Meyer Lemons Rotting from Stem End: Alternaria or Freeze Injury?

The Problem

15‑year‑old Meyer lemons on Oregon coast: fruit rot inside, look dried. One tree affected, one not. Freeze possible?

Alternaria fruit rot: Brown/black discoloration at stylar end, spreads to core. Favored by splitting from drought/frost.
Freeze damage: One tree more exposed to cold wind.
Underwatering: Tree pulls juice from fruit to survive.

Atomic Grow claimed to restore tree health, deter pests, improve fruit quality.

Plant Diseases: Meyer Lemon Fruit Drop: Post-Bloom Stress and Fungus; Lemon Black Spots and Bug‑Bored Tangerines: Extension Help Needed; Tiny Spots on Meyer Lemon Fruit: Greasy Spot Fungus; Lumpy Lemons: Wind Scar, Phytotoxicity, and Atomic Grow for Tree Health; Meyer Lemon Fruit Rot: Transplant Shock, Remove Fruit; Petunia Sticky Stems: Natural Defense, Not Pest Problem; Understanding Fruit Quality from Hybrid Seeds; Rotting Stem on Braided Pachira: Prune It Off, No Sealant Needed; Why Mature Meyer Lemon Drops Fruit in Summer; Tomato Stem Rot in Coastal Climates: Blight and Drainage Solutions

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