Questions on: Delphinium
Ron Smith, Horticulturist, NDSU Extension Service
Q: I have lots of questions, in fact 37 cents worth! I read and enjoy, save and use much of your column. First, my delphiniums seem to rot from the bottom up. I've treated with Gardengard which is for bugs, snails and slugs. Could it be silver fish? Two new plants did the same in a new spot. Could this have come from the greenhouse? Should I reset them in an entirely new place? Second, I have lilies but something is boring into the stems so they get dry and brown and break off. I've treated with Gardengard which may have helped some. I remove and burn the affected stems. Any suggestions will be appreciated. Third, how can I start old fashioned roses from cuttings? I'd hoped not to have to dig up starts. I tried rooting compound and potting soil, but the twigs just dried up. Fourth, is there any hope for baby evergreens once they lose their needles? Might they come back in the spring if I continue to water and care for them? (Bristol, S.D.)
A: Here are your answers - thanks for writing and the nice comments about the column.
- Definitely relocate the delphiniums. I don't know what the problem is, but whatever it is, don't go back. Make sure they get direct sun.
- Try a systemic like Orthene.
- Iíve enclosed a "Home Propagation Techniques" publication available from our office.
- No hope - they're history.
Q: What spray can I use to control leafminers? What causes the bottom leaves of my delphinium to die? There is something wrong with the leaves of two plants I have. I think one is an oak of some sort and the other is a Holland ivy. (Carrington, N.D.)
A: There are several sprays that can be used for leafminer controls. Sevin, Malathion or Orthene. Spray at first sign of damage, and repeat as necessary. Be sure to check for plant sensitivity of any particular insecticide by reading the label.
I have no idea what causes the lower leaves of your delphinium to die. It could be any number of factors such as nutrient deficiency, a fungal disease or environmental stress. It could also just be normal senescence.
The leaves are showing salt damage symptoms. The containers are either not freely drained, kept too wet or the natural water salts--dissolved solids--are too high.
Q. Can you tell me what kind of plant I have enclosed a leaf from? In 1997 it had beautiful blue flowers, but this year the top of the plant turned a silver color and dried up. (Sykeston, N.D.)
A. The leaf sample that was whole looked like it came from a delphinium. They generally do OK as long as the weather doesn't get too hot. The diseased material strongly resembled a combination of mildew and botrytis blightthe result of too much water, humidity and temperatures too high.
Q. I have had these beautiful delphiniums for six years. They are in a sunny, well-drained soil near peonies and have done well. Last year I lost three of them. They started turning yellow, so I fertilized them and then they died. This year the same thing is happening to the others. What's wrong with them and can I save them? (Parshall, N.D.)
A. The delphiniums are sensitive to soil-borne diseases, and it sounds as if yours are suffering from one of them. At this stage, I doubt there is much that can be done. Sorry!
If you try them again, plant in another location.
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