Scale insects on a cabbage palm (Sabal palmetto). Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County
This week I was on a couple site visits to look on some cabbage palms (Sabal palmetto) and some banana shrubs (Michelia figo). The palms had a white, waxy substance on their frond petioles and the banana shrubs had white specs on the tops of their leaves. Upon further investigation, I realized the waxy substance and specs were both different species of scales. Scale insects are serious pests of a number of ornamental plants. Here in Florida there are 13 different families of scales with the most common being armored scales, soft scales, and mealybugs. Scales have piercing-sucking mouthparts which they use to siphon fluids from the leaves, stems, and sometimes roots of many ornamental plants. Heavy infestations cause extensive leaf yellowing, premature leaf drop, branch dieback, and eventually plant death.
The life cycle of a scale begins with eggs being laid beneath wax coverings or beneath the adult female. Eggs typically hatch in 1 to 3 weeks. The newly hatched nymphs, called crawlers, move around a plant until they find a spot to feed. Once a feeding site is located, their piercing sucking mouthparts are inserted into the plant and the crawlers begin to feed and grow. The males of many scale species develop wings as adults and fly to other plants to reproduce.
Magnolia white scales on a banana shrub (Michelia figo). Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County
Armored scales get their armor by secreting a waxy covering over their bodies that is not attached. The scale lives under this covering and uses it as a protection to feed under. Armored scales can be almost any color or shape and range anywhere from 1/16 to 1/8 inch in diameter. For females, these shapes range from circular to oval to long and slender. The males typically have coverings that are more elongate and smaller than the females. As adults, the males are tiny, winged, gnat-like insects and are rarely seen.
Gloomy scale (Melanaspis tenebricosa) with armored covering removed. Photo Credit: A. G. Dale, University of Florida/IFAS
Similar to armored scales, soft scales secrete a waxy covering, but it is attached to their bodies. Soft scales can be a number of colors, shapes, and sizes and range anywhere from 1/8 to 1/2 inch in diameter. Their shapes vary from spherical to nearly flat.
Population of adult and immature tuttle mealybugs (Brevennia rehi) on a blade of zoysiagrass. Photo Credit: Lyle J. Buss, University of Florida/IFAS
Mealybugs are soft-bodied insects that possess a covering of flocculent, white, waxy filaments. They are about 1/8 inch in length and usually pinkish or yellowish in color. Mealybugs have piercing-sucking mouthparts which they use to siphon fluids from the leaves, stems, and sometimes roots of many ornamental plants. Mealybug damage produces discolored, wilted, and deformed leaves.
Scale and Mealybug Management
- Cultural Control – Plant inspection prior to purchase or installation is the first line of defense against a scale or mealybug population. Make sure to inspect the undersides of leaves and plant stems. Infested sections of plants can be pruned and plant material should be cleaned from the planting area and discarded. Also, you can increase air flow and decrease humidity by proper installation and pruning. Over-fertilizing can also increase pest populations.
Larva of a brown lacewing. Credits: Lyle Buss, University of Florida.
- Biological Control – Predators, such as ladybugs and green lacewings, are usually present in large enough numbers to suppress scales and mealybugs to a desirable threshold. However, broad-spectrum insecticides and bad weather can reduce predator numbers. Look for signs of predation by inspecting dead scales for jagged holes in their waxy coatings. If predation signs are present, use more selective chemical controls and oils as opposed to broad-spectrum products.
- Chemical Control – Timing is everything when it comes to managing scale and mealybug insects. Crawler activity is more pronounced with the flush of new plant growth in the spring. Before application, prune infested plant parts off first to promote greater penetration of insecticides into the foliage. Dormant Oils are often used in the winter to smother scale insects. These are good choices to implement because they don’t harm non-target or beneficial insects. Care must be taken to read the label and use them at the correct temperature, since use in hot weather may burn foliage. Contact products (acephate, bifenthrin, carbaryl, etc.) must be applied to inhibit the crawler stages of these insects and systemic products (acetamiprid, imidacloprid, thiamethoxam, etc.) can be used on the sessile growth stage. Plants should be sprayed thoroughly to the point of drip or “run off” from leaves, twigs, and stems. Repeated applications may still be necessary even if the timing is right, as crawler populations are often large and crawlers like to hide under old waxy scales. Systemic drenches are also a viable option. With good spray coverage, horticultural oils can kill scales at all stages of growth. Refer to the product label for phytotoxicity and temperature guidelines. Even after successful treatment, the outer coatings of the scales may remain on the plant material for weeks, which can be unsightly. The best way to determine if scales are dead is to squeeze them. They will be dry when squeezed if they are dead and they will ooze liquids if they are living (they were at least alive to the point of being squashed).
