Time Application Of Postemergence Herbicides

Properly timing the application of postemergence herbicides is critical, said Aaron Hager, University of Illinois Extension weed specialist. Recent precipitation, coupled with warm temperatures, will result in rapid growth of emerged weeds and possible reductions in corn yield if weeds persist too long.

“Unfortunately, it’s not possible to accurately predict the specific day after planting or emergence when weed interference begins to reduce corn yield,” Hager said. “This interval is influenced by many factors, and can vary based upon the weed spectrum, density of certain species, available soil moisture, etc.”

Weed scientists generally suggest an interval, based either upon weed size (in inches) or days after crop/weed emergence, during which postemergence herbicides should be applied to avoid crop yield loss via weed interference. In corn it is often recommended to remove weeds before they exceed about 2 inches tall. The longer weeds are allowed to remain with the crop the greater the likelihood of crop yield loss, Hager said.

“It’s important to remember that the labels of most postemergence corn herbicides allow applications at various crop growth stages, but almost all product labels indicate a maximum growth stage beyond which broadcast applications should not be made, and a few even a state minimum growth stage before which applications should not be made,” he said.

These growth stages are usually indicated as a particular plant height or leaf stage or both. For product labels that indicate a specific corn height and growth state, Hager advises growers to follow the more restrictive of the two.

“Application restrictions exist for several reasons, but of particular importance is the increased likelihood of crop injury if applications are made outside a specified growth stage or range,” he said.

Corn plant height is commonly used on many herbicide labels, but plant height may not always provide an accurate indication of the plant’s true physiological maturity. Hager said determining plant height may seem relatively straightforward, but using different benchmarks for measurement can lead to different plant heights.

“Generally, corn plant height is determined by measuring from the soil surface to the arch of the uppermost leaf that is at least 50 percent emerged from the whorl,” he said. “Be sure to measure several plants in a given field and average the numbers. Plant height is obviously influenced by many factors, including genetics and the growing environment. Adverse environmental conditions, such as cool air/soil temperatures, hail, etc., can greatly retard plant height and result in corn plants that are physiologically older than their height suggests.”

Many agronomists agree that leaf number is a more accurate measurement of corn developmental stage. Counting leaves and counting leaf collars are the two primary techniques used. Leaf counting begins with the short first leaf (the one with a rounded tip) and ends with the leaf that is at least 40 to 50 percent emerged from the whorl.

Counting leaf collars also begins with the short first leaf, but includes only leaves with a visible collar (the light-colored band where the leaf joins the stem). Leaves in the whorl or those without a fully developed collar are not counted. The leaf collar method quite often stages a corn plant at one leaf less than the leaf counting method, he said.

(Source: Illinois Ag Connection)

Leave a Reply

One comment on “Time Application Of Postemergence Herbicides

  1. Yes I am just a small time truck patch farmer in which I grow produce for the public and the family's. I live near the Tenneesse River, I do grow sweet corn and feild corn. My problem is a lot of grass,because of ground moisture on one end,the lowest end holding moisture,but that end produces so much better corn,espically when the dry times come, but I have found that you can not use just grass killer I mix up for my other produce, like peas,tomatoes,potatoes,brocolie,onions,carrots,watermelons,i.e; so forth.What would you suggest. Thank You;Freddie

