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Ohio State University Extension


C.O.R.N. Newsletter 2013-18

Dates Covered: 
June 17, 2013 - June 24, 2013
Amanda Douridas

Weather Outlook

The outlook for the remainder of June is for above normal temperatures and rainfall at or below normal. 

The week of June 18 will see temperatures only slightly above normal but it will go from below normal to above normal temperatures by the weekend. Rainfall will be limited in most places after June 18.
Above normal temperatures will become more entrenched for the week of June 24. Some rainfall is expected but most places will see an inch or less which is normal to slightly below.
The heat will likely relax some by around the 4th of July but it is expected to be very humid. This could increase disease risk? Rainfall will also likely increase again by early July.
2013 has been one of the quietest in the last 20 years for severe weather which follows our outlook for 2013 in 2012. Risk is down in Ohio in 2013 versus 2011-2012. This risk will likely start increasing again by 2014 so enjoy the overall reduced risk (not no risk) of 2013.
Also of note is it looks like April, May and June period will end with slightly above normal temperatures. Many think it has been cool, but outside of the very cold March we had, it is more in reference to the warmest spring on record in 2012 we are comparing 2013 too.
Soybean Aphid

Soybean Aphid

Although we have not yet found aphids on soybeans in Ohio, other states are reporting finding them in fields.  During a regularly scheduled aphid scouting trip in mid-May made by our colleagues from other states, aphids were reported as “abundant near Toledo (Secor Park)” on buckthorn, the aphid’s overwintering host.  What this probably means is that soybean aphids will be present this year in Ohio soybean fields, which would continue the two year cycle. 

If you remember from this past winter, we were not sure what might happen in this year, and thus, had not made a prediction.  However, based on what is being seen in other Midwest states, aphids will probably be present. At this time, there is no way to predict how common aphids will be, and whether they will reach economic levels.  We urge growers to plan to scout for aphids later this summer and prepare to take action if economic thresholds are reached.  And most importantly, continue to read this newsletter for further updates as we go through the summer.

Postemergence applications in soybeans – are you waiting too long?

It’s another POST soybean season, and we have largely been receiving questions similar to the past several years.  These include how to manage giant ragweed, pokeweed and a few other perennials, vines, and marestail (good luck there).  It is evident however that many fields were subject to a more comprehensive approach to marestail management, starting with herbicides applied last fall, and marestail problems are generally less frequent.  But this is possibly offset by the lack of rain to effectively activate residual herbicides in areas, which results in higher and more varied weed populations to manage with POST herbicides.  Some things to consider relative to POST treatments in soybeans:

- With regard to POST control of marestail, hiring a crew of people with hoes is probably the most effective option.  Or at least cut the top of the plants off so that seed production is prevented.  We are hearing mostly about difficulty controlling plants that overwintered in fields not treated last fall (there’s a lesson here somewhere).  Plants that have survived one herbicide treatment already are not likely to be controlled by anything.  In fields where the population is still sensitive to ALS inhibitors, a high rate of Classic or FirstRate may provide some suppression or control of small plants.  Flexstar and other PPO inhibitors have essentially no activity on marestail, and low rates of 2,4-DB are not much better.

 - The most effective approach on giant ragweed is to make an initial POST application when plants are small – 4 to 8 inches – and then make a second application about 3 weeks later.  Delaying the initial application until plants are larger in order to control late emerging plants usually results in less effective control.  OSU research has shown that the single application approach on larger plants results in a higher frequency of plant survival, and higher numbers of seed returned to the soil seedbank.  In populations that still mostly respond to glyphosate (at least 80% control/suppression with the first application), use a glyphosate rate of 1.5 lbs ae/A in the first POST application, and 0.75 lb/A in the second application.  Populations resistant to glyphosate are usually also resistant to ALS inhibitors, and the most effective strategy for these will be to mix glyphosate with Flexstar (or use Flexstar GT).  Use the highest labeled Flexstar or Flexstar GT rate for your geography, and include crop oil concentrate or a methylated seed oil.  Flexstar is usually about an 80% herbicide for control of giant ragweed, so it’s possible that a later application of Cobra may be needed.

- For pokeweed and many other perennials, a high rate of glyphosate is often more effective than anything else.  Pokeweed control can be improved by increasing the spray volume, or slowing down, to improve coverage.  Applying when plants have some size but are still completely underneath the spray boom can reduce the potential for regrowth, but be prepared to treat again later in the season when plants do regrow.  The addition of Flexstar or Cobra can help with the dessication of perennial vines, and any of the products rated 8 or better on morningglory in the “Weed Control Guide for Ohio and Indiana” can help with annual morningglory control.  The addition of Classic may improve control of dandelions.

- We have heard often about the strategy of waiting until soybeans are about to canopy to apply POST herbicides.  The principle here appears to be that the herbicide will control emerged weeds and then the shade from the crop canopy will prevent later-emerging weeds from competing with the soybeans.  This can work where the residual herbicides applied prior to planting actually control most of the weeds up to this point, so that the POST treatment is primarily addressing a few small weeds.  However, in fields where the residual herbicides are not this effective, or where certain tougher weeds are present (giant ragweed, waterhemp, etc), applying POST herbicides just prior to canopy closure is really too late.  No-till soybeans may require 8 weeks to canopy, and delaying POST applications until this late inevitably means that at least some of the weeds are large.  It’s almost always a more effective strategy in the end to make an earlier POST application to smaller weeds, and then a second application 3 weeks later if needed.  Keep in mind also that as soybean planting is delayed later into the season, the first POST application occurs later in the overall weed emergence cycle, so the likelihood of needing a second POST application is reduced.

