DEVELOPING IMPROVED MANAGEMENT PLANS FOR WEED CONTROL IN NURSERIES, GREENHOUSES, AND LANDSCAPES IN FLORIDA

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1022263
• Project Start Date: Feb 14, 2020
• Project End Date: Feb 10, 2025
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF FLORIDA
G022 MCCARTY HALL
GAINESVILLE,FL 32611

Performing Department
Mid-Florida Research and Education Center

Non Technical Summary
Florida's nursery and landscape industry is an important component of the overall state economy. In 2010, total direct sales by Florida nursery, landscape service firms and horticulture retailers total over $15 billion and total direct employment was 204,700, making the value of Florida's green industry second only to California in terms of overall industry value (Hodges et al., 2011). One of the most costly aspects of the nursery and landscape industry is weed control. Weeds compete with ornamentals for air, water, nutrients and light and can have a significantly negative impact on crop growth. Weeds also cause aesthetic damage and reduce the salability of nursery crops and decrease property values. Weeds are often the most costly pests to control in commercial nurseries and landscapes. As limited postemergent herbicide options are available for use over the top of ornamental plant species, growers and landscapers must rely on preemergent herbicide applications and supplemental hand weeding for control. Hand weeding is very expensive, and due to labor shortages, is continuing to increase. Growers have previously estimated spending between $500 and $4,000 per acre for supplemental hand weeding, and economic losses due to weed infestations have been estimated at $7,000 per acre (Case et al., 2005).In the past, weed control was not as critical of an issue for this industry; if a herbicide application was missed or a particular weed species was not controlled, more labor could be hired to manually pull escaped weeds. This practice was still expensive, but many of these businesses had disposable income and labor was readily available. However, this is no longer the case. Labor costs are continually increasing due to labor shortages (Martin and Calvin, 2010). Recent immigration reform passed in many states has caused many nursery growers to lose a large portion of their labor force (Johnson, 2011). Additionally, the recent economic recession forced many nurseries or landscape firms to close or consolidate due to poor sales. As the nursery and landscape industry is closely tied with the housing market, Florida growers and landscapers were hit especially hard during this period. Growers and landscapers are now realizing the benefits of a sound weed control program and are searching for ways in which improvements could be made and costs could be reduced.Research is needed to develop more efficient herbicide application procedures, improve management guidelines for common and regulated (i.e. noxious) weed species, and determine herbicide safety when applied over the top of ornamental plants in nurseries and landscapes. Work is also needed to add to and improve upon current integrated pest management (IPM) protocols for weed management in ornamentals by finding more effective and environmentally friendly control strategies. Improvement in these areas will increase profit margins of ornamental growers and landscapers and help to mitigate the effects economic downturns and labor shortages. Additionally, by determining the most effective weed control strategies including chemical and non-chemical methods, this work will help alleviate negative environmental impacts of the Green Industry by reducing pesticide runoff and leaching into Florida ground and surface water supplies caused by inaccurate, excessive, or unwarranted herbicide applications.

Animal Health Component

40%

Research Effort Categories

Basic

20%

Applied

40%

Developmental

40%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	2110	1140	100%

Knowledge Area
213 - Weeds Affecting Plants;

Subject Of Investigation
2110 - Ornamental trees and shrubs;

Field Of Science
1140 - Weed science;

Keywords

ornamental

weed management

nursery

landscape

Goals / Objectives
The major goals and objectives of this project are to:1. Develop management guidelines for common and newly introduced weed species that are difficult to control in nurseries and landscapes.2. Determine the safety of current ornamental herbicides for over the top application to ornamental species in nurseries and landscape plantings including ornamental grass species, herbaceous annuals and perennials, palms and tropicals, and woody nursery stock, thus giving growers and landscapers more herbicide options for these crops.3. Improve the accuracy and efficiency of herbicide applications in nurseries and landscapes to improve weed control, reduce chemical costs, and alleviate environmental impacts that may result from over application of herbicides in these systems.4. Improve upon established cultural control practices and strategies to reduce weed growth in ornamentals and develop new cultural, non-chemical control strategies in these areas.

