Propiconazole has fungistatic and fungicidal properties against Harringtonia lauricola, the causal agent of laurel wilt disease. Propiconazole injections are used by Florida, USA, farmers as a prophylactic method to manage the disease in avocado (Persea americana) trees, but its efficacy has remained questionable for more than a decade due to documented restricted mobility within the tree vascular system. This study was conducted to evaluate the absorption of propiconazole when using soil drenching as an alternative application method, assess the efficacy of propiconazole in controlling disease development when drenched or injected, and its synergistic effect on common cultural management practices used by the local farmers, such as branch removal and trunk cutting (“stumping”). To determine if propiconazole soil-drenching can provide better xylem coverage, potted and mature orchard trees were treated with different concentrations and artificially inoculated with the pathogen. Propiconazole translocation from the roots to above-the-ground tissue was confirmed in potted and orchard trees, but the concentrations in orchard trees were below the fungicidal threshold (1 ppm). Although none of the potted trees developed laurel wilt symptoms, all inoculated branches of the orchard trees did. Furthermore, noninoculated branches in more than 80% of the inoculated and propiconazole-treated orchard trees developed symptoms, even though the inoculated branch was cut at the early stages of disease development. To elucidate if propiconazole injections effectively control the disease, trees from a commercial orchard that were injected five times were challenged by artificial inoculation. Propiconazole concentration in trees was highly variable (ranging from < 0.01 to 294 ppm), but even in trees with a high concentration of propiconazole, inoculated and noninoculated branches developed symptoms. Even though drenched and injected trees were “stumped” soon after symptoms appeared in the noninoculated branches (4 to 5 months after inoculation), all of the stumps in the drenched plot and 80% of the injected trees, showed internal symptoms 5 and 4 months after the cut, respectively. Results demonstrate that the soil-drenching of propiconazole is an ineffective application method in orchard trees, and that the conventional injection does not prevent disease development after artificial inoculation. Moreover, because propiconazole does not prevent the movement of the pathogen to the trunk, the “stumping” of infected trees to reduce the disease in the orchard is an inadequate practice. This study highlights the critical need for other active ingredients with lower fungicidal thresholds, longer half-life, and higher xylem mobility.
Horticulturists and agronomists have a long history of using selective breeding to take advantage of intraspecific (within-species) variation with the goal of developing novel varieties of plant species. These efforts are responsible for the availability of countless improved food, forage, and ornamental varieties that are valued by farmers, landscapers, and home gardeners. In contrast, little attention has been paid to the idea of evaluating intraspecific variation to identify plants derived from a specific ecosystem (ecotypes) of native species that could improve the success rate of habitat restoration and enhancement projects, especially in aquatic systems. These projects often specify that plant material used for restoration be collected from local donor sites to preserve the area’s gene pool, but nearby source populations may be nonexistent or may not be well-adapted to conditions at the recipient (transplant) site. This paper, which summarizes information presented at the American Society for Horticultural Science Invasive Plants Research Professional Interest Group workshop in 2022, provides evidence that unimproved, wild-type species can be useful in aquatic habitat restoration and enhancement projects, particularly when conditions at sites targeted for restoration differ from those in nearby systems, or when sites are expected to undergo shifts in conditions because of factors such as climate change.
The objective of this greenhouse study was to evaluate tall fescue (Festuca arundinacea) seedling growth when seeded after herbicide application. Herbicide treatments included a nontreated control; 1.19 lb/acre 2,4-dichlorophenoxyacetic acid (2,4-D) + 0.32 lb/acre methylchlorophenoxypropionic acid (MCPP) + 0.32 lb/acre dicamba; 0.75 lb/acre quinclorac; and 0.06 lb/acre halosulfuron-methyl. Seeding was done at 0, 3, 7, or 14 days after herbicide application to soil media. Two identical experiments were conducted in the greenhouse: Expt. 1 seedling growth from January to March and Expt. 2 from May to July (temperatures higher). Seeding dates after herbicide application did not influence growth. Average dry shoot weight reductions and dry root weight reductions caused by postemergence herbicides were 2,4-D + MCPP + dicamba (33% shoot and 27% root in Expt. 2), quinclorac (30% shoot and 37% root in Expt. 2), and halosulfuron-methyl (51% shoot in Expt. 2; 81% root in Expts. 1 and 2). Although application of these herbicides before seeding in the field may result in no visual impact, they can impact seedling shoot and root growth, particularly under higher growth temperatures.
