Apricot Trees
Question from Tim:
Dear Pat, I live in central California, San Luis Obispo county. I have 4 trees about 20years old that dropped all their blossoms and developed sap all along the branches and of course no fruit at all? Did I prune wrong the year before? Grateful for any help. They were my father in-laws and gave us the orchard with the house I’d hate to lose them. Can You Help?
Answer from Pat:
When trees drop flowers there are several possible reasons. One is wild and sudden temperature swings. Several hot days followed by a cold snap, for example. Worse yet a frost—a night with freezing temperatures— is the most likely culprit. Another cause is insufficient nutrition in the soil. (I recommend fertilizing deciduous fruit trees just as the buds of blossoms swell. They should be fed lightly, never heavily.) Yet another reason fruit trees may drop their blossoms is because the soil is unevenly moist. Never let fruit trees dry out when they are blossoming or they will drop their blossoms. On the other hand never over-water them at that time or the same thing can happen. Just be sure to maintain good moisture in the soil at blossom time.
Finally, there is another possible problem and this could be something attacking the roots. Gophers have been a problem this year in many areas. When something attacks the roots of a plant, the first thing it drops is its flowers or its immature fruits. I don’t think that is the problem you are having since the whole tree and all the trees were affected. But just to explain further, digging up the ground or any disturbance to the soil under the tree can cause young fruit or flowers to fall off.
But also you ask about sap oozing all along the branches. It’s called gummosis. Fruit trees do this a lot and apricots are prone to it. Usually it’s nothing to worry about, but when there is a great deal of oozing sap this can come from a sudden freeze or unseasonably cold temperatures. So it seems to me most likely this is what caused your blossoms to fall off. There is nothing you can do about it but next year listen to weather reports and protect the trees on cold nights.
Photo by flying squirrel 
I have always pruned apricot trees in Santa Barbara in the winter when I prune my other deciduous trees. My friend in Santa Ynez now tells me that you can prune them in the summer. I have heard this from other people—that plums and peaches too can be pruned mid or late summer. What’s the story, Pat? Thanks
Yes this is true but I have never done it. Refer to your local Master Gardeners and Farm Advisors office for instruction and/or a pruning book published by the Extension.