Gardening in the Panhandle LIVE! Program Summary: Managing Pests

Gardening in the Panhandle LIVE! Program Summary: Managing Pests

Syrphid larva and oleander aphids.
Syrphid larva and oleander aphids. Photo credit: Lyle Buss, University of Florida.

When we think of pests we tend to focus mainly on insects. Insects make up roughly 80% of animal life, however only about one percent of insects are considered pests. The rest help pollinate crops, kill pests, clean up dead stuff, and make honey. Unfortunately, plants suffer from many more types of pests such as weeds, disease, and us. This episode of “Gardening in the Panhandle LIVE!” was all about managing pests.

Many soft-bodied insect pests can be controlled with insecticidal soap. Many insecticidal soaps are on the market that can help control pests like aphids and whiteflies. However, dish soaps are manufactured for cleaning dishes and not labeled for pest control. More information on insecticidal soaps can be found in the publication “Managing Plant Pests with Soaps”.

Although dish soap isn’t a good option for insect control, there are some things from around the house that can be used to help manage pests. The publication “Do-It-Yourself Insect Pest Traps” offers some excellent options for monitoring and managing pests with traps.

Florida is home to a plethora of insect pests. The Ask IFAS website has many articles on insect pests common in the garden.

Companion planting is the practice of planting two or more plant species close to each other to improve growth and/or pest control of one or more of the species. The article “Companion Planting: What is it?” offers some great recommendations and examples of this technique. Marigolds are an excellent companion plant because they can help deter and suppress nematode populations.

Some people prefer to only use naturally derived products for pest control. The publication “Natural Products for Landscape and Garden Pests in Florida” extensively reviews some of these products. Bacillus thuringiensis (BT) is a bacteria found in soil that can be used for caterpillar pest control.

We love our squash, cucumbers, and watermelons in the South, however there are a number of insects that like to eat them too. More information on cucurbit insect pests and their management can be found in the publication “Insect Management for Cucurbits”.

Armyworms like to feed on just about everything. The Ask IFAS website has a nice collection of publications on all types of armyworms.

Some fungi are fun to eat while others kill our landscape plants. One common fungal disease found in the landscape is Entomosporium leaf spot. This disease is very common on Indian hawthorns. The article “Keep an Eye on Your Indian Hawthorn” describes this disease and it’s control.

Aphids are a very common insect pest. In fact, some plant species have specific aphids. More information on different aphid species and their control can be found in the publication “Aphids on Landscape Plants”.

A plant in the wrong place is considered a weed. Some plants are particularly good at finding the wrong place and can take over our lawns. The publication “Weed Management Guide for Florida Lawns” offers solutions on controlling common lawn weeds.

Ticks can be pests of pets, livestock, and humans. Texas A&M has created an excellent website on everything about ticks.

Cockroaches do a nice job cleaning up litter when they’re outside, but we don’t need want them in our houses whether they’re cleaning up trash or not. The publication “Cockroaches and Their Management” is a great resource for cockroach species identification and management.

As previously mentioned, there are a lot more good insects than bad insects. For more information on predatory insects and biological controls check out the publication “Natural Enemies and Biological Control”.

Nature is fascinating and most people are lifetime learners. To help find out what you’re looking at, give the iNaturalist website and app a try.

Armadillos don’t mean any harm and can be kind of cute. However, they can make a mess of our yard and they build their dens in some undesirable locations. The publication “The Nine-Banded Armadillo” provides information on armadillos and their management.

Fire ants are pests of our lawns and pastures and their sting is brutal. For more information on fire ants please refer to the publication “Managing Imported Fire Ants in Urban Areas”.

Pests can be pesky, but they are manageable if you keep up with the art and science of their control. If you need help with identification and pest management options please don’t hesitate to contact your local Extension Office.

Past episodes of Gardening in the Panhandle LIVE can be found on our YouTube playlist.

Bot Rot: Sweet Viburnum’s Achilles Heel

Bot Rot: Sweet Viburnum’s Achilles Heel

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.

Post-Freeze Damage in Citrus: Symptoms and Recovery

Post-Freeze Damage in Citrus: Symptoms and Recovery

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.
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.
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.
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.
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. 5. Late symptoms of freeze damage on citrus trees.
Fig. No. 6. Fruits turn black and fall from the tree after freezing.
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).
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.
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
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 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
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
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.

Be on the Lookout for Crape Myrtle Bark Scale

Be on the Lookout for Crape Myrtle Bark Scale

Being a gardener in Florida is exciting. We have many plants to choose from and the weather is mostly pleasant but always seeming to surprise us. One disadvantage of living in such a place, in addition to having so many growing zones, landscape nurseries, and major shipping ports, is that invasive species that land in Florida don’t like to leave. One newcomer in the lineup of invasive pests is the crape myrtle bark scale (Acanthococcus lagerstroemiae). This invasive insect pest made its way from Texas and, as of a few weeks ago, the only Florida sighting had been in Santa Rosa County. Unfortunately, this pest has now been confirmed in Leon County. Landscapers and gardeners in north Florida should learn how to identify this pest and what options are available for control.

