Identify Weeds Early for Best Control in Cereal Grains


Before cereal growers can target weed pests successfully, they need to know their enemy. Weed species and their location and infestation levels in the field are crucial facts to have. 

That means scouting early in the year as the weeds first emerge or come out of winter dormancy, experts advise. It also means being able to identify specific weeds when they are small, and, unfortunately, quite often hard to tell apart. 

“Weed identification is key to being able to control weeds,” says Kevin Thorsness, Bayer crop protection technical representative and one of the Cereal Experts with Bayer. “You have to know what you're dealing with in order to choose the best herbicide to control those weeds, and identifying them early is important.”  

He lists two key reasons: No. 1 is to control the weeds when they're small, and No. 2 is to plan your herbicide program and “give yourself or your commercial applicator some lead time to get in the field and make that timely application.” 

Keep Weed ID Skills Current 

Brian Jenks, a weed scientist with North Dakota State University based in Minot, North Dakota, conducts training each spring to help farmers and agronomists identify weeds accurately, even when they are only 1 to 3 inches tall. Because several weed seedlings look so much alike at that stage, he advises everyone to review the basics of weed species ID in their area to reduce the chance of misidentifying – and possibly not controlling – yield-robbing weed pests.  

Many university and Extension experts offer such training as well as weed identification tools such as web-based and smartphone apps, online photo galleries and printed weed guides. The Integrated Weed Management Resource Center program led by the USDA Agricultural Research Service, recently renamed “GROW” (Getting Rid of Weeds), has links to many such resources here. (Bayer CropScience has just started a 5-year research collaboration with the GROW network of scientists to evaluate and demonstrate the on-the-farm economic value of integrating non-chemical weed management practices with herbicides to combat resistant weeds.) 

 

Learn to ID These Look-alike Weeds

While Jenks’ weed ID training slides include at least 50 weeds, he points out these examples of important look-alikes found in cereal fields, with tips of how to tell them apart: 

Kochia vs. Horseweed/Marestail

Kochia is an exceptionally competitive weed, and a few uncontrolled plants can cause severe yield losses. Growers need to be particularly vigilant in identifying it and treating it before it reaches 3 inches in height, Jenks says, hence the need to tell the difference between kochia and horseweed (marestail) seedlings. Thorsness agrees that kochia requires early and effective chemical control, ideally with herbicides with multiple modes of action, such as Huskie® FX herbicide with its three modes of action with activity on kochia.   

Kochia weed coming out of dirt/soil

Kochia 

Emerges early in spring, first true leaves are long and narrow, very hairy, especially on margins and gray/green color.

Marestail weed coming out of dirt/soil

Horseweed/Marestail

Emerges in the fall, overwinters as rosette, oval, young leaves egg-shaped, very hairy, and sparsely toothed margins (little notches).

Redroot Pigweed vs. Waterhemp vs. Palmer Amaranth 

The aggressive pigweed Palmer amaranth is making its way north into the Northern Great Plains, quickly becoming one of the most difficult to control (and noxious) weeds in croplands. It can grow 2 to 3 inches a day and produce from 100,000 to more than 500,000 seeds on a single plant. Both it and tall waterhemp have developed resistance to multiple classes of herbicides. 

Jenks says the pigweed species look a lot alike when they're small, “and are quite difficult to distinguish in the very small cotyledon stage. As they get a little bit bigger, one of the things we look for with Palmer amaranth and waterhemp is they do not have any hair on the leaves or stems, whereas redroot pigweed is quite hairy.” As Palmer amaranth grows, it distinguishes itself from waterhemp by having petioles (the branch-like structure connecting leaf to stem) that tend to be longer than the leaf blade, he says. Waterhemp seedling petioles are much shorter than the blade. Also, waterhemp leaf blades tend to be quite narrow, like little lances, while Palmer amaranth leaves are wider in the middle. 

Redroot Pigweed, a summer annual broadleaf plant

Redroot Pigweed

First true leaves are rounded with a small notch at the leaf tip; alternate leaf underside generally red, and has fine, tiny hairs.

field of Water Hemp weeds

Waterhemp

Leaves more lance-shaped, much smaller notch at end; egg-shaped to linear, green to reddish in color & upper stem is smooth and hairless.

Palmer Amaranth, annual broadleaf weed, in dirt/soil

Palmer Amaranth

Narrower and longer than waterhemp, green to reddish upper surface, red tint underneath, upper stem smooth and hairless. First true leaves wider in middle (oval or diamond shaped)

Wild Oat vs. Yellow Foxtail vs. Green foxtail

Three grassy weeds in cereal crops – wild oat, yellow and green foxtail – should be identified and controlled at two- to three-leaf stage for wild oat and at three-leaf to early tiller foxtail stage, Jenks says. Thorsness of Bayer says being able to identify them matters, because different herbicides have varying levels of activity on these grassy weeds, particularly between green and yellow foxtail. Huskie® Complete herbicide from Bayer, however, does control all three of these weeds when applied early, Jenks says, “and has given us good control of some of these green foxtail and wild oat populations that are resistant to the Group 1 herbicides.” 

Wild Oat, a summer annual grass, in dirt/soil

Wild Oat

The ligule – the thin outgrowth where the leaf blade connects to the sheath – is membranous (resembling cellophane) and relatively tall in wild oat. A few long hairs stick straight out on margin of base of the leaf blade & its stem is round.

Yellow Foxtail, a summer annual grass

Yellow Foxtail

Ligule is a short fringe of hairs. There are long silky hairs at the base of leaf and has a flat stem.

Green Foxtail weed in grass

Green Foxtail

Ligule is a short fringe of hairs, like yellow foxtail. There is no tuft of hairs at base of leaf and has a round stem.

For more information on wheat disease control options from Bayer, please contact your local Bayer Cereal Expert or visit CerealExperts.com



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