Tag: palmer amaranth

Evaluating Late Season Burndown Options for Palmer Amaranth

Ben Beale, Principal Agriculture Agent| bbeale@umd.edu and Alan Leslie, Agriculture Agent
University of Maryland Extension

A common question asked by farmers dealing with herbicide resistant Palmer amaranth is, “What are the most effective burndown options in situations where Palmer amaranth is larger then the ideal 3-4 inch control range?” We often encounter this scenario in fields left fallow for a year, fields with delayed planting due to saturated soils, and double crop fields following wheat. In the summer of 2022, we undertook a study evaluating eight different treatments for control of larger Palmer amaranth in Southern Maryland. The study was completed at a site with a history of Glyphosate and ALS-resistant Palmer amaranth. The field was fallowed through the spring and early summer, and mowed at a 8 inch height in mid July. At the time of herbicide applications on August 4,  Palmer amaranth was 5-8 inches tall and present at a high density. Most plants were not clipped (Figure 1). Germination of Palmer amaranth was delayed due to a heavy cover of winter annual weeds. Other weeds present at the site at the time of application included annual foxtail and perennial broomsedge. Enlist soybeans were planted on August 3rd in order to evaluate any potential phytotoxicity or herbicide injury. We evaluated treatments with Roundup, Liberty, Enlist and Gramoxone with some using a non ionic surfactant or crop oil as the adjuvant. We also evaluated combinations of Liberty + Roundup or Liberty + Enlist.

Figure 1. Palmer amaranth plants were 5- 8 inches tall at time of application.

Treatments:

  1. Glyphosate (Roundup Power Max) 32 fl oz/ac + Amm. Sulfate 48 oz/ac
  2. Paraquat (Gramoxone SL 2.0) 48 fl oz/ac + Non Ionic Surfactant 6.4 fl oz/ac
  3. Paraquat (Gramoxone SL 2.0) 48 fl oz/ac + Crop Oil 32 fl oz/ac
  4. Glufosinate (Liberty 280 SL) 43 fl oz/ac + Amm. Sulfate 48 oz/ac + Crop Oil 32 fl oz/ac
  5. Glufosinate (Liberty 280 SL) 43 fl oz/ac + Amm. Sulfate 48 oz/ac + Non Ionic Surfactant 6.4 fl oz/ac
  6. 2,4-D choline (Enlist One) 32 fl oz/ac + Non Ionic Surfactant 6.4 fl oz/ac
  7. Glufosinate (Liberty 280 SL) 43 fl oz/ac + Glyphosate (Roundup Power Max) 32 fl oz/ac + Amm. Sulfate 48 oz/ac + Non Ionic Surfactant 6.4 fl oz/ac
  8. Glufosinate (Liberty 280 SL) 43 fl oz/ac + 2,4-D choline (Enlist One) 32 fl oz/ac + Amm. Sulfate 48 oz/ac + Non Ionic Surfactant 6.4 fl oz/ac

A randomized complete block design with four replications was used. Plot size was 10 ft. by 30 ft., with 5 ft aisles separating plots and running checks on each side of the plots. Treatments were applied  using a ATV plot boom sprayer utilizing TeeJet AIXR 11003 flat fan nozzles at 35 psi applying 20 gallons per acre of spray solution. Application was made on August 4th in the mid-afternoon with clear bright sunshine and air temperature of 90°F. Plots were evaluated for percent control of Palmer amaranth and grass weeds 10, 20, and 30 days after treatment.

