Species specifics: Marshelder

Fast facts about marshelder

Also known as sumpweed, narrowleaf sumpweed, false ragweed or sulphurweed, marshelder produces a due camphor-like or medicinal odor from its leaves
Marshelder shares some similarities to common ragweed, including its preferred habitat, flower bract appearance and allergy-inducing pollen
Prolific seed producer of high-oil seeds similar in appearance to sunflower seeds
Can be toxic to mid-gestation cows and heifers if consumed in large amounts, potentially leading to premature mammary development, dripping milk and fetal loss

What to look for

Marshelder (Iva annua), also known as sumpweed, narrowleaf sumpweed, false ragweed or sulphurweed due to its camphor-like odor, is a native warm-season annual that can cause toxicity in mid-gestation cows and heifers.

The weed is a robust, branching broadleaf herb that germinates in early spring and grows 2 to 10 feet tall. Green to reddish-brown stems of a marshelder have a rough, sandpaper-like texture and grow in multiples upward from the base. Leaves range from 1 to 6 inches long and are triangular to lanceolate with a rough texture and toothed margins. They grow opposite one another along the stems at the end of long petioles. In the heat of the summer, leaves may droop slightlyand can emit a camphor-like odor.

Similar in appearance to ragweed, greenish-white flowers emerge in mid- to late-summer on crowded long, branching spikes at the tops of stems. Marshelder is wind-pollinated and produces thousands of high-oil seeds, similar to sunflower seeds, that mature by late fall. The pollen generated by marshelder plants is a common human allergen.

While the exact toxin is unknown, cows or heifers in mid-gestation that consume large amounts of sumpweed, especially during its 2- to 8-leaf growth stage, often show adverse reproductive signs, including premature mammary development, dripping milk and, in extreme cases, abortion. However, affected females generally breed back normally after the acute toxicity has run its course. It’s seldom sought out by livestock, but cattle cannot sort through areas of heavy infestation of marshelder and will consume it with other favorable forages interspersed with the weed, or if other forages are limited.

Where it is found

Marshelder favors marshy, seepy areas that tend to hold water in the spring, particularly along the edges of creeks or ponds. It is commonly found in moist soils or disturbed, overgrazed pastures.

As a native plant to southern, southeastern and central United States, it is commonly found in the Great Plains as far north as North Dakota and states along the Mississippi Valley.

How to treat it

Treatment should be made in spring during early development. Apply 16 fluid ounces per acre of DuraCor^® herbicide to plants less than 4 inches tall. Taller, more mature plants require 20 fluid ounces per acre of DuraCor with 1% MSO per volume of water used.

Do not treat once the plant branches.

Under normal field conditions DuraCor® is non-volatile. DuraCor has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with DuraCor to manure and urine from animals that have consumed treated forage. DuraCor is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.