Italian ryegrass is a winter annual weed found throughout the United States. This species is most problematic in small grain production, but can be a problem if not managed prior to soybean planting. Uncontrolled, Italian ryegrass has been shown to reduce soybean yields by 37% (Steckel and Bond 2018). Herbicide resistant Italian ryegrass is prevalent in the United States with populations resistant to Group 1 (Axial), Group 2 (PowerFlex), Group 9 (glyphosate), Group 10 (Liberty), Group 15 (Dual), and Group 22 (Gramoxone) herbicides. Italian ryegrass resistant to Hoelon (Group 1) was first reported in Maryland in 1998 (Heap 2021). In 2017, a population of Italian ryegrass from southern Maryland was found to be resistant to both Axial (Group 1) and Osprey (Group 2). Results showed that a field (1X) rate of Axial (16.4 fl oz/A) or Osprey (4.75 oz/A) controlled resistant Italian ryegrass 40% and 28% respectively. In 2021, a population of Italian ryegrass from Maryland’s Eastern Shore exhibited resistance to glyphosate, Select Max, and PowerFlex. Glyphosate was applied at 1.13 and 2.25 lb ae/A alone or in combination with Select Max at 16 oz/A. Glyphosate alone controlled Italian ryegrass less than 4%, regardless of application rate. Glyphosate + Select controlled Italian ryegrass 63% to 67%, regardless of application rate. It is recommended that Italian ryegrass be controlled in the fall with residual herbicides or tillage. However, Italian ryegrass can have multiple emergence periods and residual herbicide control may decline prior to soybean planting. Therefore, strategies are needed to assess Italian ryegrass control with herbicides applied in both the fall and spring before soybean planting.

Additional weed and cover crop species also need to be managed in no-till soybean prior to planting. Glyphosate and 2,4-D are commonly used for preplant weed control; however, there is expected to be a glyphosate shortage in 2022 with prices exceeding $80/gal (Johnson et al. 2021). In addition, multiple counties in Maryland have proposed bans on the use of glyphosate. Therefore, alternative herbicides for preplant weed control need to be evaluated.

1) evaluate fall and spring treatments for Italian ryegrass control prior to soybean planting,
2) confirm glyphosate resistance in Italian ryegrass populations in Maryland,
3) and evaluate non-glyphosate options for preplant weed control in soybean.

Methods:
These studies will examine the effectiveness of strategies for controlling Italian ryegrass and other problem weeds prior to soybean planting. The first objective will evaluate fall and spring herbicide treatments for Italian ryegrass control (Table 1). Roundup, Roundup + Valor, Roundup + Sharpen, and Roundup + Select Max will be applied in the fall, prior to soybean planting, or as sequential treatments in both the fall and prior to soybean planting. The second objective will confirm the presence of glyphosate resistant Italian ryegrass via a dose-response analysis. Italian ryegrass seed from surviving plants in Objective 1 will be collected from glyphosate and nonsprayed areas. A population from each research site will be established in a greenhouse and screened for glyphosate-resistance using a 0X, 0.5X, 1X, 2X, and 4X application rate. The third objective will compare glyphosate and non-glyphosate alternatives for preplant weed control in soybean (Table 2). Herbicides evaluated will include Enlist One, Gramoxone, Liberty, Roundup, Select Max, and Sharpen.

Data collection:
Field studies: Weed density will be assessed using two 0.25 m2 quadrats prior to the each herbicide application, and 2 weeks after each application. Weed control will be visually evaluated on a 0 to 100% scale (0 = no control, 100 = complete control) at the aforementioned rating dates. Italian ryegrass biomass will be collected prior to soybean planting using two 0.25 m2 quadrats.
Greenhouse study: Weed control will be visually evaluated as previously stated 2 and 4 weeks after treatment, and Italian ryegrass height and biomass collected 4 weeks after treatment.

Data Analysis:
All trials will be conducted as small-plot replicated trials. Data will be analyzed in a statistically sound procedure, based on the design of each study. Field treatments will be replicated at two different sites and greenhouse studies will be repeated twice.

