Weeds to Watch Out For

It’s time to get up close and personal to know the super weeds invading your fields.

“Super weeds” are becoming increasingly more widespread within Illinois and many of us in the agriculture industry are quite aware of their presence. These weeds typically are resistant not only to glyphosate, but also to other herbicides, making them even more challenging. Some may be resistant to two, three or even four different chemistries. By identifying these so-called super weeds early in the season we can develop a positive plan of attack to control them.

Pigweed species 

Redroot/Smooth pigweed:

• Round to oval leaves with the apex towards the middle
• Fine hairs on the stem, especially towards the newest growth
• Rough leaf surface

Waterhemp:

• Long lanceolate leaves
• No hair
• Waxy leaf surface

Powell amaranth:

• Compact seed head
• Prickly seed head

Palmer amaranth:

• Ovate to diamond leaves with the apex towards the petiole
• No hair
• Long petioles, often longer than the leaf and a rosette pattern
• Sometimes a small notch in the leaf tip
• Grow 2 to 3 inches per day
• 1,000,0000 seeds per plant
• Prickly seed head
• Leaves have a white or purple watermark

Other Species

Horseweed or marestail:

• Winter annual
• Alternating leaves
• Plant forms a basal rosette in the fall for winter survival
• Hairs on leaf margins
• Slightly lobed leaves
• Erect stems and unbranched
• White ray flowers and yellow disk flowers centered in the white ray flowers

Giant ragweed:

• Emerge in late March
• Spoon-shaped cotyledons which are fairly large ─ 3/8 to 5/8 inch wide, 1 to 1¾ inch long and 1/16 inch thick
• The first true leaves are entire and ovate with deep lobes
• Leaves are opposite with stiff hairs that point toward the tip
• Usually have three distinct lobes, but could have five
• Can reach 17 feet in height

Lambsquarters:

• Cotyledons are oblong, narrow and linear with no midvein
• Dull gray to green cast
• The first one or two pairs are opposite, while the rest are alternate
• Lower leaves have a petiole and irregular wavy toothed margins

Dawn Kielsmeier is an agronomy sales specialist with Pearl City Elevator in Baileyville, Ill. She has a B.S. in dairy science and an M.S. in agronomy, both from the University of Illinois and has been a CCA since 1993. She is a 2017 Illinois Soybean Association CCA Soy Envoy.