Ornamental Horticulture E-News Mid/Late February 2014

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 985-543-4125; E-mail [email protected]; www.lsuagcenter.com/hammond

Ornamental Plant of the Week for February 18, 2014 – Amazon Dianthus (from Allen Owings) Some of the best dianthus for Louisiana is the Amazon series. These are very prolific flower producers and can be planted September through early November or February through March. Flower heads are large and will last until mid-May in south Louisiana and until late May or early June in north Louisiana. This series also has cut-flower potential. Remove old flower stalks to encourage the continuation of the bloom season. Flower colors available in the Amazon series are Rose Magic, Purple, Cherry and Neon Duo. Amazon dianthus are Dianthus barbatus interspecific hybrids. Amazon dianthus are Louisiana Super Plants.

Ornamental Plant of the Week for February 25, 2014 – Supertunias (from Allen Owings) With an ever-increasing number of color combinations now spread over 33 available cultivars, the Supertunia petunias from Proven Winners continue to impress in container and landscape trials across the Southeast. Some of the favorites at the LSU AgCenter have been Silverberry, Bubblegum and Fuchsia. Pretty Much Picasso also belongs to the Supertunia group. There is also a mini group of Supertunias. These plants are very vigorous growers and great for late-winter to earlyspring planting. Plants can reach a height and spread of 24-36 inches. Petunias prefer full sun and well-drained soil.

Landscape News Articles (from Allen Owings and Rick Bogren) Palms Damaged by Cold – February 14 http://www.lsuagcenter.com/news_archive/2014/february/headline_news/louisianapalm-trees-suffer-from-cold-weather-.htm Late-Winter/Early-Spring-Flowering Trees – February 21 http://www.lsuagcenter.com/en/communications/news/headline_news/Flowering-treesadd-to-February-March-landscapes-.htm

Plants in the New Piney Woods Garden at the LSU AgCenter Hammond Research Station – An Abstract (from Allen Owings) The LSU AgCenter’s Hammond Research Station, Hammond, La., has greatly expanded landscape horticulture efforts in the past seven years. Research gardens are being planted and ornamental horticulture/landscape plant evaluations are being conducted on annual bedding plants, trees, shrubs, roses, perennials and more. A new research garden – Pine Woods Garden – was started at the station in late 2012. It is approximately 5 acres and is intended to be a complimentary garden addition to the existing Margie Jenkins Azalea Garden. The area includes 38 large landscape beds that are maintained with raised soil areas, irrigation and pine straw mulch. The plant focus is woody ornamental trees and shrubs, but it includes a few native wildflowers, herbaceous perennials and marginally hardy semi-tropicals and tropicals. Planting started in early 2013, and the majority of the garden is currently full. At the current time, approximately 92 genera containing 417 taxa are established in the garden. This includes a growing collection of Japanese maples and other Acer, Camellia hiemalis, rhododendrons, a Cornus collection that includes University of Tennessee and southern region unnamed selections, hydrangea, althea, taxodium, iris, gardenia, vitex, crateagus, Prunus, ilex, distylium, illicium, abelia, liriope, magnolia, duetzia, halesia, gordonia, kalmia, trachelospermum, cassia, viburnum, forsythia, myrica, quercus, podocarpus, photinia and much more. This effort to collect new cultivars and potential plants for entry into wholesale production and use in order to observe short term landscape performance is being done in cooperation with support from the Louisiana Nursery and Landscape Foundation for Scholarship and Research. In addition, industry grower partners include Panhandle Growers, Plant Development Services, Inc., Transcend Nursery, Jenkins Farm and Nursery, Bracy’s Nursery, Louisiana Growers, Windmill Nursery, Perino’s Garden Center, Greenleaf Nursery, GreenForest Nursery, Stephen F. Austin State University Gardens, Almost Eden Plants, Live Oak Gardens, Green Nurseries and Landscape, Garden Design Nursery, Nichols Nursery, USDA – ARS Poplarville, USDA – ARS McMinnville, Mississippi State University, Society of Louisiana Irises, Azalea Society of America, Willis Farms, Texas A&M Overton, Treesearch Farms, and more.

