This variation in nut size is entirely due to the variation in scab lesion coverage over the surface of the shuck. Nuts that were entirely covered by scab early during the nut expansion period are much smaller than nuts infected later in the year.
Scab infection does not spread evenly across all nut clusters in a tree. Nuts on lower and interior limbs typically have more scab than nuts found at the top of the tree's canopy. Remember, scab spreads most readily under conditions of high humidity. Following rainfall or a heavy dew, nut clusters exposed to the sun and wind at the top of a tree dry off much quicker than nuts in the shade and on low, wind-sheltered limbs.
|Giles kernels 2013|
Our experience with scab in 2013 proves one thing: If you are growing scab susceptible cultivars, using the right fungicide at the right time is essential.