Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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April 29, 2008

Iowa State University Extension Information for Southeast Iowa
By Jim Fawcett, ISU Extension Field Agronomist
4265 Oak Crest Hill Rd. SE
Iowa City, IA 52246



Alfalfa Winter-Kill


            I continue to get reports of winter-kill of alfalfa in the area. Brian Lang estimates that close to 80% of the alfalfa fields south of highway 20 in Delaware and Buchanan counties may not be worth keeping. I donít think the problem is that widespread here, but there are a number of fields where the stands have been lost. Some stands may have been saved further south due to the soils not being as wet or due to the December ice sheets melting in early January with that short winter thaw we had. There are also many fields where the stand has been lost in the lower areas due to ice sheets and wet soils, with better stands on the higher areas.

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 6Ē of growth. Itís 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 Barnhartís 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 6-10Ē 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 isnít going to happen 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 seedings of forages see Steve Barnhartís article at





            It has been a few years since planting has been delayed until May. I heard a producer (who shall remain anonymous) comment that he might try to plant some soybeans this Thursday, since heíd rather mud in beans than corn. I think it is a little early to think about mudding in either crop, since we have the whole month of May yet to get the crop planted and still get good yields. All isnít lost if we are still planting in late May. We shouldnít even 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.




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 I have seen 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 Hartzlerís article for more details at


Canada Thistle Control


            Iím starting to get questions on controlling Canada thistle. Most products work best if sprayed after the plants get some height to them but before many buds are present (usually late May or early June). The new products Milestone and Forefront are not restricted use and have given good long term control in my test plots. The attached fact sheet is based on work done in 2006 and 2007 in Johnson County.








            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 at the ISU SE Iowa Research & Demonstration Farm near Crawfordsville on June 26. More details will be posted soon.



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

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Last Update: April 29, 2008
Contact: Jim Fawcett

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