Weeds

Controlling the Spread

Palmer Amaranth, Waterhemp, Marestail, Giant Ragweed, Lambsquarters, Pigweed, Burcucumber, Foxtail, Pokeweed, and Velvetleaf are some of the problem weeds we face annually in Knox County.  The first six weeds have documented herbicide resistance in Ohio.  The weeds in bold print are on the noxious weed list which requires control.

Arguably the single most daunting task facing some of us this year may be stopping the spread of weeds such as Waterhemp and Palmer Amaranth.  Waterhemp and Palmer Amaranth are two devastating, invasive weeds now found throughout Knox County.  These weeds, like no other weeds we have ever experienced, can and will change the way we manage our farms today.  These weeds can impact both your herbicide program and your trait-based seed selection.

Populations of these species can explode in just a few years if not controlled.  Consider each female plant of these two species can produce 1 million seeds.  If only one plant survives this year, how many of these seeds will germinate next year?  It’s not impossible to see a scenario where one surviving plant can turn into a million or more new plants within a few years.

Table 1. shows the seed production capabilities and the expected seed survival rate of different weed species prevalent in Knox County.

Controlling the spread

A monumental undertaking facing some this year will be to stop the spread of these weeds.  The most common avenues for weed seeds to spread are:

  • Machinery – Seeds are easily spread by many types of farm machinery, especially combines and mowing equipment.
  • Manure – Animals consume weed seed via various feed additives (cottonseed hulls) and hay.  Seeds are then spread in the manure.
  • Humans – Humans can spread weed seed through recreational activities and by moving items from field to field (power company moving big wood pallets).
  • Birds and wildlife – often transport weed seeds through their manure or by seeds in their coat.
  • Water – Heavy rains resulting in flooding can move weed seed to downstream fields.

Over the last three years I have personally seen evidence of weed seed movement throughout Knox County by each of these methods.

Invasive weeds pose significant risks to our farms.  Effective weed control programs and preventing the spread of these weeds is critically important.  These plants can have wide-ranging impacts on our farms for years to come.  Preventing these weeds from producing seed and/or removing or killing these plants before they produce seed is best way to control the spread.

 

Conservation Tillage and Technology Conference March 11-12

Don’t miss this year’s Conservation Tillage and Technology Conference March 11-12, 2025, (Tuesday-Wednesday) at Ohio Northern University, Ada, Ohio. Connect with other great farmers and CCAs, experience new ideas, and increase your net income.

The theme is “Getting More from Less.” Cutting costs is key following a year where corn and soybean yields were reduced for many farmers. And crop prices are barely breakeven. We don’t know what the weather will be in 2025, but commodity prices are projected to stay low.

Fred Yoder, no-till farmer at Plain City and former president of the National Corn Growers Association, will be the opening keynote speaker and will appear two more times on the program. He’ll discuss economic benefits of continuous no-till. Also, he will share insights into the new USDA leadership and the Farm Bill.

Jeff Duling, Putnam County, will discuss how he works with Mother Nature to increase yields with no-till and cover crops. Part of his farmland is Paulding clay, considered the worst soil in Northwest Ohio. He has increased corn yields on it by 50 to 75 bushels per acre. He is sponsored by Pioneer.

Connor Sible, Assistant Professor, University of Illinois, will share his research on various methods of “Managing Residue (from high-yielding corn): Mechanical, Chemical, and Biological.” He is sponsored by Calmer Corn Heads.

Etienne Herrick-Sutton, University of Missouri, will speak on the Regenerative Agriculture Outlook. Rodrigo Werle, University of Wisconsin, will present information on Managing Waterhemp in Soybeans. The full conference program is available at ctc.osu.edu

With about 60 speakers total, the Conservation Tillage and Technology Conference gives plenty of opportunities to gain valuable information. The program features four faculty from Midwest universities and more than 20 OSU Extension Educators and campus faculty.

The opening General Session will start at 8:30 a.m. March 11. Master Farmer Awards and the Ohio CCA of the Year will be announced. Four concurrent sessions will begin at 10:00 a.m. The Tuesday sessions include: Soil Health, Cover Crops and No-till; Nutrient Management; Agronomic Crops Management; and Precision Ag & Technology.

