When Weed Control Goes Wrong

Beyond the possibility of resistance developing, ineffective control exacts cost to growers in lost yield.

Quantifying the losses that poor weed control can cause grower customers is no simple matter. Shane Eck, location manager at Mid Kansas Cooperative (MKC), Lindsborg, KS, says measuring losses quantitatively due to the weeds “could be tough without doing a side-by-side comparison.”

Fortunately, many researchers have taken on that “hard numbers” question.

Mark Rosenberg, Extension agronomy/weeds field specialist, South Dakota State University (SDSU) reports on one sobering test his team did: Even though glyphosate was applied two to three weeks after corn and weed emergence in high weed density plots, yield losses measured as much as 20 to 40 bushels per acre.

Mature Waterhemp in Corn
Studies show that weeds can reduce corn yields by about 1% per day starting about one week after corn/weed emergence. Pictured is mature waterhemp in corn.

SDSU specialists commonly suggest growers control weeds within three to five weeks after crop emergence to prevent lasting impacts on corn growth and yield. They also recommend preemergence herbicides to minimize yield loss as well as minimize selection for glyphosate resistant weeds.

Rosenberg says preemergence products can also help soybeans, “but mostly for the benefits of increasing the consistency of weed control, managing glyphosate resistant weeds, and increasing flexibility in the timing of post-emergence application.”

Growers can actually identify the most competitive weeds in corn: they’ll be three to four inches tall when corn reaches the V-3 to V-4 growth stage. Research at Iowa State University has shown these competitive weeds can reduce yields by about three bushels per acre for every day they are left uncontrolled. Rosenberg says SDSU studies proved these weeds can reduce corn yields by approximately 1% per day starting at about one week after corn/weed emergence. Bottom line: If these weeds are controlled early, crops will develop the vigor to compete with later emerging weeds.

Application Timing Science

Weeds may do even more than compete with crops for valuable resources. According to work reported by Bob Hartzler, Extension weed management specialist, Iowa State University, a corn plant can actually detect weeds in its vicinity by detecting changes in light quality when sunlight is reflected off of the weeds. The corn then reallocates its resources to grow taller to reduce the chance of the weed intercepting sunlight the corn wants. The phenomenon is called shade avoidance. Such resource re-channeling has a negative impact on future crop growth.

In fact, research in Canada found that corn growing with weeds was affected by the shade response as early as three days after emergence — with its highest sensitivity to the shade issue in the first week after emergence.

Hartzler has found determining that moment when weeds first cause yield loss — the “critical period” — can be complex because of the number of factors involved: weed species, number of weeds, emergence date; cropping practices including cultivar, row spacing, population, tillage and environment. He says the critical period may occur as early as two weeks or as late as 10 weeks or later after planting.

In its resources, the Weed Science Society of America (WSSA) points out that poor weed control has consequences beyond yield losses, including reduced commodity prices because of weed-seed contamination, reduced land values, costs of mechanical and cultural controls, and ultimately the additional expense of alternative herbicides or cropping systems — or both — for managing resistant weeds.

WSSA has published findings by several weed scientists, gathered over the last eight years:

  • Cases of glyphosate resistant horseweed have resulted in a net increase in production costs of just over $70 per acre in Tennessee soybeans.
  • Cases of glyphosate resistant common waterhemp have increased production costs by about $118 per acre in Missouri soybeans.

Similarly, cases of glyphosate resistant Palmer amaranth have added approximately $118 per acre in weed management costs in Georgia and Arkansas cotton production systems.

  • Cases of propanil- and quinclorac-resistant barnyardgrass have added additional costs totaling approximately $158 per acre in Arkansas rice.

From The Field

Dealers we talked with have seen yield losses in clients’ fields. When asked how bad resistance is in his territory, Jeff Consbruck, seed lead, CPI Coop, Hastings, NE, said over the past couple of years he’s seen some yield being impacted from weeds that treatments could not knock down. While CPI hasn’t seen extensive losses so far, “if we don’t get on top of this soon, we will have horror stories to tell,” he says.

Getting on top of the issue takes a commitment not all growers are willing to make. Kevin Mainord, sales and marketing director with MRM Ag Services, East Prairie, MO, estimates that about 80% of customers are adapting to new practices needed to deal with resistance — Roundup is not controlling the spectrum of weeds it used to. But 20% are not willing to go into the complexities and costs of multiple product applications.

One service MRM’s customers can purchase is scouting for both weed and insect issues. The investment offers two-for-the-price-of-one benefits.

Mainord says timing herbicide applications for optimum kill is critical. If weather becomes a problem and delays ground spraying at key windows, his company can go into a customer’s fields with aerial applications because the firm operates its own plane. Managing weeds this way adds cost, but the yield saved may be worth it.

