Page 19 - index

This fungus has been called by several names. “Mycosphaerella macrospora”
seems to be the current name, but it has also been called “Didymellina macrospora”,
“Cladosporium iridis”, “Heterosporium gracile”, and “Heterosporium iridis.”

This fungus, by whatever name you use, can also be hosted on Hemerocallis
(daylilies). In the year 2012 there had been reported a problem with daylilies referred
to as “Midwest Malaise”. It very well could be the same fungus, but shows slightly
different as it is on a different species. I suspect that it is worse this year because of
weather conditions. A wet Spring with lots of rain can leach out nitrogen from the soil,
placing a plant under stress. Then infection takes advantage of the weakened plant. The
fungus doesn’t need to transfer directly from Iris. It can have been present on the daylilies
for a number of years, but only causing minor problems that have not been particularly
noticed. So the fungus is present, waiting to take advantage of conditions, such as a wet
Spring, followed by hot weather.

Remove and dispose of infected foliage. DON’T compost. Have mulch around the
base of plants to prevent splashing of fungus spores onto leaves. Giving the plants some
nitrogen will help strengthen them. You could try a foliage fertilizer. But remove infected
leaves frst. Avoid overhead watering if you can. If you do have to water via overhead, be
sure to remove all infected foliage frst.

Soft Rot:
This is most often see in the spring. An inspection at that time would be advisable.
Any rot should be removed. I use an old tablespoon that has its edge sharpened. Then
I spray the cleaned part with a mix of half Javex and water. Other possible sterilizer/
cauterize are Lysol, powdered sulphur, or disinfectant liquid soap.

The method of
dealing with this in
warmer climates involves
digging out the plant,
cutting out all the rot,
and leaving the rhizome
to dry in the sun. For us
in Canada, particularly
southern Ontario, the
Springs are cold and
cloudy so this method
doesn’t work (no hot sun
to dry out the rhizomes).
However, this can work
later in the season when
the weather is warmer and
there is more sun.

Canadian Iris Society Newsletter 17