The extended cool and wet spring appears to be causing manganese (Mn) deficiency in winter wheat in some fields in Eastern Wisconsin. Wheat has a high relative need for Mn, similar to soybean, but deficiency is not often observed in Wisconsin. The deficiency manifests as lighter colored lines parallel to the leaf margins and may have some necrotic spots. It is unlikely that an entire field will be uniformly deficient.
Manganese deficiency is usually associated with neutral to high pH soils that are also high in organic matter. Soil tests for Mn are not accurate if soil organic matter levels are greater than 6.0%; in these soils Mn availability is considered low if soil pH is greater than 6.9. On soils with organic matter content less than or equal to 6.0%, Mn is considered low when soil test values are less than 11 ppm. Tissue testing can be used to confirm deficiency. Sample the newest fully developed leaf from 50 plants prior to heading. Manganese is considered sufficient if the tissue concentration is 25 to 100 ppm.
In the photos, the wheat is being grown on a Sebewa silt loam which is poorly to very poorly drained. In fall 2016, this field tested 6.7% organic matter (with a range of 3.7 to 10.8%) and pH of 7.8 (range 7.6 to 8.2). Because the organic matter is over 6.0%, and pH is greater than 6.9, the availability of soil Mn is considered low and Mn deficiency in soybean and wheat might be expected. However, the grower has not had issues with Mn deficiency in this field in the past, which suggests the wet fall and extended cool and wet spring may be causing low availability of Mn. The Mn level in the tissue was 6.1 ppm, which is substantially below the sufficient range of 25 to 100 ppm. Wheat grown on another field on this farm was showing similar deficiency symptoms and was growing on a well-drained Sisson fine sandy loam with a soil organic matter of 3.6 % and pH of 7.6. While Mn was not tested on this soil, the deficiency symptoms indicate that Mn availability was low.
If you suspect Mn deficiency, take plant tissue and soil samples to confirm the diagnosis. A foliar application of 1.25 lb Mn/a in a sulfate form or 0.2 lb Mn/a in a chelate form will likely increase yield. If the deficiency is severe, multiple applications at 7 day intervals may be needed to remedy the deficiency. Consider leaving a couple of strips untreated to evaluate the efficacy of the foliar application.This article was posted in Wheat.