Results

Palmer Amaranth Control

As depicted in Figure 2, treatments containing Gramoxone either with crop oil or a non-ionic surfactant, and the tank mix treatment of Liberty and Enlist One performed well throughout the study. Liberty applied either with non-ionic surfactant or crop oil, and Liberty with Roundup only achieved around 50 % control of Palmer Amaranth. It is notable that all Liberty treatments saw reduction in the level of control as the season progressed. This was evidenced in the field by Palmer amaranth plants suckering out from the base and re-growing approximately 2 weeks after the application. We did not observe suckering with the Gramoxone treatments or Liberty + Enlist treatments. Surprisingly, Enlist One treatments did not provide acceptable control of larger Palmer Amaranth plants in this study with an average control of around 25%. Enlist One control did gradually increase after the 10 day evaluation most likely due to the systemic nature of the product. As expected, we saw negligible control of Palmer amaranth with Roundup. The evaluation 20 days after treatment provided the clearest assessment of control, with no significant difference between Gramoxone treatments or the Liberty + Enlist One treatments (Figure 3). Liberty + NIS and Liberty + Crop Oil and Liberty + Roundup were not significantly different from each other, but significantly less effective than Gramoxone or Liberty + Enlist one treatments. Enlist treatment was not significantly different than the Roundup treatment. We should also note that new Palmer amaranth seedlings began to emerge just 20 days after the burn down treatments. Palmer amaranth continues to germinate throughout the summer, especially in open areas where sunlight reaches the soil. Controlling this weed takes a season long approach.

Figure 2. Palmer amaranth control at 10, 20, and 30 days after treatment.
Figure 3. Palmer amaranth control at 20 days after treatment.

Grass Control

As depicted in Figure 4, all treatments provided a satisfactory level of grass control. While Roundup didn’t have any efficacy on resistant Palmer amaranth, the enduring  benefit of this product can clearly be seen in control of other tough weeds, such as grasses with 100% control in our study. We saw no reduction in control of the grasses present when Roundup was tank mixed with Liberty. The Gramoxone +NIS treatment had slightly lower grass control at 84%, and was significantly lower than Roundup treatments. Enlist only has activity on broadleaf and was omitted in the analysis for grass control. An interesting question for further study is the potential efficacy of Gramoxone + Roundup treatments.

Figure 4. Grass control in soybean plots.

Time to Pull Palmer Amaranth

Kurt Vollmer, Weed Management Specialist | kvoller@umd.edu
University of Maryland Extension

Lately, I have seen several fields with Palmer amaranth flowers (Figure 1). It is imperative that these plants be managed before harvest (Palmer amaranth is listed as a noxious weed in Maryland and Delaware). At this point, mowing or herbicides will not improve yield nor prevent Palmer from germinating next year. Plants need to be physically removed from fields. Palmer amaranth has both male and female flowers on separate plants (Figure 2), and focus should be placed on removing the seed-producing females first. A single female can produce approximately 600,000 seeds per plant, and these seeds can remain viable for six years. Palmer seed matures within 2 weeks of flowering and if left unchecked, a single plant can infest an entire field within a few years (Figure 3).

Figure 1. Palmer amaranth emerging through a soybean canopy.
Figure 2. Female plants (left) can be distinguished from male plants (right) by the presence of sharp floral bracts whereas male flowers are soft to the touch.

Upon removal, plants should be bagged and buried or burned along the field’s edge, or disposed of in a manner as to not contaminate other areas. Palmer retains most of its seed in the fall. There is still time to remove them, but combines will spread seed. If plants cannot be removed before harvest time, areas with Palmer should be harvested last, and the combine thoroughly cleaned before moving. Be sure to mark areas where mature Palmer is present, and pay special attention to those areas next year. Taking these measures will help to reduce the Palmer seedbank and prevent the problem from becoming worse next year. In the United States, Palmer is resistant to at least 5 different herbicide groups. So far, Palmer is only resistant to 2 herbicide groups in the Mid-Atlantic. However, any escapes could indicate possible resistance. Let’s not allow any more Palmer to proliferate!

Figure 3. Number of Palmer amaranth escapes possible over successive years.

Herbicide Last Check Chart: Corn

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 corn production: marestail, common ragweed, waterhemp, and Palmer amaranth.

Click here to download a PDF copy.

 

Herbicide Last Check Chart: Soybean

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.

Click here to download a PDF copy.

Palmer Amaranth and Waterhemp Management At Harvest

Kelly Nichols, Agriculture Agent Associate
University of Maryland Extension, Frederick County

This summer, we have gotten a few calls about Palmer amaranth and waterhemp, two pigweed species that are unfortunately becoming more common. These two pigweeds are difficult to control, mostly due to their herbicide resistance and fast growth (especially in hot weather). Often, these pigweeds are not noticed until they are seen growing up over the crop canopy, especially in soybeans. By then, it is too late to control them.