The four sessions on Wednesday will begin at 8:30 a.m. and end about 4:30 p.m. Sessions include: Soil Health, Cover Crops and No-till; Agronomic Crops Management; Water Quality; and Regenerative Agriculture. Take advantage of the opportunity to discuss one-on-one with speakers, exhibitors, sponsors, and other participants. Bring a friend and/or family members.

Registration will be a flat rate $100. Register online at https://www.allenswcd.com/cttc/ or call Albert Suniga at 419-222-0846 x1005. (Registration after February 25, or on-site, will be $150.) If you are planning to stay overnight, take advantage of available but limited rooms at discounted rates at “The Inn “at the Ohio Northern University. To take advantage of this promotion, call 844-535-2805. (When reserving, mention CTTC)

2025 Corn College & Soybean School

Join us on February 27th for the 5th annual virtual Corn College and Soybean School presented by the Ohio State University Extension Agronomic Crops Team. The program will run from 9:00 AM to 4:00 PM and feature OSU Extension field and state specialists with updates and topics relevant for the 2025 growing season. CCA CEU credits will be available upon viewing the live presentations. Talks will also be recorded for later viewing on the Ohio State Agronomy YouTube channel, https://www.youtube.com/@OSUAgronomicCrops.

Please register by February 26th at noon. To register, visit https://osu.az1.qualtrics.com/jfe/form/SV_bKLRxGoOPaOkBka or scan the QR code below. There is a $10 registration fee for this event, which goes directly to support the activities and efforts of the OSU Agronomic Crops Team.

2025 Speaker and Topic Lineup

  • Battle for the Belt – Osler Ortez, Laura Lindsey & Taylor Dill
  • Corn Disease Management – Stephanie Karhoff
  • Weather Outlook – Aaron Wilson
  • Nutrient Management in Low Grain Prices – Glen Arnold
  • Water Management Considerations – Vinayak Shedekar
  • Agronomic Weed Management – Alyssa Essman
  • Soybean Disease Management – Horacio Lopez-Nicora

 

Kill Poison Hemlock Now!

– Christine Gelley, Agriculture and Natural Resources Educator, Noble County OSU Extension

While hemlock may still be vegetative today, it will soon look like this.

Poison hemlock has already emerged in a vegetative state around Noble County and beyond. Soon it will be bolting and blooming on stalks 6-10 feet tall. All parts of the plant are toxic to all classes of livestock if consumed and is prevalent along roadsides, ditches, and crop field borders.

It is a biennial weed that does not flower in the first year of growth but flowers in the second year. The earlier you can address poison hemlock with mowing and/or herbicide application, the better your control methods will be.

 

 

 

Continue reading Kill Poison Hemlock Now! →

Purple Fields Everywhere

While driving through Knox County looking at wheat fields last week, I noticed many, many “purple fields”.  The purple plants are a combination of purple deadnettle and henbit.  This time of year these plants (weeds) can be found in fields, roadsides, gardens, flowerbeds and landscaped areas.

These winter annuals begin to develop in fall, form a small rosette of leaves that overwinter, and complete their development in spring, forming flowers and seeds. They die in late spring and early summer after setting seed.

Purple Deadnettle vs. Henbit

Purple Deadnettle

Purple deadnettle and henbit belong to the mint family and thus have a square stem.  Both have two-lipped tubular flowers, opposite leaves. The leaves of purple deadnettle at the apex of the stems are tinted purple and fade to green as they mature. The leaves have a short petiole (stem) and are heart- or triangular-shaped with rounded teeth on the leaf margin.

 

Henbit

The leaves of henbit are more rounded and scalloped and clasp the stem directly – they do not have a leaf petiole.  Henbit flowers are pink to purple with darker purple spots than those of purple deadnettle. The flowers of henbit are longer and more slender than those of purple deadnettle.

