Written by: Muhammad Adnan Shahid and Mujahid Hussain
What made this freeze event damaging?
The duration of temperatures below freezing determine the amount of damage to citrus plants. In January 2023 the temperature dropped down to 17 F and stayed at that temperature for a longer time than in recent years. Unlike 2022-23, during the winters of 2013-14, the recorded low temperature was 18 F for half an hour. Similarly, during 2014-15, the temperature touched 19 F and stayed only for 15 minutes. Except for these two winters, in the past 12 years, temperatures never dropped below 20 F. What made this freezing event of December 2022 devastating is the long freezing hours between 17-20 F for 11 hours and even more the temperature stayed for about an hour at 17 F (Fig. No.1).
Fig. No.1. Shows the temperatures (17-20 F) duration during the past winters of 2011-2023. The temperature data is retrieved from Florida Automated Weather Network, UF/IFAS Extension Service (https://fawn.ifas.ufl.edu/). During these years, according to this data, only in December 2022, the temperature fell to 17 F which caused severe damage to the citrus in North Florida.
Symptoms After Freeze
Early Symptoms
The duration of appearance of symptoms after freezing was different for different citrus varieties. Even within the same varieties, the age of the plant and the rootstock are also factors that determined the duration of the appearance of symptoms. For example, in the UF 950 rootstock evaluation block at North Florida Research and Education Center in Quincy, the symptoms appeared on young UF 950 plants on Sour orange rootstock after 24 hours and after three days the plant completely turned brown.
Fig. No. 2. Shows the effects of freezing on UF 950 on Sour orange rootstock after day 1 (a) and day 3 of freezing (b). The young plants completely turned brown after three days of freezing.
However, a few symptoms that appeared after about 24 hours of freezing were similar on all plants regardless of age, variety, and rootstock. These include the blackening of new leaves and branches, hardening and yellowing of leaves, and formation of greenish and brownish patches (Fig. No. 3). The leaves of old citrus trees also became curly, stunted, and yellow. During the freezing event, the fruits on the trees became hard due to the nucleation of water.
Fig No. 3. Symptoms after 24 hours of freezing.
Low temperatures below freezing point cause the formation of ice crystals inside the plant, particularly in leaf tissue, causing a damaging effect of cell walls, and leaves appeared water-soaked upon thawing when temperature rose above the freezing point (Fig. 4).
Fig 4: Water-soaked leaves due to the ice crystals formation and their thawing inside the tissues.
Late Symptoms
One week after freezing, leaves started curling – turning brown and dry. At this stage, both leaves and fruits dropped very quickly, within a week giving plants a bush like appearance (Fig. No. 5 and 6). The fruits that remained on the tree developed multiple symptoms depending on the varieties. Fruits of some varieties formed micro-pits on the peel, however, the fruits of other varieties showed patterns of bright orange and yellow colors (Fig. No. 6a). The rotting leaves and fruits also attracted ladybug beetles, consequently this increased populations of other insects in freeze damaged citrus groves. You should keep in mind that the fruits that have been harvested after freezing need extra care as these fruits are more prone attacked by rotting fungi.
Fig. No. 5. Late symptoms of freeze damage on citrus trees.
Fig. No. 6. Fruits turn black and fall from the tree after freezing.
Fig. No. 7. The freezing caused the fruit’s peel to form patterns of bright orange and light-yellow color on the fruits (a). The rotting of leaves and fruits produces an odor after freezing that attracts ladybug beetles (b).
Bark splitting or cracking is a late symptom of freeze damage. Bark splitting or cracking will mostly be seen on stem and branches directly exposed to the sun. Bark splitting starts when sun light increases the temperature on the surface of the bark during daytime, but temperature drops after sun set resulting in unequal shrinkage and contraction of bark and inner plant tissues (Fig 8). Dropping of leaves and fruits is a good indication of plant survival, but if leaves dry while attached and don’t drop then it’s the sign of severe damage to internal tissue with a low chance of plant recovery (Fig 9)
Figure 8. Bark splitting and cracking as a consequence of freeze damage.