Palmer Amaranth
Figure 1. Palmer Amaranth

As we head into harvest, if you have Palmer or waterhemp – or want to make sure you don’t have them – scout your fields to be certain. Know how to identify Palmer (Figure 1) and waterhemp (Figure 2). The main characteristic is that these two troublesome pigweeds are completely hairless. Redroot and smooth pigweed, our most common pigweed species, have hairs on the stems and leaves. Another characteristic of Palmer is that the petiole (the little stem that attaches the leaf blade to the main stem) is longer than the leaf blade itself. (Note: Spiny amaranth, or spiny pigweed, is another pigweed that is common in pastures. It also does not have hairs; however, it will have spines on the stem. Palmer and waterhemp do not have these spines).

While you are scouting, pull out the Palmer or waterhemp plants (as many as you can). Palmer and waterhemp can produce hundreds of thousands of seeds per plant. At this point in the season, this is the best way to reduce the number of seeds that could germinate next year. Consider taking a paper bag with you to put the plants in, as smaller plants can re-root. Take the plants out of the field and bury or burn them.

Harvest infested fields last. The biggest concern with harvesting infested fields is the spread of the seeds – not only throughout the currently infested field, but also to other fields and possibly other farms. If there is only a small section of the field that is infested, consider not harvesting that section to avoid spreading the seeds. If you are not running the combine, be in communication with the person who is to ensure that Palmer or waterhemp seeds are not brought onto your farm and/or spread around your fields. If the infested harvested crop is to be fed to livestock, the processes of grinding, roasting, and ensiling can destroy weed seeds and prevent the seeds from being spread in the manure.

After harvest (or in between fields if necessary), clean out the combine. Pigweed seeds are tiny (about the size of a pencil point), and it is difficult to perfectly clean out a combine. However, cleaning can still reduce the number of weed seeds in the combine. Use compressed air and start at the front of the combine, working up to the grain tank and auger, and then to the back. Running straw through the combine can also help to clean it out. Research from the University of Delaware has shown that using compressed air in combination with running straw through the combine can potentially reduce the number of weed seeds in the combine by thousands.

Waterhemp
Figure 2. Waterhemp

For next year, consider using these strategies to control Palmer and waterhemp: plant a cover crop to provide weed suppression in the spring; rotate to corn for more effective herbicide options (compared to soybeans) or a perennial forage; use the full recommended labeled rate; use residual herbicides in both the pre- and post-emergence applications, as Palmer and waterhemp seeds can germinate throughout the growing season; use multiple effective modes of action; and rotate modes of action. More information on Palmer and waterhemp, as well as herbicide resistance weed management, can be found at www.integratedweedmanagement.org, a website run by Extension Weed Specialists from across the U.S.

 

 

Palmer Amaranth is Out and About—Are You Ready?

Ben Beale, Senior Agriculture Agent
University of Maryland Extension, St. Mary’s County

We observed Palmer amaranth germinating in fields in Southern Maryland the first week of May. These plants are now exceeding the optimal height for control. Plants are now 8-10 inches tall in fields that did not receive any burn down treatment or tillage this spring. The optimal size for effective control of palmer is 3 to 4 inches.

Palmer amaranth seedling emerging on May 9 in St. Mary’s County.

In fields that received a burn down herbicide application in May, expect to see additional plants emerging, often before the soybean crop is planted. Be sure to kill these plants before the soybeans emerge. Paraquat (Gramoxone® or generic alternatives) is an effective burn down treatment for smaller plants provided it is applied with adequate water and spray coverage is adequate.

Palmer amaranth plants in a field that has not received any burn down treatments or tillage. The tallest plants are now 8-10 inches tall. Photo taken May 24.

Other options include products like 2,4-D, saflufenacil (Sharpen®), or dicamba. Each of these products have plant-back restrictions. Glyphosate, while not effective on Palmer amaranth, can still be added to control other weeds present. Integrating several strategies into your weed management plan will help avoid resistance and increase control. Effective strategies include crop rotation, tillage, seed bank management, preventing seed movement, use of cover crops, choosing a residual herbicide program with at least two effective modes of action and use of timely post-emergent herbicide applications.

