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CULT:Re: Need help on leaf blight/spots

From: HIPSource@aol.com


There are two forms of leaf spot but fungal leaf spot is the more frequently
found one. It affects bearded and beardless irises alike and may be recognized
by small round or oval translucent spots on the leaves. In a few days these
spots enlarge, turn brown and may develop a rust border. The leaves may die
back and the plant be weakened as a result.

If you have fungal leaf spot, cut off all affected foliage well below the
spots and remove it from the garden. Do not compost it. When the spores turn
brown they can be carried by air, animals or on clothing to other plants, so
you want them gone.  If it is really bad and they need most of the leaves cut
off, so be it. Also remove all dead foliage and other drifted debris from the
beds so that air can circulate. Trim back any neighboring plants that may be
harboring moisture. You want light, air and good circulation in there.

If the irises are crowded so there is not much dirt showing, this is a good
time to divide them. Let us kow if you need to know how. If you do this, you
should soak the divided rhizomes, including the foliage, in a ten or fifteen
percent bleach and water solution for about a half an hour --rinse them off
afterward--before resetting them. 

If the plants are not crowded, get them cleaned up well and trimmed off and
consider spraying them with a strong bleach and water solution--20 percent--or
a recommended fungicide. Consult your local county extension service for their
recommendations on fungicides. The Virginia Coorperative Extension Service
currently recommends Daconil 2787, Fore, and Dithane for fungal leaf spot.

If leaf spot is a recurring problem some attention should be given to
controlling chewing insects such as aphids, and thrips. A study done on
daylilies has suggested that there must be some minute damage to the leaves to
permit entry of the fungal spores. 

It is said that if you can keep fungal leaf spot out of a garden for two years
it will be gone unless it is reintroduced. All incoming rhizomes should
receive a half hour preventive soak in a ten percent bleach-wter solution.
Submerge the foliage in this as well. Make no exceptions.

Because this is such a disagreeable looking disease, it pays to be ruthless
about eliminating susceptible irises from your collection. I have one that
someone sent me that is getting ready to be history. Nice little iris, but a
real plague ship. I can't afford to have it give its problem to the rest of
them, so out it goes.

There is another leaf spot, too, caused by bacteria. Most of the lesions are
near the leaf margins and they are larger. This likes moisture too and prefers
cooler weather. It disappears in hot dry conditions. No known cure, but it is
thought to persist on dead leaves. Here again, cut off all the diseased leaves
well below the spots and get the bed cleaned out well.

With all such diseases the very best preventative is to grow strong plants and
be scrupulous about garden hygiene. And don't forget to sterilize your
impliments after messing with those diseased leaves. Use some bleach.

Anner Whitehead

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