This event will be the third stop on the Delmarva Weed Tour and will include tours of corn and soybean herbicide research trials, integrated weed management projects for watermelon and hemp production, and tours of demonstration plots for organic weed management in corn and soybean.
Date: Wednesday, June 28th, 2023
Time: 4PM – 6PM
Location: Wye Research and Education Center
211 Farm Lane, Queenstown, MD 21658
Pesticide credits will be available for MD and DE.
Galen Dively, Professor Emeritus | galen@umd.edu University of Maryland, College Park
Listed below are the corn trait packages to make it easier to understand seed guides, sales material and bag tags. It is an abbreviated version of the Bt trait table plus related extension materials free online at: https://www.texasinsects.org/bt-corn-trait-table.html. Information listed Includes the name of each trait package, bag tag code, Bt toxins expressed (Cry1 types and Vip3A for caterpillars, Cry3 types for rootworms), refuge requirement (RIB=% refuge in the bag or REF=% structured refuge) and herbicide tolerance (GLY= glyphosate /Roundup-Ready, LL=glufosinate/Liberty Link, 2,4D or group 1 ‘fops’ type herbicides). Note that older trait packages, with limited or no commercial availability, are listed, so you can look back and interpret previous year’s planting records, seed guides, and research results.
The widely adopted use of Bt corn has resulted in major benefits to growers and the general public. However, resistance evolution in target insect populations has become a major threat to the sustainability of these crops. In some parts of the US Corn Belt, western corn rootworm rapidly adapted to Bt corn, and currently, some populations show resistance to all commercially available Cry3 traits. The high dose expression of Cry1 and Cry2 traits continues to provide excellent control and areawide suppression of the European corn borer in the US; however, the first case of resistance to the Cry1F toxin was reported in Nova Scotia in 2018 and resistance to other Cry toxins was recently confirmed in several eastern Canadian provinces. For corn earworm, we now have widespread field-evolved resistance to all Cry toxins in Bt corn. However, the Vip3A trait still provides excellent protection against this pest but studies show early stages of resistance developing since 2017, mainly in the southern states. Fall armyworm has been targeted by the Cry1F toxin since 2003, without any evidence of field-evolved resistance until 2010 when widespread control failures in Bt corn were reported in Puerto Rico and recent studies show high levels of resistance in several southeastern U.S. states.
Alan Leslie, Center Director Maryland Agriculture Experiment Station
With grant funding from the Maryland Soybean Board, we have developed a new web-based app for selecting herbicides to use in soybean production. The goal for this new tool is to provide guidance in navigating different herbicide options with a simple user interface. The web app allows you to download a summary of your custom herbicide program as a PDF document for your records. Herbicide inputs can then be used to create your custom crop budgets using the web-based crop budget tool.
To use the app, users first select the major weed species from the lists that are the key management concerns on their farm. Choices of herbicides will then appear in three tables: burndown herbicides, pre-emergence herbicides, and post-emergence herbicides. These tables show herbicide options that are effective against at least one of the weed species selected. Users then use these tables to select their burndown, pre-emergence, and post-emergence herbicides, with the option to select between zero and three chemicals for each application. The page is then pre-populated with recommended rates and estimated costs, though actual rates and costs can be inputted by the user. After all of this information is entered, users can click the button to generate a report of everything they entered.
We are interested in gathering feedback and input about this new tool and ways to improve it in the future. After testing the new pesticide selection and crop budget tools, we would appreciate if you could take a few minutes to provide feedback through our online comment form. Feedback will be used to develop better tools in the future.
Figure 1. Screenshot of the web-app tool, showing where to select key weed species, where to view herbicide efficacy information, and where to input herbicide choices.
Kurt Vollmer, Extension Weed Management Specialist | kvollmer@umd.edu University of Maryland Extension
In last month’s issue of Agronomy News, I discussed considerations for glyphosate-based burndown programs. This month I wanted to share some of my results using similar programs to manage a rye (Fig. 1) and hairy vetch (Fig. 2) cover crop. Treatments were applied on April 11, and consisted of glyphosate, glufosinate, paraquat, glyphosate + 2,4-D, glyphosate + dicamba, glyphosate + glufosinate, and glyphosate + paraquat. Currently, this is what I am seeing:
Glyphosate tank mixed with 2,4-D, dicamba, and glufosinate are doing an excellent job controlling hairy vetch, and glufosinate alone is providing similar control (Fig 3.);
Vetch control appears to be declining with individual treatments of glyphosate and paraquat, as well as the mixture of the two (Fig. 4);
Glyphosate + 2,4-D is doing an excellent job controlling cereal rye (Fig. 3b), but control with glyphosate alone has improved (Figs. 4a, 4b).
