Horseweed (marestail) control options in fallow prevent plant fields

Source: Christy Sprague, Michigan State University

The challenging conditions this spring have left many fields unplanted. Glyphosate- and multiple-resistant horseweed (marestail) dominates a majority of these fields. Horseweed and other weeds in these unplanted fields need to be controlled prior to setting seed to prevent future weed problems. To help determine some of the more effective options for horseweed control, we sprayed several treatments two weeks ago on 2 feet tall horseweed. Common lambsquarters, common ragweed and prickly lettuce were also present in this field. Below is a compilation of pictures of these treatments and a summary of the results.

Horseweed control results

Roundup PowerMax (glyphosate) alone was ineffective at controlling a majority of the horseweed plants in this field (Figure 1A), indicating this population is highly resistant to glyphosate. Glyphosate-resistant horseweed is extremely common in many Michigan fields and glyphosate alone should not be used. The addition of 2,4-D ester at 1 pint per acre (pt/A) or 1 quart per acre (qt/A), Enlist One at 1 pt/A or Clarity (dicamba) at 1 pt/A to Roundup PowerMax improved horseweed control. However, controlling horseweed with these treatments only ranged from 60–70% 14 days after treatment (Figure 1B). These treatments will not likely result in complete control of horseweed.

The addition of 2,4-D or dicamba also improved common lambsquarters and common ragweed control over Roundup PowerMax alone. While these may be some of the more inexpensive treatments, they were not the most effective and caution should be taken if 2,4-D ester or any of the dicamba formulations are used. Off-target movement by drift or volatility, especially under high temperature conditions and when sensitive crops are in the area, can occur these herbicides.

Horseweed control 2
Figure 2. Glyphosate-resistant horseweed control with (A) Liberty (glufosinate) at 32 fl oz/A plus AMS and (B) Sharpen at 1 fl oz/A plus Roundup PowerMax at 32 fl oz/A plus MSO plus AMS, 14 days after treatment. Photo by Christy Sprague, MSU.

The most effective treatments to control glyphosate-resistant horseweed were Liberty (glufosinate) at 32 fluid ounces per acre (fl oz/A) plus AMS (Figure 2A), or Sharpen at 1 fl oz/A or 2 fl oz/A plus Roundup PowerMax at 32 fl oz/A plus MSO plus AMS (Figure 2B). These treatments resulted in greater than 95% control of horseweed, common lambsquarters, common ragweed and prickly lettuce. A higher rate of Liberty (glufosinate) at 43 fl oz/A can also be used.

Initial control of glyphosate-resistant horseweed with Gramoxone 3L (new formulation) at 2.67 pt/A plus surfactant was 80%. However, by 14 days after treatment, horseweed started to regrow (Figure 3). Controlling common lambsquarters, common ragweed and prickly lettuce ranged from 70–75%.

Horseweed control 3
Figure 3. Glyphosate-resistant horseweed control with Gramoxone plus surfactant, 14 days after treatment. Photo by Christy Sprague, MSU.

Two additional treatments we examined included disking and mowing. Mowing reduced overall weed biomass, however it also removed the primary growing point and as horseweed started to regrow, additional shoots were produced. If mowing, multiple passes throughout the season will likely be required. A onetime mowing would likely be more beneficial later in the season prior to flowering and seed set. Tillage or disking did provide good horseweed control, however it will likely take multiple passes to keep the fields clean throughout the season.

Additional considerations

All these treatments were applied under good growing conditions (plenty of moisture and heat) and resulted in good herbicide activity. As weeds continue to grow and begin to flower, the effectiveness of these treatments will likely be reduced. Additionally, depending on the weed species, there could possibly be new emergence later in the season.

Crop rotation restrictions also need to be considered when choosing one of these herbicide treatments for horseweed and other weed control. Sharpen, 2,4-D and dicamba all have residual activity and could cause injury to certain cover crops and winter wheat if rotation restrictions are not followed. Winter wheat should not be planted earlier than one month after applying dicamba or 2,4-D (Enlist One). Sharpen at 1 or 2 fl oz/A can be applied any time before planting winter wheat. There is a 70-day rotation restriction between Liberty applications and planting winter wheat. Consult individual herbicide labels.

