Ironweed can become a significant agricultural pest in areas with limited soil disturbance.

July 6, 2022

3 Min Read
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July is the time for questions about ironweed, which is a common native perennial plant from the aster (daisy) family readily found in the Ohio and Mississippi valleys. It grows from three feet up to ten feet tall, depending on the specific species (of which there are seventeen in North America). It generally bears clusters of purple to magenta flowers at the peak of the plant’s stalk that are highly attractive to many pollinators.

I am anticipating that you’re already thinking something like – “What! It’s native!? But it is so awful. I have got to do something about it in my pastures.”

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It is true that ironweed can become a significant agricultural pest in areas with limited soil disturbance. It is especially displeasing to pasture managers that see it as an eyesore in the pasture mix, towering above the grasses and legumes that most livestock prefer to graze. Ironweed typically gets a start in overgrazed pastures or other disturbed land where open soil allows for seed deposition, germination, and reemergence in the following years.

When ironweed seedlings emerge it can be difficult to tell the difference between it and other common asters such as marestail, Joe-Pye weed, goldenrod, and fleabane. The good news is that all of these asters are pretty responsive to the same controls. The best of which is probably implementing a rotational grazing system with a mixture of livestock species.

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Strategic mowing a couple times a year to prevent seed production can be helpful. Tillage can break up the current root system but may also stir up additional weed seed in the soil bank. Herbicides containing clopyralid, 2,4-D, triclopyr, and/or glyphosate are generally effective either as broadcast sprays, targeted sprays, or through contact with a weed wiper.

Weed wipers are very helpful on flat ground where the implement can be easily pulled through the field at a height above the desirable forage so that only the plants above the forage canopy come in contact with the herbicide-soaked sponge. It is typical for weed wipers to limit herbicide use to one predetermined product because of how difficult it is to remove herbicide residue from the device. Weed wipers can be purchased, rented, or built for a reasonable price.

Targeted grazing can also be employed. Although these plants may not be the first preference for grazing selections, small ruminants including sheep, goats, and deer will often eat seedlings or strip the leaves off the tall stalks.

While ironweed is an easy to spot plant the competes with desired crops for resources, it is less concerning than many of the other weeds we have previously described. It is native and does have pollinator value, so if you have plenty of forage for animals to eat and don’t mind how it looks, you could choose to do nothing about it guilt-free. But odds are if you have ironweed growing vibrantly, you probably have additional weeds sharing the space that do warrant control.

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When you notice that ironweed is coming on strong, go out, take a walk, and scout for other more problematic weeds like horsenettle and cocklebur that may be hiding below the canopy. Next week we will discuss the frustration those prickly weeds can cause.

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