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- Northwest - Winter 2019
Mark Wilson, Singh, Raghuwinder, Strahan, Ronald E., Monzingo, John, Polozola, Michael, Fontenot, Kathryn, Fields, Jeb S., Kirk-Ballard, Heather
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Ginger.
Tulips.
Irises.
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Late fall and winter are a great time to order and plant bulbs. What are bulbs? Are bulbs, corms, rhizomes and tubers all the same thing?
To a horticulturist, the terms bulb, tuber, rhizome and corm all have different and distinct meanings. However, many gardeners interchange the terms when speaking casually. This can cause some confusion when someone not as familiar with the terms hears them and then tries to find more information later. Generally, gardeners refer to all swollen underground plant parts as bulbs. In reality, if we really wanted to group all of these plant part types together, we would refer to them as “geophytes.” Geophytes is a Greek term meaning “earth plant” and denotes plants that shelter their dormant budding points underground. Geophytes are sometimes just called bulbs but also include corms, rhizomes, tubers and swollen taproots.
True bulbs, such as amaryllis or daffodils, have their resting bud buried deep inside protecting layers of leaf bases. The stem of the plant is compressed within the bulb until favorable growing conditions occur. Like any other stem, once they begin to grow, they then branch and form new bulbs called offsets. Bulbs are found in many members of the lily and amaryllis family and include most of the common spring bulbs, such as tulips, daffodils and hyacinths.
Corms look like true bulbs, but they are solid, so they do not have layers of modified leaves. Corms consist of a short, swollen stem arranged vertically in the soil with buds on the outside of the starchy stem. Corms include common plants, such as crocus, gl adiolas and tuberous begonias.
A rhizome is a fleshy, swollen stem that grows horizontally at or below the soil surface with many growing points or eyes, similar to a potato. Common ornamental plants that have rhizomes include iris, canna lilies, ginger and bamboo.
Like rhizomes, tubers can be easily recognized by the eyes from which the stems grow. Unlike rhizomes, however, tubers are enlarged or swollen lateral roots. True tubers, such as caladiums, are formed from enlarged underground stems called stolons. Tubers can be cut into pieces and re-grown as long as each piece contains an eye. Common tubers and tuberous roots include dahlias, caladiums, Irish potatoes and trilliums.
Mark A. Wilson
Northwest Regional Horticulture Agent
If you are like me, fall is the best time of year. Not because of the cooler temperatures or pretty fall colors but because I do not have to mow my yard anymore. Fall and winter to me is a time I do not even want to think about my yard. I almost rejoice in the thought of not having to mow anymore for the year.
However, I love a pretty yard, and now is actually the time to start preparing your yard for the spring. There are three weeds I simply cannot stand. Henbit is generally the first new green I see coming up in my yard in late winter or early spring. This means I have to mow one little spot in my yard because of this little annoying plant. The next I usually see is annual bluegrass, Poa annua. This weed does not cut prettily and generally dulls blades. The last weed I start seeing is lawn burweed, or stickers.
Most people, and I am no exception, want to treat these weeds when they see them. The problem with that is many times they have already seeded and are ready for next year year’s fight. The best time to combat these weeds is in the late winter before they come up. Using a good pre-emergent spray is the best way to control these problem weeds. Atrazine mixed with surfactant is one of the pre-emergent chemicals you can use to help control them.
John Monzingo
Extension Agent, Claiborne and Webster Parishes
Henbit in turf.
Annual bluegrass in turf.
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!
December 
Onions can be planted from mid-December to early January. In early January, continue to plant onions sets. Bulbing onion varieties that perform well include but are not limited to: Texas Grano, Mr. Buck, Texas 1015Y, Pinot Rouge, Red Burgundy and Miss Megan. Dr. Kathryn Fontenot
Vegetable Crops Specialist
December 
Prepare rose beds for planting later this month. Prune ever-blooming roses in late January or early February. Landscape roses, like the popular Knock Out roses, should be cut back by about one-half their height. But do not cut them back lower than 2 feet from the ground). The end of January is a great time to trim your ever-blooming roses to flush out a new blooms for the spring. 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.
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!
Cordiali saluti,
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
Turfgrass Specialist
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 rsingh@agcenter.lsu.edu.
Dr. Raj Singh
Plant Pathologist, Director of Plant Diagnostics Center
Hort Hints NW region winter 2019pdf / 1.10MB