Stuart Gauthier, Singh, Raghuwinder, Strahan, Ronald E., Polozola, Michael, Fontenot, Kathryn, Fields, Jeb S., Kirk-Ballard, Heather
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Chinese windmill palms are turning up dead in landscapes at an alarming rate across Acadiana. The culprit is a disease called lethal bronzing, which is also known as date palm lethal decline or Texas Phoenix palm decline. The disease is being transmitted by leafhopper insects. Although other palms species are susceptible to this disease, it appears that the Chinese 2 LSU AgCenter Horticulture Hints Southwest Region Winter 2019 windmill palms are the most likely palm to fall victim to this fatal infection. Unfortunately, once symptoms start to show, the only recourse is to remove the sick palm from the landscape. Leaving the infection-ridden palms in place can provide a disease reservoir that the leafhoppers can use to transmit the pathogen. This is often both an expensive and heart-wrenching dilemma considering the sentimental and aesthetic value that palms can add to the landscape.
Chinese windmill palms are dying in landscapes across Acadiana as they fall victim to lethal bronzing disease. Homeowners have no recourse other than to quickly remove declining trees.
As the old adage goes, if a little is good, a lot is even better. Unfortunately, this is not the case with mulch. Trees have evolved to benefit greatly from a 2-to-3-inch layer of mulch, but when this become 2 to 3 feet of mulch, problems will arise. Piling mulch around the base of trees will keep the trunk moist and ultimately lead to trunk and root decay. Especially avoid mulching trees and shrubs that are in poorly drained areas. Mulching a wet area will only compound low soil oxygen conditions. Trees can be mulched year-round with a wide variety of mulch types. On the LSU campus trees are mulched with the clipping and pruning residue generated by the arborist crews that tend to live oaks and other trees at the university. Organic mulch is constantly decomposing; therefore, it requires reevaluation and potential replenishment on a yearly basis.
Many homeowners are over applying mulch around the base of trees. The long-term effects of volcano mulching around the base of a tree can lead to decline.
Gravel mania is becoming increasingly popular in landscapes across south Louisiana. Large pebble use is the latest rage sweeping across new subdivisions and recently renovated landscapes in our area. Many homeowners are touting the drainage, weed control, termite and low-maintenance benefits of this inert material. In some cases, entire beds are being mulched with large gravel. Because of the inert nature of gravel, many gardeners like the idea of making a one-time application of this rock to the base of their plants. Negative aspects of using a layer of gravel around landscape plants include the heat generated by hot rocks, especially around more tender bedding plants. Unlike organic mulches that will decompose and provide nourishment and tilth to beds, rocks do not enhance soil development. When it comes time to replant, replace or remodel beds, an organic mulch can be tilled into the soil; however removing a rock mulch from a planting area may require extra effort. Although it might seem like termites can be deterred by rocks, homeowners should be aware that termiticide treatments will wash off rocks, and the rock can be used as a bridge by termites to enter a home. Many homeowners disturb the termite treatment around their homes when they do landscape work, and they will often pile thick layers of cellulose-based mulch around the footing of their homes with no insecticide treatment. This creates a welcome invitation to nearby termite colonies in the landscape. It will be interesting in 10 years to see if the gravel fad will persist or will become dated like the avocado-colored countertops of the 1970s.
Gravel used in place of mulch in landscapes could have negative effect.
St. Martin Parish Extension Agent
Are you looking to give your winter landscape a pop? Consider incorporating Jolt dianthus into the garden. Some of the best cool-season bedding plants we have available in Louisiana are interspecific dianthus, and the Jolt series dianthus are no exception. Jolt offers a more compact interspecific dianthus than Amazon dianthus (also a Louisiana Super Plant named in 2010) while keeping the abundant flowers and great color. Moreover, Jolt dianthus are some of the most heat-tolerant interspecific dianthus we have, making them a perfect addition to your Louisiana landscape. Jolt dianthus will continue to bloom into the early summer months, giving you that extra push to carry your landscape into the warm season. Jolt dianthus can be planted in early fall in Louisiana landscapes. Like most bedding plants, they are susceptible to extreme freezing temperatures in the winter, so be sure to take appropriate actions if it gets too cold. However, once established Jolt dianthus can tolerate temperatures into the low 20s Fahrenheit. Jolt can also be planted in late winter for an amazing pop of color throughout the spring and early summer. Jolt dianthus have excellent dark green foliage that provides an additional pop to the three amazing bloom colors, Pink, Cherry and Pink Magic. Jolt dianthus is also great for attracting butterflies in the later fall and early spring.