Project Methods
Management guidelines for commonly and newly introduced weed species will be developed by obtaining these species (seeds, tubers, etc.) and evaluating registered and experimental herbicidal active ingredients for control, as well as the efficacy of cultural control measures. This will include evaluating currently labeled products (landscape or nursery herbicides) as well as non-labeled herbicides (including experimental, agronomic, or turf herbicides), and cultural control practices (irrigation management, use of mulch, fertilizer placement, etc.). Experiments will be carried out in field, nursery, and greenhouse settings to evaluate control measures under a variety of environmental conditions. Preemergence control will be evaluated by conducting replicated experiments using currently labeled or experimental active ingredients for control and then measuring germination percentage and weed growth following herbicide treatments. Herbicide efficacy will be determined by counting emerged seedlings and by measuring fresh weights of weeds that were not controlled using the various herbicides in comparison with a control (non-treated) group. Germination studies will be conducted both under field and laboratory conditions in order to determine the ability of common or emerging weed species to germinate under varying environmental conditions.Crop safety trials will be carried out by making over the top applications to ornamental species grown in containers or the field at various growth stages (i.e. at potting, immediately after transplanting, after establishment, etc.). Multiple herbicide applications will be applied at labeled rates, as well as at 2 and 4 times the label rate in order to measure crop response and tolerance. Crop safety will be determined by making visual assessments after each herbicide application (at 1, 2, 4 and 8 weeks after each treatment) and measuring crop growth in comparison with a non-treated control group and determining which plants are still commercially acceptable at the end of the growing season.Herbicide application efficiency and accuracy will be determined by conducting on-site visits with growers (yet to be determined) and measuring the amount of herbicide actually applied during granular herbicide applications. Herbicide trays, empty containers, and various catch cans will be used to measure the accuracy of herbicide applications at multiple commercial nurseries in Florida.Cultural control practices will be evaluated both alone and in combination with chemical controls in landscape and nursery situations. This will include evaluating different mulch:herbicide combinations in the landscape. A landscape planting has been established including two different plant types, shrubs (Ilex vomitoria 'Schilling') and a groundcover (Trachelospermum asiaticum). The landscape planting was mulched using two different materials, pinebark and pinestraw, or left un-mulched. Herbicides were applied to the pinebark, pinestraw, or un-mulched beds to determine how herbicides affect weed control in each of these mulches in comparison to mulch alone. A control group was also included which was neither mulched nor received an herbicide application. This experiment was designed as a randomized complete block design with six replications per treatment for each landscape species. This test will be conducted for 12 months to measure the weed pressure of various weed species in each treatment, the amount of hand weeding required in each treatment to keep plots at 20% weed coverage or less, and the amount and cost of all materials and labor. The results will be used to develop a cost efficient weed control guideline for landscape plantings and give homeowners and landscapers an estimated cost for each mulch and herbicide combination on a square foot basis so that costs can be scaled depending upon site. This experiment is currently being conducted at the University of Florida Mid-Florida Research and Education Center in Apopka, FL and is being repeated in space at the Gulf Coast Research and Education Center in Wimauma, FL. Additional cultural control practices are planned to be evaluated including the use of different mulch materials for weed control in container production and in the landscape, the impact of irrigation practices (i.e. uniformity, amount, frequency, placement) on weed control in nursery production and in the landscape, and the effects of fertilizer placement (i.e. topdressing, incorporation, dibble) on germination of common weeds in Florida container nurseries.All of the above trials will be repeated in either time or space and adequately replicated. Appropriate statistical procedures will be used depending on the test being conducted and the experimental design employed. Herbicide applications will be made by licensed and trained applicators using standard application equipment including hand-shakers, belly-grinders, or CO2 backpack sprayers that are carefully calibrated.Tests will be conducted at the Mid-Florida Research and Education Center and other University of Florida Research and Education Centers, including the Gulf Coast Research and Education Center in Wimauma, FL. At these centers, all resources needed to conduct these trials is already in place including application equipment, field space, irrigated container pads, and greenhouse space. Other supplies including potting media, herbicides, plant materials, nursery pots, etc. will be procured when trials are initiated. The application efficiency study will be conducted on-site at various container nurseries in Florida with industry cooperators who have yet to be determined.

