ASK THE AGRONOMIST BLOG

Stine’s Ask the Agronomist blog is your source to the latest information from our expert team, including advice and insight on field practices, product recommendations, planting and harvest updates, new technologies, crop management, innovative research and information about how to keep your farm operation running smoothly year round. 

  • Part 3: Management Strategies for Difficult-to-Control Weeds (Driver Weeds) in Soybeans
    Mike Smith Image

    Part 3: Management Strategies for Difficult-to-Control Weeds (Driver Weeds) in Soybeans

    November 07, 2019

    Posted by Mike Smith in Crop Management

    Marestail, otherwise known as horseweed, has been problematic for growers since the early 2000s, when the first glyphosate-resistant form was found in the United States. Because of this weed’s prevalence throughout the country, combined with the sheer size of the plant and number of seeds it produces, marestail is the focus for Part 3 of our series on herbicide-resistant and other hard-to-control driver weeds. This week we examine the strengths and weaknesses of marestail and recommended control tactics. 

    The Bad News (Strengths)

    • Marestail is a winter annual that emerges in the late summer through the fall and in early spring. Fall-emerging weeds typically overwinter and “bolt,” or develop a long stem with leafy growth that is difficult to control.
      • Bolted marestail is difficult to control because it can have hundreds of growing points.
      • Marestail can grow 6­–8 feet tall and develop 200,000+ seeds per plant that can be blown by the wind and carried by birds.
    • Marestail has smaller leaves, making coverage difficult.
    • Marestail can become hardened off in poor growing conditions, including hot and dry periods and extremely wet periods.
    • If left uncontrolled, marestail can reduce yields by as much as 40 percent.

    The Good News (Weaknesses)

    • Marestail is relatively easy to control in the rosette stage, compared to the bolted phase. This happens in the 30–45 days after emergence in the fall and 21–30 days after emergence in the spring.
    • Marestail responds well to soil-applied herbicides that inhibit root and shoot development.
    • Fall cover crops such as cereal rye have proven effective at keeping marestail from germinating in the fall and provide a shading effect to emerging marestail in the spring if left in the field after termination.
    • Corn and small grains are a good rotational option to fight marestail because there are more chemical options in these cropping systems.       

    Management Strategies

    • Start clean. For marestail, this means you will need to start in the fall. Apply a fall burndown to actively growing, emerged marestail. Consult your local agronomist or university extension office for specific recommendations.
    • Control new and surviving weeds with a spring burndown.
    • Use soil-applied residuals at planting to guard against late-emerging marestail.
    • For post-emerge applications, target weeds less than 6” tall using multiple herbicides with adequate coverage.
    • In some cases, narrow-row soybeans may be warranted to increase photosynthetic competitiveness and decrease marestail emergence.
    • Cover crops have shown an increased ability to delay emergence and shade emerged seedlings.
    • Cultivation in severe infestations may be necessary for a few years to get the population under control.
    • Conventional tillage demonstrates a more effective control because weeds are uprooted in the spring. In severe cases of poor marestail control, conventional tillage in the spring may be warranted.

    Trait System Usage
    Use trait systems that provide the ability to apply multiple, effective modes of action simultaneously to combat herbicide resistance. For instance, the Enlist E3® system allows Enlist One® with 2,4-D choline to be applied with both glyphosate and glufosinate and additional tank mix partners to eliminate and delay further marestail emergence. This system combines many of the strategies discussed into a flexible platform.

    To learn more about marestail and how to manage this hard-to-control driver weed on your farm, contact your local Stine agronomist or university extension specialist.

    Resources and Citations
    Management of Herbicide-Resistant Horseweed (Marestail) in No-Till Soybeans
    https://iwilltakeaction.com/uploads/files/57229-7-ta-hrm-factsheet-horseweed-final.pdf

    Plant of the Week
    https://www.uaex.edu/yard-garden/resource-library/plant-week/horseweed-8-5-05.aspx

    Marestail
    https://u.osu.edu/osuweeds/super-weeds/marestail/

    Marestail (Horseweed) Management
    https://extension.psu.edu/marestail-horseweed-management

    Adapting Soybean Burndown Programs for Large Marestail
    https://agcrops.osu.edu/newsletter/corn-newsletter/2017-12/adapting-soybean-burndown-programs-large-marestail

     

     

  • Tony Lenz Image

    Harvest Alert: Watch for Corn Ear Molds

    October 31, 2019

    Posted by Tony Lenz in Harvest

    Varying weather elements, late planting and larger thresholds of corn earworm and other damaging insects after silking have left many growers with corn ear molds in their fields. Ear molds can lead to harvestability issues for a few reasons, so growers need to be able to recognize the signs of ear mold in their fields and determine which mold they are dealing with. Here are the four main ear molds to watch for this fall.

