Expert: Long Island Gardener - 5/22/2009

Question
Hi, I planted 10 full-grown, blooming snapdragons two months ago.  They have soil rich with organic matter, full sun, enough space between and flowered twice.  They were happy and gorgeous.  Last Saturday, part of one plant looked limp.  The next day, it was dead and another started to go limp.  After 6 days, I've lost three complete plants and it looks like there's no way to stop it.  Last year, the same mystery.  I live in Mexico City at 10,000 ft. above sea level.  The climate is the same as my home town, Cleveland, Ohio, at this time of year.  What could be the cause?  Bugs - root rot  -  altitude?  I read that snapdragons don't do well in southern US, but the climate, here, is cool to warm and very sunny, but NOT DRY.  I water daily.  ???  Thanks so much - Joanne

Answer
Sounds like a  soil-borne fungus amongus, Joanne.  Water water everywhere?  Cool weather -- perfect fungus environment.  Ouch!

My money's on Verticillium Wilt:

www.ipm.msu.edu/perennials/verticilliumwilt.htm

caused by V. dahliae and V. alboatrum.  Cool weather is perfect for snapdragons, until something like this comes along.  A week or two of cool, cloudy days between a few warm, sunny days is ideal for disease development.  This plus soil temps running 70 to 75 degrees F practically guarantee you'll be seeing a full blown epidemic, spreading anywhere the spores alight.

Could have been present in the plants when you bought them; could be in your soil.  You're right: There's no way to stop it.  Not yet, anyway.

Planet Natural, the organic supplies internet retailer and a party with a vested interest in selling you an organic cure, declares, 'There is no cure ...Sulfur applications applied weekly once the symptoms have been noticed may have some effect ... Choose resistant varieties when available.  Remove stricken growth and sterilize clippers between cuts. It is best to remove the entire plant and solarize the soil before planting again in the same location. Crop rotation will have limited success because so many crops are susceptible to the disease fungi.'

Here's what they say about it at University of California's IPM Dept:

'Verticillium wilt, one of the most widespread and destructive soilborne diseases of plants, affects a large number of herbaceous and woody species throughout the world. The causal fungus, Verticillium dahliae, infects susceptible plants through the roots and plugs the water conducting tissues.'

and the URL:

www.ipm.ucdavis.edu/PMG/r280100911.html

Plugs the water conducting tissues -- Hence, the wilting.

There is hope on the horizon.  Researchers globally are working on a cure for this disease -- and you can't blame them, since it attacks a lot of food crops and wipes out farms almost overnight.  Serratia plymuthica, a common gram-negative soil-borne bacteria that likes to hang out in the rootzone of certain plants, is being studied closely so that scientists can figure out how good it is at counter-attacking Verticillium.

There is alas a potential downside to Serratia.  Some species only since the 1960s have been identified as pathogens that infect people; they've been blamed for UTI's, outbreaks of Pneumonia, Endocarditis, Osteomyelitis, Septicemia, eye infections, and other big health problems. S. plymuthica, fortunately, is currently labelled as nonthreatening to humans.

Plants are another story.  S. plymuthica has been found growing in farm soil near Broccoli, Melons, Grapes and other crops.  There, it is credited with fighting off the forces of evil Fungi including diseases caused by Rhizoctonia, Pythium, Botrytis and others.

But you can't buy this yet.  The research isn't done yet, and then they will have to find a market.

Isolating uninfected plants, then dosing them up with Harpin Protein (sold as Messenger -- and this should be sprayed on leaves, with the excess watered in) will build immunity and perhaps recovery in susceptible plants.

For now, I'm afraid, this is the best advice I can give you.  Ask me again in 5 years.  Things will be different.

THE LONG ISLAND GARDENER