Fig 9. Tree with dried leaves still on the branches – it is indication of sever freeze damage to internal tissues
Recovering Plant After Freeze Damage
The recovery of plants is entirely linked to the level of damage to the plant internal tissues during the freeze event. Freezing damage can exacerbate the plant’s health, thereby minimizing the recovery of the plant. However, plants can recover if the internal cells (cambium and xylem and phloem) are alive enough to regenerate the branches. After an extreme freeze event, like what happened in December 2022, some citrus plants will recover in spring due to the presence of living cells in the branches and stems, but if the internal transportation system is damaged, the plant again starts to die back for the next several months. You should not apply any recovery techniques immediately after the freeze event. The best strategy is to wait for the spring to see if plants are giving any indication of recovery and observe their growth at least till May-June.
Fertilization
It is true that after damage, plants require nutrients to regenerate and grow but the application of nutrients is critical as excessive fertilization can also increase the risk of damage. Do not apply any fertilizer until new growth starts in spring. Fertilizers should be applied frequently, but rates should be decided depending on the degree of damage. The plants that are severely damaged will not be able to produce fruits in the next season therefore, the rate of fertilizer should be lowered to promote a slow recovery, as the damaged plants will not be able to uptake all applied nutrients due to slow water flow caused by minimum transpiration rate in the absence of leaves. In this case, any excessive application of fertilizer can cause toxic effects that can further halt the recovery of plants. The application of micronutrients is also important for the recovery of plants.
Plant Protection
Care should be taken to protect the plants from pathogens, insects, and weeds to enhance recovery. Citrus plants regenerate in the spring and aphids and whiteflies like to attack the young leaves, branches, and shoots. Therefore, an effective plant protection plan should be devised that includes the application of insecticides and fungicides. In general, one to two applications of fungicide should be planned along with nutritional spray to prevent infection on new growth. Removal of all fruit from freeze damaged trees is also important for quick recovery (Fig 10)
Fig 10. Freeze damaged stems with living and non-living tissues. Stem with living tissues will recover easily as compared to those with dead tissues
Fig 11: Fruit are removed from freeze-damaged tree
Pruning
Pruning should be avoided because it is not clear how much damage has been done to the plant. Pruning should be delayed until spring or summer. Ideally, pruning should be done on living wood to make sure that all the damaged parts have been removed. If the citrus tree has been damaged below the rootstock/scion union, it is better to re-graft the new scion on the rootstock instead of pruning. Pruning of trees that have been damaged below the scion union will result in the generation of rootstock. Therefore, re-grafting the plant or replanting is the best option. The Fruit Physiology Lab at NFREC-Quincy is developing tissue imaging techniques for quick estimation of percentage of tissue damage in freeze affected citrus tree shoots and roots.
Irrigation
Irrigation after freeze damage should be reduced. Damaged plants do not uptake as much water as healthy plants, therefore, excessive water in roots can cause the nutrients to move away from the plants and even can cause suffocation for young emerging roots. It is not recommended to completely cut off the water supply, because this can further damage the plants.
Research
The Fruit Physiology Lab at NFREC-Quincy is developing tissue imaging techniques for quick estimation of percentage of tissue damage in freeze affected citrus tree shoots and roots. A series of preliminary studies on the use of growth hormones (brassinosteriods, abscisic acid and jasmonic acid) and nutrients (silicon, K and Zn) to improve the cold hardiness is in progress. Preliminary data indicates that the use of growth hormones and plant beneficial nutrients has the potential to reduce freeze damage (Fig 12), but more detailed research and validation in large scale field trials is required. Postdocs and graduate students in The Fruit Physiology Lab at NFREC-Quincy are fully engaged with different research projects to improve the cold hardiness in citrus by hormonal and nutritional therapies. Recently, the lab got a funding to study new scion and rootstock combinations with high cold tolerance.