Progress 10/01/20 to 09/30/21

Outputs
Target Audience:The target audience for this program includes nursery growers and greenhouse production managers and others producing container and/or field grown ornamental plants, professional lawn car or pest management professionals in the landscape services industry, homeowners, master gardeners, and county extension faculty. Changes/Problems:No major changes or problems occured in 2021. What opportunities for training and professional development has the project provided?30 presentations, webinars, and workshops were delivered to stakeholders in 2021. Four of these presentations were to national audiences and in total, 1,138 people attended these trainings. An online course was developed and delivered nationally/internationally reaching 60 growers in 5 different countries. 11 field consultations, 4 office consultations, 97 telephone consultations, and 127 text/email consultations were given when information was shared to help people manage weeds more effectively. 2 In-service trainings were provided to County Extension Faculty. Two students (1 Ph.D. and 1 M.S.) were trained by conducting research and writing peer-reviewed publications. Additionally 1 post-doctoral scholar was also trained through research and extension activities. How have the results been disseminated to communities of interest?Results were shared through publications, presentations, newsletters, farm visits, online and in-person consultations, phone/email consultations, and through over venues as described previously. What do you plan to do during the next reporting period to accomplish the goals?We plan to continue our work on the projects mentioned above, as well as begin focusing on work on several invasive plant species such as Tradescantia fluminensis and Gibasis pellucida. Specific objectives for 2022 included 1) determine the impact of different substrates on weed growth; 2) evaluate different fertilizers and placements as a weed management tool; 3) continue to develop crop tolerance data on economically important ornamental species in Florida.

Impacts
What was accomplished under these goals? 1. Experiments were conducted to optimize mulch use in container nursery production. A series of experiments were completed in which various mulch types (rice hulls, wood chips, pine bark, etc.) were evaluated for control on bittercress, spotted spurge, liverwort, and other key nursery weed species. Mulches were applied both alone at various depths and in combination with preemergence herbicides. Results indicate that when applied at a depth of at least 1 inch, the addition of a herbicide provided no added benefit to mulch use. These research trials are ongoing and final results will be updated when completed. 2. A series of experiments were completed to evaluate the efficacy of subdressing fertilizer as a weed management tool for eclipta (Eclipta prostrata). Data showed that while there was no difference in eclipta germination, subdressing at a depth of 5 cm resulted in a >50% decrease in eclipta biomass (Figure 1) with no negative effects on the growth rate of ligustrum (Ligustrum lucidum) or boxwood (Buxus microphylla). Following germination, eclipta seedlings had no access to nutrients due to the lower subdressed layer. As ornamental plant liners were planted with roots contacting this layer, no negative growth consequences were observed. 3. Substrate stratification, or layering, whereby a single nursery container is filled with substrates with different physical properties in separate layers was investigated as a weed management tool. In these experiments, aged pine bark was purchased pre-screened to varying particle sizes or was processed after purchase. These experiments have evaluated a range of stratification depths, pine bark particle sizes, and fertilizer placements on growth of liverwort (Marchantia polymorpha), bittercress (Cardamine flexuosa), and spotted spurge (Euphorbia maculata). Results show that stratification results in a decrease in germination of bittercress and spurge by 15 to 30%. Bittercress shoot biomass was reduced by 80 to 97% in stratified treatments while spotted spurge growth was reduced by over 40%. Liverwort growth was reduced by over 95% and virtually no liverwort established in any of the stratified treatments. Data suggests that stratification and strategic fertilizer placement can be an effective weed management tool and part of an overall integrated weed management program for container growers. 4. Experiments are ongoing to determine the competitive effects of weeds with containerized ornamentals under different production scenarios and in different container sizes. Although weed thresholds are often zero in nursery production due to marketability concerns, the objective of this work is to determine at what level weeds begin to reduce crop growth and further, at what point during the production cycle (at potting, smaller containers, larger containers, etc.) are weeds most competitive or damaging. In situations where labor is limited, knowing the container sizes where weeds are most competitive could help growers direct labor more efficiently. In the first experiment, ligustrum (Ligustrum japonicum) and Japanese hollies (Ilex crenata) were purchased as either 2 in., 4 in. 1 gal. or 3 gal. liners. These initial liners were then transplanted into 1 gal., 3 gal., 7 gal., or 15 gal. containers, respectively. Weed seeds were introduced and weed levels of 0, 50, or 100% determined by coverage of the media surface, were maintained by handweeding for 18 months. Preliminary results suggest that at 50 or 100% weed coverage, growth of ornamentals will be reduced by 40 to 50% regardless of container size, but growth will be impacted to a greater degree in 1 or 3 gal. pots. Plant root and shoot biomass data as well as growth index measurements collected on a bi-monthly basis are currently being processed and analyzed to more fully understand these competition dynamics. 5. Field experiments were conducted to determine if the use of indaziflam and flumioxazin could reduce the number of spot applications of glyphosate in landscape settings. Results indicated that the use of these preemergence herbicides increases costs initially, but over the course of 24 weeks become cost effective as a result of reduced glyphosate applications required to maintain an acceptably weed-free planting bed.

