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Season Isn't Over for Palmer Amaranth Growth Yet

Season Isn't Over for Palmer Amaranth Growth Yet
Plant can continue producing seeds as long as growing season lasts.

Things are beginning to wind down in your crop fields as far as corn and soybeans go. Crops may not be mature as you like, but they're headed in that direction. Unfortunately, if you're unlucky enough to have Palmer amaranth, the vicious weed that has invaded parts of Indiana from the deep South, the growing season is still trucking along.

Purdue University weed researcher and student Doug Spaunhorst says that Palmer amaranth can germinate virtually all season long from seeds that are in the ground. A tillage pass typically causes a flush of Palmer amaranth to germinate a day or two later if seeds are in the soil.

Related: A Week Can Make a Huge Difference in Palmer Amaranth Growth

Ready to produce: The seedhead doesn't wait until its full size on Palmer amaranth before it begins producing seed.

One unique characteristic of this weed is that it can continue to germinate late into the growing season. Within only a little over 30 days, depending upon growing conditions, it can begin producing seedheads. Even if the seedheads are fairly short, say only a few inches long, it can produce seeds that mature and are viable to produce more plants.

Only female plants produce seed. There are also male plants. But enough seed is produced to help the weed proliferate quickly.

In Purdue research plots near Twelve Mile Indiana, located directly across from a large dairy, Palmer amaranth stands are thick in control plots where no weed control was used. Stands are less dense where herbicides were applied, and virtually missing on plots where the most effective treatment was applied.

Related: Farmers Still Battling Palmer Amaranth

That's typically a residual herbicide program. If you're going to control them once they're up, you must get your shot at them before they're four inches tall. Otherwise the Purdue researchers have found that they're very hard, if not impossible, to bring down with herbicides. At that point hand weeding is about the only effective way to remove them from the field.

Speculation is that the infestation around the dairy started when seeds came north in feedstuffs, likely cottonseed meal, and were spread on the fields with manure.


In the coffee shop, it is known as Palmer pigweed. In university circles, it is referred to as Palmer amaranth. Whatever you want to call it, this weed is the No. 1 weed to watch. Stay on top of your control plan with our new free report, Palmer Amaranth: Understanding the Profit Siphon in your Field.


TAGS: Soybeans
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