- Author: Ed Perry
Sunburn is damage to leaves and other plant parts caused by a combination of too much light and heat and insufficient moisture. The first symptom of this problem may be leaves that appear dull or wilted. A yellow or brown “burned” area develops on the leaves, which then dies beginning in areas between the veins.
The best way to avoid sunburn is to choose plants that are adapted to the planting site. Trying to grow shade-loving plants in full sun is asking for sunburn problems. But even sun-loving plants will suffer sunburning of leaves if the plants are growing in dry soil. You need to provide your plants adequate irrigation water to prevent most sunburning problems. If you notice the symptoms early enough, you may be able to restore the color to sunburned leaves before they killed.
Sunscald, also sometimes called sunburn, is damage to tree or shrub bark caused by hot sunshine. Sunscalded bark becomes cracked and sunken, and is susceptible to attack by wood-boring insects and wood-rotting fungi. In fact, I almost always find evidence of flatheaded borer injury in trees that have sunscalded bark. Sunscalded trunks and limbs can develop cankers, become girdled, and die.
Sunscald often occurs on young woody plants. Their bark is thin and may not tolerate exposure to direct sun because they were grown in nurseries where their trunks were shaded. Older trees can be damaged if you expose branches to the hot sun by pruning heavily, especially during the summer months. Removing taller trees that provided shade, or adding pavement or buildings that reflect light onto plants can also lead to sunscald. Even in well-watered soil, sunscald may injure bark if plant roots are unable to absorb enough moisture when it's hot.
You can prevent sunscald through proper planting and pruning. Prune newly planted landscape trees very little or not at all. Leaves not only shade the bark, but manufacture foods necessary for root growth. If there is no foliage growing along the trunk of a newly planted tree, paint the trunk with white interior latex paint, diluted 50 percent with water. Old bark that has been recently exposed to the sun by pruning or limb breakage can also be painted white. Wood chips and other organic mulches can reduce reflected heat and light, thereby reducing the danger of sunscald.
As always, it's important to plant species that are well adapted to the amount of light available in your garden. Also, avoid changing the environment in any way that significantly changes the amount of light your established plants are receiving.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
From UC IPM Pests in the Urban Landscape blog.
According to Gary Goodman, District Manager of Sacramento Yolo Mosquito and Vector control, many residents are anxious and excited to get outside and enjoy the warm weather so it's important to protect yourself from mosquito bites by wearing a good mosquito repellent.
The Centers for Disease Control and Prevention (CDC) recommend using an insect repellent that contains the active ingredients DEET, Picaridin, IR3535 or the plant-based oil of lemon eucalyptus.
Aside from personal protection against mosquito bites, it's important to ensure mosquitoes are not breeding at home. Drain stagnant water from sprinklers, irrigation, and rainstorms. Be sure to check your backyard and dump any water in flower pots, kiddie pools, tires, pet dishes, bird baths and other common household containers that can hold water.
Another ongoing concern is the invasive mosquito Aedes aegypti which has been detected in several counties throughout Southern California and the Central Valley. For county level information, see this map. Invasive mosquitoes pose a significant health threat because they can transmit dangerous viruses including Zika, dengue fever and chikungunya. Surveillance efforts have continued since the initial detection last August. To date, no cases of Zika virus have been reported in California.
For more information on mosquito identification and management, see our recently revised Pest Notes: Mosquitoes. Additional information on vector-borne diseases is available on the California Department of Public Health website.
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- Author: Ed Perry
Although many coast redwoods (Sequoia sempervirons) appear to grow well in some parts of the San Joaquin Valley, the UCCE Master Gardeners are often contacted for help diagnosing redwoods with dead branches that seem to be dying.
It's important to remember that coast redwoods are native to the coasts of Central and Northern California. In this environment, the trees are shaded by each other and experience significant cooling from fog. They also receive moisture from fog drip and high rainfall. In their native forests, redwoods grow with large amounts of forest litter over their roots.
