Winter Storm Elliott brought freezing temperatures to the Panhandle on December 24th that lasted through December 28th, 2022. While we’ve seen freezing temperatures in years past, none remained below freezing for as long as Winter Storm Elliott did, resulting in significant injury to citrus in our region. Those trees that received significant freeze damage are more vulnerable to pests and diseases. One such pest we are seeing as a result of Winter Storm Elliott, are ambrosia beetles.
Granulate Ambrosia Beetle, Xylosandrus crassiusculus Photo credit: David Almquist.
Ambrosia beetles are a group of wood-boring insects that live in dead or severely stressed trees or dead wood. They are attracted to the odor that the dead/dying trees give off, which is why you may be seeing them now in freeze damaged citrus trees. Once they locate a sick tree, they bore into the lower part of the tree (about 2-3 feet from the ground), creating a tunnel or a gallery. You’ll likely notice sawdust from the galleries at the base of the tree or you may notice a toothpick like protrusion of sawdust at the base of the gallery.
Toothpick like protrusions from ambrosia beetles. Photo credit: Danielle Williams.
Several species of ambrosia beetles are considered true pests that attack living trees, but most species are secondary to another issue. Because ambrosia beetles generally prefer dead or dying trees, they are not typically a problem for citrus trees. If you are seeing signs of ambrosia beetles on your trees, the beetles are likely targeting trees that sustained major freeze damage from Winter Storm Elliott.
Unfortunately, there are no effective strategies to control ambrosia beetles once they attack a tree, so the best line of defense is to keep your trees healthy. Consider the first three UF/IFAS Florida-Friendly Landscape principles for maintaining tree health:
#1 Right Plant, Right Place: Select plants that match the site’s soil, light, water, and climatic conditions. Plants that are well adapted for our region will be lower maintenance and have a better chance of flourishing as opposed to those that aren’t. For information on citrus varieties adapted for our region, please visit: UF/IFAS Evaluating Cold-Hardy Citrus Varieties for the Panhandle | Panhandle Agriculture (ufl.edu)
#2 Water Efficiently and #3 Fertilize Appropriately: Proper irrigation and fertilization enhances plant growth. Over watering or over fertilizing can do more harm than good so it is best to follow UF/IFAS recommendation rates and application timing.
The weather is the most important factor determining where certain fruits can be successfully grown. Terms such as chilling requirement and cold hardiness play a major role in both species and variety selection.
Most fruits which grow in the Panhandle are deciduous, meaning that during the winter, they lose their leaves and go through a semi to full dormancy period. This period is a much needed rest and reset for the plant. The cool season actually helps the plant to rebound for another fruiting season and affects how well the plant will yield fruit. This is where the term “chilling hours” comes into play.
Temperatures below 45 degrees Fahrenheit are considered “chilling”. The number of hours below 45 degrees accumulated throughout the winter determines the total amount of chilling hours. Different species of citrus and dooryard fruit, along with different cultivars of these plants differ in the amount of chilling hours need for that all important rest & reset period. Satsuma is a popular fruit trees in our area, as it is by far the most cold hardy citrus. Evidence suggests that the satsuma can survive a temperature as low as 14 degrees Fahrenheit.
Figure 1. Mature satsumas ready for harvest.
Credit. Pete Anderson. UF/IFAS Extension.
What happens if the plant doesn’t receive the needed amount of chilling hours? Plant hormones can be disrupted, and both leafing and blooming could be light and come outside of the normal range of the season. So, where do we stand in the Panhandle for overall chilling hours? Typically, we see approximately 500 hours chilling hours. Therefore, its best to plant citrus and dooryard fruit that have the characteristic of needing 500 or less hours for chilling. Please see this informative document on citrus and dooryard fruit varieties: https://edis.ifas.ufl.edu/publication/MG248
Now, on to the term cold hardiness. By definition, this is the plants ability to withstand cool season temperatures without injury. Most tropical fruits cannot tolerate our Panhandle temperatures. Those of us that cut back banana trees every year know this all too well. To check your plant hardiness zone, please see the USDA Plant Hardiness Zone Map: https://planthardiness.ars.usda.gov/
Before you plant a fruit tree, make sure you understand about its cold hardiness and whether or not it has a chilling requirement. This will both save you money and a headache, in the end. If you’re in doubt about a particular variety, contact your local extension office.
Pecans are a flavorful and nutritious nut and an essential component of a southerner’s diet. The trees also provide nice shade and intense fall color to landscapes throughout the south. However, not all pecan tree varieties are suited for the Florida panhandle. There are a number of things you should consider before planting a pecan tree.