Figure 1. Hairy vetch control 2 and 3 weeks after application (WAA).Figure 2. Cereal rye control 2 and 3 weeks after application (WAA). *Glyphosate containing treatments consisted of 20.5 fl. oz./A Roundup PowerMax3®; glufosinate containing treatments consisted of 43 fl. oz./a Liberty 280®, paraquat containing treatments consisted of 3 pt/A Gramoxone SL 2.0®, 2,4-D containing treatments consisted of 2 pt./A Enlist One®, and dicamba containing treatments consisted of 12.8 fl. oz./A Engenia® *Ammonium sulfate (8.5 lb./A) was included in all treatments except the glyphosate + dicamba treatment, nonionic surfactant (0.25% v/v) was included with 2,4-D and dicamba treatments, crop oil (1% v/v) was included with paraquat treatments. *Treatments were applied using Turbo Teejet 11002 nozzles at spray volume of 15 gal/A.
As previously discussed, the same herbicide program may not have the same desired effect on all species. Here are some things to remember.
There are certain species where control with glyphosate can be difficult, even if those species are not classified as being glyphosate-resistant. Additional trials from the Mid-Atlantic have also indicated lower vetch control with glyphosate alone (Figs. 4a, 4b) compared to glyphosate tank mixtures (Figs. 3b, 3c, 3d).
Group 4 herbicides such as 2,4-D and dicamba, will not control grasses. In addition, including dicamba in a tank mix with glyphosate has been shown to reduce glyphosate’s ability to control grasses (Fig. 3c).
Contact herbicides such as glufosinate and paraquat require good spray coverage for optimal control. If plants are too large, if spray volume is too low, or if nozzles do not provide adequate spray coverage, then plants can regrow (Figs. 4c, 4d).
Figure 3. Efficacy of preplant herbicides for managing a rye/vetch cover crop 2 weeks after applicationFigure 4. Differences in herbicide efficacy for managing a rye/vetch cover crop 2 and 3 weeks after application.
Kurt Vollmer, Extension Weed Management Specialist | kvollmer@umd.edu University of Maryland Extension
It’s that time of year when growers are considering which herbicides to include in their burndown programs. Utilizing effective herbicides will help to ensure less weed competition at planting. However, growers should consider not only what herbicides they plan to use in their burndown programs, but also the weed species present in the field.
The most common preplant treatment for both corn and soybean is either a combination of 2,4-D + glyphosate or dicamba + glyphosate. These mixtures can provide good to excellent control of winter annual weeds such as common chickweed and common groundsel, as well as good control of emerging summer annual species such as common lambsquarters and foxtail species. These herbicides can also control henbit, purple deadnettle, and mustard species if sprayed before flowering and seed set. However, control may be reduced with winter annual weeds such as Carolina geranium and field pansy, as well as perennial species such as curly dock. If Carolina geranium and field pansy are present, consider adding atrazine or metribuzin to the tank mix. If curly dock is a problem consider using Harmony + 2,4-D.
The use of these herbicides will also influence planting date if using non-tolerant varieties, such as Enlist® (2,4-D) and XtendFlex® (dicamba). Generic forms of 2,4-D or dicamba should be applied 7 to 14 days before or 3 to 5 days after planting corn. The planting interval for soybean will depend on the amount of product applied. For most generic 2,4-D esters (LVE), wait at least 7 days if using 1 pt/A and at least 30 days if using 2 pt/A. However, some LVE formulations allow a 15 day application interval, be sure to consult the product label for specific instructions. The planting interval for dicamba formulations is at least 14 days if 0.5 pt/A is applied and at least 28 days if 1 pt/A is applied.
Glyphosate resistant weeds such as horseweed (marestail) and common ragweed may also be present at the time of application. Be advised that when using combinations of glyphosate and 2,4-D or dicamba, the 2,4-D or dicamba component is being relied upon to control these weeds. Therefore, these species should be sprayed when they are small (< 6 in.). Local data has shown applications of 2,4-D or dicamba made 30 days before planting to be more effective on horseweed than applications made 14 days before planting. Sharpen® is another option for controlling horseweed that is less than 6 inches tall.
Finally, it is important to note the importance temperature will play in the efficacy of these herbicides. When the temperature is lower than 60˚F, weed growth slows, resulting in reduced uptake and translocation of systemic herbicides like 2,4-D, dicamba, and glyphosate. If the temperature is below 40˚F, it is best to avoid applying these herbicides until conditions are more suitable. Fortunately, it looks like warmer days are ahead!
