It is now believed that several varieties of snowdrops carry virus; some will show little or no symptoms, while others will show obvious symptoms and may become weakened in time.
Once a plant has virus there is no cure, but regular feeding and good cultivation will help maintain the strength of the plant. Infected plants under stress, whether through cultivation problems or the weather, are more liable to display the tell-tale symptoms.
Ideally plants with virus should be discarded, but in reality, most people choose to keep the plants in isolation from healthy stock.
Virus is spread by the exchange of sap, which could be caused by any leaf sucking aphid or by bulb eating nematodes, but the most common cause of infection, I believe, is by the gardener. The practise of dead heading is a way that minute particles of sap can be transferred from one plant to another, via the gardener’s fingers. If you pull off a seed pod you will notice that a small amount of colourless sap will leak from the stem or pedicel and reside on your finger tips. If you then pull off another seed pod there could be a transfer of sap from your finger tips to this second plant. If you need/want to dead head then make sure that you pull off the ovary without getting sap on your fingers. If you use a knife/scissors, then wipe the blade with meths after each removal.
Try to handle virus infected plants as little as possible; if offsets have to be removed from infected bulbs, then use a knife and wipe the blades and bulb with meths.
Unless you are vigilant, plants that are infected can go unnoticed for several seasons until the symptoms become obvious. If in any doubt as to whether a plant has virus, then a safe-guard would be to grow the plant for the following season away from other snowdrops.
At present there is little evidence that virus can be transmitted into pollen or seeds.
A plant with virus may show any of the following symptoms :-
Leaves – colour break up appearing as streaks or blocks. In some varieties as the leaves elongate they become thin at the base, causing them to flop.
Stem – overall pale in colour with darker green blotches. In very weak plants the stem can not support the weight of the developing flower so it will flop.
Flower – the flower may fail to open. There is colour break up on the inner segment mark.
Ovary – this again can show signs of colour break up.