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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2004-01

Dates Covered: 
January 6, 2004 - January 19, 2004
Greg LaBarge

What's The Deal With Common Lambsquarters and Glyphosate?

Authors: Mark Loux

We have received numerous complaints over the past two years about poor control of common lambsquarters with postemergence glyphosate applications in Roundup Ready soybeans. Historically, lambsquarters is a weed that can exhibit decreased sensitivity (reduced control) to glyphosate, and decreased sensitivity is influenced by size or age of the plants. In greenhouse research last winter, we studied the response of a number of lambsquarters populations to glyphosate. Several of these populations were from fields where the lambsquarters appeared to be less sensitive to postemergence glyphosate applications in 2002. We observed a range of responses to glyphosate in the greenhouse, although all of the populations were controlled more effectively than the glyphosate-resistant marestail that is becoming more common in Ohio.

We conducted field research in Roundup Ready soybeans at four sites in 2003. One of these lambsquarters populations was among the least sensitive to glyphosate in the greenhouse research, while the other three sites had no history of glyphosate performance problems. We applied a range of glyphosate rates, 0.38 to 7.5 pounds acid equivalent (lb ae)/A, to three sizes of lambsquarters, 1-2 inch, 4-6 inch, and 10-12 inch. Regardless of rate, glyphosate controlled essentially all of the lambsquarters at all sites when plants were less than 6 inches tall. The 10-12 inch lambsquarters plants were generally more difficult to control, but were effectively controlled at two of the sites that had no history of glyphosate problems. At a third site, that showed decreased sensitivity in the greenhouse, there was an area within the study where control of 10-12 inch lambsquarters was reduced. In this area of lower sensitivity plants, the 7.5 lb ae/A rate did not completely kill all of the lambsquarters, but the lambsquarters never regrew and did not produce seed. However, plants surviving the 0.75 lb ae/A rate in this area did recover somewhat and produced seed. At a fourth site, that had no history of negative glyphosate performance, we also observed a few plants surviving the 7.5 lb ae/A rate, but these plants never recovered sufficiently to produce seed. So, what's it all mean? We interpret these results as follows:

1) There appears to be variability among lambsquarters populations in their response to glyphosate, but in the field, differences in lower sensitivity are expressed primarily in large plants.

2) Even in populations without lower sensitivity to glyphosate, large plants can be difficult to control under field conditions.

3) Plants less than 6 inches tall appear to be effectively controlled by glyphosate in most situations, even in populations with lower sensitivity.

4) Environmental conditions most likely affect the response of lambsquarters to glyphosate, but are more likely to affect control of large plants compared to small ones. The exact conditions producing the decreased lambsquarters control are not completely known, but may be linked to temperature, moisture, and sunlight.

5) Effective spray coverage may be another reason for decreased lambsquarters control. When spaying large weeds, small lambsquarters may be hidden under the canopy and cannot receive enough glyphosate to be adequately controlled.

Below are some suggestions for effectively managing lambsquarters in Roundup Ready soybeans:

1) Apply a preemergence herbicide that provides residual control of lambsquarters prior to or at the time of soybean planting. Most preemergence soybean herbicides control lambsquarters, with the exceptions of alachlor, Dual II, Outlook, and low rates of Domain, Boundary, and Axiom. In areas of triazine-resistant lambsquarters, Sencor, Domain, Boundary, and Axiom will not provide adequate control regardless of rate. This will greatly reduce the lambsquarters population and ensure lambsquarters will be smaller when making the in-crop glyphosate application.

2) Apply glyphosate at 0.75 lb ae/A when lambsquarters are less than 6 inches tall if possible. Increase glyphosate rates if plants are larger than 6 inches tall.

3) Under adverse weather conditions consider increasing the rate of glyphosate.

Determine Your Next Move In “The Crop Profit Game”

Authors: Greg LaBarge

Ohio crop producers looking for information to make their next growing season more profitable will have the opportunity to interact directly with Ohio State University Extension specialists during a satellite program being held January 15.

