Re: CULT:Leaf Spot Invasion
- Subject: Re: [iris-talk] CULT:Leaf Spot Invasion
- From: B* S*
- Date: Tue, 02 Apr 2002 10:08:37 -0500
On 4/1/02 10:48 PM, "Judy Hunt" <judyhunt1@bellsouth.net> wrote:
> Bill Shear said:
> <In fact, it was spraying with the fungicide that wet the plants and brought
> the bacterial spot to my attention. The spreader-sticker I was using with
> the fungicide probably actually spread the bacteria around!>
>
> Bill, how does bacterial leaf spot differ in appearance from fungal leaf spot
Bacterial leaf spot tends to begin at the tips of leaves. The spots have
"soft" watery centers and usually do not have a darker ring. The spots and
areas quickly expand and run together in wet weather until the entire leaf
is destroyed, often leading to rhizome rot. When the leaf is dry, the
progress of the disease pretty much stops, but it can be rampant if there
are several days of wet conditions. Warm, dry weather usually brings it to
an end.
Fungal leaf spot can start anywhere on the leaf and often favors the younger
leaves in the center of the fan. It generally has a "drier" appearance.
The spots have yellow or transparent centers and are surrounded by a darker
ring (see p. 52 in THE GARDENER'S IRIS BOOK), which in turn is surrounded by
a yellowish area. The spots don't run together, but a heavy attack can
cause the leaves to die and dry up.
Leaf spots harm plants by reducing the area available for photosynthesis and
causing weak growth. They are most prevelant in the spring when lush
foliage is growing fast, but fungal leaf spot can persist all season long.
Both forms of leaf spot are best controlled by sanitation. Clean up all
dead iris foliage in spring and fall, and pull dead leaves during the
summer. Burn all dead material. If fungal leaf spot gets heavy, cut off
infected leaves and burn them. For initial control, spray once or twice
with a systemic fungicide, such as Daconil. After two years of careful
work, it should no longer be necessary to spray.
Bill Shear
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