Normal fall leaves on deciduous crape myrtle. Credit: Larry Williams
Imagine you’re a leaf on a deciduous tree. In spring, you emerge and are blemish-free. You experience the first rays of light. You’ve never existed before. You begin to photosynthesize. This is what green leaves do. You’re normal.
The first windstorm occurs in April, blowing you into other leaves, branches and stems. You sustain a puncture wound. Trees don’t heal. So, any damage is permanent.
In May, a small population of aphids dine on the tree’s leaves. Ladybugs consume most of the aphids and a blowing rain dislodges the remaining few.
During the extended hot, dry weather of June and July, the tree’s owner is not watering properly and the tree begins dropping leaves. This is a normal process in many tree species during periods with insufficient moisture.
But you stay firmly attached.
The tree’s owner overdoes it in fertilizing his lawn and burns some of the tree’s leaves as a result. Most tree roots are shallow, having access to lawn fertilizer. Your leaf margin becomes brown and crisp as a result.
In August, you’re exposed to direct sunlight all day, partly because of the longer day length and partly because of the loss of other leaves that once shaded you.
In September, the tree’s owner applies weed and feed to his lawn. Tree roots growing in the lawn pull up some of the herbicide.
Tree roots grow two to three times beyond the branches, having access to herbicides applied to adjacent lawn areas. The herbicide injures many of the leaves, including you.
Shorter days and cooler temperatures of fall bring on changes in your physiology. The green pigment chlorophyll that has allowed you to produce sugars through photosynthesis since you first emerged is now breaking down.
As a result, your green color fades and fungal spots, sun scald and the puncture wound from spring become visible.
During October and November, many neighboring leaves turn loose and fall to the ground. This is part of the normal senescence process on deciduous trees.
Before you fall, the tree’s owner notices that you don’t look so good and becomes concerned about your brown spots instead of the uniform green color you had in spring. He has visions of another dead tree and rushes to his County Extension Office carrying you in hand.
A Master Gardener Volunteer explains to the tree’s owner that the spots are a natural part of the senescence process. The leaf is at the end of its life.
The tree’s owner is provided information on proper tree care.
The following spring, the tree produces new, healthy leaves, is provided better care and lives happily ever after!
An interesting phenomenon turned up in my camellia this spring. What has, for years, been a perfectly normal bush – growing its glossy, dark green leaves year ‘round and its showy flowers in the fall – suddenly changed. Its leaves started becoming variegated!
Symptoms of Camellia Yellow Leaf Mottle Virus.
Variegation refers to different colored areas of plant tissue. Most commonly, a plant will have stripes or patches of white leaf tissue along with the normal green. Sometimes, colors can vary or the placement can include stems or fruit. Many cultivated varieties of ornamental plants are selected for these interesting patterns, and sometimes food crops as well. A novel, attractive pattern can make for a very profitable plant. In the 1630s, the price of variegated tulips skyrocketed for several years in the Netherlands. During this period of ‘tulip mania’, a single tulip bulb could potentially sell for ten times the annual income of a skilled artisan. Imagine paying $200,000 for one flower!
A variegated variety of star jasmine, propagated for its coloration.
Some variegations are caused by genetic mutations. Plants that are chimeras have cells with different genetic makeups. These varieties must be propagated by cutting or grafting to preserve both sets of genes. Even if successfully propagated, sometimes individual leaves or branches of these plants might lose one color or the other. A leaf that is completely white won’t thrive; it contains no chlorophyll, which gathers energy from sunlight. A leaf that becomes completely green may outcompete the rest of the variegated plant, leading to a loss of variegation over time.
A randomly occurring genetic mutation in Florida pusley, a common weed of lawns.
Other variegations, such as those Dutch tulips and my camellia, are caused by viruses. Most are not desirable, as they decrease the health of the plant even if they don’t kill it outright. Others will quickly lead to decline and death. A mosaic virus, for example, might make your tomato leaves look interesting, but it will eventually kill the plant. In the case of a camellia, ‘camellia yellow leaf mottle virus’ is usually transmitted during the propagation or grafting process, whether intentionally or not. Camellias affected by this virus are usually not harmed, though a lack of chlorophyll in leaves leads to less energy for the plant to use in growth and producing flowers. Still, sometimes the tradeoff for fancy foliage is worth it!
Some branches on variegated plants may turn completely white (or green).
My camellia must have received a bug bite that transmitted the virus, as I haven’t done any grafting on it. I’ve noticed a few others nearby with similar symptoms. If you see this starting on your plant, you may be able to prune out the affected area before it spreads. Make sure to sanitize pruning equipment with alcohol between cuts, and dispose of infected material if you do remove it. For other unwanted viruses, the solution may be a bit more extreme. If you cannot prevent infection in the first place through sanitation and insect control, disposal of the entire plant is often the only option that will keep the virus from spreading to other nearby plants. For any plant disease or pest issue, scout regularly and address the issue before it becomes too big. Consult your local Extension office for information or check out our EDIS publications on specific topics at https://edis.ifas.ufl.edu/.