Publications

• Type: Journal Articles Status: Published Year Published: 2021 Citation: Marble, S.C. and A. Chandler. 2021. Efficacy of postemergence herbicides for control of small-leaf spiderwort (Tradescantia fluminensis) in Florida. Natural Areas J. 41:138-144. https://doi.org/10.3375/043.041.0208.
• Type: Journal Articles Status: Published Year Published: 2021 Citation: Marble, S.C. and S.H. Brown. 2021. Invasive plants with native lookalikes: How mistaken identities can lead to more significant plant invasions and delay management. HortTechnology. 31(4) https://doi.org/10.21273/HORTTECH04821-21.
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Khamare, Y. and C. Marble. 2021. Substrate stratification and fertilizer placement effects on growth of common container nursery weed and ornamental species. HortScience 56(9):S240
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Marble, C. and J. Pickens. 2021. Tolerance of three non-turf groundcovers to postemergence herbicides. HortScience 56(9):S240.
• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Smith, T., S.B. Wilson, C. Marble, JJ. Xian, 2021. Propagation of Vachellia farnesiana (Sweet Acacia): A Native with Ornamental Potential. HortScience 56(9):S159.
• Type: Other Status: Published Year Published: 2021 Citation: Khamare, Y.G, C. Prince, and C. Marble. 2021. Biology and management of torpedograss (Panicum repens) in landscape planting beds. EDIS Publication ENH1351 https://doi.org/10.32473/edis-EP615-2021
• Type: Other Status: Published Year Published: 2021 Citation: Anderson, E., P. Petelewicz, and C. Marble. 2021. Biology and management of pusley (Richardia L.) in turfgrass and landscape planting beds. EDIS Publication ENH1346. doi.org/10.32473/edis-EP610-2021
• Type: Other Status: Published Year Published: 2021 Citation: Khamare, Y.G, and C. Marble. 2021. Biology and management of poison ivy (Toxicodendron radicans) in the home landscape. EDIS Publication ENH 1345. doi.org/10.32473/edis-EP609-2021
• Type: Other Status: Published Year Published: 2021 Citation: Khamare, Y.G, C. Marble, and R. Stamps. 2021. Biology and management of benghal dayflower (Commelina benghalensis) in ornamental crop production. EDIS Publication ENH 1085. doi.org/10.32473/edis-EP350-2021.
• Type: Other Status: Published Year Published: 2021 Citation: Khamare, Y., C. Marble, S. Steed, and N. Boyd. 2021. Biology and management of tasselflower (Emilia spp.) in ornamental crop production. EDIS Publication ENH 1342. doi.org/10.32473/edis-EP606-2021

