Thursday, October 23, 2014
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Palmer Amaranth infestation deserves your attention

The plant looks deceptively similar to pigweed and waterhemp. Here's how you can correctly identify if it's affecting your farm so that you can address it.


Posted on May 8, 2014 at 4:51 p.m.

If you farm in Elkhart County, you probably know that Palmer amaranth was found in several locations last summer. Now that we know it is here, we cannot let our guard down. This weed is one that can take over your farm, and it deserves your attention.

It is safe to say we have Palmer in several areas of the county now. Plants were discovered around Goshen, Middlebury, Millersburg and Wakarusa last summer. Fortunately, there were few plants to be found in all the locations, but at 100,000 to 500,000 seeds per plant, it will not take long to spread.

The first step to managing Palmer amaranth (or any weed) is to know what it looks like. It is easy to misidentify Palmer amaranth because it looks similar to three other common amaranth species: redroot pigweed (Amaranthus retroflexus), smooth pigweed (Amaranthus hybridus), and common waterhemp (Amaranthus rudis). The resemblance is especially strong during the seedling stages of growth.

All too often, the amaranths are all called “pigweed” and not identified properly by species. The populations in northwest Indiana were misidentified as waterhemp for at least two or three years and were not managed as aggressively as the situation demanded.

The old saying “a picture is worth a thousand words” comes to mind when we talk about identifying this weed. Purdue has a publication called WS-51 Biology, Identification and Management of Palmer Amaranth. The pictures are excellent, showing comparisons with waterhemp, redroot pigweed and Palmer amaranth side by side at early growth stages. It is available free online. It would be an excellent paper to print and carry in your pickup truck. We also have copies at the extension office for those without computers.

Another suggested reference is the Purdue Corn and Soybean Field Guide, ID-179, which can ride on the dash of your truck. It contains pictures of many weeds, diseases and insects, fertilizer and pesticide recommendations, and much more in a handy pocket size guide. The guide sells for $8 and is available through extension offices.

Be sure to watch the margins of the field, along ditches and fence rows for signs of the weed. Fields where dairy manure has been applied may have a higher chance of Palmer growing there, because cottonseed meal imported from the southern U.S. is believed to be the source of most of our Palmer infestation.

If you have not spoken to your pesticide dealer about adjusting your herbicide program, you should. Whether you have discovered Palmer on your property or not, herbicide programs need to adapt to this new challenge as soon as possible. The approach weed control experts are recommending is to use several herbicides that attack the weeds at different sites and in different ways. The days of simple herbicide programs are fading away quickly.

Jeff Burbrink is an Extension educator in agriculture and natural resources. Write to him at 17746 E. C.R. 34, Goshen, IN 46528; call 533-0554; or fax 533-0254.


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