The Ohio Noxious Weed Law – A Tool in the Prevention of Waterhemp and Palmer Amaranth

Source: Dr. Mark Loux

Waterhemp and Palmer amaranth are both now listed on the Ohio noxious weed law, which means that landowners must take steps to control infestations and prevent further spread.  Since these are annual weeds, preventing spread is achieved by preventing plants from reaching maturity and producing seed.  This is the basis for our “No pigweed left behind” effort, for which the goal is to create an understanding that the only way to beat these weeds is to prevent seed.  Prevention needs to occur in any area that might be subject to infestation, such as roadsides, parks, conservation seedings, parks, etc, in addition to agricultural fields.  The entities managing these areas are responsible for recognizing and controlling infestations of waterhemp and Palmer amaranth, but this does not always occur.  Not everyone involved in crop production or land management is aware of the waterhemp/Palmer problem to begin with, and many managers are busy enough that preventing noxious weed problems has low priority.

Our advice is to pay attention to what’s happening in your area or in the areas that you farm, with the goal of becoming aware of new infestations early enough that plant maturity and seed can still be prevented, regardless of where they may be occurring.  We recommend as a first step contacting the land manager or owner to explain the issue, make them aware that they have an infestation, and request that action be taken.  However, where it’s not possible to have this conversation, or there is a refusal to take action, the Ohio noxious weed law can be used to try to force action.  A two-page summary of the noxious weed law that can be found here on the OSU Ag Law Blog, and also links directly to the law itself.

The basic idea here is that following an unsuccessful attempt to work with a landowner or manager, noxious weed issues should be reported to township trustees, and this must be done in writing.  The trustees then have the responsibility to deal with the issue, and the method for doing so varies depending upon what the land is used for and who is managing it.  If it’s necessary to use the noxious weed law, be sure to start the process early enough in summer, well before potential seed production.  There is a need to allow time for all of the steps in the process to occur, and for notifications to be received and acted on (or not).  Our experience is that not all landowners and managers will take action upon first notification, and in addition to action, their response to notification can include minimal response of protesting their need to act.  Waiting too late to start the process can result in lack of resolution of these issues in time to prevent plant maturity and seed production.  The noxious weed law has been used several times within the last two years to force managers to control Palmer amaranth, and could be used to accomplish the same for waterhemp, which was recently added to the list.  Consider the law a tool to prevent the establishment and spread of these weeds when other methods are ineffective.

You can search this blog for a complete description and pictures of all the weeds on the Ohio Noxious weed list.

No pigweed left behind

No pigweed left behind

Corn Growth & Development – V5 & V6

Today managing your corn crop requires knowledge of the different growth stages of the corn plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.  Each week throughout the growing season I will discuss the various corn growth stages and management issue at each stage.  

V5 – V6  – 350 – 400 Growing Degree Days (GDD’s)

Source: Corn Growth and Development, Iowa State University

OK, now stuff is really happening!

Plants with their first six leaves collared are defined as V6. The lower leaves are more weathered and become increasingly harder to identify and count as they tear away from the expanding stalk and decompose. All leaves are initiated byV6 although many are too small to see without magnification. Each leaf originates from a stalk node with internode tissue separating the nodes. A minor amount of internode elongation began prior to V6 with the majority occurring from this point forward

The growing point has now transitioned from below to above the soil surface due to internode elongation. The nodal root system is dominant now with the root mass approximately one third of the plant’s total biomass.