Suspected 2,4-D Resistant Waterhemp Population Discovered

Source:  ICM News, Iowa State University

We know the evolution of resistance in waterhemp populations happens faster than new herbicides are discovered, so the recent report of dicamba resistant waterhemp in Iowa by Bayer was not unexpected. Corteva has now reported the discovery of a suspected 2,4-D resistant waterhemp population in Iowa. These reports emphasize the need to use herbicides wisely and diversify weed management tactics beyond herbicides, especially as more farmers rely on herbicide group (HG) 4-based postemergence weed control in both corn and soybean.

The particulars

In late January 2024, Corteva reported the discovery of a suspected 2,4-D resistant waterhemp population in 2022 in Wright County, Iowa. A Corteva employee collected two samples of waterhemp seed, one from plants in the field and one from plants growing in the ditch adjacent to the field. While greenhouse testing with seed collected from plants in the field did not confirm resistance, plants grown from the ditch population are suspected to be 2,4-D resistant. The communication reported that the ditch had a multi-year history of 2,4-D application to manage broadleaf weeds. Corteva will continue evaluation of the populations in the greenhouse and the field. If resistance is confirmed in this population, it will become at least the fourth report of 2,4-D resistance in waterhemp, joining prior reports from Nebraska in 2009 (Bernards et al. 2012), Illinois in 2016 (Evans et al. 2019), and Missouri in 2018 (Shergill et al. 2018).

Iowa State University screened populations of waterhemp against several herbicides in 2019 at their 1X rates (Table 1). On average, waterhemp exhibited 17% survival to 2,4-D, 5% survival to dicamba, and 4% survival to glufosinate (Hamberg et al. 2023). We are rapidly losing herbicide options for postemergence control of waterhemp.

Best management practices to slow resistance development

Now is the time to evaluate how to improve weed management in fields. While herbicides will remain the primary tactic to manage weeds, farmers can implement several best management practices to slow herbicide resistance evolution and improve control of weeds like waterhemp.

  1. Choose an effective herbicide program for the weed spectrum present on a field-by-field basis.
    1. Use full rates of effective residual herbicides and plant into a weed-free seedbed.
    2. Include overlapping residual herbicides and multiple effective herbicide groups in postemergence applications to provide longer waterhemp control. Consult manufacturers for specific tank-mix recommendations.
    3. Make timely applications and choose appropriate adjuvants, nozzles, application volume, etc.
    4. Scout fields 7-10 days after postemergence herbicide applications to evaluate weed control.
  2. Use a diversity of weed management tactics, including chemical, mechanical, and cultural options. Narrow row spacing, cover crops, more diverse crop rotations, and tillage are effective tactics to suppress waterhemp.
  3. Control weed escapes prior to seed production to reduce future weed populations and prevent resistance from spreading.
  4. Reduce influx of weed seed into crop fields by managing weeds in field edges and cleaning equipment between movement from problematic fields to clean fields. The detection reported here indicates the threat of weeds in field edges.

Fall-applied Herbicide Considerations

Now that harvest is finally winding down, our thoughts change to fall weed control.   This is the best time of year to control winter annuals and some of the more difficult to manage overwintering weed species. Biennial and perennial plants are now sending nutrients down to the root systems in preparation for winter. Systemic herbicides like glyphosate and 2,4-D applied at this time will be translocated down into the roots more effectively than if applied in spring when nutrients are moving upward. This results in better control. In addition, the increasingly unpredictable spring weather patterns we have experienced in recent years can influence the timing and efficacy of spring burndown applications. Fall-applied herbicides can lead to weed free situations going into spring until early emerging annuals begin to appear in April, and are an essential component in the control of marestail and other overwintering species.

Here are some reminders when it comes to fall-applied herbicides:

  • Evaluate weed emergence and growth post-harvest to help determine if an application is necessary.
  • Fall-applied herbicides should primarily target weeds that are emerged at the time of application.
  • Species present in large quantities late-season that would necessitate the application of an herbicide include (but are not limited to): marestail, dandelion, wild carrot, poison hemlock, common chickweed, purple deadnettle, henbit, annual bluegrass, and cressleaf groundsel.
  • OSU research has not found much of a benefit from adding metribuzin or other residual products late in the fall. The exception to this is chlorimuron, which can persist into the spring. The recommendation here has generally been to keep costs low in the fall and save those products for spring when you will get more bang for your buck.
  • Herbicides generally work across a range of conditions, though activity can be slower as temperatures drop. Foliar products are most effective when daytime temperatures are in the 50s or higher and nighttime temperatures remain above 40.

