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Leaf Spot


When I grew irises in Colorado, we had relatively little leaf spot, so =
it was easier to pick out varieties that were especially susceptible.  I =
have not had a huge problem yet back in Minnesota, but I recall from my =
earlier years here that sometimes it made a great deal more sense to =
note the far fewer varieties that seemed resistant.  That is really the =
information we need for breeding purposes.

I see quite a bit of leaf spot in my large SDB collection from time to =
time.  I would not say that leafspot is nonexistent in MDBs, however, =
because the larger ones are really small SDBs.  Carl Boswell's LITTLE =
GREEN EYES unfortunately got terrible leaf spot even in Colorado (and it =
was such a cute little flower!)  The true pumila types do not have much =
leaf surface, either to get infected or to sustain the plant.  However, =
Lynda Miller's JADE STAR, which is tiny and early like the pumilas, had =
very messy foliage in mid-summer in Colorado.  Whether that was leaf =
spot, as it resembled, or a partial dormancy or something else, I do not =
accurately recall.  Plicata and "tangerine (beard) factor" traditionally =
have been candidates for heavy leaf-spot.  Ben Hager's innovative orange =
DUMPLING held true to this tradition.

Diploid MTB's in my garden are about the worst of the bearded irises for =
leaf spot (of course, I have only recently started growing TB's again, =
so not much to compare).  The highly touted BUMBLEBEE DEELITE is quite =
susceptible, as is it's child ALYOSHA K. (Shannon '97).  The other =
parent of that is TYKE, which has genes from both I. astrachanica and  =
I. cengialtii (?), and gets leafspot fairly heavily.

Now, I have heard references to both bacterial and fungal leafspot - is =
that correct?  I have always assumed the fungus and used to spray with =
Benomyl before it was banned both from our gardens and from banana =
plantations.  (I am not up on the currently used systemics.  Rick Ernst =
told me once what they use at Cooley's, but I have not filed it anywhere =
useful.)  My understanding is that the soil carries the pathogen, which =
is why the leaves get infected in a splattered pattern after a heavy =
rain.

Hybridizers / breeders were for so long concerned only with flower size, =
form, substance, color, and the branching, that they forgot to observe =
the foliage through the whole season.  Or perhaps they had just given up =
on fussing with it and so sprayed anyway and never saw it in their own =
gardens.  Some people have not liked the judging standards of the past =
ten years, because it gave short shrift to color and pattern.  But it =
has made the judges remember to look at the whole plant, if they took =
the point scoring seriously at all.  (Thank you, Phil Williams.)  Having =
just introduced a susceptible variety, I am not one to cast stones, =
although I introduced it for its interesting species background, and to =
help increase the judgeable list.

Cheers,
David   =20
Southern Minnesota
Zone 4a





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