While coast redwood trees are susceptible to some serious diseases, they are most often injured or killed by abiotic (non living) problems. High soil salinity caused by excess sodium (alkaline soil), and toxicity caused by high concentrations of specific ions such as boron and chlorides will stunt their growth and cause their leaves to turn yellow and “burn.” They grow poorly in heavy soils that are too wet, or in dry, compacted soils with poor drainage. Coast redwoods are also susceptible to iron deficiency, especially in high pH soils. They may be injured by freezing temperatures, especially in dry soil. Because they are adapted to a cool, moist environment, they will develop brown and scorched leaves during our hot and dry summers, especially if they're not adequately watered. Drought stressed trees may then be attacked by bark beetles.
In dry or compacted soils the trees grow slowly and their trunks develop a distinct taper. Under ideal soil and moisture conditions, such as along portions of the California Coast, the trunks will be nearly the same diameter from the base of the tree to several feet high. Some brown foliage in the interior of the tree is normal. In fact, it is normal for the oldest leaves to turn yellow, then brown, and finally drop from the tree in late summer and early fall. It is also normal for short twigs to turn brown and fall. New growth at the ends of branches indicates that the branches are alive and healthy, despite some dieback of twigs and leaves.
As mentioned, coast redwoods are susceptible to some diseases. In Stanislaus County, redwoods infected by Botryosphaeria canker (Botryosphaeria dothidea), crown rot (Phytophthora sp.) and Armellaria root rot (Armillaria mellea) have been identified. However, these diseases are relatively uncommon on redwoods here. If you're trying to diagnose a redwood problem, be sure to consider soil and water-related problems first.
Redwoods are forest trees. We have cultivated them for use in non-forest landscapes as street and park trees, and as specimen trees. These conditions are not always favorable to their growth or long term establishment. They grow best with shade, cool root systems, abundant mulch, and continual moisture that is relatively salt free. If you can create some of these conditions in the landscape, redwood culture and disease management will be much less problematic.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
- Author: Anne E Schellman
Every time you eat a fruit, vegetable, or nut, you may want to thank a pollinator. Without them, our diet would lack many of the vitamins and minerals we need to survive.
Often honeybees get all the kudos for pollinating, and they do a great job. But there are other pollinators involved too, including bumblebees, other species of bees*, birds, bats, butterflies, moths, wasps, beetles, and even flies.
June 17-23, 2019 is Pollinator Week, but you can celebrate pollinators all year long by creating a pollinator-friendly landscape. Here is a short list of things you can do now:
- Situate your garden in a sunny location
- Provide a variety of habitats such as shrubs, tall grasses, and low growing plants
- Leave some area of your ground bare (for ground-nesting bees & wasps)
- Use plants that provide pollen and nectar
- Use a mix of plants that bloom throughout the growing season
- Choose less toxic pesticide options and apply them in the early morning or evening
If you have questions or need assistance with any of these suggestions, feel free to contact the UCCE Stanislaus County Master Gardeners at (209) 525-6800 or ucmgstanislaus@ucanr.edu
Please join us when we recommend pollinator-friendly plants during our next free class on Low Water Use Landscaping on Thursday, June 27 from 6:00-7:30 in Modesto. Sign up at http://ucanr.edu/lowwater2019
In the fall we plan to hold a class all about pollinators, so stay tuned!
* Visit the UC Berkeley Urban Bee Lab Common Bee Groups of California to see photos of other types of bees you may find in your landscape. http://www.helpabee.org/common-bee-groups-of-ca.html
- Author: Anne E Schellman
Want to save water* in your home landscape but aren't sure how to get started? The Stanislaus UCCE Master Gardeners have a free class that can help! We will cover:
- Small irrigation changes you can make now to start saving water
- How to design a low water use landscape
- Irrigation tips
- Plants that thrive in low water landscapes
We will also answer these questions:
- Should I "break up with" (tear out) my lawn?
- What kind of water rebates are available if I do?
- How can I save water and keep my lawn?
- Are cacti and succulents the only plants I can grow to save water?
Class Details
Thursday, June 27, 2019 6:00-7:30 p.m.
Stanislaus County Agricultural Center, Harvest Hall Rooms D&E
Sign up at http://ucanr.edu/lowwater2019 or call Anne Schellman at (209) 525-6862 to reserve your space.
*Over half the water used in urban homes goes towards outdoor landscapes.
Source: Public Policy Institute of California https://www.ppic.org/publication/water-use-in-california