Re: CULT:Leaf Spot
- Subject: Re: CULT:Leaf Spot
- From: J* a* C* W*
- Date: Thu, 4 Mar 1999 20:12:03 -0700
From: "Jeff and Carolyn Walters" <jcwalters@bridgernet.com>
From: Arnold Koekkoek <koekkoek@mtcnet.net>
<< It is highly unlikely that in that spraying you got all the bad
disease-spreading agents, but you knocked them back. I'd spray again after
bloom is over, maybe again later in the summer, esp. if you have hot and
humid weather.>>
Leslie,
I agree wholeheartesly with everything Arnold has written, but I would like
to emphasize that you cannot rely on Daconil (or any other single
fungicide) to control leaf spot indefinitely. When I first used Daconil for
leaf spot two years ago it was highly effective, but it became apparent
after only three or four sprayings that it was losing its effectiveness. It
is generally recommended that you rotate three or four fungicides in
treating for leaf spot so that the organisms do not build up resistance
against any one of them.
The following is an extract from an article in the Logan Iris Society
Newsletter, based on information disseminated by Cooley's Iris Garden in
Oregon:
"There are two methods of control for fungal leaf spot. The first is to
maintain a clean and healthy environment. This includes periodic removal of
browning foliage and dead leaves. Cut bloomstalks after flowering and trim
foliage back to a height of six inches. Trim foliage back again in the
fall. Method two, used in conjunction with method one, is to spray the iris
in early spring when the new foliage is six inches high with Kocide 101.
Subsequent spraying with Daconil, Cleary 3336 and Bayleton 25, used in
rotation every ten days until the weather turns hot and dry will contain
the disease. Additional spraying after cutting back the foliage in the fall
is advisable.
Unfortunately, the fungus lives for two years, so if it was present this
year, it will be back again next year. Begin spraying BEFORE it appears.
When little or no sign of leaf spot has appeared for two years, spraying is
only necessary once or twice annually."
I have also used a copper sulfate based fungicide with good results, but
the copper sulfate solution does discolor the leaves slightly. I also use a
spreader-sticker in the tank whenever I spray fungicide or herbicide.
Jeff Walters in northern Utah (USDA Zone 4/5, Sunset Zone 2)
jcwalters@bridgernet.com
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