Visit your local nursery or garden center today to pick up Jolt dianthus for your cool-season landscape. Plant Jolt dianthus in raised beds and in full sun, or try in containers for a more eye-catching porch or small landscape. Space them about 8 to 12 inches apart in landscapes to provide adequate room to grow and fill. You do not need to deadhead Jolt, but it will promote additional flowering.
For more information on Jolt dianthus or any other Louisiana Super Plants, contact your local AgCenter extension office or visit www.LSUAgCenter.com/SuperPlants.
Dr. Jeb S. Fields
Ornamental Horticulture Specialist
Jolt Cherry dianthus Pink Magic. Photo by Ashley Edwards.
Gardening not only provides you a form of exercise but also will also increase the amount of fruits and veggies in your refrigerator (if you water and fertilize). Instead of a New Year’s resolution to make a healthy change in January, start in December by ending the year and beginning the new year on a great garden note!
December is the last month I think of as actual winter. January and February to me are very early spring. So, in this last month of winter here are a few to-do items to help keep the garden active!
Dr. Kathryn Fontenot
Vegetable Crops Specialist
Hardy shrub Louisiana Super Plants selections that can be planted now include Belinda’s Dream roses, Drift roses, Shishi Gashira camellias, Conversation Piece azaleas and Leslie Ann sasanquas.
Dr. Heather Kirk-Ballard
Consumer Horticulture Specialist
Supertunia Vista Bubblegum Petunia. Photo by Allen Owings
Winter is rapidly approaching, and one of the things that many gardeners like to do is plant their fruit trees in the fall to get a head start for the spring. A couple of good question to ask ourselves are why is this done and how does it work? This practice has traditionally been done in our area because of our milder winter and warmer soil temperatures that enable root growth much later in the season than in colder climates. This means that the true benefit is limited to a small window in the fall before we have our first sustained temperatures below freezing. Once the soil temperatures get below 7 degrees Celsius, or 45 degrees Fahrenheit, root growth will markedly decrease for the remainder of the season.
With that in mind, the added benefit of extra root growth in the fall does not mean your efforts for spring establishment should be lax. Many gardeners mistakenly believe that because they planted something in the fall, the amount of water needed in the spring for those plantings will be greatly reduced. That is not the case! In fact, I often recommend a spring planting to break that mindset and encourage better establishment care. Since you are reading this article, I believe that you can be trusted to plant in the fall and maintain a good establishment regimen in the spring.
Now let’s take some time to go over some planting basics and good spring establishment care.
More should go into planting a fruit tree than just digging a hole with hope. Ideally you should have a recent soil test and know the drainage properties of your soil. Any nutritional corrections needed should be done well in advance. You don’t want to plant a fruit tree in an environment where it will have direct contact with any fertilizer as it will burn the tree’s sensitive roots. This means in no situation should you add fertilizer to a hole in which you are about to plant a tree!
For drainage information you should dig a hole like the one you would dig to plant a tree. Fill it up to the brim with water. If it drains fully before three hours, your soil likely has a high sand component and you will need to provide extra water for establishment. If it is still holding water after four hours, your soil likely has a high clay component and drainage is hampered.
How you plant your tree is dependent on your local soil type. I generally prefer to dig a hole just big enough for the bareroot or container-grown tree that I am planting. It may be tempting to dig a larger hole and condition the soil around it, but in many cases, this can ultimately delay plant establishment and discourage it from sending roots into the native soil. Always remember to adequately water in any new plantings. This will remove any lingering large air pockets that could desiccate roots and set back your tree.
Finally, one of the major things to consider with new plantings is cultivar selection. You can do everything else right and then end up with lackluster results by planting the wrong thing. Because my area of expertise is pecans, I will focus on that. Pecan cultivars suited for home production must have scab resistance. In that regard, I would focus on Elliot and Syrup Mill as a great production pair. Elliot has long been recognized for its scab tolerance, and because it has a smaller nut, it is easier for the tree to fill up than larger cultivars. I would also strongly recommend some cultivars from Auburn University selected specifically for the homeowner market: Gafford, McMillan and Amling. They are noted for their disease resistance, and though they may not be as productive as other industry mainstays, they more than make up for it in ease of cultivation.
Care does not stop once you have planted your tree. I recommend watering new plantings thoroughly at least once a week during the growing season. If you receive rainfall events totaling an inch of precipitation, you can delay your watering until the next week. I would continue this regimen for at least two years after planting and, ideally, continue it indefinitely for the best quality production.
