Potato Virus Y
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
Remove affected material now
Take out the affected leaves, shoots or whole plants before the next wet spell, bag them as you cut, and wash your hands and tools before touching healthy plants.
Carried by insects
An insect moves it plant to plant, so controlling the carrier matters as much as treating the symptom. Check for the vector before assuming the plants infected each other directly.
It carries over to next season in soil, debris or seed — which is why rotation matters here, not just treatment.
Keep out of the compost
This survives a garden heap. Bag it for municipal green waste, which is composted industrially at temperatures a garden heap cannot reach, or burn it where that is permitted.
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
Potato virus Y is the main reason gardeners are told never to replant their own saved tubers year after year. It builds up invisibly in seed stock, cutting yields by up to 80% over a few generations, and aphids carry it between plants without ever needing to colonise them.
Symptoms
Mottled light and dark green leaves, crinkled and often with dark necrotic streaks down the stems and leaf veins. Plants are noticeably shorter than healthy neighbours and drop their lower leaves early. Tubers may show sunken rings.
Organic Treatment
Rogue out symptomatic plants and destroy the tubers under them. Do not save seed from an affected crop, and remove volunteer potatoes from previous years — they are the commonest reservoir in a garden.
Chemical Treatment
Nothing treats the virus. Mineral oil sprays reduce non-persistent aphid transmission in commercial seed crops but are not a practical garden measure.
Prevention
Buy certified seed potatoes every year — this single habit removes almost all the risk. Rotate on a four-year cycle, control aphids on nearby crops, and never grow potatoes next to a bed of overwintered brassicas that hosts aphid colonies.