Location: Southern Horticultural Research2012 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:
Progress in small fruit horticultural research included evaluating the nutrient distribution within blueberry plants, and regulating fertigation rates and output timing. Plants received the second year of fertilization and plant sampling was completed. Mineral analysis will be completed when equipment is repaired. Fields have been established for fertigation studies and fertigation treatments begun. A second year of data has been collected and samples are being prepared for analysis. Progress in small fruit plant pathology research included the determination that three related genera of Botryosphaeriaceae caused similar symptoms on detached blueberry stems and the control of all three genera is the same. Treatments to control root rot were applied to blueberry plants in a field infested with Phytophthora spp. and bee dispersal of biological control agents (BCAs) to blueberry flowers to control Botrytis blight. Treatments were applied to muscadine grapes to determine the effect of nitrogen fertilizer on disease incidence and severity. Treatments were applied to blueberry and blackberry cultivars in the field to evaluate the effect of nitrogen fertilizer treatments on their susceptibility to fruit, stem and foliar diseases. Strawberry germplasm was screened for the presence of two disease resistance markers. Progress in ornamental horticulture research included the demonstration of the versatility of wood-based substrates for crop production. The effect of whole pine tree substrate particle size on initial seedling development was evaluated. Low substrate air space negatively affected seed germination and seedling root development. Results from this study were used to further investigate factors affecting root development during cutting propagation. We are developing new techniques for monitoring the destructive Ambrosia beetle. This beetle's fungus infects trees and ornamentals with the associated pathogen that not only can their larvae eat, but it kills the entire tree. In another experiment, processed eucalyptus trees were evaluated as a container substrate for greenhouse crops. Progress in ornamental plant pathology research involved continued development of an integrated disease control strategy. A disease risk model is being developed so environmental variables can be used to accurately predict fungicide applications for controlling Rhizoctonia web blight of azalea. Floors of nursery propagation houses were sampled for the persistence of Rhizoctonia, and the potential for pathogen survival and dissemination were evaluated on the floor of empty propagation houses. Spray coverage is being evaluated to improve fungicide efficacy to control plant diseases, including Rhizoctonia web blight.
1. A new insect monitoring method and apparatus for commercial plant nurseries. The strawberry rootworm is a serious leaf-feeding pest of many woody ornamental crops, especially azalea and itea. This tiny nocturnal beetle is highly mobile yet cryptic, making visual detection impossible. Likewise, traditional trapping methods using sticky cards fail because of a deluge of overhead irrigation water that washes away the adhesive as well as any tethered insects. A lightweight foldable plastic housing was developed to prevent irrigation water from destroying sticky traps. A solar-charged light was incorporated to increase nighttime collections of the rootworm beetle. More recently, chemical lures were discovered that attract the pest and these lures have been incorporated into the trap. An invention disclosure for this “origami” trap station was reviewed and recommended for patenting by ARS.
2. Accurate timing of fungicides to control azalea web blight. 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 over three years. 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. A recommendation that can be easily implemented by nursery producers is to schedule fungicide applications on calendar-dates (July 8 and August 1 for the most susceptible cultivars), but adjust timing in response to a slower or faster disease development due to yearly weather differences by scouting for a threshold of > 30 blighted leaves in up to fourteen plants per nursery. 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. Bee dispersal of biological control agents to blueberry flowers to control Botrytis blight. Botrytis blossom blight can cause extensive crop loss of rabbiteye blueberry in years when the weather during bloom is cool and rainy. Fungicides are available to control this disease but they are costly and their application is often delayed due to weather. Biological control agents (BCAs) offer an alternative to conventional fungicides for control of Botrytis blossom blight. Previous studies have had success using bees to disperse BCAs. ARS and cooperating scientists used cage studies and field trials to show that bumble bees will carry fluorescent dyes and BCAs to blueberry flowers at the proper time to achieve disease control. When bees distributed the commercial BCA preparation of the fungus, Gliocladium catenulatum, to blueberry flowers the symptoms of blossom blight were less than those on the untreated control plants. Laboratory tests confirmed that the fungus was present on the styles of the flowers that the bees visited. Blueberry researchers, extension agents and growers may use this information as they plan future disease control options.