Q. Some of the leaves on my azalea and/or camellia are swollen and light green. What caused this?
A. This is caused by a fungus that has been relatively common this spring.
The fungus Exobasidium vaccinii causes leaves and flowers to become swollen or thickened, curled and waxy in appearance. This fungus causes leaves, and in some cases flower petals, to enlarge abnormally and is commonly referred to as azalea or camellia leaf and flower gall.
Exobasidium leaf gall on camellia. Credit: Larry Williams
Symptoms vary somewhat based on the host plant. In addition to azalea and sasanqua camellia, it can occur on blueberry, as well. Infected blueberry leaves turn an unusual bright red in spring with almost no swelling of tissue. With azaleas and camellias, leaves become large and distorted and eventually a white powder covers the galls. The white growth consists of spores, which is how the fungus reproduces. Galls ultimately turn brown and harden. Not every leaf will be infected. It’s more common for the plant’s lower leaves to be the most heavily infected but under humid conditions and in shaded locations galls may form on leaves throughout the plant canopy.
The disease relies on airborne spores produced in the whitish mold on the surface of galls in late spring to early summer to reproduce. The galls then form the following spring. It’s important to remove and dispose of infected leaves before they turn white with spores.
Once you see evidence of infected leaves, it’s too late for chemical control. Besides, there currently is no effective or practical fungicide to control this disease in the home landscape. But you can reduce the amount of infection on your plants the following year by pruning infected leaves and throwing them away before spores are produced. After removing infected leaves with galls, never leave them on the ground around the plants.
It’s best to bury, burn or place the infected leaves in a plastic bag and throw them away. This disease is more severe during a cool, wet spring. It’s advisable to not add to the problem by artificially providing the “wet weather” the spores need by frequently using an overhead sprinkler and keeping the foliage wet in the spring during disease development. This is exactly what this and many other plant diseases need – wet conditions. Yet another reason to water during early morning and on an as needed basis, versus allowing an irrigation system to frequently run when there is already adequate moisture from rain.
In the home landscape, the fungus does not cause any long-term problems for the plant. It just makes the plant’s leaves look ugly. The infected leaves will usually fall prematurely.
The crown of a tree is the leaf bearing twigs and branches and the spreading green foliage that we see. A heathy, full crown is a good indication of a healthy and vibrant tree. The crown and the foliage it supports is the energy collector and the center for photosynthesis, which is how the tree produces the energy it needs to live. For a tree to live and thrive, a full crown of leaves is essential, and an unhealthy and thin crown is an indicator the tree has issues. Crown dieback is often not noticed until it is relatively severe and at that point it can be too late. If a tree drops below a certain percentage of live crown it can no longer support itself and continues to decline. The good news is that if you notice your tree is starting to show signs of crown thinning and dieback you can likely intervene to improve its health or diagnose a problem early.
Tree Showing crown dieback, note the dead branches and lack of foliage on the outer branch tips. Photo Credit-Ian Stone
Crown dieback, which is also referred to as crown decline, is a progressive issue that starts small and can progress to the point that only small sparse areas of foliage are left. It is a tree’s response to various stressors, including environmental conditions and severe rot/decay. As a response to severe stress, the tree begins to abort part of the leaves and some of the small branch tips. If the stress continues to worsen, the tree will continue to abort more of the crown, producing progressively more dead wood. The tree is essentially trying to prune itself back to a manageable level of foliage based on the stress it is encountering. This can occur in both small, young trees and mature, established trees. A variety of conditions cause the stress that begins this process. For instance, you may notice crown dieback in young trees planted in compacted urban conditions such as parking lots and paved areas. Trees in these conditions experience stress from the compacted soil and encounter subsequent issues with water and nutrient stress. Large mature trees in an area that experienced recent construction may also exhibit dieback, especially if buffers and setbacks are not maintained or significant fill dirt is brought in. Issues from root disturbance and compaction cause stress and root dieback, which in turn causes visible crown dieback. Additionally, trees that are experiencing rot, decay, and other vascular disease issues will often begin to exhibit dieback. As the rot or vascular disease progresses, the tree is less able to transport water to the crown, which results in the crown dieback that can be seen as the crown thins. Often, in cases of rot, crown dieback will be the primary visible symptom that rot is occurring, as the rot can be concealed deep in the tree. While multiple stressors can be the cause of crown dieback, it is a clear indicator a tree is stressed and in trouble. If this condition goes unnoticed, it can progress past the point that the tree can be saved. However, if noticed and caught early, good tree care techniques can be applied that may restore the tree to heath. In cases of severe rot and decay, having the tree examined may prevent structural failure of a tree exhibiting crown dieback.