Kurt Vollmer, Wee Management Specialist | kvollmer@umd.edu University of Maryland Extension
Despite a less than ideal Memorial Day weekend, I’m sure many of us are grateful for the rain. While corn was planted several weeks ago, many places went for weeks without significant rainfall. As a result, many fields lacked adequate moisture to properly activate any preemergence herbicides that were applied. The amount of moisture required to activate a particular herbicide depends on its water solubility (Table 1). The lower the water solubility the more rainfall or irrigation is needed to activate the herbicide and move it into the root zone. Soil-active herbicides such as atrazine, Princep, Balance Flexx, and Prowl need more than 0.75 inches of water to become activated. Under ideal conditions (good activation, no excessive moisture, and sensitive weed species), most preemergence products will provide control for about 3 to 4 weeks after application. Therefore, it’s a good time to start scouting fields to see if an early postemergence application is needed. Remember, preemergence herbicides will not control weeds once they’re up!
Along with products you are considering for postemergence weed control, be sure to include a soil-active herbicide in the tank mix to help extend residual weed control. Group 15 herbicides such as Dual and Outlook can extend control of grasses, pigweeds, and other small-seeded broadleaf weeds. The addition of atrazine can help to improve the efficacy of certain postemergence herbicides as well. Finally, always be sure to consult the label for the proper application rates and tank mix requirements for your crop and soil type.
Table1. The Relative Amount of Water Needed to Activate Common Herbicides and the Duration of Residual Weed Control.
Trade Name
Amount of Water Required to Activate (inches)
Duration of Residual Weed Control (weeks)
Atrazine
> 0.75
4-5
Balance Flexx
> 0.75
2-4
Callisto
0.33
2-4
Dual II Magnum
0.33 – 0.5
4-5
Harness
0.5 – 0.75
2-4
metribuzin
0.33
2-4
Outlook
0.33
2-4
Princep
> 0.75
4-5
Prowl
> 0.75
4-5
Valor
> 0.75
4-5
Zidua
> 0.75
4-5
*Table adapted from the 2021 Mid-Atlantic Weed Management Guide.
Kurt Vollmer, Weed Management Specialist University of Maryland
This is a quick reference chart to check herbicide efficacy for some of the most problematic weeds in soybean production: marestail, common ragweed, waterhemp, and Palmer amaranth.
Kurt Vollmer, Extension Weed Management Specialist University of Maryland
On September 28, Bayer announced that the European Commission has authorized XtendFlex soybean technology for food, feed, import and processing in the European Union. XtendFlex soybeans have tolerance to glyphosate, glufosinate, and dicamba. With this approval, Bayer expects a full launch in the United States and Canada in 2021. However, no dicamba-containing products are currently registered for over-the-top applications in soybean. Previously registered dicamba products including Xtendimax, Engenia, FeXapan, and Tavium are still pending re-registration for use next season.
Over 300 agricultural organizations recently sent a letter (http://wssa.net/wp-content/uploads/Neguse-Udall-FIFRA-letter.pdf) to members of the House and Senate opposing legislation that would drastically amend the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).
Ray Weil1, Kevin Conover2, Mia Godbey1 1Dept of Environmental Science and Technology and 2Central Maryland Research and Education Center University of Maryland, College of Agriculture and Natural Resources
Weed control is almost invariably cited as one of the biggest challenges for the organic production of grain crops. Synthetic herbicides cannot be used in organic farming, leaving tillage as the main weed control option. Tillage is also the main method of terminating cover crops in organic farming, although roller-crimping can work under some circumstances. The lack of chemical means of weed control makes low disturbance or no-till organic farming extremely difficult if not impossible on a commercial scale.
This spring we conducted a preliminary trial to access the efficacy of a new organically-approved herbicide called Weed Slayer® (based on Eugenol, an essential oil from cloves, molasses, and a biological surfactant mixture). This product comes in two parts, the Clove Oil product, and the microbial surfactant product, that must be mixed together in equal parts. The manufacturer, Agro Research International, recommends a rate of 1-3 quarts/acre of each part in 20-25 gallons water/acre.
We established a cover crop stand that initially included 12 species (originally 4 legumes, 4 brassicas, and 4 kinds of grass) planted in fall 2019, but because of the very dry conditions in August-October 2019 and winter killing of the radish, we ended up with a few plots of good cover crop biomass (>3,000 lbs/acre dry matter) consisting of mainly red, white and crimson clovers, hairy vetch, annual ryegrass, and cereal rye with the occasional turnip or kale. The covers were allowed to grow into full flowering. On May 27, soybeans were “planted green” in and the plots were sprayed with three herbicide treatments: 1) RU: the normal rate of Glyphosate, 2) WS1: the recommended rate of 1 quart/acre each part of Weed Slayer®, and 3) WS2: a rate of 2 quart/acre rate of each part of Weed Slayer® (Figure 1).
Figure 1. Appearance of sprayed multi-species cover crop plot 7 days after treatments were applied.