Presentations and Key Findings:
Research will be highlighted via social media posts and on field tours at the University of Maryland Wye Research and Education Center. Reports of this study will be summarized online in University of Maryland Agronomy News and used to develop weed control recommendations. At the completion of the trials (individual objectives), fact sheets will be prepared based on the study findings.
Kurt Vollmer, Ph.D., University of Maryland Extension Weed Specialist, conducts research to develop effective weed management programs in agronomic and vegetable crops, and provides resources for county educators, agri-business and farmers for effective weed management. Dr. Vollmer has conducted field research on management of common ragweed, Italian ryegrass, Palmer amaranth, marestail, and other herbicide-resistant species. The program is well equipped with all necessary equipment to conducted applied research at the Wye Research and Education Center as well as on-farm trials.
Alan Leslie, Ph.D., University of Maryland Extension Charles County, conducts research focusing on integrated pest management solutions for pests of grain crops in Maryland. Dr. Leslie has expertise in the biology and management of many invasive and native insect pests of economic concern to soybean farmers. His current work has expanded to include management of herbicide-resistant weeds such as Palmer amaranth, while maintaining profitable cropping systems for Maryland farmers. Dr. Leslie has the equipment, expertise, and local connections necessary to carry out on-farm spray trials in Southern Maryland.

Update:
All field trials for objectives 1 and 3 have been completed. Field data helps to confirm the result of glyphosate-resistant Italian ryegrass in Maryland. Seeds were collected from surviving plants in the spring and will be subjected to a dose-response analysis (objective 2). Data from objective 3 shows multiple alternative herbicides are comparable to glyphosate for preplant weed control. Results were shared at the University of Maryland Weed Science Twilight Tour on June 29 and the Maryland Commodity Classic on July 28.

Update:
In addition to the previously reported results. A study for objective 2 was performed assessing the response of 2 resistant populations and 1 susceptible population of Italian ryegrass seed from the field studies. A 1.27 lb./A rate of glyphosate controlled the first resistant population 15% and the second resistant population 55%. Doubling the glyphosate rate to 2.53 lb./A, controlled the first resistant population 25%, and the second resistant population 87%. These results help to confirm that glyphosate-resistant Italian ryegrass is present in Maryland.

Results from objectives 2 and 3 were published in University of Maryland Extension Agronomy News (see attached). In addition results form these studies have been and will be presented at upcoming University of Maryland Extension winter agronomy meetings.

Update:
In addition to previously reported studies. A second dose-response analysis was performed on the field population of Italian ryegrass with glyphosate rates ranging from 36 to 287 oz/A. At 28 days after application 88 oz was needed to provide at least 50% control of population, and 83 oz was needed to provide a 50% reduction in plant dry weight.

Italian ryegrass is an annual weed that farmers are having difficulty controlling. This species not only reduces yields in crops like wheat and barley, but also interferes with corn and soybean planting. In no-till systems, many farmers use glyphosate-based products to manage Italian ryegrass before spring planting; however, farmers in Maryland are seeing a lack of control with this herbicide. We evaluated methods for controlling Italian ryegrass prior to soybean planting. Field trials were conducting using glyphosate and combinations of glyphosate and other herbicides to control both fall and spring flushes of Italian ryegrass. The best methods for controlling Italian ryegrass occurred when glyphosate was applied with clethodim or when glyphosate-based treatments were applied sequentially in both the fall and the spring. However, glyphosate alone provided poor Italian ryegrass control. An analysis of the field population confirmed it to have a 2-fold level of resistance to our standard application rate of glyphosate at 1.25 lb. per acre. As a result different herbicides and tactics need to be evaluated for Italian ryegrass management prior to soybean planting.

Despite the increasing number of glyphosate-resistant weeds, glyphosate's ability to control many weed species prior to planting continues to be an important component in conservation agriculture. In 2022, growers were concerned about the lack of or cost of glyphosate. We conducted field trials to assess alternative herbicides to glyphosate for preplant weed control. Results showed that glufosinate and paraquat were as effective as glyphosate-based treatments in controlling several emerged grass and broadleaf weed species. Therefore, these two herbicides may also provide an effective alternative to glyphosate-based treatments.