scab last year and lost a large part of our 'Giles' pecan crop to the disease.
During our conversation, he mentioned that he had looked over his nut crop and found no trace of the disease. The photo at right shows a cluster of 'Giles' nuts I cut from a tree this afternoon. Everything looks clean and healthy. However, a closer look over the entire shoot revealed that scab was very much present on the tree.
overwinters on the tree. Under conditions of high humidity and warm temperatures, scab spores can be released from these lesions and infect expanding leaves or nuts.
How do I know that? First, I know that the scab fungus most effectively colonizes plant parts that are rapidly expanding. Second, I know that the terminal three leaflets are the last leaflets to expand when a new pecan leaf unfurls in the spring. Sometime this past Spring, weather conditions promoted the release of scab spores from old lesions. At the same time, these three leaflets were at the perfect point in their expansion to become infected by the disease. Weather conditions must have dried up quickly after this initial infection period because later expanding leaves show no sign of scab.
The nuts pictured at the top of this post have stayed scab free so far this year because we applied a fungicide along with our casebearer spray and the nuts have yet enter their period of greatest susceptibility--rapid fruit enlargement. However, we must remain on our guard because scab can spread quickly under the right weather conditions.