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East-Central and Southeast Iowa Crop Information


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May 6, 2013




How will Corn Planted Last Week Fare?


I am fairly optimistic that most of the corn planted last week in EC and SE Iowa will be OK, since our soil temperatures did not drop as much as in the northern and western part of the state, and only got into the mid to upper 40s for a day before rebounding. Areas to the west and north that saw the snow and colder soil temperatures may have fields with some stand problems, but time will tell. It’s a tough decision when the calendar says May, the soil is fit and soil temperatures are in the 60s, but the forecast is for snow. For current soil temperatures see



Don’t Rush to Get Corn in the Ground


With the delay in planting there will be the temptation to plant in less than ideal conditions now that we are approaching the second week of May with very little of the corn in the ground.  Although corn usually yields best when planted by early May, mudding it in to achieve that goal will likely cost more yield than delaying planting a day or two. This is anything but an average spring, so I wouldn’t expect to see average results with early planting. This may be a year where corn planted in the May 10-15 window yields more than that planted in late April and early May. That’s what we saw last year.


Small mistakes made at planting time can haunt you the rest of the season. Many producers can get most of their corn planted in about 3-4 days, so starting a day too soon and planting half the corn under marginal conditions usually doesn’t make sense. Some points to consider with corn planting this spring:


1.    Don’t plant into wet soils. This can lead to sidewall compaction which can lead to season-long problems. The roots will have difficulty growing through the compacted zone made by the planter and will be pancaked into a flat plane in the direction of the planter. This can lead to uneven corn growth, rootless corn, and K deficiency symptoms due to poor root growth. Poor root growth will be an even greater problem later if the summer turns dry.

2.    Don’t plant too shallow. When soil moisture is plentiful producers are tempted to plant corn more shallow. For every corn field I see with problems caused by planting too deep, I see a hundred fields with problems caused by planting too shallow. If the seed ends up being less than 1.5 inches deep, problems such as rootless corn and K deficiency symptoms are much more likely to occur. Even if the seed is placed 1.5 inches deep, sometimes the soil can settle after planting or there can be soil erosion so that the plant actually “sees” a more shallow depth. Corn should be planted 1.5-2” deep and error on the deep side.

3.    Shoot for corn stands of 34,500-37,000 plants per acre. Ideal corn seeding rates have been increasing at the rate of about 400 seeds/A/year. Average corn yields per plant haven’t changed much in the past 50 years. Most of the yield gain has been from breeding corn that can tolerate an increased population. If you are still planting the same population you did 10 years ago, you’re paying 2013 seed prices and only getting 2003 yields.

4.    Pay attention to details at planting. A little extra time making sure planter settings, seed spacing, depth, and population, and soil conditions are correct can pay big dividends, especially with today’s prices.


What About Nitrogen Carryover from 2012?


Going into April it was looking like there would be many fields with 50 lb/A or more of additional nitrogen available this spring because of last year’s dry conditions. Unfortunately that situation has likely changed now, with April 2013 being the wettest April on record for Iowa.  Some areas of eastern Iowa have gotten 10-15 inches of rain in the past month.  Although there should not have been a lot of de-nitrification occurring because of the very cold soils, leaching of nitrate does occur in cold soils and tiles have been running.


Preliminary results from soil samples taken this spring indicate that there is much less nitrate now in the top 3 feet of soil than what we found late last fall. We may have closer to a “normal” amount of nitrogen carryover, and not the excess that it was looking like we would have. In areas that have not gotten as much rain, there may still be opportunities for cutting nitrogen rates.


How Long Do I Have to Wait After Applying Anhydrous Before Planting?


It is often recommended to wait 7 days after applying anhydrous before planting, but in reality there is no magic numbers of days to wait to prevent fertilizer burn to corn. I have seen stand reductions even when the nitrogen is applied in the fall, and corn can be planted immediately after application without problems. The main thing is to be sure to apply the anhydrous 7-8 inches deep and get a good seal. Most of the anhydrous will diffuse to a zone about 6 inches in diameter within 24 hours. If the anhydrous is applied 8 inches deep and you are planting 2 inches deep, you will still have the anhydrous zone 3 inches below the seed. When the anhydrous is applied when the soil is too wet, more will diffuse closer to the soil surface. One way to reduce future problems is to apply the anhydrous at an angle to the corn rows so if there are injury problems later you won’t be taking out entire rows of corn. At this point in the season, it may be time to switch priorities and think about getting the corn planted first and worry about the nitrogen later.




Alfalfa Weevil


We have surpassed 200 Growing Degree Days (GDD) (base 48, from Jan. 1) south of Interstate 80, which suggests that it is time to scout south-facing slopes for Alfalfa Weevil there; north of Interstate 80, the time to start scouting south-facing slopes is fast approaching. The easiest way to scout for Alfalfa Weevil is to start with a sweep net just to survey a field. If there are some alfalfa weevil in the net, then follow the proper scouting procedure in (in the paragraph above Table 1) to determine if the economic threshold is reached. Alfalfa Weevil problems in eastern Iowa have been few in recent years, but it is still best to scout for them. Alfalfa weevil quit feeding at about 900 GDD Base 48. You can monitor GDD Base 48 progress at and


Evaluating Alfalfa Stands


There do not appear to be widespread problems with winter-kill in alfalfa, but there will always be some winter-kill, especially on older stands, so stands should be evaluated. This year, it appears that older stands that were intensively harvested and new seedings are most likely to have thin stands. Dr. Barnhart, ISU Extension Forage Specialist, posted basic information on stand evaluation of alfalfa and other forages at: A publication that helps assess root health is available at: This publication also provides the other option for stand evaluation called the “Stem-Count Method”. This is actually a better evaluation method then for plant counts, but you have to wait for stands to reach 6 to 10 inches in height for the assessment to be reliable. An ideal stand has 55 or more stems per square foot. Consider replacing stands that are less than 40 stems per square foot.




Thistles in Pastures


Musk thistle and bull thistle are much easier to kill if they are sprayed when they are in the rosette stage, before they begin to bolt in the spring. Although 2,4-D and dicamba can do a good job of killing emerged thistles, products that have greater soil activity, such as Milestone (3-5 oz/A), Forefront (1.5-2.0 pt/A), and Grazon P&D (2-4 pt/A), usually provide superior control, partly because they will also control seedlings that emerge after application.


For the most effective control of Canada thistle, it is best to wait until the thistles have a chance to grow some and are about to put on buds, which is usually in late May or early June. Canada thistles have extensive underground root systems. It is easy to kill the above ground part of the plant, but much more difficult to kill the root system so they will not be back the next year. Milestone, Forefront, and Grazon usually give the most consistent control. Higher rates are needed than for biennial thistle control. Crossbow is not a good product for Canada thistle control, but is very effective on multiflora rose and other woody and broadleaf weeds. A fact sheet based on Canada thistle trials conducted in Johnson and Keokuk Counties can be found at:




June 26, 2013, 1:00 p.m.


ISU NE Research & Demonstration Farm Spring Field Day – Nashua

As details become available, they will be posted at


June 27, 2013

Special Session for Certified Crop Advisors (9:00 a.m.) &

ISU SE Research & Demonstration Farm Spring Field Day (1:00 p.m.)


As details become available, they will be posted at




If you have any questions, please feel free to contact the Iowa State University Extension Office.

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Last Update: May 6, 2013
Contact: Jim Fawcett

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