Landscape News Articles (from Allen Owings and Rick Bogren)

Transcription

1 LSU AgCenter Ornamental Horticulture E-News & Trial Garden Notes Late April 2015 Nursery, Landscape & Garden Center Updates Compiled by Allen Owings, Professor (Horticulture), Hammond Research Station, LSU AgCenter Edited by Rick Bogren, Professor (Communications), LSU AgCenter Phone ; Landscape News Articles (from Allen Owings and Rick Bogren) April 10 Henna Coleus Named Louisiana Super Plant April 17 Senorita Rosalita Cleome and Cousins Olive Cultivars Being Planted at the LSU AgCenter Hammond Research Station (from Allen Owings) Aglandau Bouteillan Maurino Manzanill Arbosana Picaul Koroneiki Pendolino Mission Grossane Frantoio Arbequina Chemlali Oueslati

2 Mid South Green Industry Conference June 2015 Crape Myrtle Bark Scale (from Dennis Ring) Note: Invasive species sneak into the United States in many ways. Then they spread initially undetected through the agriculture crops because plants are not carefully checked before purchase or watched after planting until infestations expand and result in unsightly plantings in the landscape or field. All plants should be carefully examined before purchase and after planting to reduce the potential for invasive species to become established in our nurseries, cities and yards. When unusual insects or injuries occur, notify your local agricultural agent immediately. A new scale has been observed infesting crape myrtles in north Louisiana, Hammond, uptown New Orleans and Houma. The scale is a bark or felt scale belonging in the genus Eriococcus. The azalea bark scale is a closely related species, but it has not been observed infesting crape myrtle. The new scale insect is Lagerostroemia, which feeds on Lagerostroemia indica in Japan and China. Crape myrtle bark scale infests crape myrtles and pomegranates. The scale excretes honeydew that coats leaves and limbs, resulting in a sticky coating from

3 the excess sugars excreted from the insects feeding. Sooty mold grows on the honeydew. This results in a black (sooty mold) coating that appears on the bark of the branches and trunk of crape myrtles. Additionally, white cases are visible, and they enclose the adult female scales. The insects appear as white, waxy encrustations likely to occur anywhere on the plant but often near pruning wounds or in branch crotches. Up close, the azalea bark scale insect is white to gray in color. Larger female scales bleed a pink liquid when crushed. The crape myrtle scale appears pink in color inside the case. Careful examination may reveal dozens of pink eggs under some of the larger white scale covers. Current management suggestions for this scale include: Wash the trunk and reachable limbs of heavily infested plants with a soft brush and mild solution of dishwashing soap. The egg masses and female scales will be washed off, resulting in improved effectiveness of insecticides. Also, the black mold building up on the bark of infested trees will be removed by washing. The scales and sooty mold may be removed by using water pressure. Removal of the loose bark is important because the protected areas where the scales hide are removed. This removes the areas that the scales may use for protection in the winter from unfavorable weather. Management of this insect has not been shown using horticultural oil. Applications of dormant oil in the winter may reduce the numbers of these scales. It is very important to thoroughly cover the tree. Applications of systemic insecticides may be made to the plant root zone. The greatest numbers of crawlers begin to appear in early July. It may take one to three months for trees to take up systemic insecticides. Larger trees take longer to take up systemic insecticides. Application should be made during May through early July. Systemic insecticides include dinotefuran (Zylam, Greenlight Tree and Shrub Insect Control with Safari) and imidacloprid (Merit or Bayer Advanced Garden Tree and Shrub Insect Control). The best results have been obtained with dinotefuran. Allow several weeks for these insecticides to work because they must spread through the plant. Time insecticide applications by examining the cases containing the scales egg to determine when the nymphs emerge from the eggs. The time that the nymphs emerge depends on weather conditions and plant locations. Infested branches may be treated with applications to the terminals using Orthene (acephate) or Merit (imidaclorpid) in a slurry (4:1 ratio of wettable powders to water). Such applications have been effective in controlling aphids by painting the trunk of the tree with a 6-inche-wide band. Wipe the terminals or areas of branches above the infestation clean. Apply the slurry around the branches or terminals about 6 inches wide. The phloem tissue directly takes up the insecticide, and the materials move through the plant. Additional work on management of this insect is needed. The crape myrtle bark scale has been found in Alexandria, Bossier City, Houma, Minden and Shreveport, Louisiana. It has also been found in cities in Arkansas, Oklahoma, Tennessee, Mississippi, Alabama and Texas. If you find this scale, take a sample to the county agricultural agent.