Topics:

Leave a Reply

Weed Resistance Stories

Weed ResistanceWeeds: The Fearsome Five
October 1, 2013
Although there are currently dozens of weeds that show some kind of resistance to herbicides, these five are the most troublesome. Read More
Weed ResistanceWeed Management Program Profiles
October 1, 2013
Here’s quick look at weed control strategies and their cost. Read More
Weed ResistanceRecognizing Resistance
October 1, 2013
Recognizing the presence of herbicide-resistant weeds and formulating a total management plan is becoming more important than ever. Read More
Mature Waterhemp in Corn
Weed ResistanceWhen Weed Control Goes Wrong
October 1, 2013
Beyond the possibility of resistance developing, ineffective control exacts cost to growers in lost yield. Read More

Trending Articles

Crop InputsPlatform Specialty Products To Acquire Arysta LifeScience
October 20, 2014
Once the acquisition is complete, Platform Specialty Products will combine Arysta LifeScience with previously acquired companies Agriphar and Chemtura Crop Solutions. Read More
Seed/BiotechMonsanto Offers New Support For Ferguson, Area Communities
October 8, 2014
Monsanto Co. has committed $1 million in new support for several collaborative efforts in Ferguson, MO, and surrounding communities in North St. Louis County. Read More
Seed/BiotechUnapproved Genetically Modified Wheat Found In Montana
October 3, 2014
USDA reports that one year after discovery of Monsanto's unapproved wheat in a single Oregon field disrupted U.S. wheat export sales, the GMO wheat has again been found in Montana. Read More
Equipment2014 Product Of The Year Voting
September 19, 2014
The deadline to vote for the 2014 CropLife IRON Product of the Year is October 31. Please cast your vote today to help us determine the winner. Read More
FertilizerFall Fertility 2014: Forecasting Fertilizer Use
September 7, 2014
Great crops this year have tapped the soil, and fall work is definitely called for, but how challenging will that get? Read More
CropLife 100CHS To Build $3 Billion Fertilizer Plant In North Dakota
September 5, 2014
The fertilizer plant in Spiritwood will be the single largest investment in CHS history, as well as the single largest private investment project ever undertaken in North Dakota. Read More

Latest News

LegislationNew Farm Bill Program To Provide Relief To Farmers Affe…
October 21, 2014
The USDA has implemented a new Farm Bill initiative that will provide relief to farmers affected by severe weather, including drought. Read More
ManagementGreenfield Scholars Program Aims To Sustain Agronomy Wo…
October 21, 2014
The program encourages talented students to study agronomy, crop and soil sciences while cultivating networks to develop the necessary workforce to sustain the profession. Read More
Paul SchrimpfPrecision Ag: Taking It To The Hill
October 21, 2014
A new coalition took the good news message of precision agriculture to Washington, DC, last month. Read More
ManagementUSDA Awards $18 Million In Small Business Research Gran…
October 21, 2014
The grants will provide high quality, advanced research and development that will lead to technological innovations and solutions for American agriculture. Read More
FertilizerCF Industries Terminates Merger Discussions With Yara I…
October 21, 2014
CF Industries Holdings and Yara International have terminated their discussions regarding a potential merger of equals transaction. Read More
Seed/BiotechSyngenta Ranked A Top 10 Biotech Employer For Third tim…
October 20, 2014
Syngenta ranked in the top 10 among the world’s top biotech employers, according to an annual survey conducted by Science magazine. Read More
CropLife 100Wheat Growers Break Ground For New Facility At Kennebec
October 20, 2014
Wheat Growers has broke ground for a state-of-the-art shuttle loader grain handling, fertilizer and agronomy facility in Kennebec, SD. Read More
FertilizerVerdesian Life Sciences Signs Agreement With Los Alamos…
October 20, 2014
Verdesian Life Sciences has signed a licensing agreement with Los Alamos National Laboratory to develop and market LANL’s latest nitrogen enhancement technology for plants. Read More
MicronutrientsStoller Group Announces Groundbreaking At New Office Bu…
October 20, 2014
Jerry Stoller, founder and president of Stoller Group, announced the groundbreaking at the site of the company’s future headquarters in Read More
Crop InputsBioSafe Systems Opens New Production Facility In Nevada
October 20, 2014
BioSafe Systems has completed construction of a state-of-art production facility in Sparks, NV, for its line of activated peroxygen products. Read More
Crop InputsPlatform Specialty Products To Acquire Arysta LifeScien…
October 20, 2014
Once the acquisition is complete, Platform Specialty Products will combine Arysta LifeScience with previously acquired companies Agriphar and Chemtura Crop Solutions. Read More
Seed/BiotechEPA Approves Dow’s Enlist Duo Herbicide
October 15, 2014
The Enlist Weed Control System, breakthrough technology to fight resistant and tough weeds, has received the long-awaited green light from federal regulatory authorities. Read More
MicronutrientsGypsum On Farms Could Help Keep Water Clean, Not Green
October 14, 2014
Gypsum, which has roots in the past as a farm soil treatment, also may have a bright future, and not just as a booster of crops but also as a protector of water. Read More
Photo credit: The United Soybean Board/The Soybean Checkoff.
Crop InputsVerdesian Grows Sales Staff
October 14, 2014
The new account managers will drive sales growth and support relationships with key customers in the plant nutrition and seed treatment and inoculants product categories. Read More
WebinarsUpcoming Webinars
October 14, 2014
Register for one of our upcoming Webinars or access our archive of past Webinars to view recordings of presentations that may be of interest to you. Read More
CropLife 100The Andersons Purchases Six Grain Elevators, Four Agron…
October 14, 2014
The Andersons has acquired Auburn Bean and Grain of Auburn, MI, which will increase the storage capacity of its Grain Group by about 13%. Read More
StewardshipThree Ohio Ag Retailers Honored With 4R Certification
October 13, 2014
The 4R Nutrient Stewardship Certification Program has announced its first three agriculture nutrient service providers to achieve certified status. Read More
Eric SfiligojEntering Agriculture’s New Phase
October 13, 2014
The market’s giddy ride the past few years might be coming to an end in 2015, warns one industry insider. Read More