Ear shoots, one of which will develop into a harvestable ear, are being initiated and growing along the stalk at various nodes. Ear shoots are first present at lower stalk nodes as these are initiated first with upper ear shoots following

Although the primary ear shoot is not yet visible, it is initiated at approximately V6 magnification will be necessary to see it. The primary ear is typically located at nodes 12, 13, or 14.  The potential size of an ear is a function of the number of kernel rows around the ear and the number of kernels per row. The row number will be even (versus odd) because initial rows divide laterally, forming two rows each. Row number is determined shortly after the ear is initiated, approximately V7.  Most hybrids grown commercially have 16 or 18 kernel rows per ear. The row number is strongly related to a hybrid’s genetics and impacted only by serious environmental factors such as drought, nutrient deficiencies, and improper herbicide applications.

The tassel is initiated at approximatelyV6, although it will not be visible without  magnification. It is identifiable with plant dissection by V7.

Management/Scouting: Scout for root rots, seedling blight, cutworms, slugs, billbugs, Herbicide injury, flooding, weed escapes and excess weed competition.

Hay and Straw Barn Fires a Real Danger

Jason Hartschuh, CCA, Mark Sulc, Sarah Noggle, David Dugan, Dee Jepsen, OSU Extension

Usually, we think of water and moisture as a way to put a fire out, but the opposite is true with hay and straw, which when too wet can heat and spontaneously combust. Most years this is more common with hay than straw because there is more plant cell respiration in the hay. This year the wheat is at various growth stages and straw seem to have more green stems than normal. When baled at moistures over 20% mesophilic bacteria release heat-causing temperatures to rise between 130⁰F and 140⁰F. These bacteria cause the internal temperature of hay bales to escalate, and can stay warm for up to 40 days depending on the moisture content when baled. If bacteria die and the bales cool, you are in the clear but if thermophilic bacteria take over temperatures can rise to over 175⁰F.

Assessing the Fire risk

  • Most hay fires occur within the first six weeks after baling
  • Was the field evenly dry or did it have wet spots
  • Were moistures levels kept at 20% or less
  • If over 20% was hay preservative used

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What is the Nutrient Value of Wheat Straw?

Laura Lindsey, Ed Lentz, OSU Extension

Wheat harvest is now underway. What is the nutrient value of the straw? The nutrient value of wheat straw is influenced by several factors including weather, variety, and cultural practices. Thus, the most accurate values require sending a sample of the straw to an analytical laboratory. However, “book values” can be used to estimate the nutrient values of wheat straw. In previous newsletters, we reported that typically a ton of wheat straw would provide approximately 11 pounds of N, 3 pounds of P2O5, and 20 pounds of K2O.

The nitrogen in wheat straw will not immediately be available for plant uptake. The nitrogen will need to be converted by microorganisms to ammonium and nitrate (a process called “mineralization”). Once the nitrogen is in the ammonium and/or nitrate form, it is available for plant uptake. The rate of which mineralization occurs depends on the amount of carbon and nitrogen in the straw (C:N ratio).  The USDA reports a C:N ratio of 80:1 for wheat straw which means there are 80 units of carbon for every unit of nitrogen. Mineralization rapidly occurs when the C:N ratio is ≤ 20:1. At a C:N ratio of 80:1, mineralization will be much slower. (For comparison, corn stover is reported to have a C:N ratio of 57:1.) Rate of mineralization is also influenced by soil moisture and temperature. Since mineralization is a microbial-driven process, mineralization will be slowed (halted) in the winter when temperatures are cold. Thus, no N credit is given for wheat straw since it is not known when the N will mineralize and become available to the following crop.

Besides providing nutrients, straw has value as organic matter, but it is difficult to determine the dollar value for it. Removal of straw does lower soil potash levels. If straw was removed after heavy rainfall, some of the potash may have leached out of the straw, lowering the nutrient value of the straw. However, a soil test should be done to accurately estimate nutrient availability for future crops.

