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
While palms may survive, or even thrive, for years in climates cooler than those to which they are native, eventually they may experience temperatures cold enough to cause injury. The January 21st snow and wind chill is likely to take a toll on many of the palms in Northwest Florida. We have experience with this since it also happened in January 2014 and December of 2022. Unfortunately, much of the damage in 2014 was not evident for 18-24 months and we are not out of the window for 2022. Healthy palms can hold on with stored food reserves, but repeated events can continue to weaken them. When cold damage is severe, plant tissues are destroyed and water uptake into the plant may be reduced for years. Many times, it is only the protected bud that will remain alive. These palms can still be saved if the bud remains alive. Winter is not over, even though the temperatures are now creeping higher and higher. So, evaluate what damage you may already have and prepare for any additional, yet to come. Here’s a reminder of what to do.
One of the most common problems associated with freezes is that the freeze-killed lower portion of the spear leaf is degraded by secondary fungi and bacteria that are always present in our natural environment. Palm owners are often anxious to trim off the damaged leaves following a cold weather event. Avoid the temptation to remove these fronds until danger of additional freezes has passed. Even dead leaves provide insulation to the critical bud. As the weather warms, the dead fronds need to be removed from around the bud so that the spear can begin to dry out. Drenching the bud area with a copper fungicide will reduce the secondary microbes. Repeat applications will need to continue as the palm leaves develop. Copper fungicides, unlike other fungicides, are active against bacteria and fungi. Be cautious to not use a copper nutrient spray rather than a fungicide. Delay fertilizer application until new fronds have developed. The best analysis for palms is 8-2-12 + 4Mg. Utilization of proper palm fertilization can improve cold hardiness of palms.
Palm trunk decay appeared 2 years after 2014 freeze.
Palms damaged by cold can still show symptoms six months to three years following a freeze. New leaves in the spring may appear misshapen. Usually, the palm will outgrow the damage. However, sometimes the palm loses its ability to take up water. If there is a sudden collapse of the fronds in the crown during the first hot days, the palm may die. There is nothing that can be done to save the palm.
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.
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.
