Growing nectarines, peaches, and apricots can be a challenge in Oklahoma. They are susceptible to late freezes which often kill most of the flowers and they have a lot of pest issues. The publications below will help you with your fruit tree management.

Annual Pruning of Fruit Trees

Home Tree Fruit Production and Pest Management

Common Diseases of Stone Fruit Trees and Their Control

additional related publications can be found here - https://extension.okstate.edu/fact-sheets/index.html

One last thing, I noticed there is grass growing right up to the base of the tree. I would highly recommend you remove any grass or weeds around the tree creating about a 6' diameter weed and grass free area. Place mulch over the area to protect the soil and reduce weeds. The benefit from this procedure is less competition for water and nutrients and the most important - it keeps the lawn mower and string trimmer away from the trunk. Any damage/wounds to the trunk will shorten the life if not kill the tree. 

Additional assistance can also be found at your local Cleveland County OSU Extension Center. They have a horticulturist and trained volunteers that can assist you.

Welcome to Oklahoma! If you haven't lived here long, you will soon figure out the Oklahoma climate is much different from California. We have a much more humid environment which increases our chances of foliar and other diseases. We can also have drastic weather and temperature swings. Mild winters often trigger early blooming of some plants, including fruit trees and especially peaches and related species, before the danger of freezes is over. We can reach 70F during the day and then drop to well below freezing within hours. Gardening in Oklahoma can be challenging, but it is also quite rewarding.

Happy Gardening!

Hopefully the recent dip in temperatures did not hurt your nectarines! We pretty much lost all our peaches here in Stillwater with the below freezing temperatures. Damage does depend on several factors like how long the temperatures were below freezing, air movement, micro climate conditions in your landscape, etc. 

As far as the squirrels go, good luck! The only way to keep them away is to create a barrier. For trees that is difficult. Using the tree netting and completely enclose the tree with it can deter them, but they often find their way in. For smaller plants like tomatoes in pots, creating a cage with something like chicken wire is your best bet. 

Sorry I don't have much better news for you. Hope this helps.

In order to get blemish free fruit you should begin a regular spray program to control any pests. The fact sheet Home Tree Fruit Production and Pest Management provides great information about what types of pests to watch for and when to control them. Plum curculio is the most common insect pest of our stone fruits. Pheremone traps or other traps (Monitoring Adult Weevil Populations in Pecan and Fruit Trees) are a great tool to use to monitor activity and help you know when to spray.

Insecticides labeled for control of insects on fruit trees are readily availabel in the garden centers. Visit your local garden center or contact the Cleveland County Extension Center for specific product recommendations.