Herbicides Stories

Crop InputsEU Glyphosate Controversy Heating Up Yet Again
August 17, 2016
The battle over glyphosate rages on in Europe, creating a lot of question marks over whether the herbicide will continue Read More
Winter Wheat
HerbicidesNew Wheat Herbicide Helps Growers Manage Resistant Weeds
August 2, 2016
Quelex herbicide from Dow AgroSciences is now registered by the U.S. EPA, providing wheat growers a new solution for advanced Read More
Palmer pigweed seedhead in cotton
HerbicidesStudy: Fall Weed Controls Can Make Significant Impact On Glyphosate-Resistant Palmer Amaranth
July 28, 2016
An article published in the latest issue of the journal Weed Science shows that adopting harvest-time and post-harvest weed controls Read More
Palmer pigweed in soybean stubble
HerbicidesSpecial Issue Of Weed Science Explores Human Aspects Of Herbicide Resistance
July 27, 2016
Weeds that evolve resistance to herbicides are a serious threat to global agricultural production. In this Special Issue of Weed Science, Read More
Trending Articles
Corn Field
Eric SfiligojFacing Ag Industry Challenges
September 26, 2016
At the 2016 annual Mid America CropLife Association (MACA) meeting in September, a pair of crop protection company representatives discussed Read More
Bayer Monsanto
Crop InputsBayer-Monsanto Mega-Merger: 6 Things You Need To Know
September 14, 2016
Mega mergers have become almost routine in the agricultural industry. Right on the heels of Monday’s news that fertilizer giants Potash Read More
Potash Corp Agrium
Crop InputsAgrium, Potash Corp To Merge To Create $36 Billion Company
September 12, 2016
Canada’s Agrium Inc. and Potash Corp of Saskatchewan Inc. have agreed to combine in a deal that would create a Read More
Osage Co-op Elevator Osage, IA Finished Building
OpinionAre We Crazy?
September 8, 2016
At some point in the first few months of my employment here at CropLife® magazine, I started getting curious about Read More
ManagementMAGIE 2016 Highlights and Deere Anti-Trust
September 1, 2016
CropLife Editor Eric Sfiligoj discusses the recent Midwest AG Industries Exposition and the Department of Justice’s objection to John Deere Read More
ASMARK 2016 Retailers Live! Tour - CPS
CropLife 100CPS Acquires Texas Retail Operation
August 23, 2016
Crop Production Services (CPS) has acquired the assets of Larry’s Chemical and Spray, Inc., for an undisclosed amount in an Read More
Latest News
Young Corn Field
StewardshipStudy: Ohio Farmers Doing ‘A Good Job Of Managing…
September 27, 2016
Leaders from Ohio’s largest grain farming organizations announced today that Ohio farmers are doing their part in effectively managing phosphorus Read More
Growmark FS Outlet
Industry NewsGROWMARK To Purchase Suncor’s Share Of UPI
September 26, 2016
GROWMARK and Suncor have reached an agreement in which GROWMARK will purchase Suncor’s 50% interest in UPI, Inc. in Ontario, Read More
Corn Field
Eric SfiligojFacing Ag Industry Challenges
September 26, 2016
At the 2016 annual Mid America CropLife Association (MACA) meeting in September, a pair of crop protection company representatives discussed Read More
Syngenta Seedcare Institute
Seed/BiotechSyngenta Opens New North America Seedcare Institute In …
September 23, 2016
Syngenta unveiled its new Seedcare Institute in Stanton, MN, during a recent grand opening celebration. More than 150 industry leaders, Read More
StewardshipMonsanto Invests $1.6 Million In System To Quantify Gre…
September 23, 2016
The USDA – Natural Resources Conservation Service (USDA-NRCS) recently awarded the National Corn Growers Association (NCGA) and its Soil Health Read More
Pipe rack
LegislationCourt Sides With Ag Retailers On PSM
September 23, 2016
The D.C. Court of Appeals has ruled the Occupational Safety and Health Administration violated the Occupational Safety and Health Act when Read More
ManagementPacific Coast Fertilizer Announces Interest In Longview…
September 22, 2016
Pacific Coast Fertilizer LP (PCF) announced at the Cowlitz Economic Development Council board of directors meeting its interest in developing Read More
Young corn plants in soil
UncategorizedCool Planet Raises Additional $9 Million To Commerciali…
September 22, 2016
Cool Planet has announced the first close of a new financing round to commercialize the company’s Cool Terra Engineered Biocarbon Read More
Crop InputsJim Loar Promoted To President And CEO Of Cool Planet
September 22, 2016
In a move that reflects and reinforces the company’s commitment to the agricultural market, the Cool Planet board of directors Read More
BlendersNorth Dakota Coop Debuts Dry Fertilizer Plant
September 22, 2016
North Central Grain Cooperative has begun operations at a new dry fertilizer plant at its Rolla, ND, site. It is Read More
Crop InputsMonsanto, Bayer Officials Defend Proposed $66 Billion M…
September 21, 2016
Top officials for Monsanto and Bayer defended their proposed $66 billion merger before skeptical senators on Tuesday, insisting that the Read More
ManagementUpcoming Shows & Recent Events
September 19, 2016
Editors Paul Schrimpf and Eric Sfiligoj talk about upcoming trade shows and events and review the Mid America CropLife Association Read More
Industry NewsVerdesian Life Sciences Appoints New CEO
September 19, 2016
Verdesian Life Sciences, a plant health and nutrition company, today announced that its board of directors has named Kenneth M. Avery Read More
Corn
Crop InputsEPA Settles With Syngenta For Alleged Multi-Regional Pe…
September 19, 2016
The U.S. EPA has announced a multi-region settlement with Syngenta Crop Protection, LLC (Syngenta) in Greensboro, NC, for alleged violations of Read More
ManagementMerger Mania
September 16, 2016
Editors Paul Schrimpf and Eric Sfiligoj discuss this week’s mega-ag mergers of Bayer and Monsanto and Potash and Agrium. Read More
Monsanto sign
Crop InputsMonsanto Ends Up Being A Bargain For Bayer
September 16, 2016
History will say Bayer got a bargain in its $66 billion purchase of Monsanto, writes David Nicklaus, St. Louis Post-Dispatch. The Read More
Greg Musson, Gar Tootelian
CropLife 100California Ag Retailer Steps Up To Feed Families Affect…
September 16, 2016
GAR Tootelian, Inc. (GAR) in Reedley, CA, is challenging the Central Valley to help raise enough money and provide 525,000 meals Read More
Crop InputsBayer, Monsanto CEOs Discuss Merger
September 15, 2016
Werner Baumann, Bayer CEO, and Hugh Grant, Monsanto CEO, discuss why they decided to merge their companies. Read More