The crape myrtle bark scale, as the name suggests, has a pretty specific host – the crape myrtle (Lagerstroemia spp.). However, in the United States, this scale has also been found feeding on our native beautyberry (Callicarpa americana). Due to the widespread planting of crape myrtles, these should be the gardeners primary focus when looking for this new pest. If present on the tree, it is hard to miss. These scales feed on the bark and are a snow-white color. Being a scale, they produce honeydew that is then covered in black sooty mold. So, if you see a crape myrtle with black branches, look closely and you may see the white scales. If you crush these scales and they leave a pink goo on your fingers, then you very likely have crape myrtle bark scale. Of course, you can send a picture or sample to your local county extension office for confirmation.

Black sooty mold and white scales along the trunk and branches are a tell-tale sign of crape myrtle bark scale. Credit: Mark Tancig, UF/IFAS.

If you do happen to find crape myrtle bark scale in your own landscape, or one that you manage, proper control is important to prevent it from moving along any further. Since scales suck on sap and are protected by an outer shell, systemic insecticides are the preferred product for effective control. These include the neonicotinoids, such as imidacloprid (Merit) and dinotefuran (Safari). The larval stage can be controlled with a horticultural oil, sometimes mixed with another insecticide like bifenthrin (Talstar), however, this will not control the adults. Another option is to completely remove the tree and burn all of the plant material.

Excessive sooty mold has turned these branches black. Be on the lookout for crape myrtles looking like this to help identify crape myrtle bark scale. Credit: Jim Robbins, Univ. of Ark. CES. Retrieved from bugwood.

The crape myrtle bark scale can significantly reduce the aesthetic value of crape myrtles due to the black sooty mold that covers the bark. It is also known to reduce flowering and can lead to thinning of leaves. Since crape myrtles make up a big part of our managed landscapes, let’s all work together to scout for this pest and control it when found. If you have questions, please contact your local county extension office.

Difference in flowering due to crape myrtle bark scale damage. Credit: Jim Robbins, Univ. of Ark. CES. Retrieved from bugwood.

For more information, please see this UF/IFAS document and this Clemson website for more photos and control information.

Citrus Canker on the Spread in NW Florida

Citrus Canker on the Spread in NW Florida

Citrus canker has made its way to Escambia County and may be more widespread that we realize.  This bacterial disease was first seen in Northwest Florida almost 10 years ago in Gulf Breeze. Given time and the ease of transmission of this disease, we are now seeing affected citrus trees in both the east and west portions of Escambia County.

This disease is specific to citrus with grapefruit, lemon, and lime being the most susceptible to infection.  The disease can infect all above ground tissues and often enters through natural openings and wounds of leaves, stems, and fruit.  If you find an infection early in an isolated area of the tree, you can prune out and double bag the affected tissue for disposal.  Often times, the disease is noticed only after a considerable amount of tissue and fruit are affected making it difficult to keep the disease in check.

Since the bacteria is so easily transmitted through rain and wind, it is difficult to prevent movement during our frequent storm events. People can also spread the disease by movement of unregulated citrus trees, on equipment, and even on clothing.

Citrus canker lesions appear on both the upper and lower surfaces of the leaves. Photo by Beth Bolles, UF IFAS Extension Escambia County

Lower surface with citrus canker. Photo by Beth Bolles, UF IFAS Extension Escambia County

 

 

 

 

 

 

If you suspect a citrus in your landscape has canker, do not bring a sample to your Extension office for identification.  Take a photo of plant symptoms of upper and lower leaves, fruits, and stems so that your local Extension educators can assist with identification.  The University of Florida publication https://edis.ifas.ufl.edu/publication/PP323 has quality photos and descriptions of the different stages of citrus canker, along with photos of other citrus issues.

Stem lesions on grapefruit. Photo by Beth Bolles, UF IFAS Extension Escambia County.

The bad new for homeowners is that there is not a treatment to cure citrus canker.  If the infection is small (a few leaves or a branch), it may be possible to remove and dispose of the material, following proper sanitation guidelines. Homeowners may also suppress a small infection on fruit by using copper-based fungicides, applied at appropriate intervals. These fungicides only protect plant tissue for a short time by acting as a barrier to infection. See this UF publication for timing of copper sprays for fruit.

Once susceptible citrus are heavily infected, trees will have fruit and leaf drop, along with general decline and dieback.  At this stage of the disease, homeowners should strongly consider removing the tree.  If it can be burned on site in accordance with local burn laws, that keeps the material contained and may reduce disease transmission. Otherwise, all material should be double bagged and sent to a landfill. Do not compost any material onsite or at local composting facilities.  Be sure to follow disinfecting techniques outlined in the University of Florida publication https://edis.ifas.ufl.edu/publication/PP323 for tools, hands, and clothing.

Since management of citrus canker is so difficult, prevention is the best method to protect your tree.  If you are considering a citrus, choose a more resistant selection outlined in the UF publication, Table 2.  Always purchase a citrus from a certified nursery and follow state guidelines which prohibits all propagation of citrus, unless registered to do so.