Be sure to consult your local extension agent before any major horticultural endeavor. An ounce of prevention is worth a pound of cure!
Dr. Michael Polozola II
Horticulture Agent and Pecan Specialist
December begins a bleak time for warm-season turfgrasses. Most lawns should be dormant or at least close to this stage by Christmas. Because lawns are not actively growing, fertilizer applications are not needed during the winter. Actually, you should have stopped nitrogen fertilization on home lawns by late summer (late August to very early September for St. Augustinegrass and centipedegrass).
Nitrogen fertilizer on dormant to semi-dormant St. Augustinegrass, centipedegrass and zoysia lawns can lead to increased brown patch and winter kill. Also, nitrogen applications during this time have a greater potential for leaching or movement into non-target areas.
Winter is an excellent time to collect soil samples and submit them for analysis. Samples should be a composite of soil collected from 3 to 4 inches deep at various places around the lawn. Mix well and reduce the sample to about a pint of soil and take it to the LSU AgCenter extension office in your parish or to a participating garden center. Make sure to specify the type of grass you are growing on the soil test form.
Winter is a great time to submit soil samples to the LSU AgCenter Soil Lab.
Soil samples submitted to the LSU AgCenter result in a wealth of information concerning the overall fertility of your soil. If results of the soil test indicate the soil pH is too acidic, lime will be prescribed in the soil test recommendations. Sulfur may be prescribed for soils that are too alkaline. Winter is the best time to apply lime or sulfur so that it can be activated for the growing season next spring and summer. The correct soil pH is extremely important and has everything to do with nutrient availability and fertilizer performance.
Postpone any permanent warm-season turfgrass seeding until next spring. Soil and air temperatures will be too cold for germination and growth.
Sod, such as St. Augustinegrass and centipedegrass, can be laid during winter and established successfully during the spring. But remember to maintain good moisture to prevent the sod from dying. Establishment of sod is easiest, however, when sodding is delayed until the middle of spring, well after spring green-up.
Large patch disease can come and go throughout the winter if the weather is mild. Treatment with fungicides containing myclobutanil, propiconazole, pyraclostrobin, and triticonazole and azoxystrobin will reduce the spread of large patch. Damage from large patch will slow spring green-up, and diseased areas will remain unsightly until warmer spring weather conditions help with turfgrass recovery. These diseased areas are more prone to weed problems.
Lawn burweed has seed capsules with painful sharp spines.
Broadleaf weeds, such as clover and lawn burweed (sticker weed), and annual bluegrass infesting St. Augustinegrass, centipedegrass and zoysia and dormant bermudagrass can be suppressed with a late fall application followed by a winter application of atrazine herbicide. The window for these atrazine applications is from November to early March. Herbicides containing a three-way mixture of 2,4-D and dicamba and mecoprop (trimec-type herbicides) can be used for winter broadleaf control on the same lawns that were sprayed with atrazine. MSM (metsulfuron) works well on lawn burweed and is highly effective on clovers and false garlic. Weed-and-feed products can be substituted as your first application of fertilizer during the early spring.
Lawns may show signs of green-up in southern Louisiana in late February. Do not push turfgrass growth with fertilizer at that time! Fertilizer applied too early will feed winter weeds and will result in lush turfgrass growth that is more susceptible to injury from late frosts and increased levels of large patch disease. Lawns may be fertilized in the New Orleans area by late March, but delay fertilizing central Louisiana lawns until April. Consider fertilizing lawns in north Louisiana around mid-April.
Dr. Ron Strahan
The boxwood (Buxus sp.) is an important landscape shrub in Louisiana, the south and the nation. It is a top consideration for commercial landscape professionals in selecting ornamentals for new developments. Boxwoods are considered relatively sturdy, problem-free plants but are susceptible to several plant diseases, including boxwood blight, boxwood dieback, Macrophoma blight, Phytophthora root rot and Volutella blight. Although boxwood blight has been found in several neighboring states, it has yet to be detected from Louisiana. Macrophoma and Volutella blights are foliar fungal diseases and produce tan-colored foliage followed by defoliation leading to random dieback. If left unchecked, these two diseases may considerably decline affected boxwoods under favorable environmental condition. Both these diseases can be successfully managed by integrating best cultural practices with fungicides. Boxwood dieback and Phytophthora root rot have become major problems in cultivating boxwoods for the last several years. These diseases have been reported in home and public gardens, landscapes and nurseries.
Figure 1: Diseased boxwood exhibiting light tan foliage and healthy crown and root system caused by boxwood dieback.