    Diplodia: Diplodia is one of the most common ear molds growers are finding in their fields this fall. Diplodia is white to gray in color and usually begins at the base of the ear, growing between kernels. Black spots can often be spotted on the husks and even on stalks. Diplodia usually starts growing about two weeks after silking and can greatly impact grain quality and, ultimately, yield. Diplodia can also cause stalk rots. 

    Aspergillus: Typically gray-green to light green in color, aspergillus mold starts at the tip of the ear. Damaged kernels caused by insects or hail earlier in the season give this mold a site to enter and begin growing. Nitrogen deficiencies can also cause this mold. Aspergillus can form aflatoxins, which are poisonous carcinogens that can become toxic to livestock and humans.

    Gibberella: Gibberella can be detected by its bright pink to red or even white color. It’s typically present on the tips of ears, but it can also be detected on the stalk, causing stalk rot. Gibberella favors cool and wet weather after silking. Earworm damage is a good point of entry for gibberella mold to form. Gibberella can also form vomitoxin, a form of mycotoxin that is harmful to livestock such as hogs, even with only five to 10 percent of ear rot present.

    Fusarium: White to pink in color, fusarium usually starts at the tip of the ear and can cause stalk rot. Infection starts where kernels crack during growth or when ear damage from insects is present. Fusarium thrives in warm and dry weather, and can form fumonisins, a group of mycotoxins that are toxic to livestock.

    Damage Potential
    Damage potential is greatest for all these molds from silking to harvest, especially with the excessive rainfall we’ve had this year. We’re also seeing a lot of ear molds where large amounts of insect feeding from ear worms, aphids and corn borer occurred this summer. This situation is more common in fields where conventional or straight Roundup hybrids were planted. We’re also seeing more damage in areas where late planting, excessive heat at pollination and an early frost before black layer occurred, leading to underdeveloped kernels with lighter test weights. Growers need to watch for areas of lighter test weights, as they may be a strong indicator of ear mold presence.

    As referenced above, ear molds can also develop toxins that are dangerous for animal consumption. Some animals are more sensitive to toxins, such as hogs and dairy cattle. There are different types of mycotoxins that form based on the ear mold, which is why it’s important to detect the mold before harvest and get it tested before taking it to the grain elevators.

    If growers suspect they have an ear mold infestation, it is recommended to test several locations in their fields, pulling anywhere from 10 to 20 ears in each location. If they run into higher thresholds of affected ears, management tactics must be implemented. The Ohio State University’s Agronomic Crops Network recommends, “If you have damaged ears and moldy grain, get it tested for mycotoxins before feeding to livestock, and if you absolutely have to use moldy grain, make sure it does not make up more than the recommended limit for the toxin detected and the animal being fed.” The U.S. Food and Drug Administration has established maximum allowable levels for mycotoxins and other toxins in corn, which should be properly adhered to.

    Management and Prevention
    Growers experiencing ear molds this fall need to consider a few management tactics for harvest this season and for the coming years. Grain storage and proper drying will be important in fields with a high incidence of ear mold this fall. Ideally, we would like it to dry down in the field as much as possible to avoid down corn. Make sure your combine is set to minimize even more kernel damage than is already present. Test weight is more than likely going to be lower this year, which means you may be at higher risk of kernel breakage with handling and a shorter storage life. The University of Wisconsin Crop Manager recommends storing contaminated corn separately as the fungi can grow on good corn during storage.

    Growers trying to decrease their chances of getting ear molds in the coming years need to consider a combination of crop rotation, deeper tillage and planting hybrids such as -20 or Agrisure Duracade® for better insect protection from pests like the western bean cutworm, corn borer and earworms. Stine has a number of great options in these categories for the 2020 growing season. Growers also need to consider a good fertilizer program to avoid plant stress.

    For more information and recommendations on corn ear molds this harvest, contact your local Stine agronomist or university extension office.

