Location: Southern Horticultural Research2013 Annual Report
1a. Objectives (from AD-416):
The objectives are to develop new and improved crop production practices and disease and insect control practices for ornamental, small fruit and other horticultural crops adapted to the U.S. Gulf Coast region. The developed management techniques are needed to minimize production losses and improve crop quality and yield for the purpose of increasing net income.
1b. Approach (from AD-416):
Identify and evaluate nutritional and cultural requirements, non-Apis pollination efficiency, insect pest problems, and plant disease problems to improve orchard establishment, human health benefit, crop yield, and post-harvest quality of fruit crops. Management techniques to be evaluated include planting systems, irrigation systems, fertilizer selection and timing, non-Apis bee colony establishment, suitability of bio-control organisms, pesticide selection and timing, cultivar selection, fruit handling, and post-harvest storage conditions. Identify and evaluate different organic substrates, insect pest problems, and plant disease problems to improve production options and crop quality of ornamental plants. Management techniques to be evaluated include irrigation and nutritional requirements of plants grown in different organic substrates, suitability of bio-control organisms, cultivar selection, pesticide selection and timing, pesticide application technology, disinfestant selection, and sanitation practices.
3. Progress Report:
This report serves as the final report for project 6404-21430-001-00D, entitled "Production Management Research for Horticultural Crops in the Gulf South" which will terminate November 30, 2013 and will be replaced by new project 6404-21430-003-00D entitled "Production and Disease and Pest Management of Horticultural Crops". Progress in small fruit horticultural research included findings that fertilizer rate did not greatly influence elemental distribution in ‘Tifblue’ rabbiteye blueberry plants with 75% of total-N and P and 50% of K being partitioned in woody tissues and the vast majority of the remaining nutrient distributed in leaves; and that the skin of muscadine cultivars contained antioxidants, ellagic acid, polyphenolics, and resveratrol, and not pulp and juice. Progress in small fruit entomology research included findings that Peponapis pruinosa, an unmanaged solitary bee, was a more efficacious and reliable pollinator of cucurbit crops than were honey bees, thus could save costs of purchasing pollinators; developed methods to rear parasitoid wasp species that suppress blueberry gall midge populations on Mississippi farms; discovered bumble bees can successfully distribute a biological control agent, Gliocladium catenulatum, to the stylus of blueberry flowers to prevent Botrytis blossom blight. Progress in small fruit plant pathology research included the findings that the cultural practice of raised beds and organic soil amendments did not increase long term survival or vigor of any southern highbush blueberry cultivars in fields with high inoculum pressure; and that the application of calcium nitrate fertilizer, in preference to ammonium N fertilizer, reduced severity of anthracnose crown rot on strawberries. Progress in ornamental horticulture research included usage recommendations for whole pine tree substrate to incorporate 33% peat moss to increase buffering capacity, to maintain pH between 5.0 and 6.5 for sensitive crops, and to carefully use fertilizers with high nitrate or ammonium components. Progress in ornamental entomology research included patenting of a new insect “origami” trapping station that incorporates a solar-charged light for nighttime collections for monitoring strawberry rootworm that damages azalea and several other shrubs in commercial plant nurseries, and development of two techniques for monitoring Ambrosia beetles, which threatens ornamental and native trees. Progress in ornamental plant pathology research involved development of fungicide timing recommendations to control azalea web blight by scheduling applications by calendar-date and adjusting calendar-timings due to the influence yearly weather differences using scouting protocol; use of a hot water treatment that did not harm azalea to eliminate Rhizoctonia, the web blight pathogen, by submerging azalea stem cuttings in hot water; and development of a weekly spray schedule using an environmentally friendly hydrogen peroxide formulation to control a foliar rust disease in the greenhouse.
1. Bioassay will provide rapid assessment of the sensitivity of Colletotrichum isolates to fungicides. Fruit rot diseases of strawberry represent serious problems for producers in many areas of the world, and they are particularly severe in the southeastern U. S. where disease is often favored by warm temperatures and frequent rains during the harvest season. Anthracnose diseases caused by Colletotrichum spp. can be especially devastating since they may result in both fruit rot and plant death. Sixteen agrochemicals that are currently used or have been used for control of strawberry pests and diseases were tested in a microtiter assay for in vitro activity against isolates of C. acutatum, C. fragariae and C. gloeosporioides collected from strawberry. Older, protective, multi-site fungicides (chlorothalonil, captan, thiram, and dodine) inhibited growth of isolates of all three Colletotrichum species at the highest concentration tested. The C. acutatum isolates were insensitive to benomyl, thiobendazole, vinclozolin, and iprodione. Two of the newer fungicides in the study (azoxystrobin and cyprodinil) inhibited the growth of most isolates at the lowest concentration. Two commercial formulations of these newer fungicides are now labeled for disease control on strawberries.
