Re: TB-Treating Mosaic
When irises are grown as long as 10 years in one place, two things happen.
First, while the most important nutrient elements (N-P-K) may be kept up by
the use of fertilizer, various trace elements in the soil that are needed
in unique proportions by irises become depleted. Secondly, subtle
bacterial and fungal pathogens build up, weakening the plants.
I would suggest that what you have is not mosaic, but either a problem with
trace element depletion: "tired" soil; or "sick" soil--in which pathogens
have increased to a point at which the iris are affected.
The solution is to move the irises to ground that has not grown them in at
least three years, or preferably, never. I think you will be surprised at
the renewed vigor. In your old bed, plant something different. Perhaps
you might grow a crop of red or white clover, then turn it under. In a few
years, the soil will be restored and you can put irises there again.
Some on the list would also suggest solarization of the old bed. Dig it
over, water it well, and cover it with clear plastic weighted down with
soil or rocks. Leave the plastic in place for several weeks. The soil
will be heated to the point where the suspect pathogens will be killed.
The aphids are attracted to unhealthy plants and further damage them. Keep
them under control, but instead of Malathion and Isotox, try washing them
off with a hose or spraying with Safer Insecticidal Soap.
I'm pretty sure you don't have mosaic--unless now you tell me that the
flowers are streaked with clear spots or violet streaks....
Department of Biology
Hampden-Sydney VA 23943