    Resources and Citations
    Ear Rots of Corn: Telling them Apart
    https://agcrops.osu.edu/newsletter/corn-newsletter/2018-28/ear-rots-corn-telling-them-apart

    Corn Earworm in Field Corn; Watch for Molds
    https://agcrops.osu.edu/newsletter/corn-newsletter/2019-27/corn-earworm-field-corn-watch-molds

    Corn Stalk Rots and Ear Rots
    https://ipcm.wisc.edu/download/wcm-pdf/WCM2019/WCM2019_22b.pdf

     

  • Mike Smith Image

    Part 2: Management Strategies for Difficult-to-Control Weeds (Driver Weeds) in Soybeans

    October 24, 2019

    Posted by Mike Smith in Crop Management

    For part two of our discussion on herbicide-resistant and other hard-to-control weeds (driver weeds), we’re examining waterhemp. This article highlights the strengths and weaknesses of waterhemp and the strategies available to control this driver weed.  

    The Bad News (Strengths)

    • Waterhemp typically grows in clumps or patches with large numbers of the plant concentrated in limited areas.
    • The University of Missouri has demonstrated that more than 20 plants per square foot can reduce soybean yields by 44 percent. Even late-emerging waterhemp (after 5th trifoliate) can reduce yields significantly.
    • Waterhemp is also an extremely productive weed, with the ability to grow 1.25 inches per day and produce between 250,000–500,000 seeds per plant.
    • As a dioecious weed, waterhemp grows male and female flowers on separate plants, allowing for more genetic diversity in single populations and rapid development of herbicide-resistant genes.

    The Good News (Weaknesses)

    • Waterhemp seed may overwinter in the soil for a few years, but research demonstrates that less than 15 percent of that seed will remain viable for longer than four years.
    • Seed that is emerging or recently emerged is easier to control than plants that have had the opportunity to grow and harden off in adverse weather conditions.
    • Shading — the inability to capture sunlight — growing seedlings can greatly inhibit waterhemp’s prolific tendency.

    Management Strategies

    • Know your resistance profile. Test your waterhemp population to know which herbicides will be effective. Current known herbicide resistance includes Groups 5 (triazines), 2 (ALS), 14 (PPO inhibitors), 9 (glyphosate), 27 (HPPD inhibitors) and cross resistance (single population resistant to both Groups 9 and 2). 
    • Start clean with tillage and/or effective burndown control that eliminates actively growing weeds.
    • Use an effective soil residual herbicide. Consult your local agronomist or university extension office for specific recommendations. Note that use of soil residual herbicides in multiple sequential applications is encouraged, where possible, to delay and diminish the germination and emergence of waterhemp and to allow soybeans a competitive advantage in row closure, canopy and plant density.
    • In some cases, narrow-row soybeans may be warranted to increase photosynthetic competitiveness and decrease waterhemp growth habits.
    • Cover crops have also shown an increased ability to lessen weed seed bank populations and delay emergence.
    • Manual eradication in severe infestations may be necessary for a few years to control the population.
    • Using a conventional herbicide system that relies on multiple passes with soil-applied residuals and effective post-applied herbicides with current broad-spectrum herbicides can be an effective strategy. This system is generally costly; however, increase in yield from reducing weed competition generally outweighs the cost of treatment.

    Trait System Usage
    Use trait systems that provide the ability to apply multiple, effective modes of action simultaneously to combat herbicide resistance. For instance, the Enlist E3® system allows the use of Enlist One® with 2,4-D choline to be applied with both glyphosate and glufosinate and additional tank-mix partners to eliminate and delay further waterhemp emergence. This system combines many of the strategies discussed into a flexible platform.

    To learn more about waterhemp and how to manage this hard-to-control driver weed on your farm, contact your local Stine agronomist or university extension specialist.

    Resources and Citations
    University of Arkansas Division of Agriculture Research & Extension https://www.uaex.edu/farm-ranch/pest-management/weed/field-crops.aspx

    Take Action www.takeactiononweeds.com

    Waterhemp Management in Soybeans https://weedscience.missouri.edu/publications/50737_3_TA_FactSheet_Waterhemp.pdf

    Ohio State University Weed Management https://u.osu.edu/osuweeds/super-weeds/

    Ohio State University Extension https://agcrops.osu.edu/newsletter/corn-newsletter/2014-20/postemergence-control-giant-ragweed-soybeans