The telltale intense growth of a witches’ broom in a pine tree. Photo credit: Keith LeFevre
Our topic today might seem better suited to late October, but it can be observed in the woods year-round. During a recent Master Naturalist class, we discussed the various species of pines that grow in northwest Florida. All seven Florida native species—longleaf, loblolly, pond, slash, shortleaf, sand, and spruce—grow in our area of the state. While they can be differentiated based on growing location, needle length, and growth pattern, one of our class members had seen something really bizarre in the local pines.
A witches’ broom in this spruce tree has resulted in a miniature version growing along its primary trunk. Photo credit: American Conifer Society
What he described was essentially an intense burst of pine needle growth at the tip of a branch. It stands out as deep green, dense, and unusual among the regular growth pattern of needles. The end result is essentially the production of a “mini-me,” a miniature copy of the normally growing tree, hanging off one of the branches. That afternoon while touring Blackwater River State Forest with a professional forester, we asked him about the strange phenomenon. He’d seen it many times and referred to it as a “witches’ broom.”
Mistletoe growing in a tree results from the same type of auxin disturbance as witches’ brooms. Photo credit: Carrie Stevenson, UF IFAS Extension
In normal tree growth, the trunk produces hormones called auxins, which control the division, expansion, and differentiation of cells. The hormones are concentrated in the growing tips of roots and shoots, and auxins maintain normal growth and keep smaller branches from overtaking the “leader.” Unusual growth occurs when the presence and concentration level of auxin is interfered with by an outside factor. The intense growth seen in these affected trees may be triggered in several ways, including pest, fungus, or mistletoe infestation, or death of terminal buds by environmental conditions. Phytoplasmas—bacteria that infect the phloem tissues—transferred by insect vectors (usually leafhoppers) are also blamed for the odd growth in some plants. Pines aren’t the only species affected; witches’ brooms can be found in other conifers like firs and junipers, nut species like hickory, pecan, and walnut, or in ashes, peaches, and elms.
The prolific growth of witches’ brooms is of great interest to horticulturists hoping to propagate dwarf varieties of the trees. This post by the American Conifer Society goes into great detail on how to “hunt”, cultivate, and encourage the growth of witches’ brooms into dwarf plants for the home landscape. Ecologically, witches’ brooms are not a huge problem for their host trees. Unless vulnerable to a massive outbreak of parasitic mistletoe, trees usually continue growing around them and live normal lifespans. The dense brush can even benefit wildlife, becoming a ready-made nest for birds or tree-dwelling mammals.
As the temperatures warm into the 60’s (or greater) and the rain chance remains good, keep an eye open for disease in your lawn. Large patch disease is common in turfgrass this time of the year. It is caused by the fungus Rhizoctonia solani. The fungus is present in the soil and thatch layer year-round. When the temperatures rise into the 60’s and 70’s it begins to spread. Large patch thrives under these conditions, especially when the soil is wet. With frequent showers the disease spreads quickly. The first symptom of large patch is circular, discolored areas within the lawn. The outer borders of the patches are orange to yellowish in color. In the center of the circle there are grass blades trying to green up again. They are usually unsuccessful, resulting in odd-shaped patches of dying grass that begin to connect to each other.
Picture from UF publication
A simple field diagnostic techniques to confirm large patch disease is to pull on the diseased grass shoots near the edge of the circle. The blades will come loose from the stolon easily. At the base of the leaves the stem and sheaths will appear dark brown and rotten. Yes, it is large patch.
Photo from UF publication
If the weather gets colder or hotter very quickly, the disease will go back into dormancy. Looking at the long-range temperature predictions, the rest of February will be going up and down. Remember, the groundhog said six more weeks of winter. So, start looking for a fungicide or two or contact your pest control service. However, remember fungicides don’t cure existing problems. They are utilized as a protectant for the unaffected portions of the grass. When favorable conditions are present, the turf should be sprayed in order to keep the fungus from penetrating the grass blades. Repeat applications will be needed for as long as the weather is cool and wet. Check the product label for the correct intervals. Several cultural practices promote large patch infection including over-fertilization, over-irrigation, low mowing height, poor drainage and excess thatch. This spring, after the grass has greened-up on its own, is a good time to look at these factors and make corrections. Keep a close eye because as soon as the temperatures drop again in the fall, large patch can reappear if the corrections were not complete. For more information: https://edis.ifas.ufl.edu/lh044
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.
