ASHS 2025 Conference

Many types of mulch have been shown to reduce weed growth in container crops. In the past, mulch use in nurseries was not as feasible due to its high cost, but as costs of hand weeding increase, labor shortages become more severe, and environmental awareness rises, utilization of mulch has become more popular in recent years. Parboiled rice hulls are a waste product of the rice industry and are dry rice husks removed from rice grains. They are light weight, hydrophobic and make for an ideal mulch choice in container nursery production and have been previously evaluated for use as a weed management tool in container nurseries. However, research was typically conducted on a limited number of species and studies were performed in greenhouses or other protected structures. The objective of this research was to evaluate rice hulls for control of five common nursery species in an outdoor environment in Florida during the summer season. Nursery pots (1.7 L) were filled with a standard pinebark based potting soil and amended with standard control release fertilizers via incorporation. Upon filling, pots received one of three levels of rice hulls, 0 cm or the non-treated control, 1.3 cm, or 2.5 cm. To test efficacy, approximately 30 seeds of crabgrass (Digitaria sanguinalis), doveweed (Murdannia nudiflora), longstalk Phyllanthus (Phyllanthus tenellus), spotted spurge (Euphorbia maculata), or eclipta (Eclipta prostrata) were sown either above or below the rice hull mulch layers mentioned above. Data collected included weed coverage ratings (0 to 100%) at 4, 6, 8, 10, and 12 weeks after planting (WAP) and shoot dry weights at 12 WAP. Few differences were observed among the different depths of mulch when seeds were placed below. For seeds placed on top of the mulch, the higher 2.5 cm depth generally provided greater control. For all 5 weed species, control significantly increased when seeds were placed on top of the mulch compared to seeds beneath the mulch layer. Control, as measured by a percent reduction in shoot weight compared to the non-mulched control, ranged from 80 to 100% for seeds placed on top compared with decreases of 0 to 40% when seeds were placed below mulch. Overall, data suggest that because rice hulls are more effective on weed seeds placed on top of the mulch layer, growers would likely see increased efficacy when mulching as soon as possible after potting.

Elevated temperatures can intensify weed issues by accelerating weed growth and germination, especially for C4 species, due to their heat tolerance and efficient carbon fixations, making their control more challenging. Temperature also influences herbicide absorption, translocation, and metabolism. Large crabgrass (Digitaria sanguinalis), a highly problematic C4 weed, poses a significant threat to nursery and field-grown ornamentals under these conditions. This study aims to evaluate the efficacy of postemergence herbicides at different rates (0.5X, 1X, 2X) under normal and elevated temperatures for managing large crabgrass in ornamental production. Experiments were conducted in summer and fall 2024 using a growth chamber and an open hoop house setup. Large crabgrass seeds were sown in pots filled with standard substrate, irrigated, and placed in separate growth chambers where temperatures were maintained at normal (22–28°C) and at 2-5°C above the species’ optimum range (28-34°C). Once weeds reached the 3–6 leaf stage, they were transferred to an open hoop house for herbicide application. Postemergence herbicides such as topramezone and glyphosate were applied at 0.5X, 1X, and 2X rates using a CO₂ backpack sprayer. After the restricted entry interval, treated weeds were placed back to their respective growth chambers and maintained there for four weeks. A control treatment without herbicide application was maintained in both growth chambers. Weed control ratings were visually assessed at 1, 2, 3, and 4 weeks after treatment (WAT) using a 0–10 scale, where 0 = no control (green foliage, upright growth, no damage) and 10 = complete plant death (dark brown foliage, no green tissue, collapsed structure)). At 4 WAT, all weeds were harvested, and dry weight of aboveground parts of weed was recorded. The experiment followed a completely randomized design with eight replications per treatment and was repeated twice. Data were analyzed using ANOVA in SAS 9.4, and treatment means were separated using Fisher’s LSD test. The results showed that at 4 WAT glyphosate weed control efficacy at normal temperature was 88% which reduced to 73% under elevated temperature condition. Whereas the high temperature increased topramezone efficacy by 10%. The lowest amount of weed dry weight was observed at 2X rates in high temperature conditions, but no difference was observed among rates at normal temperature. Hence it can be concluded that with an increase in temperature, higher rates of the tested herbicides will be required for effective weed management in ornamentals.

