Many are in agreement that some scaffold selection should occur on one year old almond trees. These cuts remove unwanted branches that may lead to included wood and weak branching structure in the future. Most of this pruning usually occurs in the dormant period following the first year of growth, but is this the best time?
Over the past few years, I have been observing an increase frequency of fungal cankers associated with pruning wounds. The fungi associated with these cankers are part of the Botryosphaeriaceae which is a large group of fungi that are found within the environment. They have been found to infect pruning wounds of grape, almonds, walnuts, and other perennial crops.
This past year we conducted spore trapping studies to determine when these pathogens are present in the orchard. Spore traps were placed for 7 days and collected on a weekly basis. The spores trapped on the slides were cultured and identified. What we found was similar to what has been observed in grape. Spores were released from fungi within the Botryosphaeriaceae in association with rain events (pg 3 of 2013 Proceedings of APS Pacific Division). In other words, when it rained during the seven day period, we trapped spores of the fungi that infect almond pruning wounds.
So back to the original question – when should we prune first (and second) leaf almonds? In order to prevent pruning wound infections, pruning of young trees should not occur when rain is in the forecast. Planning around the weather may delay pruning, but research by Carolyn Debuse (former advisor in Yolo/Solano County) has shown no impact when pruning as late as leaf bud break. She found that pruning after full leaf expansion did reduce tree growth during the second growing season, but the impact of pruning this late was not found after the completion of the third year of growth. Furthermore, this difference in growth with the full leaf expansion pruning treatment was only found in ‘Nonpareil,’ not in the ‘Winters’ or ‘Monterey’ (2011 report from ABCs Almond Culture and Orchard Management). Studies are still needed to determine how early we can prune without impacting tree growth.