Davis Fruit and Nut Research and Information Website at:
http://fruitsandnuts.ucdavis.edu/Weather_Services/chilling_accumulation_models/.
Below is a list of some “Low Chill” Southern Highbush Varieties that have been found to do well in our USDA Zone 9B. There are, of course, many additional cultivars available that you can choose from with similar chill hours to these:
Emerald: 250 Chill Hours, Zone 8-10
Jewel: 200 Chill Hours, Zone 8-10
Jubilee: 500 Chili Hours, Zone 5-9
Misty 300 Chill Hours, Zone 5-10
Southmoon 400 Chill Hours, Zone 6-9
Oneal 600 Chill Hours, Zone 5-9
Sunshine Blue 150 Chill Hours, Zone 5-10
Reveille - 500 to 600 chill hours. Zone 6-10
You may not be able to find some of these varieties in your local nurseries, but there may be others with similar potential. You may also be able to mail order the bushes, but my limited personal experience found that many out-of-state nurseries won't ship blueberries into California.
Here is a link to additional UC information about growing blueberries:
http://ucanr.edu/sites/gardenweb/berries/blueberries/
Finally, here is a link to some additional information about chill hours in our area posted in our blog almost a year ago along with links to earlier posts. We will be updating it when the “2016-17 chill hour season” ends February 28th. http://ccmg.ucanr.edu/HortCoCo/?blogstart=66&blogasset=12496
Good luck on your blueberries. Please let us know if you have any additional questions we can help you with.
Help Desk of the UC Master Gardener Program of Contra Costa County (SLH)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
Advice From the Help Desk of the
UC Master Gardener Program of Contra Costa County
MGCC Help Desk Client: I've attached photos of our Patriot blueberry bush. Why are the leaves turning brown and curling? The problem began about a month ago. We tried to treat with acidifying powdered fertilizer, applied to the soil and cultivated in prior to watering. We water every other day or as needed (we check soil moisture with a short stick). The plant is now sending out new growth which looks relatively healthy.
Blueberriy showing sun burn/scald and/or water stress...
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your blueberry question. You wrote that the leaves were turning brown and curling.
Your photographs were helpful. We think the plant has been experiencing sun scald and/or water stress. Several different factors may be contributing to this.
1. Blueberries have a shallow root system. During times of high moisture demand the roots may not be able to keep the leaves hydrated. This is especially true for container plants in full sun where during significant heat spells they will likely need water every day. To help the roots function, we recommend that you put an inch or two of mulch such as wood chips, or well-decomposed compost on the top of the soil (but keep it at least an inch away from the stems). This will help the soil to remain cool and reduce water loss.
2. Shallow rooted plants are susceptible to damage from cultivation. When you apply fertilizer or acidifier, just water it in without cultivating. Plants with damaged roots will have a much more difficult time absorbing sufficient water.
3. Shallow rooted plants need room to expand sideways in order to have an adequate root volume. We recommend that you re-pot your blueberry plant into a wider container in the fall once the weather cools down (e.g. November). Wait at least 4 weeks after re-potting before applying any fertilizer.
Additional information on growing blueberries can be found at this University of California website http://ucanr.edu/sites/gardenweb/files/29062.pdf.
I hope that this information is helpful.
UC Master Gardener Program of Contra Costa County (JL)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).