Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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April  14, 2011




Weather and Planting


We are now in the time period when crop insurance re-plant provisions are active. Should planting begin?  The most recent data suggests that in the counties I cover along and north of I-80, in order to achieve 98-100% of yield potential, planting should occur between April 15 and May 9. For the counties I cover south of I-80, in order to achieve 98 – 100% of yield potential, planting should occur between April 17 and May 8. See for full details. However, hopefully the predicted cold weather has caused producers to strongly consider leaving the seed in the bag as substantial soil cooling after germination begins can cause significant problems. See Roger Elmore’s article at You can see the 4” soil temperature data across Iowa at


Still Trying To Decide Nitrogen Rates with these High Prices?


The corn nitrogen rate calculator can help in selecting nitrogen rates. It has just been updated with 2010 trial results and is now based on 200 N rate corn trials in Iowa with corn following soybean and 101 trails with corn following corn. With high priced corn, it is more important than ever to have adequate nitrogen fertilizer. With high priced nitrogen fertilizer, it is extremely important to not put on too much nitrogen fertilizer. You can access the calculator at





Evaluating Over-Wintering


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. 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.





Some drills were running this past two weeks seeding oats and wheat. 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. A nice fact sheet on growing spring wheat in Iowa is at





Drills were also running last two weeks seeding waterways and forages. In general, try to complete seeding of cool season forage grasses and legumes before May 1 as seeding after May 1 increases the likelihood that seeds will germinate but less frequent rainfall will allow the soil to dry out before roots are deep enough to reach moist soil, killing the seedlings.





Thistles in Pastures


Now is the time to be spraying biennial thistles, like musk thistle and bull thistle. They 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 is attached.


Herbicide Resistant Weeds


There are concerns about  glyphosate-resistant waterhemp and marestail in the area. This problem may be fairly widespread now. It may only be a patch or two in the field, but with one waterhemp plant capable of producing up to 5 million seeds, it doesn’t take long for the trait to spread through-out the field. With generic glyphosate now close to free, it is tempting to rely on it for our weed control needs, but if it’s use continues to be abused, it will eventually be worth what it is being sold for (worthless since it will no longer be effective on any weeds). If we are going to protect the usefulness of this amazing herbicide, it’s important to take steps now, even it means paying more in the short-term. Consider using soil-applied herbicides, and tank mixing with other herbicides that can help to control these problem weeds. Ignite (Liberty) is another option now that both Liberty-link corn and soybeans are available.


Is Glyphosate Causing Problems with Soybean Diseases and Micro-nutrients?


The short answer is NO. For a longer answer see           





Alfalfa Weevil


Alfalfa weevil activity may be starting south of I-80, so alfalfa fields south of I-80 should be scouted, beginning on south facing slopes. For details on scouting for and managing alfalfa weevils, see the Integrated Crop News article at and Alfalfa weevil activity is based on Growing Degree Days Base 48. Growing Degree Days Base 48 for Burlington, Davenport, Cedar Rapids, and Dubuque are posted at



Stalk Borers


Stalk borers can be a concern for corn grown adjacent to grassy areas, such as ditches and waterways, or in areas where there was a grassy weed or giant ragweed control problem in 2010. We are approaching the end of the time for two management strategies, especially along and south Highway 34 (Burlington, Fort Madison, Keokuk, and Mount Pleasant area). The first strategy is to burn the residue in those areas, thereby destroying the eggs before they hatch. The second strategy is to spray an insecticide to those areas immediately before egg hatch to kill the larvae as they hatch. The time of egg hatch is controlled by Growing Degree Days, so the egg hatch will slowly “move north” as more Growing Degree Days accumulate there. Stalk borer activity is based on Growing Degree Days Base 41. Growing Degree Days Base 41 for Burlington, Davenport, Cedar Rapids, and Dubuque, as well as additional stalk borer management information, are posted at


Corn Flea Beetles and Stewart’s Disease potential Low


Models to predict the survival of corn flea beetles suggest that the risk of successful overwintering of corn flea beetles is low for 2011. As corn flea beetles are the vector for Stewart’s Disease, the threat of this disease is, therefore, also low for 2011. For details, see the ICM News article at



Bean Leaf Beetle Potential


Bean Leaf Beetles numbers have been very low the last few years. With fewer beetles going into overwintering hiding places, there should be fewer to deal with this spring. However, it appears the success rate of bean leaf beetle overwintering is somewhat higher than what has occurred in the last few years, which may suggest somewhat greater pressure than what we have experienced in recent years. Remember that the first planted soybeans in an area will be the “magnet” for those overwintering beetles. For more information, see the ICM News article at







SPRING FIELD DAY (afternoon) &


JUNE 15, 2011


Details will be posted soon at




Doug Nolte and the Iowa Learning Farm (Iowa State University), hosts

1021 Highway 6, West Liberty, IA

JUNE 22, 2011, 10:30 a.m. – Noon, followed by lunch


The farm is just in Muscatine County near the Johnson County line. Program details will be forthcoming.





JUNE 29 (tentative), 2011

Details will be posted soon at





July 19, 2011

Details will be posted soon at








If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: April 14, 2011
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