How to Identify a Palmer Amaranth Seedling
By Emily Unglesbee, DTN Staff Reporter
ROCKVILLE, Md. (DTN) — We’ve all seen them — the startling pictures of giant Palmer amaranth plants towering over soybean fields, with their long, spiky seed heads jutting toward the sky.
But by the time you find that monster in your fields, it’s too late to control it. The coming weeks are prime time for spotting Palmer amaranth plants when they are still small enough to kill and stop an infestation.
The problem is Palmer amaranth seedlings can look an awful lot like other plant species, particularly waterhemp and other types of pigweed.
North Dakota State University Extension weed scientist Joe Ikley has some tips on how to distinguish this weed — which may be new to many in the Midwest — early in the season.
1. THE TOOLS TO HAVE
The magic numbers for weed control are 4 to 6 inches. Weeds bigger than this are harder to kill and more likely to survive a herbicide application. Keep in mind that Palmer amaranth is an especially aggressive weed capable of growing 1 to 3 inches in a single day, depending on weather conditions.
Fortunately, a lot of common items fall within this size range for easy reference. A soda can is 4 inches tall, most index fingers are 3 to 4 inches in length and hey — how about that smartphone you carry around? It’s probably between 4 to 6 inches in length, Ikley noted.
More importantly for Palmer identification, most smartphones also have cameras that are high enough quality to help you find the tiny differences that separate a Palmer amaranth seedling from its lookalikes, Ikley said. “If you take a focused picture of the pigweed, you can zoom in on the picture and see a lot more,” he explained. “It’s like a little magnifying glass that most people don’t even realize they have in their pocket.”
2. IT’S ALL IN THE HAIR
So you’ve found a suspicious seedling. The first thing to do is see how hairy it is, Ikley said. By the time they are about 2 inches tall, certain pigweed species such as Powell amaranth and redroot or smooth pigweed will sport fine, tiny hairs on their stems, known officially as pubescence. The stems and leaves of Palmer amaranth and waterhemp, however, are smooth and hair-free.
These hairs can be hard to see, especially if your eyes aren’t the sharpest, Ikley admitted. “One trick is to hold the plant up to the light and — especially if the plant is wet — the hairs will stand out better,” he said. If you have a smartphone, try taking a focused photo on your smartphone and zoom in on the stem to spot them, he added.
Finding smooth, hairless stems and leaves effectively rules out other pigweed species — now it’s down to Palmer amaranth and waterhemp.
3. PETIOLE LENGTH
Now it’s time to check the length of the petiole — the narrow, branch-like structure that connects a leaf to the stem.
Look for a seedling with eight to 10 leaves, and pluck one of the oldest, mature leaves near the bottom of the plant, Ikley said.
Fold the petiole over the length of the leaf blade and see how long it is. A waterhemp seedling will have short petioles that will not be longer than the length of the leaf. A Palmer amaranth seedling will have long petioles that will be as long as the leaf, if not longer.
Because of the length of these petioles, as well as their alternating pattern on the stem, most of the leaves of the Palmer seedling are visible when you peer down at them from above, giving the plant a rosette appearance, like a Poinsettia.
4. THE LOOK OF THE LEAF
In general, waterhemp and Palmer amaranth seedlings also have different leaf shapes. Waterhemp leaves tend to be longer and narrower, like little lances. Palmer leaves will be fatter, particularly in the middle, giving them a more oval or diamond shape.
Some Palmer plants also have a white chevron or V-shaped pattern in the middle of the leaf — but not all. So while it can rule out a different pigweed species if present, it is not a definitive identification tool.
In general, there is a lot of genetic diversity among both Palmer and waterhemp plants and even some hybridization between the two, Ikley noted. So treat leaf shape and appearance as a useful but not final indicator of plant species.
5. CHECK THAT NOTCH
The first two or three true leaves on a Palmer amaranth plant often sport a single, stubby hair emerging from the notch at the leaf tip.
Most common waterhemp plants don’t have this, which makes it a generally useful sign of Palmer. But some waterhemp plants have been observed with leaf tip hairs in the Western Corn Belt, and some Palmer plants have been observed without it, Ikley cautioned.
Like leaf shape, use the notch hair to help confirm a Palmer amaranth seedling, but don’t rely on it exclusively. The safest and surest signs of a Palmer amaranth seedling remain smooth, hairless stems and leaves and long petiole length on the first true leaves, Ikley said.
And remember, when in doubt, you can always send a plant sample to a laboratory for official confirmation via molecular analysis.
For more details, as well as helpful pictures and illustrations, see this guide from Purdue University https://www.extension.purdue.edu/, and this guide from North Dakota State University: http://www.dtn.com/
Emily Unglesbee can be reached at Emily.firstname.lastname@example.org
Soil Testing —
Staying Profitable In Today’s Markets
With the challenge to stay profitable in these markets that have settled back in prices, we all need to look for ways we can improve. We need to be more aggressive in managing the largest asset a farmer possesses, our soil. By attending clinics on soils and learning about the tests that you should be performing, you can find large rewards in yield. These tests, done correctly and read correctly, can tell you if lime or tiling is needed. You can also learn if you need to alter your fertilizer application program, as well as timing of applications and the amount you apply per pass.
With today’s technology we can do a lot of this ourselves. There are apps available for your smart phone that allow you to do your own grid sampling. Once you have your samples pulled, deciding what tests are performed is, to me, your most important decision. Make sure you have the tests performed that provide you with all the major nutrients and micronutrients as well as pH, and your cation ratio index. You need to know your soil’s ability to hold fertilizer at any given time, to structure how much and how often you may need to apply fertilizer. Once you have your samples done and your test results back, you can discuss them with your agronomist and develop your plan for each field and crop you are growing that season to get the most out of every seed you have planted. Now, don’t forget, the work is not done yet. Once your crop has emerged, get back out there and scout those fields for stand quality and crop health. Take tissue samples in a timely manner so you can adjust for any shortages in your program. Let the growing plant tell you what it needs.
This is a short overview of what you may already be doing. I hope, if you have not been aggressive in testing, you will step back and take a hard look at what and how you are feeding the growing crop, and the crops you will be producing in the future. Remember, failing to apply the correct nutrient needs could be losing dollars, when it may cost only cents to raise the return on investment. With improved nutrient management also come other rewards. Water and run off pollution is greatly reduced by not being good, but great at your soil and nutrient management.
If you have more questions about soil testing, contact your Kussmaul Seeds dealer.