Posts Tagged ‘palmer amaranth’

Glyphosate Resistant Palmer Amaranth on Delmarva

Friday, June 29th, 2012

Barbara Scott, Research Associate; bascott@udel.edu & Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Glyphosate-resistant Palmer amaranth has been confirmed on Delmarva. There has been suspicion of glyphosate-resistance in the region, but this is the first year of confirmed resistance. This discovery is not surprising since Palmer amaranth has a tendency to develop resistance. Fields with Palmer amaranth (or suspected Palmer amaranth) should not be treated with glyphosate alone. In soybeans glyphosate should be tank-mixed with an ALS inhibiting herbicide (group 2) or PPO herbicide (group 9).

Control of Palmer Amaranth

Thursday, May 24th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Palmer amaranth was seen in a number of locations in DE and MD eastern shore last summer. We found fields near Dover and throughout Sussex County with Palmer amaranth infestations. We talked about this plant at most of our winter meetings. It looks much like smooth or redroot pigweed early in its growth. The link below will show you some bulletins on how best to identify Palmer amaranth, but the watermark is very diagnostic. However, many plants never develop these ā€œVā€ markings on the leaves.

http://agdev.anr.udel.edu/weeklycropupdate/?p=3146

This species needs to be taken very seriously; it can overwhelm a field in a few years. It is a species that has developed resistance to glyphosate very quickly and once that happens, it will make control very difficult. (If you think glyphosate-resistant marestail has been a headache; Palmer amaranth is much worse.)

Palmer amaranth grows very rapidly, which means you have only a few days to make postemergence herbicide decisions and get the field treated. Without effective control, Palmer amaranth will grow 5 to 6 feet tall. If you know you have Palmer amaranth, or you suspect you might have it, do not rely on glyphosate alone for postemergence control. Options for corn include HPPD-inhibiting herbicides (Group 27, Callisto, Impact, or Laudis); ALS-inhibiting herbicides (Group 2, Resolve, Steadfast, Permit Plus, Capreno, plus many others); and plant growth regulators (Group 4, such as Status).

Postemergence options in soybeans include PPO-inhibiting herbicide (Group 14, Reflex) and ALS-inhibiting herbicides (Group 2, FirstRate, Pursuit, Classic, etc).

We had a number of reports of poor performance with glyphosate last year for Palmer amaranth control, and so tankmixes will be essential for resistance management. Most of these postemergence options need to be applied to Palmer amaranth before Palmer amaranth plants are 4 inches tall.

Palmer Amaranth is in the Area

Friday, June 3rd, 2011

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Last year I saw a few fields in the area (Delaware and Maryland) with infestations of Palmer amaranth. Palmer amaranth is a pigweed, which looks similar to the smooth pigweed that is so common (and often called redroot). However, Palmer amaranth is a very aggressive species that grows very rapidly. It is native to the southwest region of the US, and does better than most plants under dry conditions. Palmer amaranth has been described as pigweeds on steroids because of its ability to grow very rapidly, get very tall, and be very competitive with crops. Palmer amaranth is found throughout the southern US and is moving northward. Palmer amaranth is not as sensitive to Group 2 herbicides as smooth or redroot pigweed (this includes Pursuit, Sandea, Accent, Matrix, etc.). It is sensitive to PPO herbicides (Reflex, Valor, etc); atrazine, and HPPD (Callisto, Impact, and Laudis. Furthermore, glyphosate-resistant Palmer amaranth is present in Georgia, North and South Carolina and other southern states. I am not aware of any herbicide-resistant Palmer amaranth in our area.

It is critical that you control plants early; and that you do not allow the plants to produce flowers. Plants will produce a very high number of seeds that will quickly infest fields. In the southern cotton growing regions where they have herbicide-resistant Palmer amaranth, they have had to resort to hand weeding.

To help identify Palmer amaranth, see the chart, websites, and photos below.

Characteristics Redroot Pigweed Smooth Pigweed Palmer Amaranth
Stem hairs Hairy Hairy No hairs
Stems Often ridges running length of stem Often ridges running length of stem Mostly smooth
Leaf petioles Petioles no longer than length of the leaf Petioles no longer than length of the leaf Long drooping petioles
Seed head Short, stout, prickly Long, slender, slightly prickly Very long, thick, very prickly

A couple of good publications include:

http://mulch.cropsoil.uga.edu/weedsci/HomepageFiles/PalmerBiologyEcology.pdf
http://www.extension.iastate.edu/Publications/PM1786.pdf
http://www.ksre.ksu.edu/library/crpsl2/s80.pdf

 

Smooth pigweed

 

Palmer amaranth

 

Palmer Amaranth is in the Area

Friday, September 10th, 2010

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

I have seen a few fields in the area (Delaware and Maryland) with infestations of Palmer amaranth. Palmer amaranth is related to pigweed, and early in the year they look very much alike. However, at this time of the year, the seedheads look very different. Palmer amaranth has been described as pigweeds on steroids because of its ability to grow very rapidly, get very tall, and be very competitive with crops. Palmer amaranth is found throughout the southern US and is moving northward. Palmer amaranth is not as sensitive to Group 2 herbicides as smooth or redroot pigweed (this includes Pursuit, Sandea, Accent, Matrix etc). Furthermore, glyphosate-resistant Palmer amaranth is present in Georgia, North and South Carolina and other southern states. I am not aware of any herbicide-resistant Palmer amaranth in our area.

My article last week was about cleaning equipment before moving to the next field and it certainly pertains to this species. If you suspect you might have Palmer amaranth, do not spread it from field to field.

Characteristics Redroot Pigweed Smooth Pigweed Palmer Amaranth
Stem hairs Hairy Hairy No hairs
Stems Often ridges running length of stem Often ridges running length of stem Mostly smooth
Leaf petioles Petioles no longer than length of the leaf Petioles no longer than length of the leaf Long drooping petioles
Seed head Short, stout, prickly Long, slender, slightly prickly Very long, thick, very prickly

A couple of good publications include:
http://www.extension.iastate.edu/Publications/PM1786.pdf
http://www.ksre.ksu.edu/library/crpsl2/s80.pdf

Smooth pigweed

Palmer amaranth