Plant viruses usually need to reside in living host or vector tissue (like insect mouthparts) to survive, so do not remain in the soil, though contaminated residues on pruning tools might spread some infections from plant to plant. [You can think of the situation a bit like bodily fluids in people spreading infectious disease via needles (insect mouthparts), transfusions (moving sap from one plant to another), etc.] When a plant contracts a virus, the virus becomes systemic (can spread to all plant parts) and cannot be removed via pruning, even if symptom expression is limited. Nor will it subside with winter dormancy; it will return each year, and if it poses a threat to plant health, the infected plant will decline over time.

Sap-feeding insects can transmit plant viruses, but this is thought to not be a major route of pathogen spread. Plants can pass along viruses to their seedlings, and of course cutting- or division-propagated plants sold or shared with undetected virus can spread an infection even further afield. There are propagation methods that create virus-free plants, but not all species propagate well this way, and it can be a more costly process since it uses specialized laboratory equipment. Even then, that plant's risk of potential contamination is no different than any other individual's after it leaves the lab.

There are myriad plant viruses, but not all cause serious symptoms or widespread infections. Some are mostly innocuous and cause "color breaking" or streaking in blooms or foliage, while others do cause plant decline and eventual death. In some cases, symptoms alone can be difficult to assign to any one virus, though shared viral symptoms in general tend to involve distinct rings or squiggles on foliage (with a sharp distinction between normal green coloration and bleached-looking yellow zones) or a blocky, irregular mottling. You can see a couple of examples on our Virus Diseases on Flowers page. For confirmation, plant tissues need to be tested in a lab, which is not only costly, but often not readily available to the general public and tests do not exist for all possible viruses. For an incurable condition, testing is not practical for most gardeners outside of perhaps plant collectors.

We are not aware of virus-resistant species or cultivars. They likely exist, as with any resistant individuals in a population, but we do not have easy ways of detecting them. Plus, viruses mutate over time and a once-resistant individual may no longer remain as resistant.

Foxglove is a biannual or short-lived perennial, so the original plant only lives for about two or so years before dying off naturally. If not dead-headed, they can self-seed, so you can get a perpetuating colony that way without having to replant. Given that, pest issues on a mature plant are less of a concern than they might be on a longer-lived species.

The symptoms in your photos don't resemble typical virus symptoms. They do look to be caused by mites, thrips, or leafhoppers, all of which generate "stippling" damage that creates a diffuse array of fine bleached-looking speckles. Check leaf undersides, as this is where mites tend to feed. Thrips can be equally hard to see, but they usually leave behind telltale black tar-like specks (droppings) glued to the leaf surface, here too, mainly on the underside. Leafhoppers are more skittish and run or jump away when disturbed, but tend to leave their shriveled white shed skins behind attached to the leaf if they've been residing there for a while. Few of these pests cause enough damage to warrant insecticide treatment. Spider mites can have population booms in hot, dry weather, though.

The simplest first step is to trim off foliage with heavy damage, not only to reduce whatever pest population is still present, but also to resolve the immediate eyesore since the plant will probably soon shed them anyway. A strong blast of water from a garden hose can dislodge most insect pests, especially if you rub the leaf surface while holding it so the water hits full-force. If you need to spray, either horticultural oil or insecticidal soap (a registered insecticide, not a home remedy) can be used to manage the insects/mites, but re-applications will be needed. Again, direct sprays at leaf undersides, though coating all leaf surfaces is best for maximum efficacy. Be aware that even plant-safe sprays can "burn" foliage when applied to injured leaves, and if applied in temperatures above 85 degrees or when the plant is drought-stressed.

Well-established plants that are otherwise healthy can usually afford to lose foliage to pest outbreaks or minor fungal/bacterial disease outbreaks and should regrow unscathed next year. Typically, the later in the season foliage is injured, the less of an impact is has on overall plant health because they've already replenished root energy stores from a season's worth of photosynthesis.

Miri