Stuarts in East Georgia have been shedding leaves for a few weeks. Initially, the reports of this were of healthy, green compound leaves. We sometimes see healthy, green leaves drop like this when the weather turns hot and dry but this was occurring back when we were still seeing cool temperatures and it seemed to be occurring primarily on Stuart, so this particular drop we saw earlier remains a bit of a mystery.
Now, however, we are seeing another leaf drop , primarily on Stuart, which is associated with a dying or browning of the terminal leaflets of compound leaves which progresses backward toward the base of the leaf. Eventually it moves into the leaf rachis (the main stem of the compound leaf) and the entire compound leaf may die. If you stand back and look at a tree infected with this disease the scattered dead compound leaves will look like dead brown patches in the tree.
UGA research pathologist Tim Brenneman identified this several years ago as a fungal pathogen called Neofusicoccum. I will be referring to it in the short term as “terminal die-back”.
We first began seeing Neofusicoccum around 2010 or 2011. Even then, it was most often observed in Stuart and since that time we have seen it pop up from time to time when conditions were right for it. Most minor foliar disease like this infect the leaves a month or two prior to symptom expression. Dr. Brenneman suggests use of a strobilurin or a DMI/strobilurin mix like Absolute or Quadris Top when conditions favor infection (usually prolonged cool and wet conditions). Even if a grower has used these materials their timing may have been off enough to allow infection, especially if they were stretching sprays when the conditions occurred. Once you see the symptoms its too late to do anything about it. But, even when terminal die-back occurred earlier in the season in the past we have not seen any long-term damage to the trees and generally no effect on nut quality. However, with the amount of leaf shed that is associated with it this year, the tree canopy appears weak and with a heavy crop load, there could theoretically be associated quality losses. Most of these trees I have seen are in the off year of production anyway, so the effects should be minimal and hopefully we won’t see the conditions conducive to this disease surface again next year. If so, be sure and use a DMI/Strobilurin combo during susceptible periods (cool, wet conditions). This will make it more difficult for those trying to stretch scab sprays to save money. When growing pecans it seems there’s always something challenging rearing its head, making it difficult to save on input costs. Just wanted to let folks know about this in case you observe it in an orchard.