For insect identification and additional information on scale control, please see:
A Guide to Scale Insect Identification
UF/IFAS Featured Creatures
Your County Extension Office
A couple weeks ago, I was on a site visit to check out some issues on Canary Island Date Palms. The account manager on the property requested a site visit because he thought the palms were infested with scale insects. He noticed the issue on a number of the properties he manages and he was concerned it was an epidemic. From a distance, lower fronds were yellowing from the outside in and the tips were necrotic. These are signs of potassium deficiency with possible magnesium deficiency mixed in.
Transitional leaf showing potassium deficiency (tip) and magnesium deficiency (base) symptoms. Photo Credit: T.K. Broschat, University of Florida/IFAS Extension
Nutrient deficiencies are slow to correct in palm trees. It’s much easier to prevent deficiencies from occurring by using a palm fertilizer that has the analysis 8N-2P2O5-12K2O+4Mg with micronutrients. Even if the palms are part of a landscape which includes turf and other plants that require additional nitrogen, it is best to use a palm fertilizer with the analysis previously listed over a radius at least 25 feet out from the palms. However, poor nutrition wasn’t the only problem with these palms.
Upon closer look, the leaflets were speckled with little bumps. Each bump had a little white tail. These are the fruiting structures of graphiola leaf spot also known as false smut.
Graphiola leaf spot (false smut) on a Canary Island Date Palm. Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County
Graphiola leaf spot is a fungal leaf disease caused by Graphiola phoenicis. Canary Island Date Palms are especially susceptible to this disease. Graphiola leaf spot is primarily an aesthetic issue and doesn’t cause much harm to the palms infected. In fact, the nutrient deficiencies observed in these palms are much more detrimental to their health.
Graphiola leaf spot affects the lower fronds first. If the diseased, lower fronds are not showing signs of nutrient deficiencies then they can be pruned off and removed from the site. All naturally fallen fronds should be removed from the site to reduce the likelihood of fungal spores being splashed onto the healthy, living fronds. A fungicide containing copper can be applied to help prevent the spread of the disease, but it will not cure the infected fronds. Palms can be a beautiful addition to the landscape and most diseases and abiotic disorders can be managed and prevented with proper pruning, correct fertilizer rates, and precise irrigation.
It is common in Northwest Florida for palms to show signs of nutrient deficiencies. In general our sandy soil is often nutrient poor and available nutrients can easily move out of soils with frequent rainfall. In landscapes where fertilization is occurring, often the wrong types of fertilizer are applied. Fertilizer miss-application actually increases nutrient problems for the palm.
Palms can be deficient in many nutrients but the most common deficiencies we see in landscapes are from inadequate amounts potassium and magnesium. The simple solution would be to purchase a fertilizer labeled for palms to correct the problem. The difficulty is that most easily available fertilizers for palms do not have the correct form of nutrients that are required for the problems. With the exception of nitrogen, all other nutrients are in a quick release form so while the slow release nitrogen lasts for 2-3 months, all other nutrients have been used up. In response, the palm is encouraged to grow by the nitrogen but does not have enough of the other critical nutrients to carry out vital plant functions. What we see is often older leaves that are yellowing, browning, and die off before they should because the plant is pulling any available potassium and magnesium from old fronds to support new growth. Without the application of proper nutrients to the soil, the deficiency can continue until even new fronds are affected or the palm dies.
The fertilizer used for lawns does not have all the slow release and correct forms of nutrients for the palms. Older leaves turn yellow and brown indicating potassium deficiency. Photo by Beth Bolles, UF IFAS Extension Escambia County.
There is a solution that will help keep your palms healthy and attractive. Make sure you choose a specially designed fertilizer that has all nutrients in slow release form. Look for an analysis such as 8-2-12-4 (Nitrogen-Phosphorus-Potassium-Magnesium). Also read further on the label for Polymer Coated Sulfate of Potash, Magnesium Sulfate (Kieserite), and Chelate (Iron EDTA). These are the forms of nutrients that will be beneficial to your palms.
Look in the area ‘Derived From’ (outlined in blue) on your fertilizer label to find the forms of nutrients. Photo by Dr. Monica Elliott, US/IFAS Extension.
If you have a mixed landscape where the palms are planted in the lawn, be sure to keep all lawn fertilizers out of the root zone of the palms. Lawn fertilizers do not have the correct forms of nutrients for palms. Remember also that palms roots extend many feet beyond the palm canopy so your ‘no lawn fertilizer zone’ may be past the mulch ring.
