C.O.R.N. Newsletter 2013-23

Dates Covered: 
July 23, 2013 - July 29, 2013
Editor: 
Rob Leeds

Management of Frogeye leaf spot on Susceptible Varieties in Ohio

Several reports and samples this past week with frogeye leaf spot on leaves in the upper/mid canopy.  You will be able to find pictures and a detailed factsheet of this soybean disease at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/t01_pageview3/Soybean_images.htm

And for those that prefer facebook  https://www.facebook.com/OsuSoybeanPathology.

Frogeye leaf spot is a fungal disease that is caused by Cercospora sojina.  This pathogen is typically pretty rare in the northern states, but due to the widespread planting of some highly susceptible varieties and milder winters, we now have more inoculum in the spring.  One of my previous graduate students (Christian Cruz) did the tedious work to examine soybean residue to find the viable conidia (spores).  At the end of the 2012 season, there was quite a bit of frogeye late in the season in our fungicide trials.  At present there is enough there (almost R1) to begin to plan sprays.

There has been another development with this fungus that is a bit troubling.  Numerous populations of this pathogen have been identified that are resistant to azoxystrobin (Quadris) and pyraclostrobin (Headline).  These were first found in Kentucky in 2010 and since then have also been found in states up and down the Mississippi.  To date, none have been detected in Ohio, but the truth is we have done very little sampling.

In 2007, we had frogeye develop at two of OARDC Branches on Seed Consultants line SC 9384, a susceptible line that they have very generously donated to our field studies.   Disease levels in the top canopy at the end of the season were 28.5% and 47% at Northwest (Wood County) and Western (Clark county) Branch research stations.  The disease was only present in the top canopy at Hotyeville, so fungicide applications were made at the R5, but had very little impact if any. There were no yield differences.  Western had a different story.  At this location, the mid canopy foliage also was more than 40% of the leaf area affected and yield loss was approximately 19% when the best fungicide treated plots (65 to 69 bu/A) were compared to the nontreated (Mean 54 bu/A). 

Fungicides applied at R1 on these indetermimant soybeans were not significantly different than the nontreated.  I think that this is due to the fact the plant still has a lot of growing to do and the later foliage does contribute to yield.  Some other examples from the trial include:

Another thing is that rate of the fungicide makes a difference.  For example Evito at 3.1 fl oz yielded 59 bu/A while Evito at 5.7 fl oz (both R3 only applications) yielded 65.9 bu/A.

Domark  (3 fl oz/A) at R3 followed by Domark (3 fl oz/A) at R5) yield 64.9 bu/A while Domark plus Headline (3 fl oz/A) and again at R5 only yield 67.7 bu/A. 

There are several things to learn from this study:

1.      If the strobilurins are effective, use them at the higher rates.  This will diminish the chances of fungicide resistance developing in the population.

2.      The triazoles are equally effective, if applied at the right rates and timings.

3.      Through the management of many, many pathogens with fungicides, it is always best to rotate classes of chemistries rather than combining them.  The only reason to combine chemistries is if you have multiple pathogens to control and you need more than one active ingredient in the tank.

Finally – the best approach to managing this disease though is to use a resistant variety, they are the same price as the susceptible and you won’t have to worry about this.

Corn Pollination Overview

Pollination is well underway in most Ohio corn fields. According to the National Agricultural Statistics Service for the week ending 7-21-13, 63% of the state’s corn was silking. The pollination period, the flowering stage in corn, is the most critical period in the development of a corn plant from the standpoint of grain yield determination. Stress conditions (such as hail damage and drought) have the greatest impact on yield potential during the reproductive stage. The following are some key steps in the corn pollination process.

Most corn hybrids tassel and silk about the same time although some variability exists among hybrids and environments. On a typical midsummer day, peak pollen shed occurs in the morning between 9:00 and 11:00 a.m. followed by a second round of pollen shed late in the afternoon. Pollen may be shed before the tassel fully emerges. Pollen shed begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen. Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. However, most of it settles within 20 to 50 feet.  

Will the heavy, protracted rainfall and root lodging which has occurred recently in some areas adversely affect pollination? Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet. Also, silks are covered with fine, sticky hairs, which serve to catch and anchor pollen grains. Most root lodged corn has recovered with the upper portions of plants resuming a vertical growth pattern through "goosenecking" so negative effects on pollination should be limited.

Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours. A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.

Pollen of a given plant rarely fertilizes all the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant may be pollinated by other plants in the field. The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains, which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are usually only a problem under conditions of extreme heat and drought. As noted above, poor kernel set is more often associated with poor timing of pollen shed with silk emergence – with silks emerging after pollen shed (poor “nick”). However, hybrids rarely seldom exhibit this problem unless they experience extreme drought stress.

For more on the pollination process in corn check out the following.

Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. 2011. Corn growth and development. Iowa State Univ. Ext. PMR 1009.

Nielsen, R.L. 2010. Tassel Emergence and Pollen Shed. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.agry.purdue.edu/ext/corn/news/timeless/Tassels.html .

Nielsen, R.L. 2007. Silk Development and Emergence in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/Silks.html

Weather Outlook: Normal to Slightly Below Normal Temperatures For The Next Week

After a hot and humid and mainly dry week last week followed by some locally heavy weekend rains in areas, we now return to a cooler and more typical rain pattern again.

July is averaging 1-3 degrees above normal across Ohio with rainfall ranging from normal to about 2 inches above normal. The week of July 22-28 will feature normal to slightly below normal temperatures and the best chances of rain through Tuesday July 23 then again on the weekend of July 27-28.  This trend will continue into the week of July 29-August 4 with temperatures normal or slightly below normal and rainfall close to normal or slightly above normal. Normal temperatures are highs in the 80s and lows in the 60s. Normal rainfall is about 0.75 to 1 inch per week.