Table 1 in the Weed Control Guide for Ohio, Indiana, Illinois, and Missouri provides ratings for various overwintering weed species in response to fall-applied herbicides.

Fall-applied Herbicide Considerations

Harvest is progressing in much of Ohio, though recent rains have slowed field activities in some areas. As crops continue to come off it’s a good time for a reminder about the value of fall-applied herbicides. Rains this past week may stimulate winter annual weed emergence to some extent. This is the best time of year to control winter annuals and some of the more difficult to manage overwintering weed species. Biennial and perennial plants are now sending nutrients down to the root systems in preparation for winter. Systemic herbicides like glyphosate and 2,4-D applied at this time will be translocated down into the roots more effectively than if applied in spring when nutrients are moving upward. This results in better control. In addition, the increasingly unpredictable spring weather patterns we have experienced in recent years can influence the timing and efficacy of spring burndown applications. Fall-applied herbicides can lead to weed free situations going into spring until early emerging annuals begin to appear in April, and are an essential component in the control of marestail and other overwintering species.

Here are some reminders when it comes to fall-applied herbicides:

  • Evaluate weed emergence and growth post-harvest to help determine if an application is necessary.
  • Fall-applied herbicides should primarily target weeds that are emerged at the time of application.
  • Species present in large quantities late-season that would necessitate the application of an herbicide include (but are not limited to): marestail, dandelion, wild carrot, poison hemlock, common chickweed, purple deadnettle, henbit, annual bluegrass, and cressleaf groundsel.
  • OSU research has not found much of a benefit from adding metribuzin or other residual products late in the fall. The exception to this is chlorimuron, which can persist into the spring. The recommendation here has generally been to keep costs low in the fall and save those products for spring when you will get more bang for your buck.
  • Herbicides generally work across a range of conditions, though activity can be slower as temperatures drop. Foliar products are most effective when daytime temperatures are in the 50s or higher and nighttime temperatures remain above 40.

Table 1 in the Weed Control Guide for Ohio, Indiana, Illinois, and Missouri provides ratings for various overwintering weed species in response to fall-applied herbicides.

Field Observations Thru September 15

Corn

Growth & Development

Most of the corn that I have seen this week is in either the late R4 (Dough) or the R5 (Dent) growth stage.  A few fields are approaching the final growth stage R6.

R6 – Physiological Maturity

  • Occurs approximately 66‐70 days after silking.
  • R6 is reached  after the milk line disappears and the starch has reached the base of the kernel.
  • Kernels have reached maximum dry weight.
  • Kernel moisture is  about 35% at physiological maturity.
  • Black layer occurs after physiological maturity and  serves as a visual verification that the plant is mature. Black layer typically occurs at 30%  moisture but varies by hybrid and environment.
  • Husks and many of the leaves are no longer green, but the stalk may be green.
  • Only external stress can reduce yield now,  such as plant lodging or insect feeding.

Scouting

At this growth stage look for:

  • Ear rots.
  • Stalk rots.
  • Anthracnose top dieback.
  • Stalk lodging.
  • Abnormal ear fill which identifies periods of stress.
  • Weed escapes (especially Palmer and Waterhemp).

This is also a good time to get an accurate yield estimate.

Soybeans

Growth & Development

Soybeans are continuing to mature.  Last week I highlighted the R7 growth stage, the last growth stage is R8 full maturity.

R8 – Full Maturity

  • 95% of pods reached mature color
  • Mature pod color does not necessarily indicate that beans are ready to harvest
  • 35% grain moisture in freshly matured pod
  • 15% within another 5 to 10 days
  • Below-optimum plant stands cause more branching, low pod heights & can delay maturity
  • Above-optimum plant stands increase lodging.

Scouting

At this growth stage look for:

  • Green stem syndrome.
  • Lodging
  • Sprouting seeds
  • Pod shattering
  • Weed escapes (especially Palmer and Waterhemp).

This is also a good time to check soybean yield potential.

County Rainfall Update