Pecan tree grove in North Florida. UF/IFAS Photo: Thomas Wright.
Site Selection – Pecan trees are native to the river valleys of North America. They perform best in deep, fertile, well-drained soils. The key is that the soil is well-drained. Pecan trees will not do well in soils that hold a lot of water and do not drain quickly. Pecan trees also need space to grow. Trees should be planted at least sixty feet apart and at least sixty feet from other large trees and structures. This will allow adequate light for the trees produce a good crop.
Disease Resistance – Pecan scab is the most detrimental pecan disease in the southeast. Trees advertised as scab resistant in the past may have become more susceptible over time. A few varieties that seem to be available at tree farms and have maintained their scab resistance are ‘Caddo’, ‘Elliot’, ‘Lakota’, and ‘Gafford’. Newer varieties that currently have good scab resistance are ‘Avalon’, ‘Huffman’, and ‘Whiddon’. However, these newer varieties may be more difficult to find at nurseries and farm stores.
Pollination – Pecan trees produce both female and male flowers on the same tree. Trees are split into two pollination groups. Type I pollinators produce mature pollen before their female flowers are receptive and Type II trees produce receptive female flowers before their pollen is mature. Timing of flower maturity may change with tree age, but it is a good practice to plant a Type I tree along with a Type II tree to ensure a good crop in each tree. A pollination compatibility chart can be found at UGA Pecan Compatibility Chart.
Planting – Commercially, pecan trees are most commonly planted as bare-root transplants, but container-grown trees can also be used. Bare-root trees are usually cheaper and more readily available. They should be planted while dormant, between December and March and should be planted the day they are delivered. If the root system looks dry, soak the trees in water for a few hours before planting. Container-grown trees can be planted any time of the year, but they have the best chance of survival if planted during dormancy. Trees should be planted at the depth they stood at the nursery or the depth they were planted in a container. Planting holes should be at least 18 inches wide and only native soil should be used to fill in the hole. The main causes of death in young trees are planting too deep and inadequate moisture during the first two years following planting.
Pecan trees provide focal points in the landscape and a tasty treat for the belly. For more information on growing pecans and the benefits of pecans please see these Pecan Publications from the University of Georgia.
There are many considerations to make when landscaping with small trees (under 20 feet) in the landscape that are not suitable for large trees. Some of the trees discussed can at times be considered large shrubs depending on definitions and opinions. For the purpose of this article, if it reaches 15 to 20 feet consider it a tree.
Choosing small trees for the right setting involves a number of reasons that could include the need for more privacy from other homes, use as a sound barrier from busy roads, hiding your utility area of the landscape or something unattractive nearby and making sure power lines are not obstructed. Other considerations might include soil types, drainage and holding capacity of the soils, irrigation needs, rate of plant growth and maturity height at 20 feet. Below are a few to consider for the Panhandle of Florida.
Little Gem Magnolia (Magnolia grandiflora ‘Little Gem’) and Teddy Bear Magnolia (M. grandiflora ‘Teddy Bear’) are strong hardy plants once established (within the first 6 months to a year). Both are evergreen with dark green foliage. The ‘Little Gem’ will grow to 20 feet tall by 15 to 18 feet wide. As it matures it tends to become more open and less dense which adds a nice character to show parts of the lower limbs. The ‘Teddy Bear’ will grow to 18 to 20 feet tall but at an even slower rate of maturity to 12 to 15 feet wide while maintaining its density of foliage from bottom to top. It may take a little work to locate the ‘Teddy Bear’ Magnolia.
Photo courtesy: Stephen Greer Teddy Bear Magnolia (Small compact grower)
Several hollies to consider would include the Cassine Holly ‘Tensaw’ (Ilex cassine ‘Tensaw’) and American Holly (Ilex opaca). Both are evergreen and produce red berries during the fall that are bird favorites. They have similar heights of 15 to 20 feet and widths of 10 to 12 feet. Pruning can assist in shaping and slowing these measurements, but keep in mind this will change the look of the tree and create a more formal plant presentation.
Photo courtesy: Stephen Greer Cassine Holly ‘Tensaw’
The Fringe Tree (Chionanthus virginica) has been a popular tree southeast U.S. for many years. It brings a bright spot to the landscape with white flower panicles that cover the tree in mid to late spring depending on location. For a full color effect, plant it with an evergreen hedge behind it. This oval deciduous tree will grow to 12 to 20 by 10 to 15 wide. The dark blue fruit appears in the fall and serves as good bird food source. This fruit is usually hidden behind the foliage. There might even be a nice yellow leaf change in the fall if temperatures and weather allow.
