Iron Chlorosis
This problem spreads through handling, insects or soil rather than the weather, so there is no live forecast risk — focus on prevention below.
When it strikes
Fix the cause, not the leaf
No spray will help here. The trigger is soil, water supply, nutrition or temperature, so change the growing condition and judge the result on new growth, not on damaged leaves.
Not contagious
Nothing spreads from plant to plant here. Neighbouring plants showing the same signs are reacting to the same soil, water or weather, so fix the cause rather than isolating plants.
Safe to compost
No pathogen carries over on this material, so it can go on an ordinary heap with the rest of the garden waste.
When and where to look
This problem has no weather threshold. Check it on every routine walk round the bed, especially after handling plants and after bringing new stock in.
The signs that lead here
Full problem lists for these crops
About
Iron chlorosis is a common deficiency in high-pH (alkaline) and waterlogged soils, where iron becomes unavailable even when present, affecting blueberries, rhododendrons, citrus and many ornamentals.
Symptoms
Yellowing between the veins of the youngest leaves while the veins stay green (interveinal chlorosis); in severe cases new leaves turn nearly white with browning margins.
Organic Treatment
Apply chelated iron as a foliar spray for quick correction, acidify soil with elemental sulfur or compost, and improve drainage. Avoid over-liming.
Chemical Treatment
Soil-applied iron chelate (EDDHA form for high-pH soils) and pH-lowering fertilisers for persistent cases.
Prevention
Match plants to soil pH, lower pH for acid-loving plants, improve drainage, and avoid waterlogging and excessive phosphorus.