So why did these symptoms appear so suddenly and across a wide area of the burley region?  The short answer is that we don’t know for sure. The problem may be related to one specific factor, or a combination of factors. Weather flecking may have a lot to do with what we are seeing, and it is possible that we are seeing worst-case examples of weather fleck.

Some of the spotting seems to be actual physical or mechanical injury from rain drops driving into the leaves. The symptoms of severe scorching between the veins of lower leaves and nutrient deficiency symptoms (like potassium and phosphorus) have also been common. 

One possibility that would explain this sudden onset of symptoms is nutrient imbalance in the affected plants. Plants with impaired root systems would not have been able to take up nutrients at a sufficient rate to supply the growing points, and would have re-mobilized these from the lower leaves. 

More than one nutrient could be involved, but we don’t really know with certainty.  We are in the process of having leaves analyzed for nutrient content to try and pinpoint what might be deficient.

The scorching has a passing resemblance to Spartan injury, which can occur when excess rainfall washes herbicide into the root zone. However, these symptoms are showing up in fields that were not treated with Spartan as well as Spartan-treated fields, so our feeling is that we are not dealing with herbicide injury in most cases.