We used the Canopeo app (canopeoapp.com) to measure the green cover percentage at 2 and 7 days after spraying at 6 locations within the tire tracks and within the untracked middle area of each plot. On day 7 we also measured the green cover of the unsprayed cover crop at the edge of the field (to serve as a control). We did this in two blocks about 80 feet long and 45 ft wide. At four weeks after spraying, visual observations were made to access any possible regrowth of the cover crop.
Results. Two days after spraying, the effect of the tractor tire tracks was quite evident, with less remaining green foliage in the tracks than in the untracked middle rows of the plot (Figure 2). In the untracked area, the 1 quart/acre rate of Weed Slayer® had about 25% green area remaining, which was greater than the 18% green area for the Round-Up and the 2-quart rate of Weed Slayer®. In the tire tracks, less than 10% green area remained for all three treatments.
Figure 2. Percent green (living foliage) area two days after herbicide treatments were sprayed on multi-species cover crop. Measurements were made in the tractor tire tracks (right) and in the untracked middle row (left) of the plot.
By the 7th day after application, there was no difference among the three spray treatments in green cover in the tire tracks where the only detectable green foliage was that of the emerging soybean seedlings (data not shown). There was also very little difference in the untracked middle of the plot with Round-Up and Weed Slayer®2X exhibiting statistically the same percent green area (Figure 3), which was almost entirely due to the emerged soybean seedlings. The Weed Slayer® 1 quart/acre rate had about 5% green area, which was statistically greater than the Round-Up plots, and about half due to cover crop and half to soybean seedlings. The grasses were killed earlier than the legumes by both herbicides, but by day 7 all cover crop species appeared to be nearly completely killed. Most of the green cover by day 7 was due to the soybean seedlings. However, visual inspections four weeks after the spray treatments revealed some re-growth of the hairy vetch in the Weed Slayer® plots but not in the Round-Up plots. No grass regrowth was observed.
Figure 3. Percent green (living foliage) area seven days after herbicide treatments were sprayed on multi-species cover crop. Measurements shown are for the untracked middle rows (right) of the plot.
Weed Slayer® currently costs about $60/acre for the 1 x rate (purchased online in a package of 1 gallon of each part). This is expensive by conventional grain production standards, but feasible for organic grain which brings about twice the price per bushel as conventional. An affordable, effective organic-certified burn-down herbicide for grassy species (and some broadleaves) could open up important opportunities for no-till and cover cropping practices not currently practical in organic farming.
Sarah Hirsh, Agriculture Agent University of Maryland Extension, Somerset County
In the next couple of weeks, common ragweed will begin to emerge (Figure 1). There are herbicide-resistant populations of common ragweed throughout Maryland. In 2019, common ragweed samples from St. Mary’s, Charles, Somerset, Worcester, and Wicomico counties, MD were tested and found to be resistant to glyphosate (group 9) and cloransulam (Firstrate; group 2 “ALS Inhibitors”) herbicides. Furthermore, three-way resistance to glyphosate, Firstrate, and fomesafen (Reflex, group 14 “PPO Inhibitors”) was found for two eastern shore samples from Dorchester Co, MD and Kent Co, DE. Because common ragweed populations can be resistant to glyphosate and other herbicides, pre-planting and residual herbicide control are particularly important.
Figure 1. Common ragweed seedlings 18 April 2019. Early-season control of common ragweed is critical, especially in herbicide-resistant common ragweed populations.
What steps can you take now against common ragweed?
Delay cover crop burn down. In addition to providing other agronomic benefits, cover crops may provide competition with spring weeds, including ragweed, and reduce emergence and growth. Growing conditions have been excellent this spring, so terminating a cover crop would leave an open window for weeds to proliferate.
Plan to apply something other than or in addition to glyphosate at pre-planting burndown. Research trials in 2019 indicated that a herbicide burndown of glyphosate plus Liberty at soybean planting effectively eliminated common ragweed. (Soybean was planted 18 May at one site and 3 June at a second site). The addition of 2,4-D or Banvel is another glyphosate tank mix option, and paraquat or paraquat + metribuzin is another option for smaller ragweed plants.
Apply a residual herbicide at soybean planting. Research trials in 2019 indicated that it was important to apply a residual herbicide at burndown to control post-planting common ragweed escapes. Applying the residual herbicide at soybean planting provided better common ragweed control than applying the residual herbicide at an earlier (4 April) burndown date. A second research trial comparing residual herbicide products found that Command, Linex, Dimetric, or combinations of Command + Dimetric, and Linex + Dimetric all reduced common ragweed prevalence in soybean.
Figure 2. Soybean field with herbicide-resistant common ragweed in Worcester Co, MD. Photo taken 30 Oct 2018.
Common ragweed can quickly get out of hand and dominate a soybean crop (Figure 2). However, with proactive control and scouting, herbicide-resistant common ragweed can be effectively controlled.