4. New techniques for monitoring Ambrosia beetles. Ambrosia beetles are a threat to both ornamental and native trees that infects plants with a deadly fungus. Beetle larvae can eat the fungus and also the pathogen kills the entire tree. Different baiting systems were tested to detect beetles early enough for adulticides to kill females before they attack healthy commercial trees. The best method for detecting the presence of female beetles is the use of small potted trees whose roots received injections of 90% ethanol. The sickened trees would then attract beetles, which would then lay eggs on the main trunk. A less wasteful and perhaps more effective method is the use of 2-3 inch sections of tree injected with 90% ethanol. Beetles would be attracted to these “bolts” and fatally drop into the collecting trap below.
5. Nitrogen form affects pH in whole pine tree substrates. Substrate pH outside of the recommended range (5.0–6.5) can lead to nutrient availability issues in certain crops, which can be a problem in wood-based substrates that have a low buffering capacity. Two nitrogen forms at varying proportions were applied to petunias grown in whole pine tree and peat-lite substrates over a 35 day period. Substrate pH changed in response to nitrogen form and proportion applied, yet the change was more pronounced in whole pine tree substrate. An ARS support scientist in Poplarville, MS, developed this knowledge in cooperation with scientists associated with Auburn University at Auburn, AL, and Mississippi State University at Poplarville, MS. It is recommended that whole pine tree substrates be amended with up to 33% peatmoss for increased buffering capacity. Greenhouse producers should monitor substrate pH weekly on sensitive crops so corrective measures can be taken to maintain pH in the recommended range, and producers should be particularly careful when using fertilizers with high nitrate or ammonium components.
6. Macronutrient distribution in ‘Tifblue’ rabbiteye blueberry. The study was designed to determine relationships between a standard elemental leaf tissue analysis, plant health, and macro-nutrient distribution within the leaves, trunk and roots of ‘Tifblue’ rabbiteye blueberry. Mineral analysis was preformed and mineral distribution determined on leaves, upper stems, lower stems, trunk, root ball, and fine roots from rooted cuttings feed with low to high fertilizer rates. Approximately 25% of the total nitrogen in blueberry plants was found in the leaves, with the remaining 75% distributed evenly throughout the woody parts of the plant. Phosphorus was distributed similarly with 23% in the leaves and the remaining 77% evenly distributed through the rest of the plant. In contrast, 47% of potassium was found in leaves. Mineral distribution varied very little with the rate of fertilization. This research establishes a good understanding of how elements are partitioned through a ‘Tifblue’ rabbiteye blueberry plant and will benefit future studies directed at increasing blueberry yields based on a wholistic approach to plant health.
7. Compounds of muscadine grapes (Vitis rotundifolia) that provide health benefits. Several common muscadine varieties have been shown to contain ellagic acid and resveratrol in the juice or pulp and shown to have health benefits. The purpose of this research was to determine presence of antioxidants, ellagic acid, and polyphenolics in 19 muscadine cultivars and 2 muscadine selections. Muscadine fruit skin, pulp and juice were analyzed for the major phenolics compounds, such as trans- and cis-resveratrol, trans- and cis-piceid, ellagic acid, myricetin, quercetin and kaempferol. In muscadine skin, free and total ellagic acid, myricetin, quercetin and kaempferol were found in all 21 cultivars and trans-resveratrol was found in all cultivars except Alachua. Ellagic acid was the most abundant phenolic compound in muscadine grape skins. Typically muscadine geneticists select for sweetness, firmness, skin thickness, disease resistance, and other attributes that are visual or palatable. With an increasing interest in healthier foods, muscadines may be a “hidden treasure” because of the presence of ellagic acid and other nutraceutical compounds that add value and marketability due to the potential health benefits. This southern specialty could fast become the next “super fruit”.
Smith, B.J. 2012. Survival of southern highbush blueberry cultivars in Phytophthora Root Rot Infested fields in South Mississippi. International Journal of Fruit Science. 12:146–155. DOI: 10.1080/15538362.2011.619361.