Intensive cultivation in high tunnel production systems is leading to the emergence of soilborne pest and pathogen issues which over time can compromise crop productivity and profitability. Growers facing such challenges are in search of sustainable and effective solutions capable of suppressing soilborne pests and pathogens while preserving soil health. Anaerobic soil disinfestation (ASD) is a broad-spectrum pre-planting biological approach proposed for the management of soilborne issues affecting high-value specialty crops. ASD is applied by incorporating in the soil readily labile organic amendments as a carbon (C) source, tarping the soil with an impermeable film, and irrigating the soil to saturation. Although ASD already proved to be effective against a range of soilborne pests and pathogens across different US regions, crops, and production systems, its adoption at commercial scale remains relatively limited. Factors hindering the adoption of ASD include application cost, complexity of microbial driven processes, and lack of knowledge of the method, its implementation steps, and its efficacy and benefits. Capitalizing on over six years of research aimed at optimizing the ASD application method and its integration in high tunnel production systems in Pennsylvania, a series of on-farm ASD applications were conducted over the 2023 and 2024 growing season with the purpose of demonstrating the technology and let growers evaluate first-hand its viability and efficacy. The on-farm trials were conducted on selected farms growing vegetables and small-berries in high tunnels and employing both conventional and organic production methods. Raised-bed and broadcast application were tested along with the use of clear and black film. Wheat middlings alone or in combination with feed-grade sugarcane molasses were tested as C sources testing different soil incorporation equipment and methods. Depending on the specific crop system, and the grower planting schedule, ASD was applied between the end of the Spring (before a late high tunnel crop planting) and mid-October (after an early high tunnel crop). Parameters measured included soil redox potential, temperature, pH, electrical conductivity and mineral nitrogen. The level of anaerobiosis achieved varied depending on the amount of labile carbon applied, the type of tarp used, and the temperature levels achieved. High levels of cumulative soil redox potential were achieved and the use of clear film allowed to achieve relatively higher soil temperatures and cumulative redox potential levels in most on-farm applications. Additional demonstration efforts are needed to facilitate the adoption of ASD and demonstrate its efficacy.

Organic farming with its reliance on natural fertilizers, cover cropping, and crop rotation, presents a sustainable approach to food production. However, a significant challenge in organic production is insect and disease management. Organic insecticides often have limited efficacy, are expensive, and require repeated applications. Mesotunnels, medium-sized (36-40 inches tall) tunnels covered with insect netting, have emerged as a pest management tool for organic vegetable growers. This study evaluated the effectiveness of mesotunnel and low tunnel systems for pest management and season extension in organic Chinese cabbage (cultivar ‘Minuet’) production. The first season of this two-year study was conducted in Fall 2024 on certified organic land at Iowa State University Horticulture Research Station, Ames, IA. The experiment was set up as a randomized complete block design with four replications and following treatments: i) 85 g ExcludeNet insect netting, ii) 0.55 oz Agribon row cover, iii) 85 g ExcludeNet insect netting + OMRI-listed insecticide iv) OMRI-listed insecticide, and v) an untreated control, uncovered with no insecticide. Weekly pest surveillance focused on Brassica insect pests such as aphids, loopers, harlequin bugs, flea beetles, and their damage was recorded. Hobo data loggers recorded variations in light intensity, air and soil temperature, and relative humidity to observe microclimate variations in each treatment. At harvest, yield data was categorized as marketable or nonmarketable and graded according to USDA commercial standards. Among all treatments, the highest marketable produce was recorded in ExcludeNet + OMRI-listed insecticide treatment (42%), followed by Agribon row cover (31%) and the lowest in OMRI-listed insecticide (15%) during the first harvest. The earlier maturity in these treatments was likely due to warmer temperatures and improved humidity regulation under the tunnels. The insect abundance and their damage on leaves was significantly lower in ExcludeNet & ExcludeNet + OMRI-listed insecticide treatment. Integrating netting and row covers with limited use of organic insecticides provided the highest pest suppression, suggesting that physical barriers can effectively optimize pest management and enhance marketability in organic vegetable production systems. Findings from this study will inform growers and the research community about the feasibility of insect nettings as a sustainable pest management tool in organic specialty crop systems.