Horticulture and Pathology Observations on Landscape-planted Roses at the LSU AgCenter Hammond Research Station – An Abstract (from Allen Owings and Mark Windham) The LSU AgCenter and University of Tennessee are working cooperatively in evaluating rose cultivars for the southeastern United States. New landscape plantings in 2013 at the LSU AgCenter Hammond Research Station, Hammond, La., included cultivars previously proven to be less disease susceptible in Tennessee trials – Moje Hammarberg, Knock Out, Pink Knock Out, Double Knock Out, Pink Double Knock Out, Carefree Sunshine, My Girl, and Kashmir. Chicago Peace was used as a diseasesusceptible control in this replicated planting. An additional three cultivars from Weeks Roses will be added in 2014. In addition, two Kolorscape and seven Veranda cultivars from Kordes Roses/Greenheart Farms were landscape planted in fall 2012 for evaluations of horticultural characteristics and disease susceptibility in 2013-2015. An existing planting of six cultivars in the Drift rose series continued to be evaluated in 2013. Blackspot and Cercospora leaf spot ratings were taken seasonally in 2013 using a scale from 0 to 5 with 0=0% foliage spotting, defoliation; 1=less than 2% foliage spotting, defoliation; 2=2-10% foliage spotting, defoliation; 3=11-25% foliage spotting, defoliation; 4=26-50% foliage spotting, defoliation; and 5=50-100% foliage spotting, defoliation. The only Drift rose with blackspot in 2013 was Red Drift. However, Cercospora susceptibility was high with Peach Drift, Pink Drift, Sweet Drift and Apricot Drift being most problematic. Less Cercospora was observed on Coral Drift and Red Drift. Peach Drift and Apricot Drift were the Drift rose cultivars most prone to defoliation due to disease. Proven cultivars from Tennessee were also good in 2013 Hammond, La., trials with the exception of Carefree Sunshine, which was moderately to highly Cercospora susceptible. Kolorscape and Veranda roses showed no to very low blackspot susceptibility but moderate to high Cercospora susceptibility. Kolorscape cultivars Cherri and Kardinal were more prone to defoliation than Veranda cultivars Brilliant, Blush, Cream, Chico, Lavender, Milano and Sunbeam.

Updates from LDAF Horticulture and Quarantine (from Tad Hardy)  Citrus Canker quarantine boundaries were established in November 2013 and include parts of four parishes (Orleans, Jefferson, Plaquemines and St. Charles). We are now working through the formal rulemaking process, and our focus is on creating outreach materials to distribute, making the public aware of restrictions on movement of citrus stock, fruit, etc. This impacts our citrus nursery growers and nursery retailers in the state. Other citrus quarantines: Asian Citrus Psyllid and Citrus Greening (2008) and Sweet Orange Scab (2010). Several Louisiana citrus nursery growers are building federally-compliant structures. Brown citrus aphid and black spot are two additional pests that do not occur in Louisiana but occur in Florida, so they have potential to invade our state at any time.  Texas Phoenix Palm Decline (TPD) was confirmed in City Park, New Orleans, in December 2013. Until now, it was known only from Texas and Florida. We are working toward initial LDAF training followed by delimiting survey and future

decisions on regulatory action-based on survey results and other information. Nursery growers and dealers in the area will receive close inspection for the disease.  Mango shield scale was found on Japanese blueberry plants in a landscape at a library in Harvey, La., in November 2013. This is a first reported find in Louisiana. It appears to have come from plants brought in from Florida. Plants were treated with insecticide by the landscape maintenance company that found the scale.  Reports of possible rose rosette disease continue to trickle in to LDAF and LSU. To date, we have not confirmed the presence of the disease in the state.  The National Plant Board (NPB) is moving forward with an initiative called a Systems Approach to Nursery Certification (SANC). This program is a voluntary approach to implement critical control points and BMPs in nurseries as a means to more efficiently certify interstate plant shipments. A pilot program with nurseries of various sizes in 7-10 states is planned to begin in summer 2014. This long-term initiative hopes to grease the wheels of nursery commerce.  Boxwood blight, currently found in ~7 northeastern states, has not been reported in Louisiana. The NPB has created a model Boxwood Compliance Agreement should the need arise to use it for growers who must show freedom from the disease.  Crape myrtle bark scale was reported in Louisiana in 2013 and now has been found in several central and southern Louisiana parishes. This pest seems destined to spread and become a nuisance pest as well as reduce the health of infested trees. Chemical control can be difficult to achieve.  An amended list of chemicals for use in the imported fire ant (IFA) certification program was published in fall 2013. This list, approved by USDA-APHIS-PPQ, represents only those chemicals recognized for use in the IFA program. The list is available from USDA-APHIS-PPQ or state cooperators

Louisiana Super Plants – Spring 2014   

Kauai series torenia (wishbone flower) Flutterby Petite Tutti Fruitti Pink butterfly bush (buddleia) Luna series hibiscus

