PPDL Picture of the Week
March 5, 2018
Joe Ikley, Weed Science Program Specialist, Department of Botany and Plant
Pathology, Purdue University
Even though the calendar still says
it is winter, our spring growing season is just around the corner. One of our
top weeds we battle in corn and soybean across Indiana is waterhemp (Amaranthus tuberculatus (= A. rudis)).
This plant is one of our most problematic weeds in the pigweed (Amaranthus) family. Other weedy species
in this family that we find in Indiana are Palmer amaranth, redroot pigweed,
and spiny amaranth.
Waterhemp can begin germinating in
early to mid-April across most of Indiana, and will also germinate well into
September. During the growing season, waterhemp can also grow as fast as 1 inch
per day. Waterhemp is a dioecious summer annual weed that is also a prolific
seed producer. In direct competition with soybean, an individual female plant
can produce upwards of 200,000 seed per plant. Larger plants without
competition, such as those that can thrive in drowned-out areas of a field, can
produce 1,000,000 seed per plant. Due to high seed production, a few escaped
plants per acre can turn into a major weed problem in the future.
Waterhemp is known to be
resistant to multiple herbicide modes of action. In Indiana, we have known
populations with resistance to glyphosate (group 9), ALS-inhibiting (group 2)
herbicides, and PPO-inhibiting (group 14) herbicides. Several populations have
resistance to all three modes of action within individual plants. Populations
with this stacked resistance are difficult to control in soybean, and will
require a trait other than Roundup Ready or non-GMO soybean for postemergence
control. This summer Purdue Weed Science will once again be offering herbicide-resistance
screening for waterhemp plants across Indiana.
More information on biology and
management of waterhemp can be found on the Take Action waterhemp factsheet: http://iwilltakeaction.com/uploads/files/54403-01-ta-factsheet-waterhemp-update-lr_1.pdf