November Weed of the Month: Palmer Amaranth

November’s Weed of the Month is Palmer amaranth (Amaranthus palmeri). This fast growing weed has developed resistance to multiple herbicide modes of action so it is difficult to control. Palmer amaranth produces a lot of seed, up to 250,000 per plant, and is highly competitive. It spreads quickly and will cause extensive corn and soybean crop losses.

Palmer amaranth is native to the arid southwestern United States and northwestern Mexico. It was accidentally introduced to the southeastern United States and became the most troublesome weed in cotton production, by far. It developed resistance to many herbicides with multiple modes of action and spread to row crop fields in much of the eastern half of the country. This dreaded weed was discovered in Minnesota in 2016.

Palmer Amaranth weeds

Palmer amaranth plant with seed spikes. (photo provided by the Minnesota Department of Agriculture.)

Palmer amaranth can be distinguished from closely related waterhemp and other pigweeds by a long petiole length and very tall flower and seed spikes. Unlike other pigweeds, Palmer petioles are often longer than the leaf blades. A petiole attaches a leaf to a stem. The flowering spike is much longer than that of other pigweeds. Leaves of some Palmer plants have a whitish V-shaped mark on them. Palmer amaranth is a summer annual that commonly reaches heights of 6-8 feet but can reach 10 feet.

If you find this plant, please report immediately by calling the Arrest the Pest at 888-545-6684 or emailing arrest.the.pest@state.mn.us.

Palmer amaranth detected in Minnesota

 ST. PAUL, Minn. – Crop scientists at the University of Minnesota and officials at the Minnesota Department of Agriculture (MDA) urge farmers to check fields for Palmer amaranth, an aggressive weed that can put corn and soybean crops at risk. A plant detected in a native seed planting plot on a Yellow Medicine County farm was confirmed today to be Palmer amaranth. This is the first confirmation of the weed in the state.

The MDA asks possible infestations to be reported by contacting the MDA’s Arrest the Pest line by phone at 1-888-545-6684 or by email at arrest.the.pest@state.mn.us. Landowners are encouraged to email photos of suspected infestations for identification.

“We encourage landowners to scout fields now before harvest for Palmer amaranth and report any possible infestations to the Minnesota Department of Agriculture,” said Geir Friisoe, MDA’s Director of Plant Protection. “The quicker we’re able to identify and start managing this weed, the better our chances will be to minimize the impact to our ag industry.”

Palmer amaranth

Palmer Amaranth has been found in Minnesota and the Department of Agriculture wants farmers to keep an eye on their fields to help nip this in the bud before an infestation can occur. (Photo by Bruce Potter)

 

Palmer amaranth can grow 2 to 3 inches a day, typically reaching 6 to 8 feet, or more, in height. Left uncontrolled, a single female Palmer amaranth plant typically produces 100,000 to 500,000 seeds. It is resistant to multiple herbicides.

It has been found in 28 other states, including Iowa, South Dakota, and Wisconsin.

“Palmer amaranth infestations have caused substantial yield losses and greatly increased weed management costs in cotton, soybeans, and corn in the southern states,” said Extension agronomist and crops leader Jeff Gunsolus. “This is a disconcerting, though not completely unexpected, discovery in Minnesota. We have been discussing proper identification procedures with crop consultants over the last three or more years.”

Close-up of Palmer amaranth

Palmer Amaranth has been found in Minnesota fields and it’s important for farmers to watch their fields in order to avoid an outbreak in farm fields across the state. (Photo by Bruce Potter)

 

Extension and MDA officials commend the grower and crop consultant who quickly contacted Extension after discovering a suspected Palmer amaranth plant. The weed is on MDA’s prohibited-eradicated noxious weed list, requiring all above- and below-ground parts of the plant be destroyed. Transportation, propagation or sale of the plants is prohibited.

MDA and Extension continue coordinating action steps to address the weed.

The MDA is investigating how the weed may have been introduced to the state.

In August, an Extension blog updated steps for both prevention and management at z.umn.edu/palamthbknd.

Further information is available at z.umn.edu/MDAPalmerAmaranth.

Feb weed of the month hits gardens hard

February’s Weed of the Month is about the poisonous ornamental plants that may be found growing in Minnesota community gardens. Some poisonous plants commonly grown in gardens have specific parts which are safe to eat (like tomatoes or other nightshades), while other plants are entirely poisonous. We will focus on plants which are wholly poisonous. The most common of these in Minnesota are castor bean, jimsonweed or Datura, and foxglove.

Weeds in gardens

The castor bean plant is an African transplant into Minnesota whose seeds contains ricin, an incredibly toxic compound. Be careful to avoid accidental ingestion. (contributed photo)

Castor bean plant, or castor oil plant, (Ricinus communis) is native to Africa and occasionally grown for medicinal and ornamental purposes in Minnesota. It has become naturalized in tropical and subtropical regions throughout the world, such as California. In Minnesota, it is a robust annual, growing to heights of 6- 15 feet. It has large, colorful, palmate leaves and pink or red flowers found along its stalks, which become soft, spiky, fruit-containing balls. The seeds contain ricin, an incredibly toxic compound which can be deadly if ingested. Ricin also occurs in lesser amounts in tissue throughout the plant. The seeds of this plant are so poisonous, it is said that ingestion of a single seed can kill a child. For this reason, castor bean should not be planted in any area that might be accessed by children, such as a community garden.

