Some farmers in northwest Ohio have noted purple-reddish leaves on their wheat crop (see picture). If your wheat plants turned purple, here are a couple of things to note:
Environmental: Was the shift in color fairly sudden and widespread in the field? If so, the purple leaves may be weather related. With the abnormally warmer temperatures we experienced this fall, the shift to colder temperatures may have been sudden enough to slow the wheat growth and cause the leaves to turn purple. If this is the case, make a note and watch what develops. Also, planting too shallow, late planting date, abnormally dry compaction soils can accentuate the appearance of the wheat as it adapts from warm to cold temperatures. There is nothing you can do at this time and new growth should shift back to green when warmer temperatures return in the spring.
Some of the purpling may be due to a build-up of sugars (sucrose) in the leaf tissue. The switch from warm to cool temperatures can affect the rate of sugar transport in the plant, which may trigger anthocyanin formation. Anthocyanins are reddish-purple pigments that form in stem and leaf tissue, and can help absorb excess light energy and divert it away from photosynthetic centers. These pigments act as a sort of “sunblock” to help the plant handle the sunny and cool environmental conditions while minimizing permanent damage to the leaves.
Fertility: If your wheat has been purple for a longer period of time, it may be indication of a phosphorus deficiency. For wheat production, soil phosphorus should be at least 25 ppm Bray P, according to the Tri-State Fertilizer Recommendation. We are currently re-evaluating P requirements of wheat through on-farm research to validate that wheat P needs are higher than corn and soybean. Between 2013-2015, we conducted statewide soil testing and found 41% of the soils tested had soil phosphorus levels < 35 ppm Mehlich P. If you haven’t had your fields tested recently, we suggest taking a soil sample to evaluate soil fertility.
Disease: Purple leaf discoloration may also be caused by diseases, particularly, barley yellow dwarf virus (BRDV). Indeed, BYDV could have been one of the possible causes of this problem, since conditions remained warm for several weeks after planting, favoring survival of the aphids that transmit this virus. However, contrary to what is being reported, plants with BYDV are usually not found uniformly distributed across the field or associated with tile lines. Due to the fact that this virus is transmitted by aphids, affected plant are commonly found in patches, often close to the edge of the field where aphids usually land and feed. In addition, on plants with typical symptoms of BYDV, only the tips of some of the leaves usually become discolored, not the entre leaf or the entire plant. So, based on what is being reported, it is unlikely that BYDV is the problem, however if it is, there is nothing you can do about it at this time, we will just have to wait and see what happens in the spring.