- 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.
- Author: Lauren Snowden
- Editor: Melissa G. Womack
From the UC Master Gardener Statewide Blog
The tomato is one of the most versatile and rewarding plants to grow in a summer edible garden. According to a 2014 study by the National Gardening Association, 86 percent of homes with vegetable gardens grow tomatoes. It's understandable that the tomato plant is a popular home vegetable garden staple, tomatoes offer thousands of different varieties options and flavors. Plus, nothing beats the flavor of a ripe tomato straight from the garden!
When properly cared for, a single tomato plant can produce 10 to 15 pounds (4.5 to 6.8 kg) or more of fruit. If tomato yields aren't what was expected or the fruit is damaged it could be due to a number of abiotic disorders, diseases or pests. Abiotic disorders result from nonliving causes and are oftentimes environmental, for example: unfavorable soil conditions, too much or too little water, temperature extremes, physical or chemical injuries, and other issues that can harm or kill a plant. Below are five common abiotic disorders of tomatoes and recommended remedies from the UC Agriculture and Natural Resources publication, Growing Tomatoes in the Home Garden.
1. Sunburn
Problem: Fruit turns light brown and leathery on side exposed to sun.
Cause: Overexposure to sunlight.
Solutions:
• Maintain plant vigor to produce adequate leaf cover.
• Avoid overpruning.
• Provide partial shade during hours of most intense sunlight.
2. Leaf Roll
Problem: Older leaves roll upward and inward suddenly, leaves become stiff to the touch, brittle, and leathery.
Causes: High light intensity and high soil moisture, particularly when plants are staked and heavily pruned
Solution:
• Choose less-susceptible varieties.
• Maintain even soil moisture.
• Provide shade during hours of intense sunlight.
3. Blossom End Rot
Problem: Water-soaked spot on blossom end of fruit enlarges and darkens, becomes sunken and leathery. Affects both green and ripe fruit, and is more common on sandier soils.
Causes: Calcium nutrition and water balance in the plant, aggravated by high soil salt content and fluctuating soil moisture.
Solutions:
• Maintain even soil moisture.
• Amend planting area with compost to improve water retention.
• Avoid heavy applications of high-nitrogen fertilizer.
• Soils deficient in calcium may be amended with gypsum.
Problem: Circular concentric cracks around the stem end (concentric cracking), cracks radiating outward from the stem (radial cracking), malformation and cracking at the blossom end (catfacing).
Causes: Very fast growth with high temperatures and high soil moisture levels. Wide fluctuation in soil moisture and or air temperature. Any disturbances to flower parts during blossoming.
Solution:
• Keep soil evenly moist.
• Maintain good leaf cover or provide partial shade during hours of most intense sunlight.
• Mulch around the plant 3 to 7 inches deep to maintain soil moisture and temperature.
5. Solar Yellowing and Green Shoulders
Problem: Yellow or yellow-orange instead of normal red color, upper portions of the fruit remian green even though the lower portion appears red and ripe.
Cause: High temperatures and high light intensity.
Solutions:
• Maintian plant vigor to produce adequate leaf cover.
• Avoid overpruning.
• Provide partial shade during hours of most intense sunlight.
Pests eating your tomatoes?
Other damages that are caused to tomato plants can be caused by a variety of pests. Some examples of common pests, include: hornworms, tomato fruitworms, tomato pinworms, stink bugs, white flies, and leafminers. For information about other pests on tomatoes, visit the UC IPM Tomato Page. For general help identifying and managing pests in your garden, visit the UC IPM website.
Need free gardening advice?
Since 1981, the UC Master Gardener Program has been extending UC research based information about home horticulture, sustainable landscape, and pest management practices to the public. Through a vast network of more than 6,000 certified UC Master Gardener volunteers, the program is administered by local UC Cooperative Extension (UCCE) county offices across California. Contact the UC Master Gardener Program in your county for more information about edible gardening or upcoming educational workshops, mg.ucanr.edu.
- Posted By: Mark Bolda
- Written by: Mark Bolda
The hot weather of this past week has unsurprisingly caused a certain amount of sunscald on caneberry fruit. As can be seen in the photos below, sunscald manifests itself as a white to brown discoloration of one or more of druplets on mature and immature fruit.
The current round of sunscald has accompanied the hot spell of the past three days, and this is consistent with what we have witnessed in the past. Any time on the Central Coast that we go from fairly steady temperatures in of 70oF to suddenly around 90oF with an absence of fog, we experience significant increases in sunscald.
While it may seem that the sunscald of raspberry fruit is caused by simply very hot weather, it is a little more complicated than that and it is actually radiation from the sun which is causing the problem. Apparently, this radiation causes enough physiological changes within the fruit to discolor it, but not causing it to become necrotic right away. Humid air, which in our area tends to be cool (think fog), scatters and absorbs radiation from the sun, while hot air tends not to carry too much of the radiation scattering moisture and therefore is not doing as much to scatter it and prevent it from damaging fruit druplets. Windy weather is even worse, since it is moving the moisture out and away from the canopy.
There are several solutions to this problem. One, the least practical, is to introduce moisture into the canopy via overhead irrigation. It is best of course to do this in the early morning, to ensure that the flowers and fruit are dry by the evening. Another is to use some form of shadecloth to cover the plants, which many Pajaro Valley growers are already doing to a certain extent in the form of macro-tunnels, where very little sunscald has been observed. Finally, it is known that some varieties are more susceptible to sunscald than others, so if one is consistently having problems with sunscald, switching varieties might be a good solution.