Fig 12. Effect of Silicon on cold hardiness of citrus plants sprayed with 100ppm of silicon one week before exposed to freezing temperature (-6 C) in programed freezing chamber
Conclusion
Florida has faced record freezing this winter season with recent events that occurred in the last week of December 2022 causing severe damage to citrus trees in North Florida. Citrus growers in South Florida are already fighting with the HLB disease and freeze damage in the North has added to the damage to the citrus industry in Florida. Careful planning and proper care can help damaged citrus trees to recover and start fruiting again. Trees with little damage to their woody parts will recover soon and start fruiting in the next season. However, the trees with more damage to their woody parts will take two or more years to recover enough to start fruiting. Therefore, proper assessment of the damage is important and recovery strategies should be devised according to the degree of damage. Recent freeze events gave us a big message that microsprinklers are not enough freeze protection for established trees. There is also a need to identify growth hormones, nutrients, or combinations of which can improve the cold hardiness of upper plant parts. In addition, exact estimation of recent freeze damage won’t be accurate until April-June.
People love eating potatoes, and farmers love planting them. Traditionally, Valentine’s Day is a known date for planting potatoes. This tradition goes back generations. Potato planting time in North Florida is during the coldest months of January to February, although February 14th is a popular planting day. The taste and texture of homegrown potatoes are far superior to those of store-bought spuds! Garden potatoes also provide a bounty of nutrients. The potato (Solanum tuberosum) is a member of the nightshade family. This cool-weather vegetable typically yields bigger crops in the northern portion of the U.S., however potatoes can be grown as a winter crop in warmer climates.
Potato Varieties
The most popular and successful varieties grown in Florida are based on yield, disease resistance, quality, and adaptability to warm climates. These varieties are white-skinned potatoes ‘Yukon Gold,’ ‘Gold Rush,’ ‘LaChipper,’ and ‘Sebago’, and red-skinned varieties ‘Red Pontiac’, ‘Red LaSoda’, and ‘LaRouge.’ For russet varieties, home gardeners can select varieties that mature relatively early (100-115 days), such as ‘Russet Norkotah.’ Exotic potato varieties are fun and interesting to try since these varieties are hard to find in supermarkets. They are often smaller, taking less time to cook, but are also very colorful, which can increase the nutritional content. Potatoes with bright orange flesh have more carotenoids, and those with red pigments have more anthocyanins, both having health benefits. Other fun varieties include fingerling types and varieties with blue/purple flesh. The ‘All Blue’ potato has deep blue skin and flesh and produces blue flowers. Certified seed potatoes are ideal and can be found at your local feed store or garden center.
Credit: C. Christensen
Planting Prep: Before Planting
The seed potato needs to be cut into the size of an egg, with at least one eye per section. They must be dried in a cool, dark place for a few days. Plant the sections in a 4-6 inch deep trench that receives full sun, with the cut side down and sprouts facing up. Potato plants are heavy feeders and need nutrition through the growing season. To determine what kind and quantity of nutrients to apply to the soil, get the soil tested by a qualified laboratory. Contact your local Extension office for local fertilization recommendations. Apply a 10-0-10 fertilizer at 7.5 pounds per 100-foot row, both at planting and again 3-4 weeks later, by side-dressing fertilizer about 4-6 inches to either side of the plant.
Growing, Harvesting, Storage
Potatoes are ready to dig in about three months. Since potato tubers push up above the soil surface, the soil needs to be mounded around the stems as the plant grows. Tubers exposed to the sun turn green, making them inedible. Remove the tops 2-3 weeks before digging to “toughen the skin.” After harvesting, potatoes need to be kept in a cool (60-65 degrees F) dark place for 10-14 days to allow any damages to heal. Move them to a final storage location with high relative humidity, good aeration, and cool temperatures (38-40 degrees F). Washed tubers should be allowed to dry thoroughly before storing. Under proper conditions, potatoes can be stored for 3– 6 months or more.
Palms in North Florida suffered serious damage as a result of freezing weather in December 2022. As spring approaches, we will be looking to see if the palms will recover. Learn what to do now and what to expect from your palms with UF IFAS Extension Escambia County.
