Seasonal Needle Loss
It's normal for the oldest needles of most conifers to turn yellow or brown and fall in the autumn. Needles may drop in the spring if the preceding growing season was particularly stressful or the winter was severe.
See this article for more information about seasonal needle loss.
Type of Sample Needed for Diagnosis and Confirmation
The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if your plant has a disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents. If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us