I’ve looked at some oats in our area and received calls about fields turning a red to purple color. Reddening in oats can be the result of several unrelated actions. In most cases, the color expression is due to a group of sugar free pigments called anthocyanidins. According to Dr. Dewey Lee, when there is an increase in free sugars in a leaf, these anthocyanidins convert to anthocyanins which give the leaf a red color. In oats this can occur due to such things as shifts in temperature from warm to cold, stress from acid soils, infections from pathogens, deficiencies in phosphorus, lack of nitrogen, water logged soils that reduce oxygen levels, etc. All of these problems generally result in a shift or reduction of photosynthesis which can lead to sugar or carbohydrate production that is not readily used in growth which then begin to accumulate in the plant cells increasing the production of the pigment.
Because the color expression can originate from several actions, it is best to look at all the reasons and see which one is most reasonable.
This time of the year the discoloring can be due to one or more of the following:
-Cold weather
-Barley yellow dwarf virus (you will see feeding wounds and aphid carcasses scattered over the field)
-Low soil pH
-Variation in nitrogen content
-Possibly low P content
Usually the problem is caused by cold weather.
What should you do? If you haven’t applied addition nitrogen, it would be a good idea to go ahead as soon as you can get in the field.
The total N required for oats following peanuts is 60 pounds per acre; for oats following cotton, corn, etc. 80 pounds of nitrogen is required; and for oats following grain sorghum apply 100 pounds nitrogen per acre for the season. Assuming you applied nitrogen in the fall and depending on which crop the oats are following, an additional 20 to 40 pounds would be recommended.
If you did not take a soil sample prior to planting, that’s always a good place to start when troubleshooting. Plant tissue samples are also a good tool to use to pinpoint possible nutrient deficiencies.
Herbicides
Some herbicide applications in small grains are not working well. The ideal temperatures for applying most POST herbicides are between 65 and 85 F. Weeds may be killed slowly below 60 F.
2,4-D alone does not adequately control chickweed and henbit. Mixtures with Harmony or Express are advised for these weeds.
Disease
I am finding a little bit of rust in some oats. The optimum temperature for spore germination is 68 degrees F. Dry, windy days, followed by cool nights with dew, favor leaf rust epidemics. If oats are being grown for grain, a fungicide may be a good idea where rust is found.
Triazoles are a good early curative fungicide. Strobilurins are good protectants and will last longer on the plant. Usually one single application would suffice, but check the plant at early flag leaf stage to evaluate the disease situation.
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