Asian citrus psyllid, Diaphorina citri. UF/IFAS/Entomology Photo: Michael Rogers.
In late 2016, as many of us were enjoying the harvests from our backyard citrus, a bacterial plant disease that can affect all citrus, citrus greening, was widespread in central and south Florida but had not made it this far north. That year, the vector, the insect that spreads the disease from tree to tree, had been found in Leon County and a few other surrounding Panhandle counties, but the disease had not. By mid-2017, the disease had been confirmed in Franklin County and we hoped that our cooler temperatures could keep the insect and disease at bay. Well, I regret to inform you that the disease has also now been confirmed in Leon County, growing in a residential yard in Tallahassee. Now that it is confirmed in non-coastal (and cooler) north Florida locations, I thought a review of the signs and symptoms – as well as what to do with your tree if you suspect or confirm greening – would be helpful.
The tricky part about diagnosing citrus greening is that it has symptoms that look very similar to soil nutrient deficiency symptoms, especially when first infected. This is a good time to mention that citrus require certain micro-nutrients for optimal growth and a citrus-specific fertilizer product should be used when applying fertilizer. Both the disease and certain nutrient deficiencies cause yellowing of the leaves. With greening, the yellowing is typically blotchy and/or not in any particular pattern. Nutrient deficiencies typically cause unique patterns of yellowing, such as a V-shape or artistic-like symmetrical patterns on each side of the leaf’s midvein. The soil’s acidity, or pH, can also cause some nutrients to not be taken up by the plant even if they are present. Soil testing, available from your local UF/IFAS Extension office, and scheduled fertilizations with a citrus-specific fertilizer can ensure that nutrients are not to blame for the discoloring of leaves. More advanced stages of the disease cause such symptoms as leaf drop, fruit drop, lop-sided fruit, uneven inner fruit cores, and reduced fruit quality.
Citrus greening symptoms of the fruit. Photo by Brooke Moffis.
A more obvious sign of potential problems for your citrus are the presence of the insect vector, the Asian citrus psyllid. This is a tiny little insect that goes from one leaf to the other sucking up plant saps for food and unknowingly spreading the bacterium responsible for citrus greening. You can monitor for them by looking closely at the new flushes of growth. If the psyllids are present, you will likely notice most their small, peach-colored eggs and/or white, waxy secretions. If found, it doesn’t necessarily mean that your tree has greening, but you will want to minimize the chance that they could carry it to your tree. The psyllids can be treated with pesticides, ranging from the less harsh options (horticulture oils, neem oil, kaolin clay) to the more hardcore stuff (malathion, carbaryl, imidacloprid). Of course, always read the label of any pesticide before use and/or consult a qualified landscape professional for assistance.
Blotchy leaf symptom of citrus greening. Photo by Jamie D. Burrow.
If you suspect your tree is infected, a diagnostic test can be performed by UF/IFAS plant pathologists at the North Florida Research and Education Center (NFREC) in Quincy to confirm. The test does cost $50, which may seem a little steep, but it’s an expensive lab analysis to run and may be worth piece of mind.
If citrus greening is confirmed in your tree, the right thing to do, unfortunately, is to remove and burn the plant material as there is no known cure. While the Florida Department of Agriculture and Consumer Services (FDACS) doesn’t have any removal requirements for infected dooryard citrus, tree removal is best to prevent additional spread of the disease to other trees, especially those grown by commercial producers in our area. This may seem drastic but eventually the health of the tree and quality of the fruit will decline to a point where you will want to remove it anyway. Don’t forget that movement of any citrus plant outside of the state is prohibited for the very reason of preventing spread of citrus diseases.
You may be asking, “Is it okay to replace it with another citrus tree?” The answer is yes you can, but you do risk re-infection and will want to be monitoring the new planting.
You may also be thinking, “What is going to happen to Florida citrus?” That’s a question that many researchers at UF/IFAS are trying to answer. There is some hope that intense irrigation and nutrient management, as well as specific pruning practices, can help infected trees continue to be profitable for commercial growers. Recently, UF/IFAS researchers were awarded several grants to try and figure a way out of this problem. Some of the lines of research focus on exploring the resistance found in different citrus varieties, including an Australian lime that appears to be greening resistant. This could potentially be used as a future rootstock. Another approach is to try and treat the plants with a particular peptide that would prevent the disease from binding in the insect’s gut. Isn’t that amazing?
Until a fix is found, we should be monitoring for this disease in our area and taking steps to reduce its presence through controlling the psyllids and removing infected trees. If you suspect a tree has greening, please contact your local county Extension office to review the symptoms and discuss your options.