Boxwood dieback is a foliar fungal disease caused by Colletotrichum theobromicola. Currently, it is known to cause disease in English, Japanese, Korean and Baby Gem boxwoods. Symptoms appear as a random dieback of twigs with light tan-colored foliage that tends to remain attached to affected branches. Symptomatic plants have a healthy crown and root system. A bright black discoloration of the stem is visible immediately under the bark. This bright black discoloration extends all along the infected twigs and differs from dull brown discoloration of the crown region caused by Phytophthora root rot.
Figure 2: Bright black discoloration of upper stem caused by Colletotrichum theobromicola.
Boxwood dieback has been detected from boxwood liners and is thought to be introduced to new locations via infected liners. Disease spread from plant to plant is accomplished by poor pruning practices and by the dispersal of conidia (spores produced by various fungi) via rain or irrigation water. Although environmental conditions suitable for boxwood dieback are not currently known, Louisiana’s hot and humid weather is extremely conducive for its development.
Because boxwood dieback is a recently discovered disease, effective diagnostic tools and control measures, such as fungicides, are currently limited. Therefore, landscapers and nurserymen should follow good cultural practices and create an environment that is most likely to decrease the spread and development of boxwood dieback. Because removing dead and dying twigs from plants infected by the pathogen is not known to control this disease, all symptomatic plants in the landscape should be removed and destroyed. Use sharp pruning or hedging tools and surface disinfect pruning and cutting tools to reduce its spread. Avoiding unnecessary plant injury during transportation, at planting and during pruning may also help avoid any potential infection by the pathogen.
Nursery owners should closely monitor liners and potted boxwoods for symptoms of boxwood dieback. Suspected plants must be immediately isolated from healthy plants. Propagate new boxwood lines from disease-free mother plants. Growers must follow good agricultural practices, including clean propagation areas free of plant and soil debris, and use of clean tools to avoid introduction of the pathogen during propagation. Remember, symptoms of boxwood dieback may take up to three months to appear after an infection occurs.
Figure 3: Phytophthora affected boxwoods exhibiting symptoms similar to those caused by boxwood dieback.
Figure 4: Dull brown discoloration of boxwood crown and root roots caused by Phytophthora species.
Phytophthora root rot affects the roots and crown of boxwoods. After infection occurs, roots start to rot and lose their ability to absorb water and nutrients. Reddish brown lesions appear on the infected roots. Rotted roots turn light to dark brown and easily slough off. Aboveground symptoms become obvious after considerable root rot has occurred. In the beginning, random sections in the canopy wilt and turn tan colored. A dull brown discoloration of affected crowns occurs at soil line. As the disease progresses, the entire plant turns a light tan color and defoliation occurs.
Phytophthora is a soil-borne pathogen and produces motile zoospores (infection propagules), which can swim in irrigation water. Soil compaction and poor drainage highly favors disease development. In landscapes, the disease is favored by poor landscape practices that create conditions conducive for disease development, such as deep planting, overcrowding of plants, excessive mulching, over-fertilization, over-irrigation, planting in clay rich soils, soil compaction and poor drainage.
Disease management in the landscape starts with avoiding diseased plants because once Phytophthora is introduced, it can persist in soil for a long time. Well-drained soils with good organic matter content are recommended for new plantings. Good cultural practices, including proper planting depth, spacing, fertilization and irrigation, may help reduce infection. Roots injured during planting become highly susceptible to Phytophthora infection. In landscapes where disease is prevalent, prophylactic treatment with fungicides containing active ingredients such as aluminum tris,fosetyl-Al, mefenoxam or phosphite may help avoid infection. These fungicides do not eliminate the disease, and repeated applications may be required to suppress the disease. Follow fungicide labels for rates and frequency of applications.
Current known distribution of boxwood dieback caused by C. theobromicola in Louisiana. Color coded parishes in Louisiana are confirmed for presence of boxwood dieback disease. Color coded parishes on the map include: Richland, Rapides, Acadia, Iberville, West Baton Rouge, East Baton Rouge, Livingston, St. Tammany, Orleans, Jefferson, Terrebonne, St. Martin, and St. James.
Laboratory testing is required to confirm boxwood dieback because it can easily be misdiagnosed as Phytophthora root rot. Disease management strategies practiced for managing Phytophthora root rot will not provide management of boxwood dieback. If you suspect boxwoods exhibiting similar symptoms described in this article, please contact Dr. Raj Singh at 225-578-4562 or email@example.com.
Dr. Raj Singh
Plant Pathologist, Director of Plant Diagnostics Center