4 Bacterial Gall Loropetalum (from Raj Singh and Yan Chen) Bacterial gall on loropetalum is caused by a plant pathogenic bacterium called Pseudomonas savastanoi. The bacterium is also known to cause galls/knots on olives and oleanders (Fichtner, 2011; Kavak and Üstün, 2009). Other important known hosts include ash, privet and forsythia. On loropetalum, the bacterium causes irregular, rough galls/knots with dark-colored callus (Hagan and Cooner, 2013). These galls can be found on both shoots and stem. The bacterium rapidly girdles small lateral shoots, resulting in shoot dieback. As the disease develops, the galls enlarge and girdle the main stem, leading to plant death. Disease develops rapidly during extended periods of wet and warm weather. For example, Cooner et al reported that artificially inoculated loropetalum produced galls in eight weeks in a greenhouse at 90 percent relative humidity and 86 degrees F (2013). Water splash from rain or sprinkler irrigation spread the bacterium from infected to healthy parts of the same plant or to neighboring plants. Natural openings or wounds are required for the bacterium to penetrate the host tissue and cause infection. Disease is introduced into landscapes on infected plants, where it spreads to healthy plants during pruning and hedging. Contaminated pruning or cutting tools play an important role in pathogen spread. Overcrowding of plants and overhead sprinkler irrigation favor disease development in landscapes where bacterial gall prevails. In nurseries, the disease is first introduced on contaminated plants, and later the bacterium survives on infected stock plants. Cuttings obtained from the infected stock plants for propagating liners serve as a major source of pathogen spread in nurseries. Environmental conditions suitable for propagation are also very conducive for disease development and spread. Disease management in the landscape starts with removing entire plant that has galls on the main stem. If disease is detected at an early stage where galls are present on small shoots, removal of infected plant material several inches below the gall helps reduce disease spread. Buy disease-free, healthy plants and inspect the stems and shoots for any galls/knots. Avoid overcrowding plants and select sites with good air movement to promote rapid drying of plant tissue. Avoid unnecessary injuries, and surface-disinfect cutting or pruning tools between cuts. Avoid overhead sprinkler irrigation. If not feasible, water plants early in the morning. Preventive applications of copper-containing fungicides during favorable environments for disease development may help avoid infection and suppress bacterial growth in landscapes where disease is prevalent. Nursery owners must take all precautions to avoid introducing disease into their nurseries. Shipment of infected liners or stock plants is the most efficient mode of disease transmission during trade. Buy liners or stock plants from a reliable source. Maintain newly arrived loropetalums in a separate location for about three to four months in the nursery. During this time, carefully inspect these plants on routine basis for development of any galls/knots and shoot dieback symptoms. Remove symptomatic plants immediately and dispose them off properly. Nursery owners must educate their crew about the disease and how it spreads. If propagation is done on-site, keep this area as clean as possible. Surface-disinfect tools and other equipment used in the propagation area. Avoid reusing potting mix or pots to prevent infection from carrying

5 over. Maintain disease-free, healthy stock plants away from propagation areas and keep them healthy. Preventive applications of copper-containing fungicides may help avoid infection and suppress the disease. But remember, these fungicides will not cure the galls/knots. References: Conner K. N., Olive, J., Zhang, L., Jacobi, J., and Putnam, P. L First report of bacterial gall on Loropetalum chinense caused by Pseudomonas savastanoi in the United States. Plant Disease 97 (6): 835. Fichtner, E. J Olive knot. University of California Statewide Integrated Pest Management Program Agriculture and Natural Resources Publication Hagan, A. K. and Conner, K. N Bacterial gall on Loropetalum. The Alabama Cooperative Extension System Agriculture & Natural Resources Plant Pathology Series Publication Kavak, H. and Üstün, N Oleander knot caused by Pseudomonas savastaoni pv. nerrii in Turkey. Journal of Plant Pathology 91 (3): Figure 1. Loropetalum galls caused by Pseudomonas savastanoi on a main stem and a smaller shoot. Figure 2. Extended periods of humid and warm weather can promote bark split on loropetalums where the pathogen can infest

6 Sweet Olive Leaf Scorch (from Raj Singh) Sweet olive (Osmanthus fragrans Lour.) is an evergreen, upright shrub native to Asia. It is a small ornamental tree that can grow up to 20 feet tall. Sweet olive s dark, shiny green leaves and white, fragrant flowers make it a popular ornamental plant among home gardeners and landscape professionals. Sweet olive is susceptible to a bacterial disease called leaf scorch caused by Xylella fastidiosa. Different strains of this bacterium are known to cause several economically important diseases, including, Pierce s disease of grapevine, plum leaf scald and leaf scorch of almond, coffee, pear, pecan, oak, oleander and several other landscape trees. The bacterium resides in the xylem vessels (water-conducting channels) of the plant, where it multiplies and blocks these channels and eventually obstructs the flow of water and nutrients within the plant. The bacterium is transmitted and spread by xylemfeeding insects, such as sharp shooters, leaf hoppers or spittle bugs. Symptoms of sweet olive leaf scorch include chlorotic mottling of the leaves that starts from the tips and margins and progresses toward the midribs (Figure 1). As disease develops, leaf tips and margins become necrotic (Figures 2). Severely infected plants defoliate and die (Figure 3). Presently there are no chemicals available to manage sweet olive leaf scorch. Cultural practices that improve plant vigor, such as proper watering and fertilization, may help the infected plants live longer. Pruning symptomatic branches will not save the plant. Detection and removal of infected plants at early stages may help reduce subsequent spread of the pathogen. Symptoms of marginal leaf scorch are often attributed to other causes, such as salt injury or water and heat stress. Positive diagnosis of bacterial leaf scorch requires specialized testing of infected plants. The LSU AgCenter Plant Diagnostic Center is equipped with serological tests to diagnose this disease. Visit our website ( to find information on submitting samples. Figure 1: Chlorotic mottling of leaves caused by Xylella fastidosa.

7 Figure 2: Necrosis of leaf tips and leaf margins caused by Xylella fastidiosa. Figure 3: Defoliation of sweet olive caused by Xylella fastidiosa.

8 Margie Jenkins Azalea Garden Horticulture Lecture Series and Spring Industry Open House May 15 Hammond Research Station LANDSCAPE HORTICULTURE INDUSTRY FIELD DAY and SELNA TRADE SHOW THURSDAY OCTOBER 8, 2015 LSU AGCENTER HAMMOND RESEARCH STATION

9 Louisiana Super Plants Listing of All Plants (from Allen Owings)

10 LSU AgCenter Plant Diagnostic Clinic LSU AgCenter Soil Testing and Plant Analysis Lab