2. Accurate timing of fungicides will control azalea web blight in commercial nurseries. Fungicides are the main tool used to control Rhizoctonia web blight on container grown azaleas, yet accurately predicting when to spray is difficult thus control is poor some years. Fungicide applications were timed by calendar-dates, scouting for disease levels in azalea plants and weekly rain frequency, and disease control was evaluated on container grown azaleas at two locations for three years. Fungicide timing can be easily implemented by nursery producers by scheduling applications on calendar-dates (July 8 and August 1 for the most susceptible cultivars). Scouting allows producers to also adjust calendar-timing in response to a slower or faster disease development due to yearly weather patterns by looking for a threshold of > 30 blighted leaves internally within shrubs. An ARS scientist in Poplarville, MS developed this knowledge in cooperation with scientists from Auburn University at Auburn, AL and the University of Georgia at Athens, GA. The value of scouting is easily justified in comparison to the high cost of fungicides, as scouting requires about 10 minutes per week for an azalea crop that comprises 20 to 50% of the plant selection inventory at many ornamental plant nurseries in the southern and eastern region of the United States.
3. A new insect monitoring method and apparatus for commercial plant nurseries. An ARS scientist at the Thad Cochran Southern Horticultural Research Laboratory in cooperation with the Horticultural Research Institute is working with the Office of Technology Transfer to develop a lightweight foldable plastic station that protects sticky cards from heavy rain, intense sunlight, and constant irrigation within nursery and orchard environments. This technology will benefit researchers, farmers and field scouts who routinely use sticky traps to monitor adult populations of insect pests, primarily beetles and moths, but this apparatus may prove very effective at monitoring highly invasive fly pests such as spotted wing drosophila. This “origami” style trap station protects both the trapping device and its insect catch so that a more accurate insect count can be made. The station can withstand extreme environments in tropical, xeric, and temperate zones. Its integral light diode also permits the sampling of nocturnal insect species for both integrated pest management and ecological studies.
4. Bioassay will provide rapid assessment of the sensitivity of Botrytis cinerea isolates to fungicides. Fungicidal sprays are widely used for control of Botrytis fruit rot; however, this fungal pathogen often develops resistance to frequently used fungicides. A 96-well plate micro-dilution broth bioassay developed for fungicide discovery was used to provide strawberry growers with a rapid assessment of the sensitivity of Botrytis cinerea isolates against 16 fungicides. Three sensitivity phenotypes were identified: benzimidazole and dicarboximide resistant, benzimidazole resistant and dicarboximide sensitive, and an intermediate response to both fungicides. Codon at position 198 in the ß-tubulin gene confirmed benomyl resistance. This bioassay rapidly identifies fungicide resistance and allows growers to quickly adjust their disease management strategy.
5. Blueberry seed production and berry quality improves with changes in the shape of flowers. ARS scientists at the Thad Cochran Southern Horticultural Research Laboratory have shown some blueberry cultivars have flowers that are more easily pollinated by bees than flowers of other cultivars. Fruit quality in terms of berry size and seed set improved as longer pistils increasingly exposed stigmas to pollinating orchard bees. Data suggest that shorter flower petals that extrude their pistils as little as 2 mm beyond the opening of the flower make better contact with visiting bees, which ultimately quadruples pollination and seed set, which in turn yields larger, earlier maturing berries. These data imply that plant geneticists, by including floral traits as breeding criteria, could provide farmers with higher yielding blueberry cultivars that can be efficiently pollinated by a greater diversity of bee species.
6. Detached leaf assay provides accurate, rapid, non-destructive method of identifying anthracnose resistant germplasm. Inoculation of detached strawberry leaves with spores of the anthracnose fungal pathogen may provide an accurate, rapid, non-destructive method of identifying anthracnose resistant germplasm. Two assessments of anthracnose disease severity were compared on detached strawberry leaves inoculated with Colletotrichum fragariae and C. gloeosporioides: a quantitative assessment made via computer based image analysis and a visual assessment made by two independent raters. The image analysis provided a precise measurement of percent lesion area of infected leaves; however the visual assessment was rapid and almost as accurate as indicated by the strong positive correlation between percent lesion area and the visual disease scores. Compared to whole plant inoculations, inoculation of detached leaves eliminates the need to sacrifice whole plants, decreases the space needed for the plants, and can be accomplished in a laboratory setting without the possibility of the pathogen being introduced into the environment. Results are obtained more rapidly, thus benefiting breeding programs whose goals are to develop resistant cultivars. Detached leaf inoculations will be used by plant breeders and plant pathologists as a rapid preliminary screen to eliminate susceptible germplasm from large populations of strawberry seedlings in breeding programs.
7. A new southern highbush blueberry cultivar named ‘Pearl’ was released. This cultivar is a cross between northern highbush blueberries and wild blueberries native to the south. ‘Pearl’ has very large light blue berries that are firm with a small picking scar, and excellent flavor. This new cultivar has several advantages for growers in the southeastern U.S. over the rabbiteye blueberry cultivars that are widely grown in the region including an earlier ripening period, good yield potential, mechanical harvest ability, and very large berries with excellent fruit quality. These attributes will enable producers to participate in the lucrative early U.S. fresh market where opportunities for marketing rabbiteye blueberries have diminished due to expanding acreage in the region and other states.Smith, B.J., Wedge, D.E., Pace, P.F. 2012. A microtiter assay shows effectivness of fungicides for control of Colletotrichum spp from strawberry. International Journal of Fruit Science. 13:1-2, 205-216.