Cervical Strain or Musculoskeletal Injury: Given the patient's occupation in landscaping, which involves physical labor and repetitive movements, a musculoskeletal injury or strain to the neck and shoulder muscles is highly plausible. The pain's location and radiation pattern, exacerbated by movement, further support this diagnosis.

Cervical Spondylosis: This condition, involving wear and tear on the cervical spine, can cause neck pain that radiates to the shoulder, especially with movement. The patient's age and occupation could contribute to this condition.
Cervicogenic Headache: Pain starting behind the ear and radiating down the side of the neck and shoulder could be indicative of a cervicogenic headache, which originates from the cervical spine.
Thoracic Outlet Syndrome: Although less common, this condition, involving compression of the nerves and/or blood vessels that pass into the thoracic outlet (the space between your collarbone and first rib), could explain the pain pattern, especially if the patient's work involves repetitive arm movements.

Cervical Disc Herniation: While less likely than musculoskeletal strain, a herniated disc could cause severe pain and neurological symptoms. Missing this diagnosis could lead to prolonged suffering and potential neurological damage.
Spinal Fracture: Especially in older adults or those with osteoporosis, a fracture in the cervical spine could present with neck pain. This is a critical diagnosis not to miss due to the potential for serious complications.
Infection (e.g., Osteomyelitis, Discitis): Infections of the spine, though rare, are serious conditions that require prompt diagnosis and treatment to prevent severe consequences, including paralysis and death.
Tumor: Both primary and metastatic tumors can occur in the cervical spine, causing pain and neurological symptoms. Early detection is crucial for treatment and prognosis.

Temporal Arteritis: This inflammatory condition of the blood vessels could present with pain behind the ear and is more common in older adults. However, it typically involves other symptoms like headache, jaw claudication, and visual disturbances.
Neurological Conditions (e.g., Multiple Sclerosis, Peripheral Neuropathy): Certain neurological conditions could present with pain and sensory changes in the neck and shoulder. These are less likely but should be considered if other symptoms are present or if the patient does not respond to initial treatment.