Progress 02/14/20 to 09/30/20

Outputs
Target Audience:The target audience for this program includes nursery growers and greenhouse production managers and others producing container and/or field grown ornamental plants, professional lawn care or pest management professionals in the landscape services industry, homeowners, master gardeners, and county extension faculty. Changes/Problems:Due to the COVID-19 pandemic, research was delayed in early/mid-2020 but is now on track. Research production was lower than in typical years but all goals and objectives are still on track for successful completion. What opportunities for training and professional development has the project provided? 56 total presentations [state/county presentations in Florida, at Pest Management University Courses, Master Gardener groups, local programs, etc.] 7 national and multi-state invited presentations to extension audiences 2 Revenue generating courses - Weed Management Online (offered internationally) and Pest Management University (Foundations and Master tracks, 2.5 day training courses for pesticide applicators). Estimated income of $10,000. 8 field consultations, 5 office consultations, 215 email consultations, 102 phone/text consultations 1,212 clientele reached throughout Florida, nationally, and in 5 different countries Developed 2 online training modules in response to pandemic: 1) Understanding and Using Landscape Herbicides and 2) Glyphosate Use and Alternative Herbicides for the Landscape. Both courses available at https://ifas.catalog.instructure.com/ and available for free. Developed online training video with Paul Fisher (posted on YouTube): 5 Quick Tips for Reducing Nursery Weed Control Costs https://www.youtube.com/watch?v=z7_BkZqLmfw. Developed online In-service Training for FL county extension faculty, How Herbicides Work: Helping your Clientele Understand and Use Herbicides Developed slide set comparing/contrasting plant identification apps for smart phones: https://www.dropbox.com/s/6u1f8vf5e33q1nv/Free%20Plant%20ID%20App.pdf?dl=0 How have the results been disseminated to communities of interest?Results were disseminated through publications, poster presentations at national conferences, presentations, newsletters,farm visits, personal communications, and additional training opportunites outlined above. What do you plan to do during the next reporting period to accomplish the goals?We plant to continue our work in each project objective area. We aquired over $200,000 in funding in 2020, with most stillactive through 2021. Specific objectives for 2021 will be to 1) determine the impact of different substrates on weed growth,with focus on substrate layering; 2) evaluate irrigation practices and their impact on weed growth and herbicide efficacy; 3)perform field evaluations for control of praxelis; and 4) continue to develop crop tolerance data on economically important species in Florida

Impacts
What was accomplished under these goals? 1. Guidelines for management of Praxelis clematidea were refined in 2020 and herbicide recommendations were developed including flumioxazin, indaziflam, and glyphosate. In 2020, rates were identified that were effective and in all cases consistent of current label rates of each product. 2. Fiesta (Fe HEDTA) herbicide was trialed over the top of 3 different container ornamental species including Ilex crenata, Viburnum tinus, and spirea prunifolia. Moderate to significant injury was observed with all species. Preemergence herbicides including dithopyr, isoxaben, prodiamine, pendimethalin, dimethenamid-P, and indaziflam were evaluated for safety as over-the-top applications to over 30 different ornamental varieties. Results were summarized and shared with growers and chemical manufacturers in order to make recommendations. 3. Two videos were filmed in which herbicide calibration and application practices are demonstrated. These videos were filmed at a local nursery and have an intended audience of container nursery growers. Topics discussed included calibrating backpack sprayers, hand-crank spreaders, and large boom equipment. Other aspects of pesticide safety and pest scouting were also discussed. These videos are currently being edited. 4. Multiple experiments were established to evaluate the use of stratifed substrates as a weed management tool.Substrate stratification is a method of filling nursery containers with pine bark (or other substrates) with different particle sizes in "layers" in order to improve soil moisture dynamics. Currently, substrate stratification, or layering, is being investigated by some researchers as a method to increase the efficiency of production inputs such as irrigation and fertilization, and is typically performed using larger particle bark as the bottom substrate and finer particle bark as the top substrate to achieve more uniform moisture distribution within containers. The objective of this study was to evaluate the effect of stratified substrates and strategic fertilizer placement on the growth of common nursery weeds and ornamental crops. In contrast to typical methodology, this study evaluated use of coarse bark (screened to 1.3 or 1.9 cm) as the top substrate and finer bark (0.95 cm) as the bottom substrate with the goal of reducing water holding capacity in the top 5 to 7.5 cm of the substrate to reduce weed germination and growth. Results showed that substrate stratification significantly decreased the growth of bittercress (Cardamine flexuosa) by 85% to 90% in comparison with substrates that were not stratified. While stratification initially reduced growth of ligustrum (Ligustrum japonicum), at 6 months after potting there was no difference in ligustrum shoot or root weight in comparison with non-stratified industry standard substrates. The results indicate that substrate composition along with strategic fertilizer placement can be utilized as an effective weed management strategy.