If you have a tree on your property that is exhibiting crown dieback, it is a good idea to have the tree examined by a professional to determine the extent and nature of the issue. Key signs of dieback are bare branch tips and dying foliage during spring and summer. It is natural to have some dead wood in a tree, but extensive dead wood around the entire perimeter of the crown is a cause of concern. With good diagnosis, the proper tree care techniques can be applied to help a tree recover. Waiting and hoping a tree with crown dieback will recover on its own is not a good course of action. Recognizing crown dieback and taking early action is the key to success. Contacting a Certified Arborist (www.treesaregood.org ) is a good step in getting an opinion on the extent of dieback, if the tree is recoverable, and how to best address the issue. You can also contact your local County Extension Office or Florida Forest Service County Forester for assistance.
What is a titi? Google it. Wiktionary says it is “a New World monkey of the genus Callicebus, native to South America, distinguished by their long soft fur”. But deeper into the definitions you will find “a shrub or small tree of the southern Unites States, having glossy leaves and elongated clusters of flowers, occurring in wet soil conditions”.
Titi is just a common name for two species that grow in the wetlands. Black titi (Cliftonia monophyla), also referred to as buckwheat tree, is the first to bloom in the spring. Native seedlings produce clusters of small white flowers at the tip of the branches. The sweet-smelling blooms provide a nectar source for bees in February and March. Following pollination, golden-brown seed pods will form, resembling buckwheat grains; hence, the other common name. The seed persists through the fall, providing added aesthetics and a food source for native and migratory birds. Pink-flowering sports of the Black titi have been propagated for the native plant nursery trade. ‘Chipolo Pink’ is one of the most popular (pictured).
The other species is Red titi (Cyrilla racemiflora), also called Swamp titi. It will send out multiple drooping white flowers in a finger-like cluster from the previous year’s wood. Blooming begins in the late spring and continues into the summer. Unfortunately, the nectar has shown to be a source for purple brood disease in bees, a terminal condition for the baby bees.
So, when deciding on native plants for your wetlands edge or rain garden, look for the Black titi and the new cultivars on the market. Then research other summer-flowering nectar sources like Clethra alnifolia, Sweet pepperbush, and their many new cultivars.
Sweet Viburnum (Viburnum odoratissimum) is thought of as being an ironclad landscape shrub, generally a rapid, healthy grower free of insects and disease. However, this spring, many Sweet Viburnum specimens across the Panhandle have experienced varying degrees of dieback, from individual shoots to entire sections of shrubs, caused by the fungal pathogen Botryosphaeria – commonly known as Bot Rot.
Typical symptom of Bot Rot on Sweet Viburnum. Photo courtesy of Daniel Leonard.
Bot Rot almost always appears after some kind of major stress event that impacts susceptible plants – drought, pruning wounds, nutritional deficiencies, or another environmental stress. We haven’t been afflicted lately with any serious drought conditions and the disease occurrences are too widespread to have been a result of isolated pruning or poor plant nutrition. However, the Panhandle did experience a major environmental event around Christmas 2022 that was plenty stressful for landscape plants, a weeklong Arctic blast of extreme cold. This abrupt hard freeze event in an otherwise mild winter is my best guess for what brought about the increased incidence of Botryosphaeria we have experienced this spring.
The Botryosphaeria fungus enters plants via wounds – in this case one probably caused by cold – and begins destroying the plant’s vascular system in the area. As the pathogen progresses, it eventually causes sunken cankers to appear, girdles the affected branch, and cuts off “circulation” in that stem. The first symptom of Bot Rot that gardeners notice is shoots rapidly wilting and exhibiting a blighted appearance, with brown, dead leaves holding onto affected limbs. Unfortunately, dieback isn’t always limited to individual shoots and can spread back into plants to eventually encompass whole branches. Entire plants dying from Bot Rot infection is not uncommon.
While there aren’t any fungicides that are effective in controlling or preventing Bot Rot, gardeners can arrest its spread by pruning out infected branches. To completely rid the plant of the fungus, make sure to prune 4” or so below the last infected plant tissue (symptomatic tissue will appear dark and discolored; healthy tissue will appear light and greenish). After pruning each affected plant, it is important to sanitize pruning equipment with either a 10% bleach solution or 70%+ isopropyl alcohol to prevent spreading pathogens to other healthy plants! Plants that have been irreparably disfigured by Bot Rot or outright killed may be pulled and discarded offsite.
While this year’s Bot Rot infestation has been extremely frustrating and similar future freeze events can’t be ruled out, gardeners should not give up on Sweet Viburnum, an excellent specimen or screening shrub. Keeping plants healthy with proper pruning, good fertility, and adequate irrigation is the best defense to ward off future infection when we experience harsh environmental conditions! For more information on Bot Rot, Sweet Viburnum, or any other horticultural topic, contact your local UF/IFAS County Extension Office! Happy Gardening.
