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
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/.
Citrus scab, caused by the fungal pathogen Elsinoë fawcettii, is a common disease affecting citrus trees in the home landscape such as satsuma mandarins, tangelos, grapefruit, and other tangerine hybrids. This disease affects the leaves, fruit, and twigs of citrus trees, creating unattractive, wart-like lesions. While citrus scab is rarely fatal to the tree, it can reduce the quality and marketability of the fruit.
Citrus scab on young satsuma mandarin fruit. Photo Credit: Danielle Williams
Identification and Symptoms
The most noticeable symptom of citrus scab is the development of corky, irregularly shaped lesions on the surfaces of leaves and fruit. These lesions start as small, pale, slightly raised areas that gradually enlarge and turn dark brown to light gray. On leaves, the lesions often appear on the lower surface, giving them a warty appearance. Fruit may exhibit scab lesions, which can cause deformities and discoloration, making them less appealing for consumption, however it does not make the fruit inedible.
Raised lesions of citrus scab on leaf. Photo Credit: Danielle Williams.
Understanding the Disease Cycle
Citrus scab thrives in warm, moist conditions and is primarily spread through wind-driven rain that carries the fungal spores to new infection sites. The spores can overwinter in infected plant debris and on asymptomatic parts of the tree, leading to new infections during the growing season. Recognizing this cycle can help residents take preventative measures during critical times of the year.
Management and Control
To keep citrus scab at bay, homeowners should employ a combination of cultural practices as well as careful chemical use when necessary.
Cultural Practices
Sanitation: Regularly remove and dispose of fallen leaves, fruit, and other plant debris to reduce the number of overwintering spores. This practice is particularly important in the fall and early spring.
Pruning: Prune the tree to improve air circulation within the canopy. This reduces humidity levels around the foliage, making the environment less conducive to fungal growth.
Irrigation Management: Avoid overhead irrigation. Overhead watering can splash spores onto healthy tissue, spreading the infection. Instead, water trees at the root zone or use microsprinkler irrigation.
Chemical Control:
Fungicides: Applying fungicides can help protect new growth from infection. Copper-based fungicides are commonly used and can be effective. It is important to read and follow the product label on application timing and directions for use. Typically, fungicides for controlling scab should be applied in early spring when new growth begins.
Conclusion
Regularly inspect your citrus trees for signs of citrus scab, especially after periods of rain and humidity. Early detection and treatment are crucial to prevent widespread infection. Maintaining a healthy tree through proper fertilization, watering, and pest management can also reduce the tree’s susceptibility to diseases like citrus scab.
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.