Publications

• Type: Journal Articles Status: Published Year Published: 2020 Citation: Marble, S.C. and J.M. Pickens. 2020. Response of three Deep South non-turf ornamental groundcovers to applications of postemergence herbicides. J. Environ. Hort. 38:91-100.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Khamare, Y., S.C. Marble, and A. Chandler. 2020. Eclipta prostrata interference in container-grown ornamentals with subdressed fertilizer. Weed Science. http://dx.doi.org/10.1017/wsc.2020.44.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Khamare, Y., S.C. Marble, N.S. Boyd, and S.T. Steed. 2020. Pre- and postemergence control of Praxelis clematidea: An emerging weed in Florida nurseries. Weed Technology. https://doi.org/10.1017/wet.2020.53.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: Berthold, D.E., A. Elazar, F. Lefler, S.C. Marble, H.D. Laughinghouse. 2020. Control of algal growth on greenhouse surfaces using commercial algaecides. Scientia Agricola. https://doi.org/10.1590/1678-992x-2018-0292
• Type: Other Status: Accepted Year Published: 2020 Citation: Khamare, Y., C. Marble, S. Steed, and N. Boyd. 2020. Biology and management of praxelis (Praxelis clematidea) in ornamental crop production. EDIS Publication ENH 1321. https://edis.ifas.ufl.edu/ep585
• Type: Other Status: Published Year Published: 2020 Citation: Smith, T., C. Marble, S. Steed, and N. Boyd. 2020. Biology and management of garden spurge (Euphorbia hirta) in ornamental crop production. EDIS Publication ENH1322. https://edis.ifas.ufl.edu/ep586.
• Type: Other Status: Published Year Published: 2020 Citation: Smith, T., C. Marble, S. Steed, and N. Boyd. 2020. Biology and management of galinsoga (Galinsoga quadriradiata) in ornamental crop production. EDIS Publication ENH 1329. https://edis.ifas.ufl.edu/ep593
• Type: Other Status: Published Year Published: 2020 Citation: Smith, T. and C. Marble. 2020. Biology and management of Florida betony (Stachys floridana) in ornamental plants in landscape planting beds. EDIS Publication ENH1333. https://edis.ifas.ufl.edu/ep597
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2020 Citation: Marble, S.C. 2020. Newly emerging invasive plants with native look-a-likes. American Society of Horticultural Sciences. Orlando, FL. August 13
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2020 Citation: Marble, C. and Y. Khamare. 2020. Stratified substrates and strategic fertilizer placement as a weed management tool in container nursery crops. American Society of Horticultural Sciences. Orlando, FL. August 12
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2020 Citation: Marble, C., Y. Khamare, and A. Chandler. 2020. Identification and management of Praxelis clematidea: a new and troublesome weed in central Florida. American Society of Horticultural Sciences Southern Region. Louisville, KY. Feb 1-2.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2020 Citation: Khamare, Y., Marble. C., Altland, J.E., & Chandler, A. (2020). Influence of substrate stratification and fertilizer placement on growth of ligustrum (Ligustrum japonicum) and germination and biomass of bittercress (Cardamine flexusa) in containers. International Plant Propagators Society (Southern region) conference. Virtual. October 28, 2020