The recommendation from the University of Florida is 1.5 pounds of fertilizer over a 100 square foot area. Broadcast this on top of the ground and lightly water after application. In North Florida, you will likely apply the correct palm fertilizer about at least two times in May and end of August or 1st of September. If you are not able to use a palm fertilizer with the correct form of slow release nutrients, it is best not to fertilize palms at all.
Figure 1: Palm damage after storm event.
Credit: Edward F. Gilman, UF/IFAS.
A common question after a tropical storm or hurricane event is will my palm tree recover? Palms grow different from other trees, so there’s definitely a different way to care for them post-storm.
The growing point of a palm tree is the bud, located in the top of the tree. This is where the palm fronds emerge. If this bud area becomes damaged, no new leaves will develop and unfortunately the tree will die. If by chance the palm tree has multiple-stemmed trunks, the undamaged trunk(s) should survive. Often times palm trees are so tall that it is very difficult to visibly determine if the bud has been damaged. Time will tell.
It’s important to wait at least 6 months to see if palms develop new growth. Palms usually rebound slowly after a storm. It may take a couple of years before the palm tree produces a full canopy of fronds. If a damaged palm tree is determined to be in peril and current rainfall is not sufficient, it’s important to irrigate three times a week for at least six weeks to assist in recovery.
After the storm strikes, it may be beneficial to perform pruning of the canopy. Start by removing any hanging broken or dead fronds that could be hazardous to people or property. It’s a good idea to remove any fronds that are covering the bud, as well. This will allow new fronds to form. Leave any bent green fronts attached. These fronds still have vital nutrients that the tree is utilizing. Once the frond turns brown, then it is safe for removal.
Storm damage cleanup is extremely dangerous, even for professionals. During cleanup after the storm, remember that safety comes first. Some general safety tips are essential, as in, do not work alone. It’s important to keep a well-stocked first aid kit too. Avoid overexertion at all costs. This is the most common cause leading to injury. Be sure to survey the area, identify the hazards and have a plan for the cleanup. Above all, create a safe area to work within.
Palm tree recovery from storms is a slow process, so please be patient and safe. Contact your local county extension office for more information.
Supporting information for this article can be found in the following the UF/IFAS publications:
“Assessing Damage and Restoring Trees After a Hurricane” by Edward F. Gilman, Mary L. Duryea, Eliana Kampf, Traci Jo Partin, Astrid Delgado & Carol J. Lehtola: http://monroe.ifas.ufl.edu/pdf/Hort/Assessing_Trees_After_Hurricane.pdf
An Equal Opportunity Institution.
When you don’t know what’s ailing your plant, ask an expert.
Many gardeners get stumped when a favorite plant of theirs comes down with a strange “something”. Many of these gardeners know about UF/IFAS Extension and call their local horticulture and agriculture agents for assistance in figuring out what’s going on. However, even these experts are often stumped by what they see. Fortunately, the agents have another layer of experts to fall back on. In addition to the resources in Gainesville, we have the Plant Disease Diagnostic Clinic, located at the North Florida Research Center in Quincy. Plant pathologists here can help determine what fungus, bacteria, virus, or viroid may be the problem.
Plant pathologists are basically plant doctors. They use all sorts of sophisticated techniques to determine what is the cause of a particular plant problem, from growing out fungal spores to examining DNA. Not only do these plant doctors tell us what the ailment is, they also provide recommended cures, or control options. They are also doing research to prevent different diseases from taking hold in our area and reduce the impact on our local growers.
Plant pathologist at work!
At a recent workshop in Quincy, we learned that plant pathology researchers are working on a fungus that affects watermelons, virus and bacteria that can wipe out a farmer’s tomato crop, and a virus that could impact our local roses. Working as a team of scientists, they study these pathogens in the lab and conduct controlled field experiments to figure out which techniques are most effective. Some of this research is leading to different methods and/or products that can help growers and gardeners alike keep their fields and landscapes healthy.
So, if your plants have problems, please contact your local Extension Office. If they don’t know the answer, then the network of scientists, including plant pathologists, in the UF/IFAS Extension family can be called on for backup to provide you with the best possible answer.
While palms may survive, or even thrive, for years in climates cooler than those to which they are native, eventually they will experience temperatures cold enough to cause injury. Here in Northwest Florida, it was January 2014. Unfortunately, much of the damage was not evident until the summer of 2015. The palms held on with stored food reserves.
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. The stem slowly weakens until it can’t support the weight of the crown and it collapses.
Winter is upon us again. So, if you still have palms in the landscape, be prepared, should we experience some extreme weather. 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.
Palms damaged by cold can still show symptoms six months to a year following a freeze. New leaves in the spring may appear mis-shaped. 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.