Noxious Weeds in Cover Crop Seed and Seed Germination

Source: Alexander Lindsey, Laura Lindsey, Mark Loux, Anne Dorrance, Stan Smith, John Armstrong, OSU Extension

Seed quality is key to establishing a good crop (or cover crop). Some of the critical components of seed quality are percent germination, mechanical analysis for purity (% other crops, % inert, and % weeds), and a listing of noxious weeds identified by scientific/common name and quantity found. As producers are looking for seed sources to provide living cover on acreage this year that was previously earmarked for corn or soybeans, it is important to pay attention to the quality. These tests may also be required on seed lots for use in some relief programs as well. Commercial or certified seed used for cover crops should have a seed tag that shows variety and the seed quality measurements above. However, if the seed is sourced from out of state, the noxious weeds listed (or NOT listed) on the tag by name may differ from those had the seed been sourced from Ohio.

Only the noxious weeds for the state where the seed was originally going to be sold are required to be listed on the tag by name and quantity (Federal Seed Act, part 201.16). Each state determines which species are included on this list, and can differ from state to state. If seed is outside of Ohio for use on-farm, producers may want to have the seed tested for an “all state noxious-weed exam” prior to planting if this was not done previously on the seed lot. Only 1.1-1.2 lbs of seed is needed for the test, but it is critical the sample is representative of the lot to ensure quality test results. This test would screen the seed sample supplied for the weed contained in this list: https://www.ams.usda.gov/sites/default/files/media/StateNoxiousWeedsSeedList.pdf, and may serve as a more comprehensive exam than was conducted at the time of initial seed lot labeling. One service provider that can conduct this exam is Central Ohio Seed Testing (a subsidiary of the Ohio Seed Improvement Association; https://ohseed1.org/about-our-lab/). Samples can also be sent to ODA for an Ohio noxious weed exam (https://agri.ohio.gov/wps/portal/gov/oda/divisions/plant-health/grain-warehouse-feed-and-seed/). Depending on the source of seed and the planned use, a seed lot may be eligible to be tested for free through ODA between June and December (up to three per farmer). Conducting a noxious weed exam could help slow the movement of problematic weeds throughout the state and minimize future weed problems.

Another issue to consider is the quality of seed in storage that was not planted this year due to weather. Storing seed in an environment where the temperature (in F) plus the % relative humidity are less than 100 (Harrington’s rule) helps to minimize the rate of seed deterioration (or loss in germination and vigor). Seed germination is an important consideration for determining seeding rate to ensure the critical final stand for yield is achieved for crops like corn and soybeans. Most seed germination percentages on a seed tag for agricultural seeds (like corn and soybeans) are valid for 12 months from the last date of the month in which they were completed, with the exception being cool season grasses which are valid for 15 months beyond the month of testing (Ohio Revised Code, Chapter 907.07). Be sure to check the seed tag for both the date of the test as well as the germination when planning seeding rates.

You can search this blog for a complete description and pictures of all of the weeds on the Ohio Noxious weed list.

Corn Growth & Development – V3 & V4

Today managing your corn crop requires knowledge of the different growth stages of the corn plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.  Each week throughout the growing season I will discuss the various corn growth stages and management issue at each stage.  

V3 – V4  – 350 – 400 Growing Degree Days (GDD’s)

Photo source: Iowa State University

The V3 stage is reached approximately 10 – 20 days after emergence.  At this stage the photosynthesis process begins and the plant no longer relies on the seed as its food source.

The nodal root system takes over for the seminal root system.  The nodal roots continue grow and begins to develop root hairs.

The corn plant is erect due to the combined strength of the leaf sheaths layered on top of each other.  Leaves are still developing and the growing point remains underground.

Management/Scouting: Scout for root rots, seedling blight, cutworms, slugs, billbugs, Herbicide injury, flooding, weed escapes and excess weed competition.

Ohio NRCS Announces Disaster Recovery Funding to Plant Cover Crops on Flooded Cropland Acreage

NRCS just announced a new Disaster Recovery Funding program.  This funding will be administered through the EQUIP program.  Signup with Doug at the NRCS office beginning Monday.  Many of the details are not available yet.  Click on the link below for more details.

FY19 OH EQIP Disaster Recovery NR2