Louisiana Super Plants – Fall 2014  

Rabbiteye blueberries Mesa series gaillardia

LSU AgCenter Plant Diagnostic Clinic

Facts about Rose Rosette (from Raj Singh and Allen Owings) Rose rosette disease (RRD) has become a main topic of conversation for every rose enthusiast. Recently, the LSU AgCenter Plant Diagnostic Center has received several inquiries about this disease, but so far, we have not positively identified RRD in Louisiana. Rose rosette disease seems to be most distributed at the current time in Texas, Oklahoma, Arkansas, northern Mississippi, northern Alabama, northern Georgia, Tennessee and Kentucky. More recently, Florida has also reported detection of RRD in three counties on Knock Out roses. Although RRD produces unique symptoms on roses, these can be easily misidentified with symptoms caused by other biotic and abiotic causes. Rose rosette is a devastating disease of roses, and all cultivars are susceptible, including Knock Out roses and wild multiflora rose (Rosa multiflora). The disease is caused by a virus known as Rose rosette virus. Symptoms produced by RRD are highly variable, depending on the cultivar or species of the rose and plant age. Several different types of symptoms have been reported on infected roses, but some of the more recognizable and diagnostic symptoms of RRD include witches’ broom, abnormal discoloration of foliage, excessive thorniness, and thickened new canes. Witches’ broom is caused when a cluster of new shoots emerges from a single point and rapidly elongates (Fig 1). This symptom itself is not just specifically caused by RRD. But improper use of herbicide such as glyphosate (Roundup and many other products) may also result in distortion and clustering of new growth (Fig. 2). Abnormal discoloration and distortion of new foliage (Fig. 3) have been constantly associated with RRD, but feeding injury from chilli thrips, which is a very significant rose-growing issue in Louisiana, also cause similar symptoms (Fig. 4 and 5). Reddening of new foliage and shoots is also related to RRD (Fig. 3). But keep in mind that some rose cultivars produce red new growth, which is normal (Fig. 6).

Infected canes produce excess thorns, which are green or red in color and soft in the beginning but later harden off as the disease progresses (Fig. 7). Presence of excess thorns, especially on new infected canes, is one of the most reliable diagnostic symptoms of RRD. Another symptom that may be used to diagnose RRD is that the infected canes are thicker than the parent cane (Fig. 8). Remember, these symptoms can be used to suspect RRD, but positive confirmation of the disease requires molecular testing . Rose rosette disease is transmitted by a tiny eriophyid mite, Phyllocoptes fructiphilus, or by grafting. The eriophyid mites crawl from plant to plant or move long distance with wind. The virus is systemic and can persist in the live roots of infected rose bushes; however, the virus is not soil-borne. Management of RRD in already-infected roses is not possible. Once infected, there is no cure. Several precautions can be taken to avoid introduction of RRD or to reduce its spread from infected to healthy roses. Remove infected roses completely, including roots. New growth from infected roots may serve a source of inoculum of the virus. Dispose of infected roses immediately by burning. If burning is not feasible, bag the infected roses before removal. The wild multiflora rose is highly susceptible to RRD, and the eriophyid mites may serve as a source of inoculum for both the virus and the mites. Remove symptomatic multiflora roses that exist in the area close to the cultivated roses. Start with disease-free, healthy roses and inspect for any RRD symptoms before purchase. Properly space out new roses to avoid mites crawling from one plant to another. Clean tools and other equipment used for pruning. An integrated management of eriophyid mites, including miticides along with cultural practices, may reduce the vector population and spread of the rose rosette disease. Check with your local county agent or LSU AgCenter Insect Management Guide for information on use of miticides If you suspect RRD in your roses, consult the LSU AgCenter Plant Doctor Raj Singh at 225-578-4562 or email at [email protected].

Fig 1. Witches’ broom symptoms caused by rose rosette disease (Photo Credit: James Jacobi, Auburn University).

Fig 2. Distortion of new growth caused by glyphosate injury (Photo Credit: Raj Singh, LSU AgCenter).

Fig 3. Abnormal discoloration and distortion of new foliage caused by rose rosette disease (Photo Credit: James Jacobi, Auburn University).

Fig 4. Distortion of new growth caused by chilli thrips feeding injury (Photo Credit: Raj Singh, LSU AgCenter).

Fig 5. Chilli thrips feeding on rose leaf (Photo Credit: Raj Singh, LSU AgCenter).

Fig 6. New growth with normal red pigmentation (Photo Credit: Raj Singh, LSU AgCenter).

Fig 7. Excess thorns produced by canes infected with rose rosette disease (Photo Credit: James Jacobi, Auburn University).

Fig 8. Canes infected with rose rosette disease are thicker than the parent cane. (Photo Credit: Ashley Brake and Molly Giesbrecht, Texas A&M)

LSU AgCenter Soil Testing and Plant Analysis Lab