More information on management of palmer amaranth is available from University of Maryland Fact Sheet 1086, Palmer Amaranth in Maryland.

 

Palmer Amaranth Confirmed in Kent County, MD

Scott W. Rowe, Kent County Weed Control Coordinator, and Nate Richards, UME Ag Educator – Kent County

Mature palmer amaranth plant in soybean field
Palmer amaranth plant in a soybean field. Image: Scott Rowe, Kent County Weed Control.

On August 8, 2018, Kent County Weed Control Coordinator, Scott Rowe, discovered a Palmer amaranth plant growing from a drainage gutter on Flatland Rd. (SR 514) in Chestertown. The identity of this plant was confirmed by University of Maryland Extension (UME) – Kent County Ag Educator, Nate Richards, other UME personnel and Mark VanGessel, University of Delaware Weed Science Professor.  

Since that initial discovery, the Weed Control team have found or confirmed infestations on road rights-of-way and in fields across the county. Locations include Smithville Road area, Pomona, Massey and areas northwest and east of Chestertown. Some local growers and Ag Supply reps have reported having managed or treated infestations in Kent County prior to the 8/8/18 discovery. The infestations have been found in both non-organic and organic culture fields. Most infestations are light, involving one to several plants; however, a couple involve entire fields.

Palmer amaranth is a highly competitive annual pigweed that originated in the desert southwest and has been moving eastward and northward for several years. It reproduces by seed only; weed scientists report that a single plant can produce from 100,000 to 500,000 seeds. The tiny seeds are easily transported via field and road equipment, and ag commodities such as hay, straw, other feedstuffs and manure. Palmer amaranth has become established locally in southern Maryland, the lower Eastern Shore and lower Delaware. Populations in these areas are generally resistant to glyphosate (e.g., Roundup) and ALS inhibitors (e.g., Pursuit, Raptor, Accent, Harmony, FirstRate), and may have resistance to other herbicide classes.  

Palmer amaranth can be distinguished from other pigweeds by its vegetative and reproductive parts: the main stems are hairless while redroot pigweed has a fuzzy stem; the leaf petiole (leaf stem) on larger Palmer plants – not on seedlings – is usually longer than the leaf blade while the petiole on other pigweeds is shorter; the inflorescence (flower stalks) of Palmer are longer, less branched, and less compact than redroot pigweed. The Penn State (PSU) website listed herein has excellent photo comparisons of the different pigweeds, and photos showing the difference between the male (pollen producing) and female (seed producing) plants of Palmer amaranth.

Now that it’s here, what to do? Since Palmer amaranth is such a prolific seed producer and there are limited effective herbicides for control, it is essential to manage it ASAP so it doesn’t get out of hand. Growers should scout their fields now. If they have very light to light infestations, they should hand pull all plants that have headed, or at least the female plants, bag them, remove them from the field and bury or burn them. The large paper lawn and leaf bags work well for burning. If plants haven’t headed, pull them and let them lie, making sure they can’t re-root. During harvest, growers should consider harvesting infested fields last and thoroughly cleaning combines and other equipment before leaving any infested field. If combine operators discover a patch during harvest, they should consider leaving the patch for later, bagging/burning ASAP, and recording the location for intense management next season.Combines, stalk cutters and tillage equipment are wonderful seeders!

The time to start managing Palmer amaranth is NOW! Growers should watch for publications and workshops that will be forthcoming and do what they can to learn how to manage this pest. The websites listed herein are excellent resources to help understand Palmer amaranth and its management. Some of the content in this article was gleaned from these websites.

https://blog.umd.edu/agronomynews/2017/04/06/management-of-palmer-amaranth-in-2017/

https://extension.psu.edu/invasive-pigweeds-palmer-amaranth-and-waterhemp#section-14

https://ag.purdue.edu/btny/weedscience/documents/palmer_bio_id_mngmt_pg.pdf