October 8, 2019 - 8:32am -- ferencak.2

For those that planted small grains, in particular oats, on prevented plant acres with the intention of harvesting for supplemental forage, that harvest time is approaching.  Some questions regarding rust and potential nitrate toxicity have been raised and I want to address those questions in the context of the approaching harvest.

There are reports here in Wayne County and across the state as well, of August planted oat fields with heavy levels of rust.  Should a fungicide be applied to these fields?  The issue of crown rust on oats planted as a cover crop was addressed in the September 3rd issue of the OSU Extension CORN newsletter (https://agcrops.osu.edu/newsletter/corn-newsletter/2019-29/oat-crown-rust-forages).  I also found an August 30 article from the University of Wisconsin asking the question about fungicide application to oats planted for fall forage harvest. 

In the CORN newsletter article by Pierce Paul and Anne Dorrance, OSU Extension agronomic crop disease specialists, they state “the crown rust fungus does not produce toxins that are harmful to humans or animals, so feeding rust-affected plants would not be a concern from the standpoint of mycotoxin contamination.”  However heavy rust infection will affect palatability and feed intake. 

While there is evidence that severe rust infections decrease palatability and intake, is this enough to justify a fungicide application?  Most of the research done with fungicide application on oats appears to have been done to protect grain production.  There is a lack of research regarding use of fungicides on oats planted for a fall forage crop.  The question becomes when do you get an economic return from a fungicide application?  Again, we don’t have good data to definitively answer the question.  After reading and talking with several Extension folks who have worked with oats for forage, I think the bottom line is if you were going to use a fungicide and get an economic return, the time to use the fungicide was earlier.  We have a limited growing season left.  For those planning to use oats as stored forage, harvest will take place in the next few weeks, so the likelihood of an economic return from a fungicide is low.  Consider an early harvest if rust is heavy.

Regarding the question of nitrate toxicity, this is definitely a consideration for cereal grain forages such as wheat, cereal rye, triticale, barley and oats.  These species respond to nitrogen fertilizer and can be used as nitrogen scavengers.  Oats in particular can present a high risk for nitrate toxicity under conditions of high nitrogen levels and drought.  Our recent stretch of dry weather raised concerns about potential nitrate toxicity.  Drought stressed forages can accumulate toxic levels of nitrates.  Typically, the concentration of nitrates is highest in the lower one-third of the plant.

Mark Sulc, Extension Forage Specialist, recently wrote about the potential for late season forage toxicities (https://agcrops.osu.edu/newsletter/corn-newsletter/2019-33/be-aware-late-season-potential-forage-toxicities), and here are some of his comments regarding management of potential nitrate toxicity situations:

  • Generally, forage nitrate levels drop significantly 3 to 5 days after sufficient rainfall, but it is always safer to send in a sample for testing before grazing or feeding forage soon after drought stress periods.
  • Making hay does not reduce nitrate levels in the forage, but the hay can be tested and diluted sufficiently with other feeds to make it safe for animals.
  • Ensiling forage does reduce the nitrate content because the fermentation process converts nitrates to volatile nitrous oxides, or “silo gases”. These gases are highly toxic to humans. Safety practices include removing tarps from a portion of the silo a day or two before removing the silage from the bunker.

Rory Lewandowski is an OSU Extension Agriculture & Natural Resources Educator and may be reached at 330-264-8722.

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