Landscaping in the Panhandle of Florida comes with many opportunities and challenges in this diverse plant environment of coastal, flatwoods (aka pine woodland), sandhills, and clay soil areas running adjacent to the Alabama/Georgia lines. Sandy soil is the predominate soil of the panhandle area from coastal saltwater marshes and brackish bay waters to wetlands and drier well drained quartz sandy soils of the sandhills. Unique ecosystems can be found in all these areas. One of the areas with the largest plant diversity is the Longleaf Pine savannahs found in the sandhills. Now comes the question of landscaping decisions for your residential living.
Native landscape plants. Photo Credit: Stephen Greer, University of Florida/IFAS Extension – Santa Rosa County.
Understanding your soils and how to improve them where you live is critically important before putting the first plant in the ground. We live in an area of abundant rainfall and this will impact the chemistry of your soils. Make an appointment with your local horticulture agent at the University of Florida IFAS Extension office in your county to discuss your soil and landscape ideas. Taking soil samples will likely be needed. With instruction you can easily collect the samples needed to be sent and received to determine the best options.
With abundant rainfall, leaching of key nutrients will occur removing base cations that can include potassium (K), magnesium (Mg), calcium (Ca) and others. This all leads to soils being more acidic in nature. Nutrient resources may need to be added and checked every 2-3 years, just be sure to follow the soil sample recommendations. Soils near wetland areas can leach differently than the deep quartz sandy soils of the sandhills. Adding organic amendments is a recommended practice. Just how much will depend on your soil setting; talk with your horticulture Extension agent. Often new homesites and commercial construction areas have soil brought in to raise or level construction locations. Understanding the movement of water through these newly added layers to the existing soil below will determine drainage and nutrient movement within this site. It can be confusing making decisions about adding soil nutrients, lime, and organic amendments.
Challenges in new soils in landscape. Photo Credit: Stephen Greer, University of Florida/IFAS Extension – Santa Rosa County.
Once all this is settled you can start thinking about how to enjoy this wonderful Panhandle outdoor living opportunity. Creating living spaces comes in many ways from building patios, porches, decks, outdoor kitchens, and strategically places chairs and benches. Talk with your family and others who may enjoy these places with you. Gazebos or barbeque grill areas may be in the plans. Placing these into the landscape takes planning. Draft designs and think of creative solutions for the site. Look at the site elevation changes from high areas to low wetland areas. Will you need “No See Um” screen for the porch to keep out the small insects or install ceiling fans to keep the breeze moving?
There are many questions to be asked. Create a list to be addressed before beginning a project and then determine the cost. Enjoy the adventure!
This article was written by: Joanna Jaramillo Silva1, Rachel Mallinger2, Xavier Martini3
1 Ph.D. Student, University of Florida, Department of Entomology and Nematology
2 Assistant Professor, University of Florida, Department of Entomology and Nematology
3 Assistant Professor, North Florida Research and Education Center, University of Florida, Department of Entomology and Nematology
Bees are the primary pollinators of plants, essential in natural and crop environments for guaranteeing global food security to the human population. Florida is home of more than 300 species of native wild bees, which rely on pollen and nectar from flowers to survive. However, a global pollinator decline reported for honeybees and wild species (including insects, birds, and bats), is decreasing the worldwide provision of pollination services. Food limitation (pollen and nectar), resulting from decreasing flower diversity and quantity, is one of the multiple causes of pollinator decline. Pollinator-friendly plants are receiving attention from people of various disciplines such as the scientific community, stakeholders, Master Gardeners, and citizen science groups willing to participate in pollinator conservation efforts.
Domestic gardens
Domestic gardens comprise a substantial proportion of land in the urban landscape and are often the most significant component of green space; they play essential roles in conserving plant genetic resources, insects, and other wildlife, and have social and economic value. Gardens behave as islands of usable habitat surrounded by urbanization, and they present varying benefits for pollinators. There is generally a positive relationship between high pollinator abundance, flower diversity, and bloom evenness. Gardens for pollinators propose to solve the pollinator crisis by enlarging greenspaces in urban areas by planting more flowers in urbanized environment and by improving the diversity of floral resources for pollinators.