“The Crop Profit Game”, sponsored by Ohio State Extension, is designed for Extension specialists to share research and information that will give producers profitable management tips to implement in 2004. The event will begin at 7 p.m. and will be available for viewing at local Extension offices throughout Ohio. Contact your local Ohio State Extension office for start times and participation costs.

The host for the program will be Dale Minyo of ABN, who will lead participants through several short presentations and panel discussions that will focus on viewer questions. Panel members will include Anne Dorrance, Ohio State Extension soybean plant pathologist; Mark Loux, Ohio State Extension agronomist in weed science; Jim Beuerlein, Ohio State Extension soybean and small grains agronomist; and Bruce Eisley, Integrated Pest Management specialist, plus several other Ohio State specialists.

Topics of discussion will include competitiveness of Ohio’s crop industry; soybeans, wheat and corn management; insect, disease and weed control; and making technology pay. A detailed agenda is available at county Extension offices or by logging on to

For additional information regarding program costs, registration or the agenda, contact your local Ohio State Extension office.

Agronomy Workshops Schedule

Authors: Greg LaBarge

Over the next two month producers and ag industry will have the opportunity to participate in several workshop being hosted by local county Extension Office in conjunction with the Agronomic Crops Team. Certified Crop Advisor and pesticide credits will be given where appropriate. Full program details can be found at


For more details

Tuesday, January 27, 2004
Delaware County, Ostrander
Scioto Twp. Hall
3737 Ostrander Rd.
Host Agent: Rob Leeds

Thursday, January 29, 2004
Miami County, Piqua
Upper Valley Applied Technology Center
Looney Rd.
Host Agent: Harold Watters

Friday, January 30, 2004
Pickaway County, Circleville
Pickaway Co. Public Library
1160 N. Court Street
Host Agent: Mike Estadt


For more details

Tuesday, February 3, 2004
Lorain County, Pittsfield
Pittsfield Twp. Hall
SR 303 & SR 58
Host Agent: Jim Skeeles

Thursday, February 5, 2004
Mercer County, Celina
Central Services Bldg.
220 W. Livingston St.
Host Agent: Todd Mangen


For more details

Tuesday, February 17, 2004
Huron County, Norwalk
First Presbyterian Church
21 Firelands Blvd.
Host Agent: Gary Bauer

Thursday, February 19, 2004
Henry County, Hamler
Hope Lutheran Church Education Bldg.
Intersection of SR 18 and CR 10
(Between Holgate and Hamler)
Host Agent: Dusty Sonnenberg


For more details

Tuesday, February 24, 2004
Butler County, Hamilton
Janet Clemons Center
282 N. Fair Ave.
Host Agent: Steve Bartels

Tuesday, March 2, 2004
Wayne County, Wooster
Fisher Auditorium, OARDC
Host Agent: Terry Beck

Wednesday, March 3, 2004
Coshocton County, Newcomerstown
Sunset Acres Farm
21284 TR 257
Host Agent: Paul Golden

Thursday, March 4, 2004
Seneca County, Tiffin
Public Safety Building
Seneca County Fairgrounds
Host Agent: Clark Hutson

Advanced Crop Management Workshop for CCA’s and Other Ag Professionals

Authors: Edwin Lentz

Registration flyers and program details were mailed over the Holidays for this new program being offered. The flyer and registration form may be obtained from the web at

Workshop sessions will be taught by recognized Ohio specialists, and will allow the CCA to obtain 3 hours of soil and water management, 2 hours of nutrient management, 3 hours of crop management and 3 hours of integrated pest management. This workshop will be held on the Ohio Agricultural and Research Development Center main campus in Wooster. Dates and times are February 11 (10:00-6:00 pm) through February 12 (8:00-noon).Cost of workshop will be $150 which includes educational materials for participants, food and refreshments. Contact Ed Lentz at or by phone (419-422-6106) for more information.

Archive Issue Contributors: 

State Specialists: Pat Lipps & Anne Dorrance (Plant Pathology), Jeff Stachler (Weed Science), and Bruce Eisley (IPM); Extension Agents: Roger Bender (Shelby), Greg La Barge (Fulton), and Harold Watters (Miami).

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.