Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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October 22, 2013



Much of the area may be receiving the first hard freeze of the fall tonight.


Sorghum and Sudangrass


Most concerns with the first fall frost deal with managing sorghum species including sudangrass. When these species are injured with the frost, the plant tissue releases prussic acid for a few days, which can be toxic to livestock. If plants are only partially killed, which is likely with a light frost, new shoots may start to grow which have more concentrated levels of prussic acid. Livestock should be removed immediately if a frost occurs and kept out for 5-6 days. If new shoots develop, livestock should be removed until the shoots are the appropriate height to graze (18-20 inches for sudangrass and 24-30 inches for sorghum-sudan), or until 5-6 days after a hard freeze which kills all shoots completely. For more information on managing sorghum species in the fall, see Steve Barnhart's article at




Because of the concerns with sorghum species, there is the false belief that alfalfa also becomes toxic with the first fall freeze. Alfalfa does not become toxic with the freezing temperatures, but there is a slightly greater risk of bloat, so the standard bloat prevention practices should be used (i.e., don't turn hungry cattle out into an alfalfa field where they might gorge themselves on the lush alfalfa).


Because of the shortage of hay this year there will be the temptation to try to get a last cutting of alfalfa this fall. Alfalfa has been under a lot of stress with the drought, which makes the fall rest period even more important this year. Temperatures in the upper 20s will not stop alfalfa growth, with more growth likely in the next week to 10 days. It's best to wait until after a killing freeze (mid 20s) to try to take another cutting of alfalfa to minimize the stress on the plants going into the winter. However, the later into October we get, the less will be any new top growth during the remainder of the year.





Integrated Crop Management Conference

December 4-5, 2013


Details are posted at:


Ag Chemical Dealer Update

December 2, 2013

9:00 a.m. to 4:00 p.m.

Highlander Clarion in Iowa City

Details are posted at


Crop Advantage Series


January 10, 2014

Catfish Bend Convention & Event Center, Burlington


Elwynn Taylor, Extension Climatologist

Mike Owen, Extension Weeds Specialist  and Chad Hart


January 23, 2014


Featuring Mike Owen, Extension Weeds Specialist


January 29, 2014

Highlander Clarion in Iowa City

Featuring Mike Owen & Elwynn Taylor


Details 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: October 22, 2013
Contact: Jim Fawcett

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