Question
QUESTION: For the second year in a row, my monkshood has grown tall and strong for
most of the season, then developed black tips and failed to bloom. Last year I
blamed Japanese beetles, for I first noticed the problem when they were
chewing nearby perennials. This year I watched carefully, and I'm positive
that, pesky though they are, the beetles have not attacked the monkshood in
the least. No other plant in my small garden here in Vermont (zone 4) is
affected. What might it be, and what should I do?

ANSWER: Also known as 'Wolfsbane', Aconitum napellus ('Monkshood') is a popular Shade Garden perennial with outstanding resistance to disease and insect pests.  I suspect it's the Shade it grows in so well that might make it vulnerable to Fungus attack.

Connecticut's Agricultural Experiment Station posts a page on Aconite care and feeding:

www.ct.gov/CAES/cwp/view.asp?a=2823&q=377820

The problems that interest me most about this plant are its tendency to get Leaf Spot, caused, they say, by any of numerous Fungi, or assault by a Bacterium identified as Pseudomonas syringae pv. delphinii with properties worthy of its own science fiction novel.  P syringae thrives under dark, wet, cool conditions, 55 to 75 degrees F.  Symptoms can include 'sharply delimited necrotic areas on plant leaves'.

Solution:  Fertilizer, especially chemical fertilizers high in Nitrogen, over-stimulates cells to produce soft tissue, vulnerable to attack.

In another lifetime, I would recommend a Fungicide, to treat any guilty Fungi, but there is not much you could have done with Bacteria.

In August 2008, I would start with Messenger, the Harpin Protein product that jump-starts immune responses and accelerates healing.  And I would avoid Fungicides; they wipe out good Fungi as well as bad, and that is as they used to say throwing the baby out with the bathtub or something like that.  Instead, keep leaves dry, and move this plant to a Sunnier spot where the morning dew on leaves will evaporate quickly and the plant will receive more photons for photosynthesis.

The Messenger will build muscle to counter-attack Fungi and Bacteria.  It is also a timely treatment because you are going to transplant it (see below); Harpin Protein is ideal for that.  The Messenger will also boost resistance to pathogenic Bacteria.  Laying off the chemical fertilizers meanwhile will halt growth of soft, disease prone tissue.  Give your plants good Soil, rich in Humic Acids, instead.

Failure to flower may be a side effect of the stress on this plant ... or simply not enough Sun.  Yes, these are Shade plants.  Deep Shade, however, may be a little too dark for your Monkshoods.

THE LONG ISLAND GARDENER


---------- FOLLOW-UP ----------

QUESTION: The monkshood is already, in fact, in a sunny spot (the tag said it would do all
right in either shade or partial sun). Could that be what's wrong, that it's getting
scorched (even though the leaves look okay)?

Answer
Unless you have a very heavy hand with the watering can, I'd say we can dismiss Fungus from the list of suspects at this point.  They can't handle that much u/v.

Scorch does not wreck leaf edges.  But something else does: under-watering or extreme heat for too long.  

Japanese Beetle damage looks like holes around the leaves, usually the edges where they just took a bite and went to town.  Slug damage looks more like a variety of Swiss Cheese, filigreeing leaves overnight.

The 'black' part of your description almost always points to a Fungus or bacteria.  We won't rule out bacteria yet.  I should have asked you earlier for your zipcode so that I can find your weather history in that location, but since I didn't, please think back and consider whether the 55 to 75 degrees F temperature range applies to you.  That's the cool Summer Pythium range.

It is possible, however, that your plant is dealing with a nutrient problem.  Classic symptoms for both Potassium deficiency and Aluminum toxicity include necrosis -- death and darkening -- of leaf edges and tips.  Plants grown in coastal regions, near salt water, show these symptoms due to exposure to Salts, both airborne and in Soil.  Plants grown in heavily fertilized plots that have reached the point of build-up of chemical Salts show the same symptoms.

Give me more information, please, about the location of this plant and your Soil situation.  I would also recommend a Soil test.  It may be your shortcut to finding out what if anything may be wrong with your Soil.

L.I.G.