Following the long drought/heat wave we had in May, you will likely see some leaf drop now that we have had some rain. This leaf drop occurs anytime we have a sudden shift in environmental conditions. It can occur going from wet to hot/dry and vice versa. This is nothing to be alarmed about (See blogs from 2014, 2015, 2016). Desirable is very sensitive to this leaf drop but under these conditions it can be found on most any variety. You will likely see some nut drop as well. We were already seeing a pretty heavy nut drop on Desirable before the rain.
Many growers were 3-4 weeks out from their last spray and didn’t have time to cover their orchards prior to the rain moving in. In such a situation, the best choice of fungicide to go back to when you can get the sprayers out again, especially for Desirable, Pawnee, and other scabby varieties, will be Amistar Top, Absolute (or any of the group 3+group 11 fungicides), Elast/Group 3 fungicide, or Elast/Tin. Spraying Tin alone in this situation would likely not provide the protection of these other products.
This is a very critical spray, especially if you were stretched out on your interval. The nuts are beginning to size and if they get some scab on the nuts at this stage it is a battle the rest of the way to save them. I would recommend coming back again no longer than 2 weeks following this spray with Elast/Tin as you will likely see some level of scab developing if the nuts were not protected prior to the rain. If you sprayed within 7-10 days prior to the rain you should be ok, but get another spray on ASAP if you are over 10 days.