 

Weeds in gardens

Jimsonweed is an annual ornamental plant occasionally grown in Minnesota. All parts of the plant, including seeds, contain alkaloids, which are toxic when ingested. (contributed photo)

Jimsonweed (Datura stramonium) is an annual ornamental plant in the Nightshade family occasionally found growing in Minnesota. It grows to a height of two to four feet and has long, trumpet-shaped, white to lavender blooms which extend above the leaf canopy, and distinctive, spiky, ball-shaped fruit. All parts of this plant, including the seeds, contain alkaloids which are toxic when ingested. If the plant were to go to seed, it could spread seedlings around a garden, which could then become intermixed with crops and accidentally ingested. Jimsonweed historically has been used as a recreational drug, occasionally resulting in overdose and death. The potential for accidental or intentional poisoning is high enough that it is advisable to prohibit these plants from growing in a garden alongside edible crops.

Weeds in Gardens

Foxglove is occasionally planted in Minnesota for ornamental purposes, but the entire plant is extremely toxic if ingested. It’s also a self-feeder, and can become extremely invasive if left unchecked. (contributed photo)

Foxglove (Digitalis purpurea) is a popular biennial ornamental plant. The foliage begins as a basal rosette in the first year. In the second year, it sends up long stalks which grow up to five feet tall and are lined with trumpet-shaped flowers. Many varieties are available, with flower colors ranging from white to pink to yellow. It is commonly grown to attract pollinators like bumblebees and hummingbirds. The entire plant is extremely toxic. Intentional ingestion can occur by individuals seeking medicinal folk-remedies and accidental ingestion by confusing foxglove with other edible herbs or by curious children. Foxglove is also prolific self-seeder and can become an aggressive invasive weed.

The best way to prevent issues with these plants is not to plant them in the first place, or strictly limit them. These plants, and all poisonous plants, should be prohibited from any community garden. They should not be planted anywhere where children might encounter them or close to any edible crops. Please contact Minnesota Poison Control with any concerns about potential human poisoning at 800-222-1222poisonhelp@hcmed.org, or www.mnpoison.org.

MDA Weed of the Month: Brown, Meadow, and Diffuse Knapweeds

December’s Weed of the Month is not one, but three species of knapweed: brown knapweed (Centaurea MDA-logojacea), meadow knapweed (C. x moncktonii), and diffuse knapweed (C. diffusa). All three species are native to Eurasia, and it’s thought they were introduced to western North America for forage. In Minnesota, infestations of meadow knapweed have been reported in St. Louis and Koochiching counties, brown knapweed has been reported in Koochiching County, and diffuse knapweed has been found in Duluth.

Several characteristics of these knapweed species have helped them thrive and become a threat to Minnesota. They outcompete pasture grasses and native plants, leading to large bare patches of soil that is more susceptible to erosion and water runoff. Once established, the knapweeds reduce hay quality and pasture productivity. The plants can also hybridize between species, which makes identification difficult and increases the risk for an aggressive plant that can invade many soil types and growing conditions.

Here’s a look at Brown Knapweed, the December weed of the Month from the Minnesota Department of Ag (photo from www.summit post.org)

Here’s a look at Brown Knapweed, the December weed of the Month from the Minnesota Department of Ag (photo from www.summit post.org)

Knapweeds can be biennial or perennial. They reproduce primarily by seed, which can be spread with infested hay, on equipment, or by wind and water movement. The flowers are tight clusters of individual flowers called florets. The flower color ranges from pink to white. The plants produce a rosette of leaves, which then sends up a flowering stalk in the summer.

To prevent the knapweeds from further spreading throughout Minnesota, several management strategies are available.

  • Make sure to clean equipment, vehicles, and footwear after being in a knapweed infested area.
  • A combination of hand-pulling and digging is an option for small infestations.
    Here’s a look at meadow knapweed, another invasive species seen in farm fields around Minnesota (Photo from unioncountyweedcontrol.org)

    Here’s a look at meadow knapweed, another invasive species seen in farm fields around Minnesota (Photo from unioncountyweedcontrol.org)

    Seedlings are tap-rooted and can be hand-pulled; however, the large taproots must be removed or the plant will regenerate from the root.

  • Herbicides are a very effective management tool for meadow knapweed. For specific herbicide recommendations, contact your University of Minnesota Regional Extension Educator.
  • Mowing does not control meadow knapweed and the mower may spread seed.
  • All infestations must be monitored and treated until the seedbank is depleted.

To report infestations of these species of knapweeds or any other noxious weeds on the eradicate list,

please use the Early Detection and Distribution MAPping System at www.eddmaps.org.