Pollinator friendly plants
There are different categories of floral traits: qualities that attract pollinators such as floral size and color, and physical characteristics that reward the pollinator (nectar and pollen quantity and quality). Flowers with higher quality and quantity rewards are more attractive to pollinators. Nectar provides the main sugar source for insect pollinators; its energetic value is determined by its sugar concentration. The volume of nectar produced by flowers will directly affected visitation by honeybees and bumblebees, butterflies, and birds. Pollen on the other side, consists of the main source of protein for most pollinators.
RECOMMENDATIONS
1. Provide a Mix of floral shapes and sizes.
There is usually a positive correlation between flower size and nectar volume: long tube flowers usually provide more nectar, whereas open or flat flowers provide more pollen. In addition, flower shapes are also associated with different pollinator types (Fig. 1). Long-tongued insects (Butterflies, and some bees) visit deep corolla tube flowers, while short-tongued pollinators (wasps, flies and some bees) remain on short tube or open corolla flowers.
Figure 1. Examples of plants with long tube flowers, short-medium, and open corolla flowers (From left to right: Butterfly on a Pardon my pink (Monarda didyma) (Credits: Joanna J. Silva); Carpenterbee on Salvia Indigo spires (Salvia longispicata x farinaceae) (Credits: Kelly Thomas); Sweat bee on Gaillardia pulchella) (Credits: Joanna J. Silva).
2. Provide a mix of flower colors
Color patterns influence the flower’s attractiveness and increase the efficiency of pollination by helping insects orient on the flower and guide them to the reward (Fig. 2). Bees prefer white, yellow, or blue-purple flowers. Orange, pink, and red flowers attract other pollinators such as butterflies.
Figure 2. Examples of native plants to Florida that display different colors Native to Florida (From left to right: Butterfly on Spanish needles (Bidens alba), Tickseed coreopsis (Coreopsis leavenworthii), Sckullcap (Scutellaria arrenicola), Pitcher sage (Salvia azurea), Swamp Rose-mallow (Hibiscus grandiflorus), Carpenterbee on False-Rosemary (Conradina grandiflora), Spotted beebalm (Monarda puctata), Blanket flower or Firewheel* (Gaillardia pulchella) . Credits: Joanna J. Silva *A recent discovery suggests that Firewheel is not considered native to Florida, but it is widely cultivated. It is probably not native to the rest of the eastern USA as previously thought (ISB: Atlas of Florida Plants (usf.edu), Gaillardia – University of Florida, Institute of Food and Agricultural Sciences (ufl.edu)).
3. Include a pollinator hotel
Add a bee nest box for the native bees that build their nests above ground. Solitary bees and wasps will take up residence in a pollinator hotel after you place it outside.
4. Provide flowers throughout the year.
Pollen and nectar collection varies seasonally for honeybees, while many other solitary bee species collect pollen continuously during adult foraging to feed their larvae. Design the garden to have three or more different plants blooming at any given time during the growing season, which is March through November in northern areas of the state (Fig. 3).
Figure 3. Honeybee on Viburnum (Winter) (Credits: Joanna J. Silva), Honeybee on Salvia Indigo spires taking nectar (Spring-Summer) (Credits: Walker Bensch), False Rosemary and Muhlly grass (Muhlenbergia capillaris) (Fall) (Credits: Joanna J. Silva).
5. Include native plants.
A “Florida native plant” refers to a species occurring within the state boundaries prior to European contact, according to the best available scientific and historical documentation. Florida is home to over 4,867 species of plants; 3,314 species are considered native of which 230 species are endemic.
6. Chose the right plant for each location.
Success depends on using the right plant in the right place, especially by considering plant’s cold hardiness (Fig. 4). Plant selection for landscapers, nurseries, and gardens requires individual site criteria and an evaluation of individual plant performance under different environmental circumstances, such as water, soil, and temperature.
Figure 4. Hardiness zones in Florida (http://planthardiness.ars.usda.gov).
