Plum Pox (Sharka)
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
Plum pox virus is the most serious disease of stone fruit in Europe and is a notifiable quarantine organism in many countries. Spread by aphids and by grafting infected material, it has no cure — an infected tree stays infected and becomes a source for every plum, peach and apricot nearby.
Symptoms
Pale green rings, blotches and vein-banding on leaves in spring, easiest to see on a dull day. Fruit develops sunken rings and brown internal blotches, tastes poor and drops early. Stones of infected plums often show pale rings.
Organic Treatment
There is no treatment. Report suspected cases where the virus is notifiable, and remove and destroy confirmed trees including the roots — leaving an infected tree standing guarantees spread to the whole neighbourhood.
Chemical Treatment
No chemical affects the virus. Insecticides against aphids do not prevent transmission either, because the aphid transmits it within seconds of probing, long before it takes up any insecticide.
Prevention
Buy only certified virus-free trees from a reputable nursery. Remove wild and neglected Prunus nearby, control aphids on young trees to reduce pressure, and never graft with wood of unknown origin.