Sunn hemp (SH, Crotalaria juncea L.) is used in Florida strawberry production as an off-season summer legume cover crop to provide agroecosystem services such as weed and plant-parasitic nematode (PPN) suppression. Bicultures of SH with sorghum-sudangrass (SS) (Sorghum bicolor Moench × S. sudanense [Piper] Stapf) are of interest to reduce the cost of SH use. Our study objective was to determine whether bicultures retain the weed and PPN suppression benefits provided by SH grown in monoculture. A replacement series experiment was conducted in summer 2022 and repeated in 2023 in north-central Florida in a PPN-infested field. A factorial treatment arrangement of five SH:SS biculture proportions (100:0, 75:25, 50:50, 25:75, and 0:100) and three seeding rates (20, 40, and 60 lb/acre) were evaluated in a randomized complete block design with four replications. A no-cover crop, weedy control was also included in each block. Data were collected on cover crop biomass and carbon: nitrogen ratio (C:N), weed density, weed biomass, and PPN populations at eight weeks after planting. Bicultures consistently produced higher total cover crop biomass than the SH monoculture. Bicultures were as effective as the SH monoculture in reducing total weed density and resulted in either lower or equivalent total weed biomass. Averaged over year, only the 60 lb/acre seeding rate had a lower total weed density than the 20 lb/acre rate. In 2022, both the 40 and 60 lb/acre seeding rates resulted in lower weed biomass than the 20 lb/acre rate, while seeding rate had no significant effect on total weed biomass in 2023. Root-knot nematode populations in both years and sting nematode populations in 2022 were detected at levels too low for analysis. However, in 2023, the lowest and highest sting nematode populations occurred with the SH and SS monocultures, respectively; and sting nematode populations increased as the proportion of SS in the bicultures increased. Bicultures with ≤50% SS had significantly higher sting nematode populations than the weedy control. An increase in C:N was observed as SS proportion in bicultures increased. Thus, we conclude that SH/SS bicultures maintain the weed biomass suppression benefits of SH monocultures while increasing cover crop biomass. However, bicultures may lead to higher sting nematode populations, which will be of concern in organic strawberry production where soil fumigation is not permitted. Growers will also need to consider the effects of the higher C:N ratio of biculture residue on nitrogen fertilizer immobilization.

Minnesota (MN) in the US ranks 2nd for corn silage production and 3rd for soybean production. Studies have shown that off-target movement (drift) from an unshielded sprayer, in row crops, can range from 1 to 16% of the target dose; however, boom height and wind can double or triple these doses. Pre-study 37 pesticide residue tests were conducted in five Minnesota nurseries in 2018. Nine different herbicides were detected in the 37 tests. Glyphosate (sold as Roundup Power Max 32% glyphosate) became the focus of 2019 studies, conducted at concentrations of 0, 6, 18 and 54% for glyphosate as drift events. Relating ppm’s disclosed in laboratory analyte foliar residue samples collected by various state agriculture departments after drift events to injury symptom, development, and growth reduction or time after application have ever been conducted for nursery crops. From personal communication with nursery owners experiencing neighbor’s drift event (MD; KY, OH, MI, FL) the average time from the drift event to recognizing problems, and sample collection is six weeks (6 weeks after drift event) (6 WADE). Slower metabolism of glyphosate at higher residues, explained our finding that the largest residues were detected in all, but one species/ treatments used with glyphosate, versus three other herbicides examined or in combinations. Higher residues meaning higher injury, does not occur with glyphosate. Potentially high residues mean slow metabolism for glyphosate, and thus less injury. In five cases glyphosate applied alone had no impact on growth measured as caliper over the season, even though glyphosate had the highest residue in three of the five. In only one case was caliper growth reduction highest with glyphosate (Syringa 18%) over the entire study. In terms of phytotoxicity rating, glyphosate caused no commercially unacceptable injury in four cases. Residues increased with all rates on the three species evaluated between 3 DADE and 6 WADE. With Acer freemanii and Tilia cordata residue levels declined slightly between 6 WADE to 14 WADE with all rates. Only, Syringa reticulata showed an increase in foliar residues between 6 WADE to 14 WADE. Since carry over injury the next year (or three) is a concern with all glyphosate applications to perennial plants, all trees were observed in 2020. None were commercially acceptable and in severe decline (regardless of rate) in spring 2020, only 6% glyphosate on Syringa survived to the fall , and by spring 2021 were dead.