Autonomous (i.e., robotic) mowers have recently garnered interest with the public and within the turfgrass industry. However, limited research has been conducted on their use for mowing warm-season turfgrasses. An experiment was conducted at the University of Florida’s West Florida Research and Education Center (Jay, FL, USA) to investigate the performance of an autonomous mower using a lower than recommended height-of-cut on St. Augustinegrass (Stenotaphrum secundatum). Treatments included an autonomous mower with a height-of-cut of 2.5 inches set to mow daily and a conventional mulching mower with weekly mowing at recommended height-of-cut of 3.5 inches. Data collection included weekly digital images that were subjected to digital image analysis to determine overall turfgrass quality, percent green cover, and uniformity. The autonomous mower resulted in greater overall turfgrass quality from January to March and in November, and greater green cover from November to April compared with conventional mowing. Additionally, the autonomous mower produced greater turfgrass uniformity than conventional mowing. Results indicate that autonomous mowers can be successfully used to maintain St. Augustinegrass at a lower than recommended height-of-cut.
Aerification and topdressing are important cultural management practices that help prevent organic matter accumulation and soil compaction in golf greens. However, these practices result in surface disruption and decreased putting quality during recovery. A 2-year study was conducted on a ‘TifEagle’ hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) putting green to determine the effect of different aerification methods and topdressing materials on soil properties and turfgrass recovery. Plots were aerified four times per year (May to Aug.) using 1/2-inch hollow tines, 1/4-inch hollow needle tines, hollow tines 2X + hollow needle tines 2X, or sand injection, and topdressed with either 90:10 (sand:peat) or green-dyed sand. Visual quality, normalized difference vegetation index, percent green cover, dark green color index (DGCI), surface firmness and volumetric water content were measured before initial aerification and at 7 and 21 days after aerification. Saturated hydraulic conductivity (Ksat) and organic matter (OM) content were measured monthly. Aerification with hollow tines and hollow tines 2X + hollow needle tines 2X resulted in lower firmness and OM and higher Ksat compared with hollow needle tines and sand injection. Sand injection showed the highest percent green cover and similar OM content compared with hollow tines and hollow tines 2X + hollow needle tines 2X. Green-dyed sand showed a higher percent green cover and DGCI compared with 90:10 sand:peat. Using hollow tines only or alternating them with hollow needle tines is the best option to decrease OM content while increasing Ksat in hybrid bermudagrass greens; however, their use could result in slower turfgrass recovery compared with other aerification methods.
New York, USA, is a regional hub for processing carrot (Daucus carota ssp. sativus) production and Nantes-type cultivars are preferred for slicing. Diameter is critical in carrots for slicing, with roots larger than 1 5/8 inch being rejected. The potential to manipulate carrot root diameter and hence suitability for slicing by foliar-applied gibberellic acid (GA3) was tested in four small plot replicated field trials over 3 years (2020, 2021, and 2022). In the most efficacious treatments, GA3 resulted in a 23.1% to 135.4% increase in foliar biomass at the expense of root weight and diameter. Increases in foliar biomass are beneficial to facilitate top-pulling harvest. Reductions in root diameter from GA3 ranged from 9.5% to 19.6%, and in 2020 and 2022, increased the proportion of roots suitable for slicing. GA3 did not significantly affect root length and number. In two 2021 trials, GA3 increased color intensity quantified by a colorimeter, but this change was not noticeable to the naked eye. The optimal number of GA3 applications was seasonally dependent, ranging from a single application at 107 to 108 days after planting (DAP) in 2021, to two applications at 74 + 92 DAP in 2022. Three GA3 applications per season or late applications (up to 14 days prior to harvest) were not beneficial.