The early outlook for August is for near normal temperatures and rainfall near or above normal. Soil moisture conditions remain ideal across most of the corn and soybean region. This is the opposite of 2012 and was forecast last year for this growing season across our region. The exception is across north central and northeast Ohio which is considered quite wet currently. These small scale anomalies at sub-state level are very difficult to predict on the climate and seasonal outlook scale.

Low-Drift nozzles: When were they introduced, and how much have they prevented drift complaints/cases/incidences on non-target sensitive crops, personal property, or people?

This is the time of the year we need to pay extra attention to reducing spray drift because some of us are applying herbicides that could create serious problems if the herbicide drifts away from the application site and deposits on crops sensitive to that particular herbicide, such as Dicamba products or Glyphosate. One way we can reduce spray drift is through using low-drift nozzles. Recently someone asked me the question on top of this article. I thought I should share a summary of my answer to this person with you.

When was the first low drift nozzle developed, and what others followed it:
Manufacturers have gradually changed designs of their nozzles in order to improve spray patterns and reduce the number of drift-prone droplets. In the USA, the most established sprayer nozzle manufacturer is Spraying Systems, also known as TeeJet. They started the development in their nozzles to achieve the two goals I mentioned above back in late 70’s when they came up with a series called LP nozzles (LP stands for Low Pressure). However at low pressures they noticed that the3 spray angle would decrease. Then the next breakthrough came in 1985 with their XR (stands for Extended Range) nozzles which allowed users to operate their sprayers at pressure as low as 15 psi without seeing any noticeable change in the spray pattern. When operated in low pressures, these nozzles would reduce the number of drift-prone droplets noticeably. The first nozzle in what we call today “low-drift nozzles” was “DriftGuard” developed in 1992. Not many people buy these nozzles these days because “better” (more effective) low-drift nozzles were introduced about 2-3 years later. Several companies introduced what is called as “Air Induction Low-drift nozzles”. Today, the most popular types of low-drift nozzles sold are this type.

How much have they prevented drift complaints/cases/incidences on non-target sensitive crops, personal property, or people?

Low drift nozzles work. They reduce the number of drift-prone droplets significantly. However, unfortunately I don’t have a good answer to the question on how these nozzles have prevented drift complaints.  No such data exist. However, there are indications that these nozzles must have been reducing incidents of drift because people have been switching from the conventional nozzles to “low-drift nozzles” over the years.  At least the information I got from one major nozzle company, the “low-drift” nozzles have been overselling their highly popular conventional nozzles. If these nozzles were not reducing the risk of drift damage, people would not have been paying more to buy the low-drift nozzles.  Another indication that these nozzles are reducing the risk of spray drift is the recent decision BASF, a major agricultural chemical company, has made. For their product called “Status”, basically a Dicamba product,  BASF is supplying low-drift air induction nozzles to buyers of Status, free of charge. BASF must have credible data in their hands that there will be fewer complaints related to drift damages as long as people are using Air Induction nozzles. Otherwise, they would not be providing free nozzles (costing up to $300 per buyer, depending on the size of the sprayer boom and the number of nozzles on the boom )to each buyer of Status herbicide.

Software for Nutrient Management Plan Development Workshop August 8th

If you are interested in developing Nutrient Management Plans for clientele involved in NRCS EQUIP or other cost share programs this workshop is design to teach a few tips and tricks to the software used in the planning process. Bring along your laptop and we will walk through an example farm and develop a plan from the information gathering to a final document. The next workshop is scheduled for August 8th in the Marion County Extension Office, 222 W Center Street, Marion, OH from 9:30 am until 3:30 pm.

Details on the Day. The workshop will focus on MapWindow GIS & MMP Tools, MMP software and Ohio Nutrient Management Templates as approved tools for development of Fertilizer Only or Precision Fertilizer Only Nutrient Management Plans for NRCS programs such as EQUIP. The training will use a sample farm to demonstrate the utilization of these two programs to generate a plan that can be presented to NRCS for approval.

MapWindow GIS is an open source GIS product that is used to develop nutrient management plans by defining fields and farms then downloading spatial data such as soil types which provide base information needed for MMP is Nutrient Plan development. Data generated is exported to MMP through the MMP tools which have been added. The version used for the workshop is dated 3/4/2013 and is available through http://www.purdue.edu/agsoftware/mmp/ (See Right hand side of landing page)

MMP Version 0.32 is the current version of the program from Purdue and is linked for download through http://www.purdue.edu/agsoftware/mmp/

The current templates for Ohio plans that work with MMP have been developed by NRCS State Agronomist Mark Scarpitti can be found at http://efotg.sc.egov.usda.gov/treemenuFS.aspx. The templates will be provided on the workshop disk given out during the workshop.

Improved Drainage Water Management Plan to be Showcased at 2013 Farm Science Review

Recent heavy rains in the Midwest stress the need for proper water management plans like that of the Farm Science Review’s year-round effort to improve the water quality at the Molly Caren Agricultural Center, which will be emphasized with the installation of 40 acres of drainage lines and structures during the 2013 Review by the Ohio Land Improvement Contractors Association (OLICA). Read more details at the Farm Science Review website.

http://fsr.osu.edu/media/news/archives/2013/improved-drainage-water-management-plan-to-be-showcased-at-2013-farm-science-review

 

 

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About the C.O.R.N. Newsletter

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.