Palmer amaranth grows rapidly and seeds quickly, making it
difficult for farmers to control. (Superior Ag Resources/Tom
WEST LAFAYETTE, Ind. - Palmer amaranth now has
been confirmed in 17 Indiana counties and is no longer confined to
the northwestern part of the state.
Palmer amaranth grows quickly and creates seeds very rapidly,
making it hard for farmers to control. Populations earlier were
found in the northwestern counties of LaPorte, Newton, Jasper,
Pulaski and Cass. Since then, more have been confirmed in Benton,
Porter, St. Joseph and White counties in that part of the state,
Adams, Kosciusko, Huntington and Noble counties in other northern
areas, Henry in the east-central, Clay in the west, and Posey and
Vanderburgh in the extreme southwest.
"Palmer amaranth is potentially the most aggressive agronomic
weed Indiana producers have ever dealt with and must be managed with
an aggressive control program," said Bill Johnson, Purdue Extension
weed scientist. "Seed bank populations will increase quickly in
fields where Palmer amaranth is not correctly identified or managed,
leading to several years of expensive control programs."
Identifying this weed can be tricky because it closely resembles
three other common amaranth species: redroot pigweed, smooth pigweed
and common waterhemp. They can be differentiated by the presence or
lack of hair, leaf shape, petiole length, apical meristem growth
pattern, seed head structures and the leaf blade watermark.
Identifying characteristics of Palmer amaranth:
* No hair.
* Leaves are wide and ovate to diamond-shaped.
* Petioles, stemlike structures that connect the leaf blade to
the main stem, are as long or longer than the leaf blade itself.
* The apical meristem grows to capture as much light as possible,
resulting in a rosette-like appearance when looking directly down to
the top of the plant.
* Females have a long main terminal seed head that can reach up
to 3 feet long.
If growers identify what they believe to be Palmer amaranth in
their fields, they should report it to Johnson at 765-494-4656, email@example.com, or Travis Legleiter
at 765-496-2121, firstname.lastname@example.org.
The best method of control, Johnson said, is a multistage
approach of crop rotation, thorough tillage, full rates of
pre-emergence residual and post-emergence herbicides, hand weeding
and monitoring ditches and field borders, and cleaning equipment
before moving from infested to non-infested fields.
Many herbicides are labeled for Palmer amaranth control in corn,
and growing corn for a few years consecutively might be the best
option for growers who don't want to invest in expensive soybean
This far along in the growing season, Legleiter said the best bet
for farmers who find Palmer amaranth in their fields is to see if
specific herbicides are allowed in reproductive-stage soybeans and
to hand-remove escapes to prevent seed production. Herbicides are
available for treating the plant in ditches and fencerows.
More information is available in Johnson and Legleiter's
publication, Palmer Amaranth Biology, Identification, and
Management, available for free download from Purdue Extension's The
Education Store at http://www.the-education-store.com/. Search for
For Palmer amaranth updates, visit Purdue Extension's Pest and
Crop Newsletter at http://extension.entm.purdue.edu/pestcrop/index.html.