Foxglove on a sharp decline. Disease?
Any thoughts what might be wrong with my foxglove? This is their third year. They bloomed every year I've had them and started with a bang this May and June, with the tallest most numerous shoots yet, and then petered out and now look like blah. Years past, they bloomed happily all summer. I've been feeding them and mulching and watering nearly every day. I don't notice any unusual pests other than a few nibbles in the beginning of the early season on the lower leaves, which I sprayed a little bonide a couple of times. I've been deadheading and cutting up the old stems into the bed, but no improvement, no new plants germinating. They keep declining. Do they have a disease, or am I just experiencing biennial blues? If the latter is the case, will they seed through the mulch? I'm concerned they look so dry and pathetic and wilted right now that's indicative something else is going on.
Frederick County Maryland
Inspect the base of the stems for signs of Southern Blight; this is the time of year plants begin to collapse from such infections. If this is the case, the plant and several inches of soil in this location need to be removed and discarded. More information and pictures of fungal growth and spores can be found here: https://extension.umd.edu/hgic/topics/southern-blight
Have the plants been watered often? While we are experiencing very hot, mostly-dry weather and many gardens would benefit from irrigation, Foxglove are sensitive to being over-watered. (Whereas the nearby hydrangeas would appreciate the moisture.) If root rot has set in, nothing can be done except to replace the plants.
Biennials cannot set seed if they are deadheaded; the seed must be allowed to ripen fully on the plant, which they may not be doing if trimmed too early. It's best to allow them to stay on the plant and disperse on their own over the winter. Otherwise, the pods probably won't be ripe and harvest-able until at least late summer, and the pods will be dry, brown, and about to crack open.
As this is their third year (and probably the last for the parent plants), no treatments are recommended. No fungicide will eliminate root rot or southern blight; even if the cause is a different disease, fungicides are preventative and not curative, so any infection that has progressed to the point of collapse like this is untreatable.
Here are some close ups of the roots. The soil around seems dry. I don't think I see any blight. Is this root rot then or something else?
The presence of isopods (sowbugs, woodlice, pillbugs, rolly-pollies) suggests that the soil isn't as dry as it appears - they need damp conditions to prosper. If Southern Blight is not the cause, any number of other fungal root/crown rots could be. All of these pathogens thrive and spread best in damp conditions with poorer air circulation.
Daily watering is quite often; soakings are good when they're needed, but they should not be needed nearly that frequently if the roots have been well-irrigated each time. Depending on how you are watering (hose, sprinkler, watering can, soaker hose), it is difficult to say how much volume to apply and how long you should be putting water down, but you want each soaking to wet the soil about 6" down. Then, wait for the top 4" or so to dry again before repeating. Certainly, if we receive rain (especially overnight, when less will evaporate), this helps to space-out the watering frequency the plants will need. Foxgloves are quite sensitive to over-watering and can collapse from the subsequent root loss; there is no treatment or cure except to remove dead plants and keep the area drier via less frequent irrigation.