Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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May 7, 2008




The wet weather is slowing down spring field work and has already delayed the planting of wheat and oats. Those planning to try some spring wheat this year may want to change those plans if the rain continues next week. Potential yields decline for both oats and wheat about 10% per week for each week planting is delayed after April 15, and an additional 15% per week if planting is delayed beyond May 1. Lance Gibson has a nice fact sheet on growing spring wheat in Iowa at




Check Alfalfa for Winter-Kill


There does not appear to be widespread problems with winter-kill, but some fields in the area do have patches where ice sheets formed and smothered out the alfalfa. The smothered out areas tend to be in low spots where ice accumulated, and are more likely to have occurred in fields where the alfalfa was cut or grazed short in the fall. With the winter-kill and the difficulty of getting new seedings established this spring due to the wet weather, we may be seeing short supplies and some very high hay prices. With this in mind it might be wise to keep some of the marginal stands and perhaps try to thicken the thin areas up by inter-seeding some oats or annual ryegrass (not cereal rye), if the weather permits, to try to get one more year from the stand. As we get later into May, oats (or wheat, triticale, or barley) would have less risk of emergence problems due to dry surface soils because of the larger seed. Oats should be drilled at about 1.5 bu/A (half the full seeding rate).


The usual point to consider reseeding is when stands are less than about 40 stems per square foot (3 crowns per sq ft on stands 4+ years old). Some plants are just starting to green up now with others showing about 6” of growth. It’s important to check a few taproots, especially on the slow to green-up plants, to make sure most of the root is firm and white. See Steve Barnhart’s recent article in the ICM News for more information at



Time to Scout for Alfalfa Weevil


 With the possibility of tight supplies of hay and high prices it is especially important to be watching for pest problems this year and protect the crop when needed. With the cool temperatures, the alfalfa weevils have been slow to hatch, but should now be hatching south along and south of highway 92, and will be hatching later this week along and south of highway 30.  Check south facing slopes first for the presence of the alfalfa weevil larva. A sweep net can help to check areas quickly. If larvae are found, check 30 stems by counting larva in the upper leaves. With hay prices over $100/T, an insecticide will likely be justified with less than one larva per stem on 6-10” alfalfa. See the April 11, 2005 ICM Newsletter for a picture and more scouting and threshold details




How Late Can I Seed Alfalfa?


Ideally small seeded forages should be seeded by May 1, but that hasn’t happened this spring for many producers. The main risk as we get later into May is that the surface soil will dry out quickly with the warmer temperatures, leading to germination and emergence problems with small seeded crops that need to be seeded only about a quarter to a half inch deep. Around May 15 is the usually cutoff date for seeding small seeded forages, but late May seedings can be successful if May is unusually cool. For more discussion for things to consider with late seedlings of forages see Steve Barnhart’s article at

Don’t Mud the Corn Crop In

We are approaching the end of the ideal planting window for both corn and soybeans. Although timely planting by the first week of May is important for obtaining optimum yields for both crops, any potential yield gained can be more than lost if the crop is mudded in to try to beat the clock. Small mistakes made at planting time can haunt you the rest of the season. There is little change in yield potential until planting is delayed after May 10, and even with late May plantings, yields usually do not drop by more than about 10%; it is too early to think about mudding in corn since we have the whole month of May yet to get the crop planted and still get good yields.


We shouldn’t be thinking of switching to an earlier corn hybrid until late May.


If we do start planting under marginal conditions, Mark Hanna suggests adjusting the depth gauge wheels so they are just touching the soil without much pressure; see Mark’s article at


Some points to consider with corn planting this spring:
1.   Wait until soil conditions are fit.  Planting into wet soils 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, as Elwynn Taylor has been predicting.
2.   Use a planting depth of 1.5 – 2 inches. 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 final corn stands of 30,000-34,000 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 2008 seed prices and only getting 1998 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.  Again, see Mark Hanna’s article at


Planting Corn following an Anhydrous Ammonia Application


An often-asked question this spring is, “How long after applying anhydrous ammonia do I need to wait before planting corn?”  As long the anhydrous is placed at a 6-8” depth and there is a good seal, there is no need to wait before planting. This is also true with tilling the soil as long as it is fairly shallow tillage. If the anhydrous is applied at a more shallow depth or the zone that the gas spreads is greater (common with dry soils), applying the anhydrous at an angle to the corn row direction can minimize yield losses if there is a loss of stand due to fertilizer burn by assuring that an entire corn row is not injured. There is not a magic number of days to wait to avoid problems, but the longer the better.  Reggie Voss wrote a good article about this in the spring of 1993, which can be read at; it is now 15 years later, but the answer is still the same.




Burndown Herbicides


With the increased Roundup costs and delays in getting the burndowns on, there may be more interest in including 2,4-D as part of the burndown program. It can improve control of some weeds, including horseweed (marestail).  According to the label, planting of soybeans needs to be delayed 7 days after spraying 1 pt/A of 2,4-D ester (4 lb gal), and most labels suggest not spraying 2,4-D from 7 days before to 3 days after planting corn. Most of the problems seem to be with corn is when the 2,4-D is included with an amide like Dual or Harness and the spraying is done within that 10 day window. Injury is also more common when planting is done in less than ideal conditions and the seed furrow remains open, so we could be seeing more problems this year. See Bob Hartzler’s article for more details at






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The Spring Field Day at the ISU Southeast Research and Demonstration Farm will be one the afternoon of June 26, 2008.  Certified Crop Advisors can obtain 5 hours of credit (including 2 hours of soil and water) by attending a special session in the morning followed by the afternoon tour. More details will be posted soon at





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Last Update: May 16, 2008
Contact: Virgil Schmitt

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