A range of organic fertilizers are available for vegetable crops; however, there is a lack of information regarding the performance and rates of organic fertilizers commonly used in the production of Vidalia onion (Allium cepa). Two commercial organic fertilizers, a mixed source organic fertilizer [MIX (10N–0.9P–6.6K)] and a pelleted poultry litter [PPL (5N–1.8P–2.5K)], were evaluated in two soil types at application rates of 0, 100, 150, 200, 250, and 300 lb/acre nitrogen (N) to determine their impact in the production of Vidalia onions in Georgia, USA, with the objective of determining an optimal fertilizer source and application rate. Field trials were conducted in the 2019–20 and 2020–21 growing seasons in Watkinsville, GA, USA (Cecil series sandy clay loam soil) and Tifton, GA, USA (Tifton series loamy sand soil) on certified organic land. There were significant interactions among location, year, and fertilizer application rate for total marketable yield. In Watkinsville, total marketable yields of onions at different N rates ranged between 1320 and 4565 lb/acre in 2019–20, and between 9951 and 28,749 lb/acre in 2020–21. In Tifton, total marketable yields ranged from 3776 to 9264 lb/acre and 7094 to 14,066 lb/acre in the 2019–20 and 2020–21 seasons, respectively. Aboveground onion N accumulation at harvest was affected by an interaction among location, study year, and fertilizer rate. The largest plant N accumulation was in Watkinsville in 2020–21, ranging from 26 to 50.8 lb/acre N in the 0- and 300-lb/acre N treatments, respectively. In 2020, there were no differences in soil inorganic N at harvest between plots receiving the MIX (9 lb/acre N) or PPL (9.8 lb/acre N) in either location. In 2021, soil inorganic N was greater in plots receiving the MIX fertilizer (14.8 lb/acre N) compared with the PPL fertilizer (11.2 lb/acre N). Yields increased linearly with additional fertilizer; therefore, an optimal application rate for organic fertilizers was not determined.
In strawberry (Fragaria ×ananassa), initial bare-root crown diameter and early-season flower cluster removal have been two factors suspected of influencing fruit yield and size. This study evaluated the effect of these two factors on the day-neutral strawberry varieties Monterey and Cabrillo. Bare-root crowns with three different diameters were categorized into small (< 0.5 cm), medium (> 0.5 to 1 cm), and large (> 1 cm) at planting. Each of the crown diameter treatments was split into two plots for flower removal or no flower removal in the early season and data on canopy diameter, fruit yield, and fruit size collected in the subsequent months of production. The study was conducted over two growing seasons (2019–20 and 2020–21). No difference was found in plant canopy diameters measured in February, ∼3 months after planting, between any of the treatments in either year. Although early-season flower removal and some crown sizes resulted in lower fruit yield in March and April, none of these treatments resulted in any fruit yield or size differences in subsequent months nor in season end totals.
A long-term, landscape grass hardiness study was initiated in Summer 1987 at the University of Minnesota Landscape Arboretum in Chanhassen, MN, USA [United States Department of Agriculture Plant Hardiness Zone (USDA PHZ) 4b, –20 to –25 °F]. This location averages a 158-day growing season (frost free), summer temperatures of 79.9 °F, and winter temperatures of 10.4 °F. Over 35 years, 392 different kinds of plants from the grass (Poaceae) and sedge (Cyperaceae) families were planted to evaluate winter survival, landscape value, flowering, and pest resistance. Most plants (n = 271, 69%) survived at least 4 years, 186 (47%) survived 10 years, 81 (21%) survived 20 years, and 29 (7%) survived 35 years. Sixty-eight plants (17%) were deemed not winter hardy in this location (USDA PHZ 4b), and 53 are listed with insufficient data for a hardiness rating. Changes in maintenance as well as challenges encountered with long-term trials of herbaceous plants are discussed.