- A final note about late-planted soybeans and POST application of herbicides.  When soybeans are planted later in the season, the progression through growth stages occurs during a shorter period of time.  Flowering can occur when plants are relatively small, and delaying POST applications until plants are a certain size may result in treatment of plants at a more advanced growth stage compared with early planting.  Glyphosate labels specify that the herbicide can be applied through the R2 stage.  The R3 stage starts when a pod of at least 3/16 inch long appears at one of the four uppermost nodes with a fully-developed leaf on the main stem.  Applying after the R2 stage increases the risk of injury to soybeans.  Injury is not necessarily likely for late applications, but can range from transient “yellow flash” to abortion of pods on the upper part of the plant.  Labels for other herbicides may also specify application prior to flowering (Table 14 in the OH/IN Weed Control Guide).  Late application of some POST herbicides with substantial residual in soil, such as Flexstar, can also increase the risk of carryover especially if dry weather occurs afterward.

New videos available on the OSU weed science website

We have posted several new brief videos on the OSU weed science website –  Subjects include flumioxazin injury to soybeans and the management of spring residual herbicide treatments to maximize marestail control.  You can also find a video and other information on the identification of Palmer amaranth and other pigweed species.

Impact and Management of Phosphorus across Various Tillage Practices; A Nutrient Application Field Day

Impact and Management of Phosphorus across Various Tillage Practices; A Nutrient Application Field Day

Phosphorus fertilizer is essential to Ohio crop production when applied at correct rates, timing and placement.  But, if nutrient applications are not managed, farm field phosphorus can be lost into water resources and promote Hazardous Algal Blooms (HAB). Major water quality problems have occurred in Lake Erie, Grand Lake St. Marys and other Ohio water resources in recent years.  Within these aquatic ecosystems, harmful organisms - Hazardous Algae Blooms (HAB) - have been prevalent in recent years.

To protect Ohio water resources, phosphorus fertilizer must be put in the right place.  “Right place likely holds the greatest opportunity for improvement (in water quality as it related to farm field P loss),” The Right Place to Put Phosphorus ; Dr. Tom Bruulsema, Northeast Director of IPNI;

Thus to examine the impact of tillage on phosphorus loss and other crop production factors that influence crop yields, the following field day to be held July 18, 2013 from 8:30 AM, to 2:30 PM in Wood County, Ohio – a quarter mile west of the intersection of I-75 and Hwy 582 - about 6 miles north of Bowling Green.

8:30        Registration

9:00        Welcome

9:30        Phosphorus (P) Basics

10:10     Cropping System Rotation #1

11:10     Cropping System Rotation #2

Noon     Lunch – Compliments of Northern Ohio John Deere Dealers:  Findlay Implement, Shearer Equipment and Kenn-Field Group

12:45     Cropping System Rotation #3

1:45        Phosphorus State of the Union

The three cropping systems that will be utilized in a rotation are:

  1. Phosphorus movement in Full width till systems and related equipment solutions
  2. Phosphorus movement in No-till systems and related equipment solutions
  3. Phosphorus movement in Strip-till systems and related equipment solutions

Within each cropping system, the following will be discussed:

The discussion content will focus on the potential mechanisms of phosphorus movement within a tillage system.  For example: In a full width tillage system (including conventional tillage and conversation tillage systems) there will be a field demonstration of the ability of various tillage tools to effectively incorporate phosphorus in to the soil profile. Topics covered with the specific tillage demonstration will include particulate P movement via erosion associated with that tillage system, relationship of P soil test levels to P loss, phosphorus solubility within the tillage system, and impacts of tillage on phosphorus stratification, relationship of P stratification to soil test P and soluble P loss.

The field day will be held in Wood County, Ohio – a quarter mile west of the intersection of I-75 and Hwy 582 which is about 6 miles north of Bowling Green.  The program is free but an email RSVP is required to .  Please include your name and a phone number where you can be reached in the email.    Four and a half hours of CCA credits have been applied for including 1 hour of soil and water and 3.5 hours in nutrient management.   Contact Steve Prochaska at 740-223-4041 or with any questions. 

OSU Weed Science Field Day – July 10

The 2013 OSU Weed Science Field Day will be held on Wednesday July 10 at the OARDC Western Ag Research Station.  Registration starts at 8:30 and a field tour with presentations by OSU faculty, staff and students will start at 9 am.  There is also, as usual, the opportunity to view studies of interest on your own.  The cost is $30, which includes the tour book and lunch.  Please RSVP to Bruce Ackley,, and include the number of people in your group.  Payment can be via cash or check the day of the event.  Address of the research station – 7721 South Charleston Pike, South Charleston, OH.  Location – about 5 miles south of I-70 on SR 41.  There will also be an opportunity to purchase the fashionable Columbia sun hats with OSU weed science logo that our crew has been sporting in recent years ($30).


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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.