Increasing use of sustainable plants in production and landscape design
Research and extension was conducted in Florida, Alabama, Georgia and Tennessee during 2009 to identify optimal ornamental plant material for the southeastern US and to evaluate green industry professional adoption or acceptance of pest-resistant plants. Extensive evaluation of herbaceous and woody ornamentals for resistance to key pests has identified plants to recommend for their reduced input requirements. Research in Georgia concentrated on new invasive or emerging pests.
Research during the 2008-2009 year addressed objective 1:
1) Identify optimal plant material
Lesser canna leafroller and Japanese beetle on Canna
Twenty-two cultivars of canna lilies, Canna x generalis, were evaluated for potential resistance to the lesser canna lily leafroller, Geshna cannalis, and the Japanese beetle, Popillia japonica. Both of these pests cause defoliation of the plants resulting in reduced plant fitness and aesthetic injury. Cultivars sustaining the most damage by leafrollers were ‘Richard Wallace’, ‘Firebird’, and ‘Black Knight’. While Japanese beetle injury varied, cultivars most consistently damaged by beetles were ‘Lenape’, ‘Scarlet Wave’, ‘Dawn Pink’, and ‘Crimson Beauty’. While all plants sustained at least some injury, cultivars that consistently had the least amount of damage by leafrollers were ‘Maudie Malcolm’, ‘Striped Beauty’, and ‘Journey’s End’. ‘Maudie Malcolm’ and ‘Striped Beauty’ were similarly avoided by Japanese beetles, while ‘Journey’s End’ sustained moderate injury from this pest. Tall cultivars with red or orange flowers and some red in their foliage were especially vulnerable to infestation by the lesser canna leafroller.
Lace bugs on Pennisetum ornamental grasses
Leptodictya plana Heidemann is an emerging pest on ornamental grasses in the southern United States. Thirty-two selections of commercially available ornamental grasses and sedges and five trial accessions of Pennisetum purpureum were evaluated for susceptibility to L. plana feeding and oviposition. No- choice studies were conducted in a greenhouse by securing four lace bugs to leaf blades of each plant using clip cages. Lace bugs stayed attached for five days. Damage and number eggs were recorded. Choice studies were conducted in the laboratory by placing leaf blades from each genus of plant species into a large petri dish in a spoke pattern. There were no plants tested that consistently received zero percent damage in either trial. Plants that sustained the least damage included Acorus spp., Cordyline spp., and Panicum spp. Pennisetum spp. entries exhibited the highest overall percent damage and were the only genera of plants that supported oviposition.
Lace bugs on Pieris
Stephanitis takeyai Drake and Maa (Hemiptera: Tingidae), the Andromeda lace bug, is an important pest of Pieris D. Don spp., a popular landscape plant. Cultivated Pieris taxa have not been evaluated for their pest resistance and this information would be useful to growers as well as breeders. The azalea lace bug, S. pyrioides was included in the study because of its importance as the major economic and cosmopolitan tingid species which is also known to infest other ericaceous hosts. Both lace bugs are Asian indigenes as are most cultivated Pieris currently in production. Over 60 Pieris taxa were evaluated for their susceptibility to the two species of lace bugs based on leaf damage, adult survival on leaves and emergence of nymphs using no-choice Petri dish assays. The taxa P. phillyreifolia and P. japonica ‘Variegata’ were consistently resistant to both species of lace bugs while P. japonica ‘Cavatine’ was consistently susceptible to both. P. japonica ‘Temple Bells’ and was notable in being highly susceptible to S. takeyai, but resistant to S. pyrioides. Oviposition was noted only with S. takeyai on some Pieris taxa, whereas S. pyrioides did not oviposit on any of the Pieris taxa. Choice assays (with 10 Pieris taxa) and whole plant assays (with 5 Pieris taxa) using S. takeyai alone were also conducted, confirming the resistance of P. phillyreifolia and susceptibility of P. japonica ‘Temple Bells’.
Wide variability in leaf shape, size, texture, color and growth habit exists among Pieris taxa, even among taxa within the same species. Screening of Pieris taxa for their reaction to Stephanitis lace bugs (Hemiptera: Tingidae) revealed gradients in susceptibility to the lace bugs. This study also examined some of the potential mechanisms of resistance in selected Pieris taxa to S. takeyai, based on their differences in lace bug susceptibility and also the possible role of leaf parameters in plant resistance. Experiments with extracts of leaf-surface lipids revealed that Pieris leaf wax does not have a role in resistance. Leaf wax extracts from the resistant species P. phillyreifolia applied on leaves of the susceptible cultivar P. japonica ‘Temple Bells’ did not affect feeding, oviposition or survival of S. takeyai, and neither did the reverse affect the resistance of P. phillyreifolia. Leaf penetrometer measurements indicated significantly higher force was required to puncture P. phillyreifolia leaves. This species also had higher fiber, lignin and cellulose content and lower leaf moisture content. Ultrastructural studies on leaves of selected Pieris taxa revealed significant differences in the number and size of stomata. P. phillyreifolia leaves had the highest number of stomata per unit area but they were the smallest in size, whereas P. japonica ‘Temple Bells’ leaves had a lower number but the largest stomata. Resistance in Pieris taxa to S. takeyai may be attributed to a combination of different factors among which leaf toughness, moisture and stomatal characters may have a significant role.
Hemlock wooly adelgid and their predators on hemlock
Understanding how fertilization affects host resistance to hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is important since fertilizers are often used to grow resistant selections to a suitable size for testing. We evaluated four hemlock species under three different fertilizer regimes to assess whether or not fertility affected resistance to the adelgid and to determine if feeding preferences of the predators Laricobius nigrinus Fender and Sasajiscymnus tsugae (Sasaji & McClure) based on eggs obtained from adelgids raised on plants fertilized or not. Treatments were long-term fertility (June 2008 to June 2009), short-term fertility (March to June 2009), and no fertilizer. Plants were fertilized with 240 ppm N using water soluble fertilizer (NPK: 20-20-20) in a biweekly interval. Plants (> 1-yr old) were artificially infested with adelgids on 31 March 2009. Among unfertilized hemlocks (n = 10/species), foliar N content was highest in Tsuga mertensiana (Bong.) Carrière, and lowest in T. chinensis (Franch.) E. Pritz. Significantly more progredien ovisacs or sisten eggs were present on T. mertensiana than on the other hemlock species with none on unfertilized T. chinensis. Fertilizing T. heterophylla (Raf.) Sarg. had no effect on adult A. tsugae feeding. However, densities of developing A. tsugae nymphs, were higher on unfertilized T. heterophylla than on fertilized T. heterophylla regardless of fertilizer. Both L. nigrinus and S. tsugae consumed more adelgid eggs that developed on fertilized T. canadensis than from unfertilized ones. This predatory preference was not noted on T. heterophylla or T. mertensiana.
Impacts and Contributions/Outcomes
Pest resistant and low input plants identified in this project will impact environmental stewardship by reducing the amount of pesticides, water and fertilizer from production through final landscape establishment.
University of Tennessee
Office Phone: 8659747324
University of Georgia
Department of Entomology
Biologiocal Sciences Bldg
Athens, GA 30602
University of Florida
North Florida Research and Education Center
Quincy, FL 32351-5677
Office Phone: 8508757162
University of Georgia
Department of Horticulture
Athens, GA 30602
Office Phone: 7065422861
327 Funchess Hall
Auburn, AL 36830
Office Phone: 3348443818
University of Florida
Department of Entomology
Office Phone: 8508577100